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Microwave-assisted synthesis of ordered mesoporous organosilicas with surface and bridging groups

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MICROWAVE-ASSISTED SYNTHESIS OF ORDERED MESOPOROUS
ORGANOSILICAS WITH SURFACE AND BRIDGING GROUPS
A dissertation submitted to
Kent State University in partial
fulfillment of the requirements for the
degree of Doctor of Philosophy
by
Bogna E. Grabicka
December, 2010
i
UMI Number: 3437677
All rights reserved
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UMI 3437677
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Dissertation written by
Bogna E. Grabicka
M. Sc., Poznan University of Technology, Poland, 2003
Ph. D., Kent State University, 2010
Approved by
_______________________, Chair, Doctoral Dissertation Committee
Dr. Mietek Jaroniec
_______________________, Members, Doctoral Dissertation Committee
Dr. Anatoly Khitrin
_______________________
Dr. Hanbin Mao
_______________________
Dr. Qi-Huo Wei
_______________________
Dr. Elizabeth Mann
Accepted by
_______________________, Acting Chair, Department of Chemistry
Dr. Michael Tubergen
_______________________, Dean, College of Arts and Sciences
Dr. John R. D. Stalvey
ii
TABLE OF CONTENTS
LIST OF FIGURES.……………………………………………………………...
viii
LIST OF SCHEMES…………………………..………………………………....
xxii
LIST OF TABLES…………………………..…………………...........................
xxiv
ACKNOWLEDGEMENTS…..………………………………………………….
xxviii
I.
II.
Introduction………………………………...………………...
1
1.1.
Surfactant-templated ordered mesoporous silica……………
2
1.2.
Polymer- templated ordered mesoporous silica.…….………
4
1.3.
Ordered mesoporous silicas with surface organic groups…..
7
1.4.
Ordered mesoporous silicas with bridging organic groups....
13
1.5.
Microwave-assisted synthesis of ordered mesoporous
silicas………………………………………………………..
17
1.6.
Research Objectives and Summary…...……......…………...
24
Experimental section………………….……………………...
32
2.1.
Characterization ordered mesoporous silicas……………….
32
Nitrogen adsorption analysis………………………………..
33
Powder X-ray diffraction (XRD) measurements………...….
38
Elemental analysis……………...…………………...............
38
High resolution thermogravimetric measurements………….
38
Transmission electron microscopy (TEM) analysis……...…
39
Calculations section………...……………………………….
39
The BET specific surface area…………………..…...……...
39
Single-point pore volume…………………………...………
40
Pore size distribution………………………...…………..….
41
2.2.
iii
Pore diameter…………………….…..……………………...
42
Unit cell parameter………………………………………….
43
Materials and reagents…………………...…..………….…..
44
Co-condensation synthesis and adsorption properties of
cage-like mesoporous silicas prepared under conventional
and microwave conditions………………………………...
47
3.1.
Experimental…….…………………………………………..
48
3.1.1.
Conventional synthesis of SBA-16.…………………..……..
48
3.1.1.1.
Effective method for removal of polymeric template from
SBA-16 silica.…………….....................................................
48
3.1.1.2.
Adsorption studies of thermal stability of SBA-16
mesoporous silica……………………...................................
49
3.1.1.3.
Effects of hydrothermal treatment and template removal on
the adsorption and structural properties of SBA-16…...……
50
3.1.2.
Synthesis of SBA-16 under microwave irradiation…………
51
3.1.2.1.
Microwave-assisted synthesis of SBA-16…………………..
51
3.2.
Optimization of synthesis conditions of cage-like
mesostructures via conventional method.…………………...
55
3.2.1.
Effective method for removal of polymeric template from
SBA-16 silica....................................................................
55
3.2.2.
Adsorption studies of thermal stability of SBA-16
mesoporous silica…………………...………………………
64
2.3.
III.
iv
IV.
3.2.3.
Effects of hydrothermal treatment and template removal on
the adsorption and structural properties of SBA-16
mesoporous silica….………………………………………..
70
3.3.
Microwave-assisted synthesis and adsorption properties of
cage-like mesoporous silicas..................................................
75
Ordered mesoporous materials with organic surface groups...
88
4.1.
Experimental………………………………………………...
89
4.1.1.
Synthesis of mono- and bifunctional channel-like SBA-15
and cage-like SBA-16 materials with ureidopropyl and
ureidopropyl-mercaptopropyl surface groups…………........
89
4.1.2.
Synthesis of channel-like SBA-15 organosilicas modified
by ureidopropyl surface group: Effect of organosilane
addition at different synthesis stages………………………..
91
4.1.3.
Microwave-assisted synthesis of mono- and bifunctional
channel-like SBA-15 and cage-like SBA-16 materials with
ureidopropyl and ureidopropyl-mercaptopropyl surface
groups……………………………………………………….
92
4.1.4.
Synthesis of vinyl-functionalized channel-like SBA-15
mesoporous material via conventional and microwave
methods................................................................................
4.2.
Mono- and bifunctional channel-like SBA-15 and cage-like
SBA-16 materials with ureidopropyl and ureidopropylmercaptopropyl surface groups…………………………..…
101
4.3.
Effect of ureidopropyl organosilane addition at different
synthesis
stages
of
channel-like
SBA-15
organosilicas…………………...……………..……………..
113
v
95
V.
VI.
4.4.
Microwave-assisted synthesis of mono- and bifunctional
channel-like SBA-15 and cage-like SBA-16 materials with
ureidopropyl and ureidopropyl-mercaptopropyl surface
groups……………………………………………………....
4.5.
Synthesis of vinyl-functionalized channel-like SBA-15
mesoporous material via conventional and microwave
methods……………………………………………………...
Ordered mesoporous materials with ethane bridging
group…………………………………………………………
117
134
144
5.1.
Experimental………………………………………………...
145
5.1.1.
Conventional synthesis of SBA-15 organosilicas with
ethane bridging group……………………………………….
145
5.1.2.
Conventional synthesis of SBA-16 with ethane bridging
groups……………….............................................................
146
5.1.3.
Microwave-assisted synthesis of ethane-bridged channellike organosilicas………...………………………………….
147
5.2.
Results and discussion for ethane-silica mesostructures
prepared under conventional conditions ……………………
5.3.
Thermal stability of SBA-16 with ethane bridging
groups……………………….……………………….……...
161
5.4.
Results and discussion for ethane-bridged channel-like
organosilicas prepared under microwave conditions………..
165
151
Ordered mesoporous organosilicas disulfide and
isocyanurate bridging groups………………………………...
175
6.1.
176
Experimental………………………………………………..
vi
VII.
6.1.1.
Synthesis of disulfide-functionalized SBA-15 and SBA-16..
176
6.1.2.
Synthesis of disulfide-funtcionalized SBA-15: addition of
organosilanes in different stages of the process………….....
178
6.1.3.
Microwave-assisted synthesis of SBA-15 with disulfide
organic group……..…..…………….……………………….
179
6.1.4.
Synthesis of SBA-15 with ethane and iscoyanurate bridging
groups………………...……………………………….…….
180
6.1.5.
Microwave-assisted synthesis of SBA-15 with isocyanurate
organic group……..................................................................
181
6.2.
Results and discussion for SBA-15 and SBA-16 with
disulfide groups...………………………………………...…
187
6.3.
Study of the effect of addition of disulfide organosilanes at
different stages of the process…………...………...………..
198
6.4.
Results and discussion for SBA-15 with disulfide groups
obtained under microwave irradiation.…………...................
202
6.5.
Results and discussion for channel-like SBA-15 with ethane
and iscoyanurate bridging groups……….…………………..
209
6.6.
Results and discussion for SBA-15 with isocyanurate
organic groups prepared under microwave irradiation...........
217
Conclusions…………………………………………………..
224
VIII. References…………………………………………………..
vii
228
LIST OF FIGURES
Figure 1.
Comparison of nitrogen adsorption-desorption isotherms at – 196 °C for
SBA-16-e-350 and c-550 samples and the corresponding pore size distributions
(PSD).
Figure 2.
(a) Comparison of nitrogen adsorption-desorption isotherms at -196 °C for
a series of extracted SBA-16 samples calcined at different temperatures. The
isotherms for e-450, e-350, e-250 and e are offset vertically by 110, 235, 400 and 680
cc STP g-1; (b) Comparison of nitrogen adsorption-desorption isotherms at -196 °C
for a series of SBA-16 samples calcined at different temperatures. The isotherms for
c-450, c-350 and c-250 are offset vertically by 193, 418 and 678 cc STP g-1; (c), (d)
the corresponding pore size distributions calculated according to the KJS method for
extracted and calcined samples, respectively. Due to the space limitations, the
samples are named as e-x and c-x instead of SBA-16-e-x and SBA-16-c-x,
respectively.
Figure 3.
(a) Comparison of XRD patterns for c (composite), e (extracted), e-350,
and c-550 SBA-16 samples; (b) Comparison of the thermogravimetric curves (TG)
measured in flowing nitrogen; (c) Evolution of the mesopore diameter as a function
of the calcination temperature for two series of the SBA-16 samples; and (d) DTG
curves obtained by differentiation of the TG curves in Panel b. Due to the space
limitations, the samples are named as e-x and c-x instead of SBA-16-e-x and SBA16-c-x, respectively
viii
Figure 4.
Comparison of nitrogen adsorption-desorption isotherms measured at –
196 °C for the SBA-16 samples denoted as SBA-16-x-y-b, where x denotes either
extraction (e) or calcination (c), y denotes temperature of calcination and b refers to
the previously reported [58, 59] synthesis modified by using low acid concentration
and eliminating the addition of sodium chloride and the corresponding pore size
distributions (PSD).
Figure 5.
X-ray diffraction (XRD) patterns (A, B), nitrogen adsorption isotherms (C,
D) measured at – 196 °C and the corresponding pore size distributions (PSDs) (E, F)
calculated according to the KJS method [279] for the cage-like SBA-16 mesoporous
silicas calcined at various temperatures for 4 hrs in the flowing air.
Figure 6.
Evolution of the mesopore diameter (A and B), the BET surface area (C
and D), minimal pore-wall thickness (E and F) and the total pore volume (G and H)
plotted against the temperature of calcination for the SBA-16 silicas studied
Figure 7.
Nitrogen adsorption isotherms at -196ºC for the extracted-calcined SBA-
16 samples synthesized by varying duration time of the first stage of synthesis and
hydrothermal treatment step at 100ºC for 6, 12, 24 and 48h, shown in Panels A, B, C
and D, respectively.
Figure 8.
Pore size distributions (PSD) obtained for the extracted-calcined SBA-16
samples synthesized by varying time of the first stage of synthesis and hydrothermal
treatment step at 100ºC for 6, 12, 24 and 48h, shown in Panels A, B, C and D,
respectively.
ix
Figure 9.
Comparison of the TG (A) and DTG (B) curves obtained for the silica-
polymer composite, extracted and extracted-calcined at 350ºC representative samples
of SBA-16 prepared for 4h (the first stage of synthesis) and 24h (hydrothermal
treatment at 100ºC).
Figure 10.
Nitrogen adsorption isotherms measured at -196 °C (Panels A , B and C)
and the corresponding pore size distributions (PSDs) (Panels D, E and F) calculated
by the KJS method [279] as well as the powder X-ray diffraction patterns (Panels G,
H and I) for the ordered mesoporous silicas obtained under microwave irradiation at
40 °C during the self-assembly stage and at 100°C in the hydrothermal step
Figure 11.
Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and
the corresponding pore size distributions (PSDs) (Panels C and D) calculated by the
KJS method [279] as well as the powder X-ray diffraction patterns (Panels E and F)
for the ordered mesoporous silicas obtained under microwave irradiation at 40 °C
during the self-assembly stage and at 120°C in the hydrothermal step
Figure 12.
Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and
the corresponding pore size distributions (PSDs) (Panels C and D) calculated by the
KJS method [279] as well as the powder X-ray diffraction patterns (Panels E and F)
for the ordered mesoporous silicas obtained under microwave irradiation at 40 °C
during the self-assembly stage and at 140°C in the hydrothermal step
Figure 13.
Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and
the corresponding pore size distributions (PSDs) (Panels C and D) calculated by the
KJS method [279] as well as the powder X-ray diffraction patterns (Panels E and F)
x
for the ordered mesoporous silicas obtained under microwave irradiation at 40 °C
during the self-assembly stage and at 160°C in the hydrothermal step.
Figure 14.
STEM images of the selected ordered mesoporous silicas obtained under
microwave irradiation at 40 °C followed by hydrothermal treatment at 100°C (sample
100-12-24: panels A and B show TEM and SEM images, respectively) and 120°C
(sample 120-6-6: panels C and D show TEM and SEM images, respectively).
Figure 15.
High-resolution TG profiles (top panels) and the corresponding DTG
profiles (bottom panels) recorded in flowing nitrogen for channel-like SBA-15
mesoporous silicas obtained via co-condensation route using various concentrations
of ureidopropyl (U) ligands (A and C), bifunctional ligands: ureidopropyl (U) and
mercaptopropyl (SH) (B and D), respectively.
Figure 16.
X-ray diffraction (XRD) patterns (A and B), nitrogen adsorption isotherms
(C and D) measured at – 196 °C and the corresponding pore size distributions (PSDs)
(E and F) calculated according to the KJS method [279] for the channel-like SBA-15
mesoporous silicas having various concentrations of ureidopropyl (U) ligands (A, C
and E), bifunctional ligands: ureidopropyl (U) and mercaptopropyl (SH) (B, D and F),
respectively.
Figure 17.
High-resolution TG profiles (top panels) and the corresponding DTG
profiles (bottom panels) recorded in flowing nitrogen for cage-like SBA-16
mesoporous silicas obtained via co-condensation using various concentrations of
ureidopropyl (U) surface ligands (A and C), bifunctional surface ligands:
ureidopropyl (U) and mercaptopropyl (SH) (B and D), respectively.
xi
Figure 18.
X-ray diffraction (XRD) patterns (A and
isotherms (C and D)
B), nitrogen adsorption
measured at – 196 °C and the corresponding pore size
distributions (PSDs) (E and F) calculated according to the KJS method [279] for the
cage-like SBA-16 mesoporous silicas having various concentrations of ureidopropyl
(U) surface ligands (A, C and E), bifunctional surface ligands: ureidopropyl (U) and
mercaptopropyl (SH) (B, D and F), respectively. The isotherms in Panel C for SBA16, SBA-16-U1 and SBA-16-U2 were offset vertically by 90, 165 and 50 cc STP g-1.
The isotherms in Panel D for SBA-16-U1 and SBA-16-U1-SH1 were offset vertically
by 75 and 50 cc STP g-1.
Figure 19.
X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C)
calculated according to the improved KJS method [279] for the channel-like SBA-15
mesoporous silicas with ureidopropyl surface groups synthesized by delaying the
addition of ureidopropyltrimethoxysilane (U) into the TEOS-polymer mixture from
zero to 120 minutes; numbers at the samples codes denote the delay time in minutes.
The adsorption isotherms and PSD curves for U60, U40, U20, U15, U10 and U0 were
offset by 210, 440, 615, 800, 1100, 1390 cc STP g-1 and 1.0, 1.8, 2.6, 3.4, 4.2, 5.3 cc
g-1 nm-1, respectively.
Figure 20.
High-resolution TG (top panels) and the corresponding DTG profiles
(bottom panels) recorded in flowing nitrogen for channel-like SBA-15 mesoporous
silicas obtained via microwaved-assisted synthesis (m) and conventional route (c)
xii
with ureidopropyl (U) surface ligands (A, C), bifunctional surface ligands:
ureidopropyl (U) and mercaptopropyl (SH) (B, D), respectively.
Figure 21.
High-resolution TG (top panels) and the corresponding DTG profiles
(bottom panels) recorded in flowing nitrogen for cage-like SBA-16 mesoporous
silicas obtained via microwaved-assisted synthesis (m) and conventional route (c)
with ureidopropyl (U) surface ligands (A, C), bifunctional surface ligands:
ureidopropyl (U) and mercaptopropyl (SH) (B, D), respectively.
Figure 22.
Nitrogen adsorption isotherms (A, B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C, D) calculated according to the KJS
method [279] for the channel-like SBA-15 mesoporous silicas obtained via
microwaved-assisted synthesis (m) and conventional route (c) with ureidopropyl (U)
surface ligands (A, C), bifunctional surface ligands: ureidopropyl (U) and
mercaptopropyl (SH) (B, D), respectively. The isotherms in Panel A for SBA-15,
SBA-15-U-c, SBA-15-U-m6, SBA-15-U-m8 and SBA-15-U-m12 were offset
vertically by 1850, 1550, 1250, 850 and 400 cc STP g-1. The isotherms in Panel B for
SBA-15, SBA-15-U-SH-c, SBA-15-U-SH-m6, SBA-15-U-SH-m8 and SBA-15-USH-m12 were offset vertically by 1750, 1500, 1150, 825 and 400 cc STP g-1. The
PSD curves in Panel C for SBA-15, SBA-15-U-c, SBA-15-U-m6, SBA-15-U-m8 and
SBA-15-U-m12 were offset vertically by 4.5, 3.8, 2.9, 2.2 and 1.0 cm3 g-1 nm-1. The
PSD curves in Panel D for SBA-15, SBA-15-U-SH-c, SBA-15-U-SH-m6, SBA-15U-SH-m8 and SBA-15-U-SH-m12 were offset vertically by 4.5, 3.6, 2.8, 2.1 and 1.1
cm3 g-1 nm-1.
xiii
Figure 23.
Nitrogen adsorption isotherms (A, B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C, D) calculated according to the KJS
method [279] for the cage-like SBA-16 mesoporous silicas obtained via microwavedassisted synthesis (m) and conventional route (c) with ureidopropyl (U) surface
ligands (A, C), bifunctional surface ligands: ureidopropyl (U) and mercaptopropyl
(SH) (B, D), respectively. The isotherms in Panel A for SBA-16, SBA-16-U-c, SBA16-U-m6, SBA-16-U-m8 and SBA-16-U-m12 were offset vertically by 1150, 1000,
750, 500 and 150 cc STP g-1. The isotherms in Panel B for SBA-16, SBA-16-U-SH-c,
SBA-16-U-SH-m6, SBA-16-U-SH-m8 and SBA-16-U-SH-m12 were offset vertically
by 1150, 1000, 900, 600 and 325 cc STP g-1. The PSD curves in Panel C for SBA-16,
SBA-16-U-c, SBA-16-U-m6, SBA-16-U-m8 and SBA-16-U-m12 were offset
vertically by 2.0, 1.6, 1.2, 0.8 and 0.4 cm3 g-1 nm-1. The PSD curves in Panel D for
SBA-16, SBA-16-U-SH-c, SBA-16-U-SH-m6, SBA-16-U-SH-m8 and SBA-16-USH-m12 were offset vertically by 2.0, 1.65, 1.24, 0.8 and 0.4 cm3 g-1 nm-1.
Figure 24.
X-ray diffraction (XRD) patterns for channel-like SBA-15 mesoporous
silicas obtained via microwave-assisted synthesis (m) and conventional route (c)
with ureidopropyl (U) surface ligands (A), bifunctional surface ligands:
ureidopropyl (U) and mercaptopropyl (SH) (B).
Figure 25.
X-ray diffraction (XRD) patterns for cage-like SBA-16 mesoporous
silicas obtained via microwave-assisted synthesis (m) and conventional route (c)
with ureidopropyl (U) surface ligands (A), bifunctional surface ligands:
ureidopropyl (U) and mercaptopropyl (SH) (B).
xiv
Figure 26.
Nitrogen adsorption isotherms (A and B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C and D) calculated according to the
KJS method [279] for the channel-like SBA-15 mesoporous silicas obtained via
microwave-assisted synthesis and conventional route (conv) having various
concentrations of vinyl ligands (V). The isotherms in Panel A for V10-MW-6, V10MW-8, V10-MW-12 and V10-MW-24 were offset vertically by 1350, 950, 650 and
300 cc STP g-1. The isotherms in Panel B for V15-MW-6, V15-MW-8, V15-MW-12
and V15-MW-24 were offset vertically by 1500, 1100, 800 and 400 cc STP g-1. The
PSD patterns in Panel C for V10-MW-6, V10-MW-8, V10-MW-12 and V10-MW-24
were offset vertically by 3.8, 3.2, 2.1 and 0.9 cm3 g-1 nm-1. The PSD patterns in Panel D
for V15-MW-6, V15-MW-8, V15-MW-12 and V15-MW-24 were offset vertically by
2.6, 2.3, 1.5 and 0.6 cm3 g-1 nm-1.
Figure 27.
Nitrogen adsorption isotherms (A and B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C and D) calculated according to the
KJS method [279] for the channel-like SBA-15 mesoporous silicas obtained via
microwave-assisted synthesis and conventional route (conv) having various
concentrations of vinyl ligands (V). The isotherms in Panel A for V20-MW-6, V20MW-8, V20-MW-12 and V20-MW-24 were offset vertically by 1200, 925, 500 and
200 cc STP g-1. The isotherms in Panel B for V30-MW-6, V30-MW-8, V30-MW-12
and V30-MW-24 were offset vertically by 475, 450, 225 and 125 cc STP g-1. The
PSD patterns in Panel C for V20-MW-6, V20-MW-8, V20-MW-12 and V20-MW-24
were offset vertically by 2.6, 2.1, 1.2 and 0.5 cm3 g-1 nm-1. The PSD patterns in Panel D
xv
for V30-MW-6, V30-MW-8, V30-MW-12 and V30-MW-24 were offset vertically by
0.5, 0.375, 0.225 and 0.125 cm3 g-1 nm-1.
Figure 28.
X-ray diffraction (XRD) patterns for channel-like SBA-15 mesoporous
silicas obtained via microwaved-assisted synthesis (MW) and conventional route
(conv) having various concentrations of vinyl ligands (V).
Figure 29.
High-resolution TG (top panels) and the corresponding DTG profiles
(bottom panels) recorded in flowing nitrogen for channel-like SBA-15 mesoporous
silicas obtained via microwaved-assisted synthesis (MW) and conventional route
(conv) having various concentrations of vinyl ligands (V).
Figure 30.
A comparison of X-ray diffraction (XRD) patterns (panel A), nitrogen
adsorption-desorption isotherms measured at – 196 °C (panel B) and the
corresponding pore size distributions (PSDs) calculated according to the improved
KJS method [279] from nitrogen adsorption branches (panel C) for the extracted
SBA-15-type periodic mesoporous ethane-silicas synthesized using various triblock
copolymer P123-BTESE bridged silsesquioxane weight ratios ranging from 0.73 to
4.39. The isotherms and PSDs for PMO-1, PMO-1.5, PMO-2, PMO-2.5, PMO-3 were
offset by 175, 360, 530, 710, 1000 cc STP g-1 and 0.16, 0.5, 0.95, 1.85, 2.35 cc g-1
nm-1, respectively.
Figure 31.
Evolution of the BET surface area (A), wall thickness (nm) (B), mesopore
diameter (C), volume of micropores (D), volume of ordered mesopores (E) and the
total pore volume (F) for the extracted SBA-15-type ethane-silicas synthesized using
xvi
different triblock copolymer P123-BTESE silsesquioxane weight ratios between 0.73
and 4.39.
Figure 32.
High-resolution thermogravimetric (TG) weight change curves with the
corresponding differential TG (DTG) profiles recorded in flowing air for the
template-containing (dashed line) and template-free (solid line) SBA-15-type periodic
mesoporous ethane-silicas obtained for different triblock copolymer P123-BTESE
bridged silsesquioxane weight ratios ranging from 0.73 to 4.39, respectively
Figure 33.
A comparison of nitrogen adsorption-desorption isotherms measured at –
196 °C (panel A, B, C), the corresponding pore size distributions (PSDs) calculated
according to the improved KJS method [279] from nitrogen adsorption branches
(panel D, F, H), X-ray diffraction (XRD) patterns (panel E, G, I) for the SBA-15-type
periodic mesoporous ethane-silicas obtained using various triblock copolymer P123BTESE silsesquioxane weight ratios ranging from 0.73 to 4.39, respectively
Figure 34.
High-resolution TG curves with the corresponding differential TG (DTG)
profiles (panel A, B, C) recorded in flowing air for the extracted (solid line) and the
same material subjected to calcination (dashed line) in air atmosphere at 540 °C
during three hours for the SBA-15-type periodic mesoporous ethane-silicas obtained
using various triblock copolymer P123-BTESE silsesquioxane weight ratios ranging
from 0.73 to 4.39, respectively
Figure 35.
X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C)
xvii
calculated according to the KJS method [279] for the cage-like SBA-16 ethane-silica
calcined at various elevated temperatures for 4 hrs in the flowing air
Figure 36.
Powder X-ray diffraction patterns for the extracted ethane - bridged
PMOs.
Figure 37.
Nitrogen adsorption isotherms measured at -196 °C (A) and the
corresponding pore size distributions (PSDs) (B) calculated by the improved KJS
method [279] for the extracted ethane-bridged PMOs. The isotherms and PSDs for
ES-8, ES-12, ES-24 and ES-36 were offset by 1200, 900, 600, 300 cm3 STP g-1 and
1.2, 0.9, 0.6, 0.35 cm3 g-1nm-1, respectively.
Figure 38.
A comparison of nitrogen adsorption isotherms measured at -196 °C for
the extracted ethane-bridged PMOs obtained by the conventional, ES-C samples, and
microwave method, ES-24 sample. The data for the ES-C samples was taken for the
comparison from ref [198].
Figure 39.
TEM images of the ethane-containing PMO (sample ES-24).
Figure 40.
Thermogravimetric
weight
change
(TG)
profiles
(A)
and
the
corresponding differential TG (DTG) curve (B) measured in flowing air for the
extracted ethane-bridged PMOs.
Figure 41.
X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C)
calculated according to the KJS method [279] for the channel-like SBA-15
mesoporous silicas having various concentrations of bis(propyl)disulfide (DS)
bridging groups
xviii
Figure 42.
X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C)
calculated according to the KJS method [279] for the cage-like SBA-16 mesoporous
silicas having various concentrations of bis(propyl)disulfide (DS) bridging groups.
The isotherms in Panel B for SBA-16-DS1 and SBA-16-U1-DS2 were offset
vertically by 50 and 10 cc STP g-1
Figure 43.
High-resolution TG profiles (A) and the corresponding DTG profiles (B)
recorded in flowing nitrogen for channel-like SBA-15 mesoporous silicas obtained
via co-condensation route using various concentrations of bis(propyl)disulfide (DS)
bridging groups.
Figure 44.
High-resolution TG profiles (A) and the corresponding DTG profiles (B)
recorded in flowing nitrogen for cage-like SBA-16 mesoporous silicas obtained via
co-condensation using various concentrations of bis(propyl)disulfide (DS) bridging
groups.
Figure 45.
X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C)
calculated according to the improved KJS method [279] for the channel-like SBA-15
mesoporous silicas with disulfide bridging groups synthesized by delaying the
addition of bis(triethoxysilylpropyl) disulfide (DS) into the TEOS-polymer mixture
from zero to 120 minutes; numbers at the samples codes denote the delay time in
minutes. The adsorption isotherms and PSD curves for DS60, DS40, DS20, DS15,
xix
DS10 and DS0 were offset by 420, 550, 820, 1080, 1280, 1520 cc STP g-1 and 1.1,
2.1, 3.6, 4.6, 5.6, 7.0 cc g-1 nm-1, respectively.
Figure 46.
Powder X-ray diffraction patterns for the extracted disulfide - bridged
PMOs.
Figure 47.
Nitrogen adsorption isotherms measured at -196 °C (A) and the
corresponding pore size distributions (PSDs) (B) calculated by the improved KJS
method [279] for the extracted disulfide-bridged PMOs. The isotherms and PSDs for
DS-6, DS-8, DS-12 were offset by 1050, 700, 350 cm3 STP g-1 and 3.5, 2.7, 1.25 cm3
g-1 nm-1, respectively.
Figure 48.
A comparison of nitrogen adsorption isotherms measured at -196 °C for
the extracted disulfide-bridged PMOs obtained by the conventional (DS-C sample)
and microwave methods (DS-24 sample). The data for the DS-C sample were taken
for the comparison from ref [107].
Figure 49.
Thermogravimetric
weight
change
(TG)
profiles
(A)
and
the
corresponding differential TG (DTG) curves (B) measured in flowing air for the
extracted disulfide-bridged PMO (DS-24).
Figure 50.
A comparison of small angle X-ray scattering patterns for a series of the
extracted PMOs studied.
Figure 51.
A comparison of nitrogen adsorption-desorption isotherms at – 196 °C
for a series of the extracted PMOs; the isotherms for EI-2, EI-1 and EI-0 were offset
vertically by 86, 263 and 437 cc STP g-1, respectively, and b) the corresponding pore
xx
size distributions (PSDs) calculated according to the KJS method [279]; PSDs for EI2, EI-1 and EI-0 were shifted by 0.3, 0.88 and 1.58 cc g-1 nm-1, respectively.
Figure 52.
Comparison of the thermogravimetric weight change (TG) curves
measured in flowing air for as-synthesized (EI-3-P123) and extracted (EI-0 and EI-3)
PMOs, and the corresponding DTG curves
Figure 53.
Nitrogen adsorption isotherms measured at -196 °C (A) and the
corresponding pore size distributions (PSDs) (B) calculated by the improved KJS
method [279] for the extracted isocyanurate-bridged PMOs obtained under
microwave irradiation at 40 °C during the self-assembly stage and at 100°C in the
hydrothermal step . The isotherms and PSDs for ICS-100-6-12, ICS-100-6-24, ICS100-12-12, ICS-100-12-24 were offset by 50, 150, 250, 400 cm3 STP g-1 and 0.2,
0.45, 0.70, 1.00 cm3 g-1 nm-1, respectively.
Figure 54.
Nitrogen adsorption isotherms measured at -196 °C (A) and the
corresponding pore size distributions (PSDs) (B) calculated by the improved KJS
method [279] for the extracted isocyanurate-bridged PMOs obtained under
microwave irradiation at 40 °C during the self-assembly stage and at 120°C in the
hydrothermal step . The isotherms and PSDs for ICS-120-6-12, ICS-120-6-24, ICS120-12-12, ICS-120-12-24 were offset by 150, 400, 600, 700 cm3 STP g-1 and 0.25,
0.50, 0.80, 1.10 cm3 g-1 nm-1, respectively.
xxi
LIST OF SCHEMES
Scheme 1. Schematic illustration of template removal for cage-like mesoporous SBA16.
Scheme 2. Schematic illustration of functionalized channel-like SBA-15 by
ureidopropyl surface (A) and ethane bridging (B) organic groups.
Scheme 3. The IUPAC classification of adsorption isotherms
Scheme 4. The IUPAC classification of adsorption-desorption hysteresis loops
Scheme 5. Chart illustrating the synthesis procedure for cage-like mesoporous SBA16 silica via conventional (top) and microwave-assisted (bottom) methods.
Scheme 6. Schematic illustration of the polymeric template removal from assynthesized SBA-16 by two different methods: (i) commonly used calcination at
550 °C (top scheme) and (ii) combined extraction followed by controlledtemperature calcination at 350 °C (bottom scheme). The large circles connected
with straight channels represent interconnected spherical cages (ordered
mesopores), whereas curved thin ribbons denote irregular micropores within walls
of ordered mesopores.
Scheme 7. Schematic comparison of the synthesis of organosilicas with surface
groups by conventional (top) and microwave-assisted (bottom) methods.
Scheme 8. Schematic illustration of mesoporous channel-like structure SBA-15 silica
(A) and interconnected cylindrical channels (large circles with thin channels)
containing ureidopropyl surface ligands (B) (open circles), bifunctional
xxii
ureidopropyl (open circles), and mercaptopropyl (filled circles) surface ligands
(C).
Scheme 9. Schematic illustration of mesoporous cage-like structure SBA-16 silica
(A) and interconnected spherical cages (large circles with straight channels)
containing ureidopropyl surface ligands (B) (open circles), bifunctional
ureidopropyl (open circles) and mercaptopropyl (filled circles) surface ligands
(C).
Scheme 10.
Schematic
illustration
of
vinyl-functionalized
SBA-15
organosilica.
Scheme 11.
Schematic illustration of ethane-bridged silica under conventional
conditions (top; ethane-modified SBA-15 (A) and SBA-16 (B)) and microwave
synthesis conditions (bottom).
Scheme 12.
Schematic illustration of hexagonally-arranged interconnected
cylindrical channels via irregular micropores (large circle with thin ribbons) of
SBA-15-type periodic mesoporous organosilica containing ethane (-CH2-CH2-)
bridging groups incorporated inside framework.
Scheme 13.
A comparison of the synthesis of SBA-15 (A) and SBA-16 (B)
organosilicas by conventional (top) and microwave-assisted (bottom) methods.
Scheme 14.
Schematic illustration of bifunctional SBA-15 with isocyanurate
(A) and ethane groups (B).
Scheme 15.
Schematic illustration of SBA-15 with isocyanurate organic
groups.
xxiii
Scheme 16.
Schematic illustration of disulfide-functionalized SBA-15 (A) and
SBA-16 (B).
xxiv
LIST OF TABLES
Table 1.
Structures of surface organosilanes employed in the syntheses of the
materials studied.
Table 2.
Structures of bridging organosilanes employed in the syntheses of the
materials studied.
Table 3.
Structural properties determined from XRD, elemental analysis and
nitrogen adsorption data for SBA-16 silicas studied
Table 4.
Structural properties determined from elemental analysis and nitrogen
adsorption data for the SBA-16 silicas synthesized according to the recipes
reported by Kim at al. [57] (samples having a in the sample code) and Zhao at al.
[58] (samples having b in the sample code); the latter recipe was modified by
eliminating the addition of sodium chloride and using low acid concentrations
Table 5.
Adsorption parameters for the SBA-16 silicas studied
Table 6.
Adsorption and low angle XRD data obtained for the extacted SBA-16
samples synthesized by varying duration time of the first stage of the process and
hydrothermal treatment at 100ºC for 6, 12, 24 and 48h.
Table 7.
Adsorption and structural parameters of ordered mesoporous silicas
obtained under microwave irradiation.
Table 8.
Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the organic-functionalized channel-like SBA-15
mesoporous silicas.
xxv
Table 9.
Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the organic-functionalized cage-like SBA-16
mesoporous silicas.
Table 10. Selected structural parameters of the organic-functionalized channel-like
SBA-15 mesoporous silicas
Table 11. Selected structural parameters of the organic-functionalized cage-like SBA-16
mesoporous silicas
Table 12. Selected adsorption and structural parameters for the SBA-15 silicas with
ureidopropyl groups.
Table 13. Molar composition of the synthesis gels used and the corresponding elemental
analysis data for the organic–functionalized channel-like SBA-15 mesoporous silicas
Table 14. Molar composition of the synthesis gels used and the corresponding elemental
analysis data for the organic–functionalized cage-like SBA-16 mesoporous silicas
Table 15. Selected structural parameters of the organic-functionalized channel-like
SBA-15 mesoporous silicas
Table 16. Selected structural parameters of the organic-functionalized cage-like SBA-16
mesoporous silicas
Table 17. Selected structural parameters for the vinyl-functionalized channel-like SBA15 mesoporous silicas
Table 18. Adsorption parameters for SBA-15-type ethane-silicas studied
Table 19. Adsorption parameters for SBA-16-type ethane-silicas studied
Table 20. Adsorption and structural properties for the ethane-PMOs studied
xxvi
Table 21. Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the channel-like SBA-15 with disulfide groups.
Table 22. Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the cage-like SBA-16 with disulfide groups.
Table 23. Adsorption parameters for the channel-like SBA-15 with disulfide group
Table 24. Adsorption parameters of the cage-like SBA-16 with disulfide groups
Table 25. Selected adsorption and structural parameters for the SBA-15 silicas with
disulfide groups
Table 26. Adsorption and structural properties for the disulfied-bridged PMOs
studied
Table 27. Synthesis
gel
compositions,
elemental
analysis
data
and
thermogravimetric weight loss data for the PMOs studied
Table 28. Adsorption properties of PMOs determined from nitrogen adsorption data.
Table 29. Selected adsorption and structural parameters for the SBA-15 silicas with
isocyanurate groups.
xxvii
ACKNOWLEDGEMENTS
I would like to express the deepest appreciation to my advisor, Professor Mietek Jaroniec,
for his encouragement, supervision and support from the preliminary to the concluding level of
my graduate studies. His wisdom, knowledge and commitment to the highest standards inspired
and motivated me. He has the attitude and the substance of a genius: he continually and
convincingly conveyed a spirit of adventure and excitement in regard to research.
I am heartily thankful for kindness and advices I received from Prof. Andrzej
Krysztafkiewicz from Chemistry Department at Poznan University of Technology, Poland. His
mentorship, help and assistance made it possible for me to pursue my interests.
My sincere appreciation goes to the Center for Nanophase Materials Sciences at the Oak
Ridge National Laboratory, which is sponsored by the Division of Scientific User Facilities, US
Department of Energy, for the TEM images.
I would like to thank the Department of Chemistry and Biochemistry at Kent State
University for providing me with a graduate assistantship and giving me the opportunity to be
here and all members of my doctoral committee for their generously given time and valuable
expertise to better my work. All these years of PhD studies has certainly shaped me as a person
and has led me where I am now.
I am also grateful to my colleagues and friends with whom I have interacted during the
course of my graduate studies. It was a pleasure to share doctoral studies and life with
extraordinary people. Particularly, I would like to extend many thanks to Stacy Grant and Rafal
Grudzien for a successful collaboration and the encouragement through all these research studies.
Their friendship and hospitality have supported, enlightened, and entertained me over the many
years.
Most importantly, none of this would have been possible without my family. I thank my
parents, Urszula and Zygmunt, as well as my brother Pawel. They have been a constant source of
unconditional support and strength all these years. They have aided and encouraged me
throughout this endeavor.
xxviii
1. Introduction
The discovery of ordered mesoporous silicas (OMSs) in 1992 opened new
possibilities in the area of nanomaterials with organic functionalities. The latter can be
synthesized by using commercially available organosilanes in the presence of structure
directing agents such as ionic surfactants, neutral surfactants and non-ionic block
copolymers. Incorporation of various surface and bridging groups into the mesopore
walls and framework of silica allows tailoring the surface and framework chemistry of
OMSs for various advanced applications. The resulting organic-inorganic hybrids have
gained growing popularity because of their potential applications in adsorption, catalysis,
chromatography and host-guest chemistry for immobilization of biomolecules. Usually,
functionalization of OMS is carried out to achieve the desired surface properties of
nanomaterials without significant changes in their specific surface area, pore volume,
pore size and structural ordering. Since the preparation of nanomaterials under
microwave irradiation offers several advantages such as the ease of preparation and
temperature programming, short synthesis time and low cost, it is worthy to explore this
approach for the development of novel organosilicas. A wide range of applications of
microwaves in various areas of chemistry makes this type of irradiation a powerful tool
for the preparation of nanomaterials. Thus far, the choice of this technique is rarely
presented in the literature devoted to the synthesis of ordered mesostructures, especially
ordered mesoporous organosilicas (OMOs).
1
2
This dissertation is focused on the microwave-assisted synthesis of channel- and
cage-like ordered mesoporous organosilicas with different surface and bridging groups
and on the monitoring their adsorption and surface properties by varying the chemical
composition as well as time and temperature of hydrothermal synthesis. This study shows
a great potential of the microwave-assisted synthesis and highlights a wide range of
opportunities in employing this method for the preparation of various nanomaterials.
1.1.
Surfactant-templated ordered mesoporous silicas
The discovery of OMSs in 1992 by Mobil Company researchers [1] is considered
as a major breakthrough in materials science, which has played a crucial role in the
development of both nanoscience and nanotechnology. This discovery opened enormous
possibilities in the area of nanomaterials with organic functionalities [2-13], which can be
synthesized by using various organosilanes in the presence of structure directing agents
such as ionic surfactants [2-3, 7-13], neutral surfactants [13] and non-ionic block
copolymers [4-6].
The first OMS were obtained by using ionic surfactants [14-23] and include the
most popular hexagonal MCM-41 [1-2, 14-21] and FSM-16 [14, 21], cubic MCM-48 [12, 21-23] and lamellar MCM-50 mesostructures [21, 24-25] (meso indicates the features
in the range between 2 and 50nm). The aforementioned hexagonal materials refer to 2D
3
(two-dimensional) ordered honeycomb structures (P6mm) consisting of parallel and
nonintersecting cylindrical mesopores, while MCM-48 refers to a 3D (three-dimensional)
cubic bicontinuous structure (Ia3d). These materials can be obtained in the presence of
TEOS (tetraethyl orthosilicate), TMOS (tetramethyl orthosilicate) or sodium silicate as
silica sources and cationic- or anionic- surfactant as a template [1-2, 14-23, 27]. The most
famous MCM-41 was obtained by using tetraethyl orthosilicate (TEOS) or sodium
silicate and alkyltrimethylammonium surfactants as the structure-directing agents [1-2,
14-21]. A typical sample of MCM-41 is characterized by a 2-6 nm pore diameter, high
surface area (up to 1200 m2/g) and large pore volume, as well as high uniformity and
narrow pore size distribution. Moreover, there are extensive possibilities in tailoring the
structural properties of OMS by taking advantage of wide assortment of cationic
(CnH2n+1)(CH3)3NX, 6  n  22 and X: OH, Cl, Br) and anionic surfactants with variable
length of alkyl chain, varying the size and shape of the head groups, and by using
various expanders (e.g., 1,3,5-trimethylbenzene, 1,3,5-triisopropylbenzene) [1-2, 14-32].
The area of ordered mesoporous materials (OMMs) has been expanded
enormously through the use of ionic surfactant-templated ordered mesoporous silicas.
Their structural properties, hydrothermal, chemical and mechanical stability are
important for various applications, like catalysis, separations, adsorption processes and
immobilization of molecules [1-2, 14-36].
4
1.2.
Polymer-templated ordered mesoporous silicas
The possibility of using non-ionic block copolymers as soft templates opened new
prospects for the development of OMSs [26, 37-41]. Polymeric templates are
inexpensive, environmentally friendly and commercially available, all of which make
them attractive for the synthesis of nanomaterials. Among them, non-ionic poly(ethylene
oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers, Pluronics of a
general formula: EOX POY EOX where letter x refers to the number of ethylene oxide
group and y to the number of propylene oxide group, are the most popular. A very
mainstream OMS, SBA-15, was synthesized by using Pluronic123 (EO20PO70EO20)
triblock copolymer with hydrophilic EO and hydrophobic PO groups. This OMS has a
2D hexagonal structure of parallel mesochannels interconnected by irregular micropores
and can be obtained by using Pluronic P123 as a soft template and TEOS (tetraethyl
orthosilicate) or sodium silicate as silica sources under acidic conidtions [21, 37, 42-45].
It is important to point out that it was the first polymer-templated mesoporous ordered
silica, which revolutionized the field of ordered mesoporous materials [37-52]. In
comparison to the ionic surfactant-templated MCM-41, the SBA-15 material is
characterized by larger pore diameters (8-15nm instead of 2-6nm in the case of MCM41), thicker pore walls and larger pore volume as well as additional micropores
interconnecting ordered mesopores. This important finding opened new perspectives for
the development and applications of nanomaterials as well as stimulated further
advancements in nanoscience and nanotechnology [38, 41, 46-52].
5
The available assortment of block copolymers permitted the synthesis of not only
2D mesomaterials, but also three-dimensional mesostructures such as SBA-16 [21, 5358] (3D cubic mesostructure with Im3m symmetry group; body-centered packing), which
can be obtained by using Pluronic F127 (HO(C2H4O)106(C3H6O)70(C2H4O)106H) in the
presence of TEOS (tetraethyl orthosilicate), TMOS (tetramethyl orthosilicate) or sodium
silicate as a silica source under low acidic conditions. As might be noticed, the triblock
copolymer F127, EO106PO70EO106, possesses much longer segments of hydrophilic
groups in contrast to P123, EO20PO70EO20, used to fabricate the SBA-15 material.
Another example of an important structure directing agent is B50-6600
(EO39BO47EO39), a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide)
triblock copolymer template, used to synthesize FDU-1 [21, 59-65]. This material has a 3D
face-centered (Fm3m) cubic-like mesostructure. It is noteworthy that the family of cagelike OMSs is very attractive because of their unique structural properties facilitating
transport of molecules in the entire 3D arrangement of cages. Namely, each cage in SBA16 and FDU-1 mesostructures is connected via small apertures with 8 or 12 neighboring
cages, respectively. Such 3D mesoporous structures are propitious for the immobilization
of biomolecules and transport of reactants due to improved accessibility of pores as
compared to 2D networks. All these factors make cage-like mesostructures attractive for
adsorption, catalysis and related applications [21, 66-68].
Overall, a wide assortment of non-ionic triblock copolymers allows one to
prepare ordered mesoporous materials with desired 2D- or 3D-network such as SBA-1
[69], SBA-12 [70-71], SBA-14 [70], KIT-5 [72], PSU-1 [73], SBA-15, SBA-16, FDU-1
6
and so forth [21]. In addition, all the structural properties of polymer-templated materials
can be tailored by varying synthesis conditions such as temperature and time of the
process (the self-assembly and hydrothermal treatment stages), addition of salts and other
additives, adjusting polymer/silica ratio, and by selecting the synthesis method (for
instance conventional or microwave irradiation) [74-81]. Another important aspect in the
fabrication of high quality ordered mesoporous materials is the template-removal process
[82-93]. An example of the importance of this process can be shown for SBA-16, a cagelike mesostructure [80, 87-93]. Generally, after the self-assembly and hydrothermal
treatment processes, the as-prepared materials can be treated using solvent extraction,
calcination, microwave irradiation, supercritical fluid extraction and so forth [82-93], to
remove the template from the sample. Primarily, template removal employs extraction
using ethanol/acid solutions and temperature-controlled calcination under flowing gas,
individually or as a two-step process. The aforementioned techniques give satisfactory
results. Unfortunately, they also manifest some disadvantages and undesirable side
effects such as unsatisfactory template-removal efficiency in the case of extraction and
the risk of shrinkage and structural collapse in the case of calcination. Additionally, each
type of mesoporous material demonstrates characteristic template needs and requires a
proper choice of template-removal technique. Schueth et al. succesfully removed the
template from the channel-like SBA-15 by combining extraction with sulfuric acidethanol solution and calcination at 200-540°C [85-86]. The method was satisfactory and
characterized by a high efficiency in removing the triblock copolymer P123 from the
channel-like mesostructure at low temperatures. Grudzien et al. demonstrated the
7
successful removal of Pluronic F127 (EO106PO70EO106) from as-synthesized SBA-16
prepared in the presence of sodium chloride at low acid concentrations by a quick
extraction with HCl/EtOH followed by calcination in flowing air at ~350°C [92]. This
method afforded cage-like Im3m mesosilicas with much higher values of the BET surface
area, unit cell parameter, mesopore size and total pore volume in contrast to those
previously reported values for SBA-16 samples. The so far cited papers [1-93] refer to
OMSs obtained by hydrothermal synthesis in a conventional oven. An alternative to this
approach is microwave-assisted synthesis, which will be discussed in detail later.
1.3.
Ordered mesoporous silicas with surface organic groups
The growing attractiveness of OMSs in various applications, especially catalysis,
separations and nanotechnology, has stimulated many scientists to pursue vigorous
research in this field. In comparison to other porous materials, the popularity of
functionalized mesoporous silicas is due to their high surface area (around 1000 m2/g),
high pore uniformity, a large variety of mesostructures, a wide range of pore sizes
(allowing for immobilization of bioactive guest molecules) and an almost unlimited
ability of surface and framework modifications by organic groups. First, attention was
concentrated on zeolites and their ability to be organically functionalized [21, 94].
However, the potential for employing them as a carrier material is limited by the small
pore diameter and overall, by low volume of the microporous network.
8
In general, researchers have been trying to design nanomaterials with high
specific surface area, large pore volume and large pore widths, which can accomodate
high loadings of organic groups (bridging groups, which are incorporated into the
framework, and/or surface groups, which are chemically attached into the mesopore
walls) without a significant deterioration of the ordered structure. There are two major
methods used to tailor the surface properties of OMSs: (i) post-synthesis grafting of the
template-free OMS by using reactive organosilanes (C2H5O)3-Si-R, where R denotes an
organic group [2, 7, 10], or reaction of the template-containing OMSs with organosilanes
[8, 9]; the latter leads to the removal of the template and chemical attachment of desired
surface groups [8, 9], and (ii) the co-condensation (one-pot synthesis) of organosilanes
[3-6, 11-13], (C2H5O)3-Si-R and tetraethyl orthosilicate (TEOS) in the presence of
structure directing agents.
The first approach, known as post-synthesis modification, involves surface
functionalization of the surfactant-free OMSs [2, 7, 10, 98] (OMS, in which the template
was removed by calcination or extraction) and the surfactant-containing OMSs [8, 9]. An
important advantage of post-synthesis modification is the possibility of tailoring of the
pore diameter in OMOs by varying the size of the attached ligand [2, 7, 10, 98].
The second approach involves co-condensation (one-pot synthesis) of appropriate
organosilanes often along with either tetraethyl orthosilicate (TEOS) [13, 95, 96] or
sodium metasilicate. This approach has became the most popular route and yields OMSs
with a high concentration of functional ligands without substantial deterioration of
mesoscopic ordering or causing structural shrinkage as in the case of calcination (which
9
may lead to a significant decrease in the mesopore diameter, up to 25 %). The cocondensation method is applied to decorate not only the surface of the pore walls, but
also the framework [97, 100, 101, 102] - the latter materials are known as periodic
mesoporous organosilicas (PMOs) [103-106].
As might be noticed, the main difference between co-condensation synthesis and
post-synthesis modification of the surfactant-containing OMSs is that in the first case all
precursors participate in the structure formation. In the second strategy, the silicasurfactant mesostructure is formed before introduction of the reactive organosilane in
order to displace the surfactant template and to introduce the surface ligand. Therefore,
the one-pot synthesis method eliminates structural shrinkage, which appears during
preparation of the initial OMS being subjected to post-synthesis grafting, as well as
allows for the introduction of high loadings of functional organic groups. The high
efficiency and simplicity of the one-pot synthesis strongly favors this strategy over the
post-synthesis grafting in the fabrication of functionalized mesostructures. It permits
simultaneous control of the pore structure and the surface properties as well as allows for
relatively high loadings of desired groups. There are numerous reports showing the
effectiveness of one-pot synthesis, allowing one to introduce one or more functional
groups
such
as
ureidopropyltrimethoxysilane
[13,
107-110],
3-
mercaptopropyltrimethoxysilane [107-108, 110-114, 140], N-(3-triethoxysilylpropyl)4,5-dihydroimidazole [115-119], vinyl [120-127], methyl [128], carboxylic [129-129],
aminopropyl [131-133], phenyl [134], 3-aminopropyltrimethoxysilane [13, 135-139] and
benzyltriethoxysilane [140].
10
The choice of surface organic groups, the method of introduction of these groups
to the pore walls, temperature of the synthesis as well as the addition of micelle
expanders strongly influences the quality of the obtained materials, in particular the
loading and distribution of surface groups. The aforementioned factors are important for
tailoring properties of organosilicas [107-145]. It is noteworthy that a purely siliceous
mesostructure of SBA-15 (silica having hexagonal arrangement of cylindrical mesopores;
p6m symmetry group) [142-143] is formed within one hour after TEOS addition [144].
Therefore, addition of reactive organosilanes at different stages of the mesostructure
formation seems to be important for fabrication of OMOs. Wang et al. reported SBA-15
with methylaminopropyl surface groups, synthesized using different periods (between 0
and 4 hours) for the pre-hydrolysis of organosilanes [145]. However, only four different
times were used and no firm conclusions were reported. Grudzien et al. [141], presented a
more
detailed
study
of
the
consequence
of
the
delayed
introduction
of
ureidopropyltrimethoxysilane (UPS) and bis(triethoxysilylpropyl) disulfide (BTDS) on
the structural and adsorption properties of the resulting channel-like mesoporous
organosilicas. It is noteworthy, that such an investigation was performed for an organic
group on the pore walls as well as for a bridging group placed in the silica framework.
The popularity of mesoporous organosilicas with different organic groups is
growing because of their importance for adsorption, catalysis, chromatography and hostguest chemistry [117-118, 149-152] and their attractiveness for environmental
applications, especially for the removal of various pollutants from air and water, such as
hazardous heavy metal ions (like mercury, lead and cadmium). The latter can be reduced
11
or eliminated by using ion-exchange resins [153-154], natural zeolites [155], activated
carbons [156] and other porous materials [157-158]. In particular, the specially designed
OMOs with ligands such as 1-allyl-3-propylthiourea and benzoylthiourea [151, 159-161]
were shown to be attractive adsorbents for the removal of mercury ions. Another example
of an effective organic group is N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole, which
has been used for the removal of precious metal ions (such as Pt and Pd) and carbon
dioxide [115-119]. This organic group can easily be attached to the walls of channel-like
as well as cage-like structures.
A particular attention was given to vinyl group because of its ability for high
ligand loadings, and high reactivity of the double bond useful for additional modification
of silica materials [120-127] such as bromination or epoxidation. Kruk and co-workers
presented a study with vinyl loadings in the range of 25-100% using a cationic surfactant
[125]. However, the most representative materials were fabricated up to 65% of vinyl
loadings. Higher concentration of attached organic groups caused a phase separation,
which was reflected in the poor quality of materials. In contrast to the ionic surfactanttemplated
materials,
the
vinyl-functionalized
polymer-templated
silicas
were
characterized by relatively low loadings of organic groups. Wang and co-workers studied
the influence of the concentration of vinyl groups and acid, temperature and the addition
of inorganic salts [120, 126]. Likewise, they demonstrated that the structural changes of
this organosilica caused by the change of concentration of vinyl group in the range up to
15%, resulted in a hexagonally ordered material. Moreover, for 15% or higher loadings of
this ligand a cubic OMO with Ia3d symmetry was formed [120, 126].
12
Among highly accessible surface organic ligands, a special consideration has been
paid to ureidopropyl and mercaptopropyl groups, due to possible high loadings of these
groups and the attractiveness they offer to bind heavy metal ions, such as Cr, Zn and Ni
in the case of ureidopropyl ligand [135, 162] as well as Hg (II) and Au in the case of
mercaptopropyl surface group [163-166]. The high interest in mercaptopropylmodification is also related to the ease of oxidation of thiol group to sulfonic one, which
is highly desired in catalysis [96, 113-114]. So far, the study of the aforementioned
groups demonstrated the affectiveness of synthesis of channel- and cage-like mono- and
bifunctional OMOs [107, 109].
The ureidopropyl ligand possesses two amine groups attached to a carbonyl,
allowing the creation of a chelate complex with some metal ions, which is very useful for
binding of heavy metal ions. In 2001, Gong and co-workers presented the ureidfunctionalized MSU-X material, where the fabricated silica was modified with ureid
ligands only or simultaneously with ureid and phenyl groups [13]. Also, the ureidopropyl
functionalization of MCM-41 was succesfully performed by Huh and co-workers (2003) by
using cetyltrimethylammonium bromide ionic surfactant under basic pH [167]. In 2005,
Grudzien and co-workers succesfully obtained mono- and bi-functional channel- and cagelike mesoporous silicas, SBA-15 (P6mm) and SBA-16 (Im3m) by using block copolymer
templates [107]. The ureidopropyl functionality was also incorporated to periodic
mesoporous organosilicas, by Wei and co-workers using co-condensation of
bis(triethoxysilyl)ethane and ureidopropyltrimethoxysilane [168]. The resulting material
showed high structural ordering at low concentrations of surface ligands (0-10%); the
13
structural ordering of this channel-like organosilica, decreased gradually with increasing
percentage of ureidopropyltrimethoxysilane. Also, the surface area of this material
decreased from 1004 to 539 m2/g when ligand concentration increased from 5% to 30%;
analogous behaviour was observed for the pore volume. Recently, Grabicka and Jaroniec
reported the synthesis of ureidopropyl organosilicas under microwave conditions [268].
Overall, a great deal of studies have been performed using co-condensation as a
main strategy to attach ureidopropyl, vinyl, mercaptopropyl and other organic groups to
the pore wall of polymer-templated channel-like (SBA-15) and cage-like (SBA-16) silica
[107-114, 120-127, 140-141, 149-150, 159-161]. The channel-like organosilicas have
been more popular in comparison to cage-like materials. In addition, the mono- and
bifunctional mesoporous organosilicas have been primarily prepared using conventional
oven [107-168]. To the best of our knowledge, there are a few reports on surfacefunctionalized SBA-15 and SBA-16 silicas with mercaptopropyl, vinyl and ureidopropyl
ligands fabricated under microwave irradiation. In addition, the microwave irradiation
was used only in the final synthesis step, i.e., hydrothermal treatment [226-230].
1.4.
Ordered mesoporous silicas with bridging organic groups
A substantial breakthrough in the area of OMMs was reported in 1999 by Inagaki,
Ozin and Stein groups, who independently reported periodic mesoporous organosilicas
(PMOs), which are ordered mesostructures obtained by co-condensation of bridged
silsequioxane precursors (AO)3Si-R-Si-(AO)3 [103, 105-106]. The difference in using the
14
bridged silsesquioxanes (AO)3Si-R-Si(OA)3 as the silica-containing precursors instead of
trialkoxyorganosilane (AO)3Si-R (R is a functional group and A is ethyl or methyl group)
results in an ordered mesostructure possessing bridging organic groups in the framework
instead of hanging group on the surface. PMOs can be obtained by the self-assembly of
bridged silsequioxanes [(AO)3Si]nR (where n= 2 or 3; R denotes a bridging organic group
and A = CH3 or C2H5). The structure directing agents used in the synthesis of PMO can
be ionic surfactants [103, 105-106], oligomeric surfactants [169] and nonionic block
polymers [170-172]. Incorporation of organic bridging groups R into the framework has
been used to create the desired physical and chemical properties of PMOs, which make
them attractive for various applications such as adsorption, catalysis, drug delivery,
immobilization of biomolecules and so forth [6, 173-174]. Benefits of incorporating
organic groups into the framework include limited blockage of pore entrances, altered
flexibility and hardness of modified materials and high loading of organic functionality.
Overall, the introduction of organic group into the mesostructure results in unique
chemical, physical and mechanical properties of the final material. Small organic
bridging groups such as methylene, ethane, ethylene, butylene, phenylene and acetylene
[11-13, 175-176] as well as larger groups like benzene, bis-4-(triethoxysilyl)phenyl-ether,
biphenylene, 2.5-bis(triethoxysilyl)thiophene and isocyanaurate rings have been
incorporated into siliceous materials [177-184]. The resulting PMOs showed high BET
surface area, tailored ordered porosity and high concentrations of organic groups. The
first studies were devoted to channel-like materials obtained by using both ionic
surfactants and nonionic block copolymers; namely MCM-41 and SBA-15-type materials
15
with various organic groups incorporated into the silica framework, such as benzene and
thiophene were reported by Ozin et al [105] and Inagaki et al [185].
The aforementioned works stimulated significant developments in the field of
ordered
mesoporous
materials,
which
resulted
in
various
bridge-containing
mesostructures, including MCM-41, SBA-15, KIT-5 [186], FDU-1 [188], SBA-1 [189],
and SBA-16 [171, 190]. Of particular note, channel-like as well as cage-like structures
with one or two functional groups have been reported [149, 191-193]. The mono- and
bifunctionalization allows for enormous diversity of organosilica materials. There is a
tremendous potential in the modification of silica framework and in the simultaneous
introduction of organic groups onto the silica surface. One of the most popular small
bridging groups is ethane in the synthesis of organosilicas [103, 194-202]. This organic
linker was used to obtain channel- and cage-like mesostructures under a wide range of
acid concentrations in the presence of various salts [103, 194-202].
Among many bridging groups, a great deal of attention was given to
functionalization of mesoporous organosilicas to enhance their affinity towards heavy
metal ions. Zhang and co-workers (2003) obtained a tretrasulfide-PMO by cocondensation of (1,4)-bis(triethoxysilyl)propane tetrasulfide in the presence of non-ionic
surfactant. Such an adsorbent, containing thioether spacers, attracts selectively Hg2+ ions
in the presence of other metal ions [203]. This high selectivity of the aforementioned
adsorbent towards of Hg2+ ions was also reported by Liu at al., along with additional
preference towards phenols, illustrating its affinity to organic pollutants [204].
16
Another important bridging group is tri[3-(trimethoxysilyl)propyl]isocyanurate
(ICS), characterized by a ring attached to three trimethoxysilyls via flexible propyl
chains. Such a group exhibits a high affinity towards heavy metal ions and promises good
properties for environmental applications [38, 146-150]. In 2005, Olkhovyk and Jaroniec,
successfully incorporated the bulky isocyanurate group into the channel-like SBA-15
mesostructure [149]. The study showed a gradual increase in the concentration of the ICS
group in the organosilica material. The resulting ICS-PMO material was highly porous; at
a 25% concentration of the ICS bridging group, the modified organosilica possessed high
BET specific surface area (622 m2/g), total pore volume (0.81 cc/g) and good structural
ordering with a narrow pore size distribution. The ICS-modified samples with higher
concentrations of ICS retained the channel-like PMO mesostructure, however their
porous properties decreased with elevated loading. The potential of isocyanurate group in
the modification of silica for use as an adsorbent against toxic pollutants stimulated a
continuous development of mono- as well as bifunctional PMOs with bulky ICS group
[38, 146-150].
Overall, the progress in the development of periodic mesoporous organosilicas is
significant [103, 105-106, 169-204]. Mono- as well as bifunctional channel- and cagelike mesostructures shows a wide range of potential applications in adsorption, catalysis,
drug delivery, immobilization of biomolecules, chromatography, sensors and especially
in environmental protection. The ability of synthesizing organosilica materials with
tailored properties for a desired application has tremendous research potential.
Microwave-assisted synthesis clearly provides a synthetic route to obtain high quality
17
mesoporous organosilicas with comparable properties to those obtained under
conventional conditions.
1.5.
Microwave-assisted synthesis of ordered mesoporous silicas
Recent studies have showed that microwave-assisted synthesis permits to obtain
good quality OMMs with uniform pore structures [211-225]. The microwave technique
appears to be a very powerful tool for the fabrication of mesoporous solids. Exploration
of this technique started in the 1940’s as a heating method. Further development of this
method proved its attractiveness in chemical analysis like ashing, digestion and extraction
[see review 250]. An important impact for microwave chemistry was done independently
by the Gedye and Giguere’ research groups, which employed microwave irradiation for
transformations of organic compounds and demonstrated the opportunity of acceleration
of chemical reactions under microwave conditions [205, 206]. The 1990’s brought
significant achievements in this field. Bose et al. called this technique “a Buensen burner
of 21st century” [207]. Microwave-activated reactions are now a very important part of
research in the organic chemistry field. A wide range of applications in biochemistry,
electrochemistry, biocatalysis as well as in polymer chemistry, make the microwave
technique as a powerful tool in chemistry [242-264].
Generally, the microwave process shows numerous advantages over conventional
synthesis. The microwave-assisted synthesis affords materials with comparable or often
better properties than those generated under conventional conditions. Furthermore,
18
synthesis conditions such as temperature and pressure can be strictly and easily
controlled. This technology provides a rapid and homogenous heating of the entire
sample, which is very desirable and exceptional in contrary to the conventional
conditions. Microwave technique also creates new opportunities for controlling the
particle size distribution and morphology of ordered porous materials [205-265].
Initially, the application of microwave irradiation was used for the fabrication of
microporous materials, zeolites, and was proven to have a tremendous significance in
materials chemistry [208-210]. The high impact of this procedure encouraged researchers
to broaden microwave application to other porous materials. The rapid energy transfer
and high energy efficiency as well as direct heating of all reactants in the microwave
vessel were successfully used to synthesize various materials such as MCM-41 [211215], MCM-48 [211-212], SBA-15 [216-219], SBA-16 [220-221], FDU-1 [221-222] and
related mesoporous materials [223-225]. As might be noted, this method can be used for
the synthesis of surfactant-templated mesoporous materials (like MCM-41 and MCM-48)
as well as block-copolymer-templated materials such as SBA-15 (2-D hexagonal
symmetry; P6mm), SBA-16 (3-D cubic symmetry; Im3m) and FDU-1 (3-D cubic
symmetry; Fm3m).
Wu and Bein obtained MCM-41 via microwave irradiation as one of the first
nanoporous materials in 1996 [211]. This surfactant-templated material was fabricated at
100 – 160ºC in the presence of mesitylene and ethylene glycol. In addition, the time
required for the hydrothermal step was reduced, and the hexagonal phase could form
even after 20min in 150ºC. Park at al. noticed the correlation between the addition of
19
ethylene glycol during MCM-41 syntheses under microwave irradiation [214]. The
resulting MCM-41 particles were more homogenous. MCM-48 material (symmetry Ia3d)
is another example of the use of microwave irradiation to fabricate the silica-based
mesostructures, where CTAB was involved in the process [211-212]. Although, the
microwaved bicontinuous cubic mesomaterial offers similar properties to that prepared
via conventional hydrothermal method, it presents some structural disordering.
The most popular polymer-templated mesoporous material, SBA-15, was also
prepared by microwave irradiation; a good quality mesostructure, comparable to the
materials fabricated via conventional process was obtained [216-219]. Newalkar et al.
obtained the hexagonal SBA-15 type silica by using non-ionic block-copolymer
poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer
(Pluronic 123; EO20PO70EO20) with the addition of sodium chloride and ethanol [216218]. They adapted a microwave technique to the hydrothermal stage of the process,
which significantly reduced the time required to 2 hours at 373K. They observed the
influence of salt content on the porous structure. The structural parameters (BET surface,
micropore volume, volume of primary mesopores and total pore volume) of the resulting
SBA-15 samples decreased with increasing salt amount.
Another example of the block-copolymer-templated material is SBA-16, which
was fabricated under microwave conditions [220-221]. This material was obtained using
triblock copolymer EO106PO70EO106 (F127) during much shorter time [220]. However,
the microwave technique was rarely exploited to obtain cage-like mesostructures and its
usage was limited to only one step of the process, hydrothermal treatment, whereas the
20
first stage of the synthesis was performed under conventional conditions. Moreover, the
hydrothermal treatment process was carried out at a maximum temperature of 120ºC for
30-120 min. The next example of adopting this type of homogenous heating was the
fabrication of FDU-1 cubic-like silicas by using the structure directing agent B50-6600
(EO39BO47EO39), a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide)
triblock copolymer template [221-222]. The microwave-assisted hydrothermal treatment
step was substantially reduced, even to one hour, instead of 6-24 hours needed under
conventional conditions. The microwave technique was also employed for the
preparation of PSU-1 cage-like mesostructured material [221, 223]. The aforementioned
studies showed that both SBA-16 and FDU-1 materials can be hydrothermally treated for
2 hours under microwave conditions at 373K instead of 24 -168 hours in a conventional
oven.
The successful use of microwaves in the synthesis of pure silica materials resulted
in the expansion of this approach to the production of ordered mesoporous organosilicas.
Thus far, mesoporous organosilica materials with attached organic ligands on the surface
of the siliceous pore walls as well as with bridging organic groups in the silica
framework, fabricated under microwave conditions, have been very rarely reported [226230].
Furthermore, it is important to mention that only one step in all of the
abovementioned syntheses was performed under microwave irradiation [205-264].
Recently, a 2D channel-like structure, SBA-15, was prepared by co-condensation of
TEOS using temperature-programmed microwave-assisted synthesis; in contrast to the
21
previous reports, both steps of the synthesis, self-assembly and hydrothermal treatment,
were carried out under microwave irradiation [265]. It is noteworthy that the total
synthesis time was reduced significantly (from 72 hours to 3 hours). The resulting
material showed good adsorption properties reflected by high specific BET surface area,
large pore volume and high structure ordering. In 2010, Grabicka and Jaroniec showed
that the microwave-assisted synthesis affords good quality SBA-16 samples at lower
temperatures of hydrothermal treatment (100-120oC) [266]. The microwave-assisted
synthesis was successfully used to screen a wide range of temperatures and time in order
to establish optimal conditions for the synthesis of SBA-16. The obtained cage-like
materials exhibited a desirable quality of porous network and possessed textural
parameters comparable to SBA-16 silicas produced via conventional way.
To the best of our knowledge the microwave technique was very seldom used to
prepare mesoporous organosilicas, known as PMOs [227-230]. Thus far, only a few
papers were published on this subject. These initial studies were limited to microwaveassisted hydrothermal treatment only, whereas the first stage of the synthesis was
performed under conventional conditions. Also, the resulting organosilicas showed quite
poor quality. Kim et al. reported spherical particles (1.5-2.8 m) of ethane-silica, which
were prepared under microwave irradiation and used as a column packing material for
HPLC [227]. It is noteworthy to mention, that adsorption isotherms for these particles
were not provided. Adsorption isotherms reported by Yoon et al., show relatively broad
condensation steps, indicating broad pore size distribution [229]. In addition, the
hydrothermal treatment was performed under microwave irradiation in three temperatures
22
(95 ºC, 115 ºC and 135 ºC). The choice of temperature did not dramatically influence the
structural properties of the fabricated materials.
In 2009, a 2D channel-like SBA-15 structure with ethane and disulfide groups
was successfully synthesized by employing microwave-assisted synthesis method [267;
see Chapter V and VI]. The aforementioned organosilicas were prepared by cocondensation of 1,2-bis(triethoxysilyl)ethane
and bis(triethoxysilylpropyl) disulfide,
respectively, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)
triblock copolymer (Pluronic 123; EO20PO70EO20). Reduction of the synthesis time from
72 hours in the case of conventional recipe (24 hours for co-condensation step and 48
hours for hydrothermal treatment) to 36 hours was achieved when the self-assembly
process and hydrothermal treatment were performed under microwave irradiation. The
resulting materials exhibited high surface area, large pore volume and large pore
diameters. Recently, monofunctionalized channel-like SBA-15 and cage-like SBA-16
mesostructures, with surface organic ligands such as ureidopropyltrimethoxysilane as
well
as
ureidopropyltrimethoxysilane
and
3-mercaptopropylsilane,
and
tetraethylorthosilicate (TEOS) as a silica source, were obtained by using temperatureprogrammed microwave-assisted synthesis [268; see Chapter IV]. The self-assembly and
hydrothermal treatment stages were performed under microwave irradiation. The study
demonstrated the success of microwave-assisted synthesis to incorporate functional
organic groups on the surface of the siliceous pore walls of channel- and cage-like
mesoporous materials. Another example of the successful application of the temperatureprogrammed microwave-assisted synthesis is a vinyl-functionalized channel-like SBA-15
23
mesostructure obtained by co-condensation of triethoxyvinylsilane with tetraethyl
orthosilicate (TEOS) [269; see Chapter IV].
The recent works on the temperature-programmed microwave-assisted synthesis
of mesoporous materials show that this strategy is useful for the development of novel
organic-inorganic hybrid nanomaterials [see reviews 259-264]. All advantages of
microwave technique, synthesis time, reduction of energy and cost, and particularly the
possibility of screening a wide range of conditions such as time, temperature, chemical
composition, pH and additives, provide a positive prognosis for the synthesis of
mesoporous materials under microwave irradiation.
24
1.6.
Research Objectives and Summary
The main objective of my Ph.D. research was to explore the synthesis of channeland cage-like ordered mesoporous organosilicas with different surface and bridging
groups under microwave irradiation and to monitor their adsorption and surface
properties by varying chemical composition as well as time and temperature of
hydrothermal synthesis.
Nowadays, the commercially available microwave systems have the capability to
control the synthesis time and temperature allowing an easy screening of a variety of
experimental factors such as pressure, pH, polymer/precursor ratio and so on. It is
noteworthy that the possibility of a significant reduction of the synthesis time facilitates
the fundamental studies of the self-assembly processes, which is extremely beneficial for
the development of novel mesoporous organosilicas with surface and bridging groups.
Nitrogen adsorption at -196C, powder X-ray diffraction (XRD), high-resolution
thermogravimetry (TG) and elemental analysis (EA) were mainly employed to
characterize the ordering, porosity and surface properties of the mesostructures studied.
The first part of this dissertation was devoted to the improvement of polymertemplated cage-like SBA-16 materials via conventional method and under microwave
irradiation. At the beginning, the study was focused on the fabrication of high quality
mesostructures by using conventional recipe. Several synthesis parameters such as time
and temperature of the self-assembly process and hydrothermal treatment, acidity of the
synthesis gel, polymer/precursor ratio, and salt addition as well as the importance of
25
efficient template removal, were studied. Uniform cage-like mesostructures with
preferential adsorption properties were obtained. The template removal step was crucial
for obtaining the satisfactory quality of cage-like mesostructures; a need of combining
extraction in ethanol-acidic solution with temperature-controlled calcination in flowing
air was shown (Scheme 1). These studies were helpful for the research, which was aimed
at optimization of the synthesis conditions under microwave irradiation in an effort to
improve the quality of SBA-16 materials.
The microwave irradiation technique was employed during the entire synthesis
process, self-assembly and hydrothermal treatment steps. This method was propitiously
used to screen a wide range of temperatures and time in order to establish optimal
conditions for the synthesis of SBA-16. The microwave-assisted synthesis afforded high
quality SBA-16 samples at lower temperatures of hydrothermal treatment (100-120oC).
The obtained cage-like materials exhibited the well-developed porosity and improved
textural parameters as compared to the SBA-16 silicas prepared via conventional method.
Employing microwaves for the fabrication of mesoporous silica confirmed the
significance of microwave technique in the preparation of nanomaterials and provided
foundations for the usage of this type irradiation for the synthesis of ordered mesoporous
organosilicas.
The second part of my dissertation research (Chapter IV) is focused on the
preparation of ordered mesoporous silicas with surface organic groups (Scheme 2a) via
conventional and temperature-programmed microwave-assisted routes. The preliminary
studies showed a successful introduction of organic surface groups into the mesopore
26
walls of channel-like (SBA-15) as well as cage-like (SBA-16) structures by using
triethoxyvinylsilane,
(3-mercaptopropyl)trimethoxysilane
and
ureidopropyl-
trimethoxysilane. The choice of these organic ligands was established by taking into
account their reactivity and affinity toward heavy metal ions. It is noteworthy that the
one-pot conventional monofunctionalization and bifunctionalization of the polymertemplated materials were successful, showing the possibility of introducing not only high
loadings of organic ligands, but also obtaining high quality porous materials with uniform
pores, high specific BET surface areas and large pore volumes. This initial research was
essential for the microwave-assisted synthesis of organosilicas with aforementioned
surface ligands. Mono- and bifunctionalization of SBA-15 and SBA-16 materials under
microwave irradiation was simple and effective. The resulting materials possessed
favorable structural and adsorption properties. Moreover, the study of vinylfunctionalized samples showed some structural changes with increasing incorporation of
vinyl group on the surface of silica pore walls.
The next section of my dissertation is devoted to periodic mesoporous
organosilicas obtained (Scheme 2b) by conventional and microwave-assisted methods.
The incorporation of organic groups into the silica framework was carried out to achieve
the desired properties of the resulting materials without significant changes in the specific
surface area, pore volume, pore size and structural ordering. We synthesized the channellike and cage-like periodic mesoporous organosilicas with bis(triethoxysilylpropyl)
disulfide and tri[3-(trimethoxysilyl)propyl] isocyanurate bridging groups (Chapter V)
and with 1,2-bis(triethoxysilyl)ethane (Chapter VI). A special emphasis was placed on
27
the development of PMO with bridging groups having high affinity toward heavy metal
ions such as mercury and lead. The main objective of these studies was to maximize the
loading of bridging groups in the silica framework and simultaneously, to fabricate
organosilicas with uniform pores and narrow PSDs. These investigations were crucial for
exploring the microwave approach for the synthesis of various PMOs. Similarly to the
research of surface-modified mesomaterials under microwave irradiation, the bridgedmaterials were not widely studied as well as the resulting organosilicas showed quite
poor quality. We optimized time and temperature of the self-assembly and hydrothermal
treatment stages in order to achieve good structural ordering and high pore uniformity
under microwave conditions. This study shows that the syntheses of 2D channel-like
SBA-15 structures with ethane and disulfide groups, requires 72 hours, in the case of
conventional recipe (24 hours for co-condensation step and 48 hours for hydrothermal
treatment), and about 36 hours under microwave irradiation. The resulting materials
exhibited high surface area, large pore volume and large pore diameters. Also, a high
concentration of isocyanurate bulky groups was achieved and successfully showing the
opportunity of using microwave technique for the synthesis of PMOs with bulky bridging
groups.
28
This dissertation is based on the following publications:
1. B.E. Grabicka, M. Jaroniec, Adsorption 2010 16 385
2. R. M. Grudzien, B.E. Grabicka, M. Jaroniec, J. Mater. Chem. 2006 16 819
3. R.M. Grudzien, B.E. Grabicka, M. Kozak, S. Pikus, M. Jaroniec, New J. Chem.
2006 30 1
4. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Applied Surface Science 2007 253
5660
5. Pasquale F. Fulvio, Bogna E. Grabicka, Rafal M. Grudzien, Mietek Jaroniec,
Adsorption Science and Technology 2007 26 439
6. B.E. Grabicka, D.J. Knobloch, R.M. Grudzien, M. Jaroniec, Adsorption Progress in Fundamental and Application Research: Selected Reports at the 4th
Pacific Basin Conference on Adsorption Science and Technology, Tianjin, China
22 - 26 May 2006" (Li Zhou, ed.), World Scientific Publ. Co., Singapore, 2007
189
7. B.E. Grabicka, R.M. Grudzien, J. P. Blitz, M. Jaroniec, “Nanoporous Materials,
Vancouver, BC, Canada 25-28 May 2008” (A. Sayari and M. Jaroniec,
eds),World Scientific Publ. Co., Singapore, 2008 149
8. B.E. Grabicka, M. Jaroniec Microporous and Mesoporous Materials 2009 119
674
29
9. R.M. Grudzien, B.E. Grabicka, O. Olkhovyk, M. Jaroniec, J.P. Blitz,
“Nanoporous Materials, Vancouver, BC, Canada 25-28 May 2008” (A. Sayari
and M. Jaroniec, eds),World Scientific Publ. Co., Singapore, 2008 665
10. R.M. Grudzien, B.E. Grabicka, R. Felix, M. Jaroniec, Adsorption 2007 13 323
11. R.M. Grudzien, B.E. Grabicka, D.J. Knobloch, M. Jaroniec, Studies in Surface
Science and Catalysis 2007 165 443
12. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Colloids and Surfaces A:
Physicochemical and Engineering Aspects 2007 300 235
13. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Adsorption 2006 12 293
14. R.M. Grudzien, B.E. Grabicka, S. Pikus, M. Jaroniec, Chem. Mater. 2006 18 1722
15. B.E. Grabicka, M. Jaroniec, Microwave-assisted synthesis and characterization of
mesoporous organosilicas with ureidopropyl and mercaptopropyl groups. 2010,
in preparation
16. B.E. Grabicka, M. Jaroniec, Microwave-assisted co-condensation synthesis and
adsorption properties of vinyl-modified mesoporous organosilicas. 2010, in
preparation
17. B.E. Grabicka, M. Jaroniec, Adsorption properties and characterization of
mesoporous organosilicas with large isocyanurate bridging groups synthesized
under microwave irradiation. 2010, in preparation
30
Scheme 1. Schematic illustration of the template removal from cage-like SBA-16
mesostructures.
31
Scheme 2. Schematic illustration of channel-like SBA-15 with ureidopropyl surface
groups (A) and ethane bridging groups (B).
II. Experimental section
2.1. Characterization of ordered mesoporous materials
Characterization of ordered mesoporous materials was done by several techniques
to confirm the good quality of materials, successful incorporation of surface and bridging
groups onto surface of silica pore walls and into silica framework, respectively, as well as
to determine the effectiveness of template removal from composite materials. The most
important method employed in this work was gas adsorption, which was used to obtain
information about the structural and surface properties of the nanoamaterials studied. The
powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), transmission
electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric
analysis (TG) were used to investigate the structural ordering, particle morphology,
thermal stability and the template removal process. Moreover, the attachment of surface
groups to the silica pore walls and the incorporation of bridging groups into the silica
framework, was confirmed by elemental analysis and thermogravimetric analysis.
32
33
Nitrogen adsorption
This analytical technique is one of most popular and important methods used to
characterize the structural and surface properties of porous materials. It provides
significant information about quality of fabricated materials by indicating specific surface
area, pore volume, pore diameter, pore size distribution, pore uniformity and pore
accessibility.
Nitrogen adsorption measurements were performed using ASAP 2010 and ASAP
2020 volumetric analyzers manufactured by Micromeritics, Inc. (Norcross, GA).
Adsorption isotherms were measured at -196 °C over the interval of relative pressures
from 10-6 to 0.995 using high purity nitrogen of 99.998% from Praxair Distribution
Company (Canton, OH, USA), which was used to measure the amount adsorbed as a
function of the equilibrium pressure. Prior to each adsorption measurement the silica and
organosilica samples were outgassed under vacuum in the port of the adsorption
instrument for at least 2 hours at 200 °C and 110 °C, respectively, until the residual
pressure dropped to 6 or less µmHg. Such temperature was chosen on the basis of
thermogravimetric analysis to avoid the degradation of surface and bridging groups and
to remove adsorbed species such as water.
Nitrogen adsorption includes the following stages: (i) at low relative pressures molecules
adsorb on the surface creating a single layer (monolayer formation), (ii) at higher
pressures molecules form subsequent adsorbed layers (multilayer formation) and (iii)
when the pressure reaches the critical value for a given pore diameter molecules instantly
fill the remaining pore space; the latter process is known as capillary condensation. After
34
compleating adsorption branch, desorption is measured; this process involves the
emptying of pore voids and it is known as capillary evaporation. Both parts of isotherm
adsorption and desorption, often do not coincide at moderate or high relative pressures,
which results in hysteresis loop providing information about the shape of pores and their
connectivity.
According to the IUPAC classification [271, 273] of adsorption isotherms, there are six
different types of isotherm curves (Scheme 3). Type I is characteristic for nonporous or
microporous materials. As might be noticed in Scheme 3, the type I isotherms level off at
high pressures. Type II and III are characteristic for macroporous or nonporous materials,
and reflect the formation of multilayer at higher pressures, which is manifested by a
gradual increase in the amount adsorbed with increasing pressure. It is noteworthy, that
the aforementioned types of isotherms do not have hysteresis loop. Type IV and V
isotherms are characteristic for mesoporous materials, where in addition to monolayer
and multilayer formation the capillary condensation takes place in mesopores. At higher
pressures the isotherm follows a steep step due to capillary condensation in mesopores
and then levels off. Usually, capillary condensation and capillary evaporation do not
coincide, thus giving rise to a pronounced hysteresis loop. The initial parts of adsorption
isotherms (monolayer range) differ for Types IV and V isotherms, as well as Types II and
III isotherms. Type IV and IVc isotherms refer to mesoporous solids; however the latter
takes place in materials with small uniform mesopores, below 4 nm.
As regards classification of hysteresis loops, IUPAC recommends four types of loops
(Scheme 4.) [271]. As can be seen in Scheme 4, the H1 type is characterized by almost
35
vertical adsorption and desorption steps, and this type is observed for uniform porous
materials with facile pore connectivity. The type I of hysteresis loop is characteristic for
materials with cylindrical pore geometry and uniform pore entrances, such as SBA-15
silicas. The H2 shows a triangular shape hysteresis and a very steep desorption closure,
effected by small pore openings or pore constrictions. This type of hysteresis is for
materials with cage-like spherical pores such as SBA-16 (Scheme 4) and FDU-1. The H3
and H4 hysteresis loops were observed for materials with slit-like pores; in the case of the
H3 loop, the adsorption branch does not level off close to the saturation vapor pressure,
whereas H4 loop shows parallel and almost horizontal both branches.
36
Scheme 3. The IUPAC classification of adsorption isotherms
37
Scheme 4. The IUPAC classification of adsorption-desorption hysteresis loops
38
Powder X-ray diffraction (XRD) measurements
Powder X-ray diffraction (XRD) measurements were recorded using a
PANanalytical, Inc. X'Pert Pro (MPD) Multi Purpose Diffractometer with Cu K
radiation, operating voltage of 40 kV, 0.01° step size and 20 s step time over a range
0.5°< 2θ <3.5°. Microscope glass slides were used as sample holders for these
measurements. The samples were manually ground prior to the XRD analysis and all
measurements were performed at room temperature.
Elemental analysis
Quantitative estimation of organic groups was performed by CHNS analysis.
Nitrogen, carbon and sulphur content for all organosilicas was determined using a LECO
model CHNS-932 elemental analyzer from St. Joseph, MI
High resolution thermogravimetric analysis
Thermogravimetric measurements were performed under flowing nitrogen on a
TA Instruments Inc. (New Castle, DE, USA) model TGA 2950 high-resolution
thermogravimetric analyzer. The weight change (TG) patterns were recorded over a
temperature range from 35 to 900 °C. This instrument is equipped with an open platinum
pan and an automatically programmed temperature controller. The high-resolution mode
was used to record the TG data. In this mode the heating rate is adjusted automatically
39
during measurements to achieve the best resolution; the maximum rate of 3 - 10 °C min-1
was used. The weight of the analyzed sample was typically within 5-10 mg.
Transmission electron microscopy (TEM) analysis
The TEM images were obtained by using a Hitachi HD-2000 Scanning and
Transmission Electron Microscope (STEM). The unit was operated at an accelerating
voltage of 200kV and a current at 30 mA. The sample powders were dispersed in ethanol
by a moderate sonication at concentrations of 5 wt% of solids. A lacy carbon coated 200mesh copper grid was first dipped into a sample suspension and then dried under vacuum
at 80 ºC for 12 hours prior to the TEM imaging
2.2. Calculations section
The BET specific surface area
The specific surface area (SBET, m2/g) for the samples under study was calculated
by employing the Brunauer-Emmett-Teller (BET) method [274] in the range of relative
pressures from 0.05 to 0.2 [272] according to the following equation:
S BET  n m  N A   N 2 ,
(1)
where nm is the monolayer capacity (a monolayer on the surface is formed by adsorbed
gas molecules; moles/g); NA is Avogadro’s number (6.23 · 1023 molecules/mol);  N is
2
40
the cross-sectional area of nitrogen or argon at -196 °C, which is estimated to be
0.162  10 -18 m 2 / molecule or 0.138  10 -18 m 2 / molecule, respectively.
The monolayer capacity, nm, and the BET constant C can be calculated from the slope
and intercept from the linear BET equation:
p
po

p 

n  1 
po 


C  1   p  ,
1

nm  C nm  C  po 
(2)
where n is the amount adsorbed expressed in cm3 STP/g; p/p0 is the relative pressure
(dimensionless); C is the BET constant associated with adsorption energy. The BET
model is based on the following assumptions: (i) energetically homogenous surface, (ii)
localized adsorption, i.e., molecules once adsorbed on the surface are motionless, (iii) no
lateral interactions on the surface between adsorbate molecules, and (iv) infinite number
of layers is formed.
Single-point pore volume
The single-point total pore volume (Vt, cm3/g) [272] was estimated from the amount
adsorbed at a relative pressure p/po of 0.99, where p and po denote the equilibrium
pressure and saturation vapor pressure, respectively.
41
Pore size distribution
The pore size distribution was calculated from the adsorption branch of nitrogen
adsorption isotherms by using the imporved KJS (Kruk, Jaroniec and Sayari) method
[275]. This method employs the BJH (Barrett, Joyner and Halenda) algorithm [276] with
a relation between the pore size and capillary condensation pressure derived on the basis
of adsorption data for high-quality MCM-41 materials with cylindrical pores (2 – 6.5 nm)
and fitted by the Kelvin-type equation [275]:
 p 
2    VL
r   
 po  R  T  ln po
 p

 p 
 t    0.3
  po 


(3)
where r is the pore radius (nm); VL is the molar volume of the liquid adsorbate (for liquid
nitrogen is 34.68 cm3/mol);  is the surface tension (for liquid nitrogen at -196 °C is
8.88·10-3 N m-1); T is the absolute temperature (-196 °C for liquid nitrogen); R is the
universal gas constant (8.314 J/mol·K; t(p/po) is the statistical film thickness (nm) for
nitrogen adsorption on the reference silica, which is determined by using the following
equation in the relative pressure range within 0.1 and 0.95:

t 





60.65
p


  0.1 

po 
 p 
 0.03071  log  

 po  
0.3968
(4)
The pore radius (nm) expression after substitution of all numerical values (3) assumes the
following form:
42
 p
 p
0.416
 t    0.3
r   
 po  log po   po 
 p
 
(5)
The primary mesopore diameter (wKJS, nm) is defined at the maximum of the pore size
distribution (PSD).
The volume of complementary pores for the SBA-15 and SBA-16 silicas was
calculated by integration the PSD curve up to 5 nm and 4 nm, respectively; this
integration limit was established on the basis of the first peak of the distribution function
representing complementary pores. This volume denoted as Vc (cm3/g) includes the
volume of irregular micropores present in the mesopore walls as well as small apertures
that connect ordered cage-like mesopores
Pore diameter
The PSD analysis was performed under the assumption of cylindrical pore
geometry, while cage-like SBA-16 and FDU-1 mesopores are rather spherical; thus, the
KJS method leads to a systematic underestimation of the size of spherical cages by
approximately 2 nm [278]. Therefore, the primary mesopore diameters were also
evaluated by using proper geometrical relations between the pore size (wd, nm), volume
of complementary pores (Vc, cm3/g), volume of primary mesopores (Vp, cm3/g) and unit
cell (a, nm) derived for the Im3m (Equation 6) and P6mm (Equation 7) symmetry groups,
respectively [277-279].
43

1 / 3
Vp
w d  0.985  a  
1/   V  V 

c
p 


1 / 2
Vp
w d  1.05  a  
1/   V  V 

c
p 

(6)
(7)
where the symbol  denotes the organosilica density, which was assumed to be 2.0 g/cm3.
It is noteworthy that the pure amorphous silica density is 2.2 g/cm3. The pore wall
thickness (b, nm) for Im3m and P6mm symmetries was assessed by using the following
Equations 8 and 9, respectively.

b  a 3 / 2  wd

b  a  w d 
(8)
(9)
Unit cell parameter
The unit-cell parameter (a, nm) for SBA-16 (Equation 10) and SBA-15 (Equation
11) was evaluated using the interplanar spacing (d, nm) corresponding to (110) and (100)
peaks, respectively, on the powder XRD pattern.
a  d110 
2
a  d100  2  31 / 2
(10)
(11)
The interplanar spacing was calculated as follows:
d   / 2 sin 
(12)
44
where d is the interplanar distance (nm),  is the wavelength (0.154056 nm in this
study),  (degrees) is the position of the (110) or (100) first diffraction peak.
2.3. Materials and reagents
Structure directing agents: triblock copolymers, poly(ethylene oxide)-bpoly(propylene oxide)-b-poly(ethylene oxide) Pluronic P123 (EO20PO70EO20) and
Pluronic F127 (EO106PO70EO106) were obtained from BASF Corporation. Silica source:
tetraethyl orthosilicate (TEOS) was received from Across Organics (98 %). The
organosilanes:
ureidopropyltrimethoxysilane
(U),
3-mercaptopropylsilane
(SH),
bis(triethoxysilyl) ethane (ES), tri[3-(trimethoxysilyl)propyl] isocyanurate (ICS) and
bis(triethoxysilylpropyl) disulfide (90 %) (DS) were obtained from Gelest, Inc.,
Morrisville, PA, whereas triethoxyvinylsilane (V) was from Acros Organics, Morris
Plains, NJ.
Concentrated hydrochloric acid (37%) and ethanol (95 %) used for extraction as
well as sodium chloride were obtained from Fischer Scientific (Pittsburgh, PA).
Deionized water (DW) was obtained using in-house Ionpure Plus 150 Service
Deionization ion-exchange purification system.
All chemicals were used as received without further purification.
45
Table 1. Structures of simple organosilanes employed in the syntheses of the
organosilicas studied.
Organic Group
Abbr.
Organosilane structure
O
O
O
Ureidopropyl
U
Si
N
NH2
O
ureidopropytrimethoxysilane
O
O
Mercaptopropyl
SH
Si
SH
O
(3-mercaptopropyl)trimethoxysilane
O
O
Vinyl
V
Si
O
triethoxyvinylsilane
46
Table 2. Structures of bridged organosilanes employed in the synthesis of periodic
mesoporous organosilicas.
Organic Group
Abbr.
Organosilane structure
S
Si
Disulfide
Si
S
DS
bis(triethoxysilylpropyl) disulfide
O
O
O
Ethane
ES
Si
Si
O
O
O
1,2-bis(triethoxysilyl)ethane
O
O
O
O
Si
N
O
N
O
Isocyanurate
Si
N
O
O
O
ICS
Si
O
O
O
tri[3-(trimethoxysilyl)propyl]isocyanurate
III. Co-condensation synthesis and adsorption properties of
cage-like mesoporous silicas prepared under conventional
and microwave conditions*
The use of non-ionic block copolymers as soft templates opened tremendous
prospects for the development of ordered mesoporous materials. The aforementioned
templates are inexpensive, environmentally friendly, and commercially available. A wide
assortment of block copolymers enables an extension of OMSs not only to 2D
mesomaterials, but also to three-dimensional mesostructures. Among them, one of the
most popular is SBA-16 (3D cubic mesostructure with Im3m symmetry group; bodycentered packing), which is usually obtained by using block copolymers with longer
segment of poly(ethylene oxide) blocks like Pluronic F127 (EO106PO70EO106). It is
noteworthy to mention that the cage-like mesostructures are very attractive and promising
for potential applications, because of their unique structural properties. Such a
mesoporous system is well suited for immobilization of biomolecules, transport of
reactants, and because of its specific structure, the risk of pore blocking is lower in
comparison to 2-D networks and the access to each pore from any direction is easier.
*
This Chapter is based on the following publications:
B.E. Grabicka, M. Jaroniec, Adsorption, 2010 16 385 [266]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec J. Mater. Chem. 2006 16 819 [56]
R.M. Grudzien, B.E. Grabicka, M. Kozak, S. Pikus, M. Jaroniec New J. Chem. 2006 30 1 [64]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec Appl. Surf. Sci. 2007 253 5660 [93]
Author’s related articles: P.F. Fulvio, B.E. Grabicka, R.M. Grudzien, M. Jaroniec Adsorpt. Sci. Technol.
2007 26 439 [80]; P.F. Fulvio, R.M. Grudzien, B.E. Grabicka, M. Jaroniec. to be submitted [280];
47
48
This part of dissertation is devoted to the synthesis of cage-like mesostructures of
SBA-16 under conventional and microwave conditions (see Scheme 1). The aim of this
stage of research was to optimize the synthesis conditions under microwave irradiation in
order to obtain the most popular cage-like OMS. Moreover, this study provided
foundations for microwave-assisted synthesis of cage-like OMOs presented in further
section of this dissertation.
The quality of the resulting OMSs was studied by nitrogen adsorption, powder Xray diffraction (XRD), thermogravimetric analysis (TGA and DTGA) and elemental
analysis.
3.1. Experimental
3.1.1. Conventional synthesis of SBA-16
3.1.1.1. Effective method for removal of polymeric template from SBA-16 silica
A large pore cubic silica, SBA-16, was prepared by using triblock copolymer
(EO106PO70 EO106, F127) as a structure directing agent, tetraethyl orthosilicate (TEOS) as
a silica source and sodium chloride at low acid concentrations (see Scheme 6). The
synthesis procedure was based on the recipe reported earlier by Qiu et al. [58]. In the
typical synthesis, 2 g of F127 and 7.05 g of NaCl were dissolved in 80 ml of 0.5M HCl at
40 °C. After 2-3 hours stirring 8.4 g TEOS was added dropwise. The resulting mixture of
49
the following molar composition: 1 TEOS: 0.00367 F127: 0.864 HCl: 2.7699 NaCl:
100.231 H2O was stirred for 20 h at 40 °C, and subsequently subjected to the
hydrothermal treatment for 24 h at 100 °C. The product was filtered, washed with
deionized water and dried at 80 °C. The resulting white solid was divided into two parts;
the first one was extracted with a mixture containing 100ml of ethanol and 2ml of 36%
HCl at 60-70 °C for 24 h (about 75 % of polymer was removed) followed by drying,
whereas the second one was dried only. After drying in oven at 80 °C both parts were
calcined in the flowing air at various temperatures: 200, 250, 300, 350, 400, 450, 500 and
550 °C for 4 h with a heating rate of 3 °C min-1. The template-free SBA-16 mesosilicas
are denoted as SBA-16-e-x and SBA-16-c-x, where e-x refers to the samples initially
extracted followed by calcination at temperature x, whereas c-x denotes the samples
subjected directly to calcination at temperature x.
3.1.1.2. Adsorption studies of thermal stability of SBA-16 mesoporous silica
All silica samples were synthesized using 2 g of polymeric template and 7.05 g of
sodium chloride, which were added to 20 ml of 2M HCl and 60 ml of deionized water
(DW) at 40 ºC. After complete dissolution of polymer F127, 8.4 g of TEOS was pipetted
dropwise followed by strirring for 20 hrs at 40 ºC. The resulting slurry inside a
polypropylene bottle was closed tightly and subsequently placed in an oven for 24 hrs at
100 ºC under static conditions. The precipitate was filtered, washed with DW, and dried
in an oven at 80 ºC. Thus prepared silica was divided into two parts; one part was
50
extracted three times with 2 ml of 36 wt.% HCl and 100 ml of 95 % ethanol at 70 º C.
Both as-synthesized and extracted samples were subjected to calcination at 350, 550, 700,
800 and 900 º C for 4 hours under air atmosphere. The resulting materials are denoted as
S-cT or S-ecT, where S, c, ec and T refer to silica, calcined, extracted–calcined silica and
temperature of calcination, respectively.
3.1.1.3. Effects of hydrothermal treatment and template removal on the adsorption
and structural properties of SBA-16
The large pore SBA-16 silica samples were prepared according to a previously
reported procedure. The triblock copolymer Pluronic F127 (EO106PO70EO106) was used as
the structure directing agent, TEOS as the silica source and sodium chloride at low
hydrochloric acid concentrations. In a typical synthesis, 2g of F127 and 7.05g of NaCl
were dissolved in 80ml of 0.5mol/l HCl at 40ºC under stirring for 2-3h. To this system
8.4g of TEOS were added dropwise. The resulting mixtures were stirred for 2, 4, 6, 10 or
20h followed by different hydrothermal treatment times of 6, 12, 24 and 48h at 100ºC
using Teflon sealed containers. The precipitated products were then filtered, washed with
deionized water and dried under air atmosphere at 80ºC. The resulting solid products,
about 0.5g of each, were extracted with a mixture of 100ml of EtOH 95% and 2ml of
concentrated HCl at 60-70ºC for 24h. After a second stage of drying at 80ºC the samples
were calcined in flowing air at 350°C for 4 h with a heating rate 3 °C min-1. The resulting
51
template-free mesoporous silicas were denoted as SBA16-st-HT, where st and HT are the
first step of the self-assembly synthesis and hydrothermal treatment times, respectively.
3.1.2. Synthesis of SBA-16 under microwave irradiation
3.1.2.1. Microwave-assisted synthesis of SBA-16
A series of OMSs was synthesized by self-assembly of tetraethyl orthosilicate
(TEOS) as a silica source and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene
oxide) triblock copolymer (Pluronic F127; EO106PO70EO106) as a structure directing agent
under microwave conditions. The recipe used was analogous to that reported by Zhao et
al. [58]. All samples were prepared by using 2g of Pluronic F127 polymer and 7.05g of
sodium chloride, which were dissolved in 80ml of 0.5M HCl under magnetic stirring at
40 oC. The addition of sodium chloride improved the structural ordering and enhanced
the mesoporous network of cage-like ordered silica materials [81]. After 4 hours of
stirring, 8.4g of TEOS were added dropwise. The resulting mixture was transferred to
Teflon vessels, which were installed in microwave oven (MARS 5, CEM Corp.). Both
steps of the synthesis, i.e., initial self-assembly and subsequent hydrothermal treatment,
were carried out under microwave irradiation (see Scheme 5). In the first step, the
synthesis mixture was stirred using magnetic bars from 2 to 12h at 40°C. After this step,
magnetic stirring was off and temperature was increased to 100, 120, 140 or 160ºC and
kept at this temperature for 1 to 48h; the exact durations of the initial synthesis step
carried out at 40oC and the hydrothermal treatment performed at higher temperature as
52
well as temperature of the aforementioned treatment are specified in the samples
notation. The resulting slurry was filtered, washed with deionized water, and dried in
oven at 80 °C. All samples were calcined at 350C for 4h under air atmosphere with the
heating rate of 5 °C min-1, by placing four obtained samples of each series in the quartz
boats, in the tube furnace. The removal of polymeric template was done in the same
manner for all series of the samples. The obtained OMS samples were denoted as x-y-z,
where x stands for the hydrothermal treatment temperature (100-160 °C), y and z refer to
the duration (in hours) of the initial self-assembly at 40oC and hydrothermal treatment at
higher temperature (100-160°C), respectively.
53
EO106PO70EO106
+
Si(EtO)4
selfassembly
hydrothermal
treatment
24h at 40 C
24h at 100 C
filtration,
washing,
drying
extraction
in
EtOH/HCl
solution
calcination
4h at 350 C
24h
at 60-70 C
EO106PO70EO106
+
Si(EtO)4
self-assembly
6-12h at 40 C
hydrothermal
treatment
12-24h
at 100 C
filtration,
washing,
drying
calcination
4h at 350 C
microwave-assisted synthesis
Scheme 5. Chart illustrating the synthesis procedure for cage-like mesoporous SBA-16
silica via conventional (top) and microwave-assisted (bottom) methods.
54
Scheme 6. Schematic illustration of the polymeric template removal from as-synthesized
SBA-16 by two different methods: (i) commonly used calcination at 550 °C (top scheme)
and (ii) combined extraction followed by controlled-temperature calcination at 350 °C
(bottom scheme). The large circles connected with straight channels represent
interconnected spherical cages (ordered mesopores), whereas curved thin ribbons denote
irregular micropores within walls of ordered mesopores.
55
3.2. Optimization of synthesis conditions of cage-like mesostructures via
conventional method
3.2.1. Effective method for removal of polymeric template from SBA-16 silica
Nitrogen adsorption–desorption isotherms for two represantative SBA-16
samples denoted as SBA-16-e-350 (e-350) and SBA-16-c-550 (c-550) are shown in
Figure 1. Figure 2a and Figure 2b show a comparison of nitrogen adsorption
isotherms for a series of the SBA-16-e-x and SBA-16-c-x samples calcined at
different temperatures, respectively. The BET specific surface area, total pore
volume, volume of primary mesopores, pore diameter, carbon percentage and unit
cell parameter for those samples are listed in Table 1. The calcination temperature
range was between 200 and 550 °C. These isotherms are type IV with a broad
hysteresis loop starting at a relative pressure at ~ 0.6 - 0.7 and abruptly ending at ~
0.45, which indicates the presence of good-quality cage-like pores. As can be seen
from Figure 1, SBA-16-e-350 features steeper capillary condensation step and much
larger volume of mesopores than those in SBA-16-c-550. Moreover, the capillary
condensation step for SBA-16-e-350 is shifted to higher relative pressures, indicating
larger pore size as shown in the corresponding pore size distributions (see PSD inset
in Figure 1). As expected, calcination process at 550°C (c-550) caused a meaningful
shrinkage of the structure compared to the step by step template removal (e-350),
which can be seen by the offset of the micropore peak (~2.2 nm) towards smaller
56
values, the decrease in the micropore volume from 0.45 to 0.37 cc g-1 as well as the
reduction of the mesopore size and the volume of mesopores.
Figure 2 with adsorption isotherms for calcined and extracted-calcined SBA16 samples shows that the optimal temperature of the template removal is between
250 and 550 °C. A comparison of the samples calcined at lowest and highest
temperature from this series indicates that the extracted sample calcined at 200 °C
(denoted as e-200) has larger pore diameter and contains a small amount of polymer
residue (C = 1.88 %, see Table 1) that reduces slightly its total pore volume as well
as the extracted-calcined at 550 °C (e-550) and only calcined at 550 °C (c-550)
samples are characterized by smaller structural parameters. The observed pore size
reduction is confirmed by the pore size distributions shown in Figure 2c and Figure
2d, which present two well-resolved peaks indicating the presence of micropores (at
~2 nm) in the mesopore walls and the small pores that interconnect ordered
mesopores as well as the ordered spherical mesopores.
Figure 3a shows the X-ray diffraction patterns for the representative samples,
which provided information about ordered structure of the resulting mesomaterials.
As can be seen from this figure, the presence of major intensive peak at 2θ = ~ 0.77
attributed to the (110) reflection and two minor less-resolved peak at 2θ = ~ 1.05 and
1.5 attributed to the (200) and (211) reflections, confirm the formation of ordered
mesoporous materials with Im3m cubic symmetry.
57
Figure 1. Comparison of nitrogen adsorption-desorption isotherms at – 196 °C for SBA16-e-350 and c-550 samples and the corresponding pore size distributions (PSD).
58
Table 3. Structural properties determined from XRD, elemental analysis and nitrogen
adsorption data for SBA-16 silicas studied.
a
Sample
SBET
(m2 g-1)
Vt
(cc g-1)
Vp
(cc g-1)
wKJS
(nm)
%C
a
(nm)
c-200
1084
0.68
0.29
7.66
1.70
16.74
e-200
1086
0.86
0.42
8.74
1.88
17.47
c-250
1126
0.75
0.29
7.70
1.60
16.30
e-250
1133
0.89
0.64
8.73
1.18
16.50
c-300
1175
0.76
0.39
7.68
0.89
16.26
c-350
1166
0.74
0.32
7.42
0.43
15.41
e-350
1187
0.84
0.39
8.56
0.38
17.14
c-400
1107
0.69
0.30
7.44
0.12
15.94
c-450
1030
0.66
0.24
7.26
0.07
15.51
e-450
980
0.75
0.38
8.34
0.15
16.90
c-500
944
0.60
0.22
7.03
0.05
14.83
e-500
1085
0.76
0.35
8.30
0.04
16.42
c-550
941
0.60
0.23
7.02
0.04
15.02
e-550
1044
0.63
0.21
7.26
0.04
15.23
e
871
0.73
0.37
8.56
5.13
17.22
SBET, BET specific surface area; Vt, total pore volume; Vp, volume of primary mesopores; wKJS,
diameter of mesopore cages; % C, carbon percentage; a, unit cell parameter.
59
Figure 2. (a) Comparison of nitrogen adsorption-desorption isotherms at -196 °C for a
series of extracted SBA-16 samples calcined at different temperatures. The isotherms for
e-450, e-350, e-250 and e are offset vertically by 110, 235, 400 and 680 cc STP g-1; (b)
Comparison of nitrogen adsorption-desorption isotherms at -196 °C for a series of SBA16 samples calcined at different temperatures. The isotherms for c-450, c-350 and c-250
are offset vertically by 193, 418 and 678 cc STP g-1; (c) and (d) the corresponding pore
size distributions calculated according to the KJS method for extracted and calcined
samples [279], respectively. Due to the space limitations, the samples are named as e-x
and c-x instead of SBA-16-e-x and SBA-16-c-x, respectively.
60
a
e
e-350
c-550
Pore Diameter (nm)
c
e
8.0
7.5
7.0
80
70
60
c
e
e-350
c-550
200 400 600 800
Temperature ( °C)
c
8.5
90
2
3
4
2-theta (°)
0.6
-Deriv. Weight (% /°C)
1
Weight Change (%)
Intensity (a.u.)
c
b
0.4
c
e
e-350
c-550
0.2
0.0
250 350 450 550
Temperature (°C)
d
200 400 600 800
Temperature (°C)
Figure 3. (a) Comparison of XRD patterns for c (composite), e (extracted), e-350, and c550 SBA-16 samples; (b) Comparison of the thermogravimetric curves (TG) measured in
flowing nitrogen; (c) Evolution of the mesopore diameter as a function of the calcination
temperature for two series of the SBA-16 samples; and (d) DTG curves obtained by
differentiation of TG curves shown in Panel b. Due to the space limitations, the samples
are named as e-x and c-x instead of SBA-16-e-x and SBA-16-c-x, respectively.
61
In addition, the unit cell parameter for the c-x samples gradually decreases with
increasing temperature (see Table 1).
Shown in Figure 3b and Figure 3d are thermogravimetric curves that exhibit
the
weight
loss
between
100
and
800°C
related
to
the
polymer
removal/decomposition, which is about 38, 23 and 3% for the c, e and e-350
samples, respectively. Elemental analysis indicated that the extracted sample retained
about 5.13 % of the carbon residue, which after calcination at 350 °C was reduced to
0.38 %. Such a difference presents the importance of the extraction step for the
template removal from cage-like mesostructures.
A comparison of the pore diameter as a function of the calcination temperature
for both series of the e-x and c-x samples is shown in the Figure 3c. As can be seen
for the c-x samples, the pore width for the sample calcined at 200 °C was about 7.66
nm and almost linearly dropped to a value of 7.02 nm with increasing calcination
temperature, whereas the pore width for the e-x series of SBA-16 started at 8.74 nm,
slowly decreased to the value of 8.34 nm for e-450 and at 550 °C sharply declined
due to the structure shrinkage.
Moreover, the proposed method of the template removal was tested for the SBA16 prepared by using two different recipes; the recipe analogous to that reported by Zhao
et al. [58] but without addition of sodium chloride and the recipe reported by Kim et al.
[57]. Due to a small yield of extraction 32 % and 37 % of polymer was removed,
62
Figure 4. Comparison of nitrogen adsorption-desorption isotherms measured at – 196 °C
for the SBA-16 samples denoted as SBA-16-x-y-b, where x denotes either extraction (e)
or calcination (c), y denotes temperature of calcination and b refers to the previously
reported [57, 58] synthesis modified by using low acid concentration and eliminating the
addition of sodium chloride and the corresponding pore size distributions (PSD).
63
Table 4. Structural properties determined from elemental analysis and nitrogen
adsorption data for the SBA-16 silicas synthesized according to the recipes reported by
Kim at al. [57] (samples having a in the sample code) and Zhao at al. [58] (samples
having b in the sample code); the latter recipe was modified by eliminating the addition
of sodium chloride and using low acid concentrations
SBET
(m2 g-1)
Vt
(cc g-1)
Vp
(cc g-1)
wKJS
(nm)
%C
-
-
-
-
10.24
SBA-16-e-350-a
1169
0.69
0.22
6.76
0.33
SBA-16-c-550-a
1094
0.63
0.18
6.79
0.04
SBA-16-comp-a
-
-
-
-
16.17
SBA-16-e-b
-
-
-
-
10.14
SBA-16-e-350-b
1204
0.72
0.26
7.81
0.42
SBA-16-c-550-b
1082
0.65
0.22
7.44
0.03
SBA-16-comp-b
-
-
-
-
14.94
Sample
SBA-16-e-a
Notation: SBET, BET specific surface area; Vt, total pore volume; Vp, volume of primary mesopores; wKJS,
diameter of mesoporecages; % C, carbon percentage; “comp” refer to the composite (as-synthesized)
samples; -, parameters not determined.
64
respectively, the effect of the pore volume enlargement was less pronounced (see Figure
4 and Table 4). As can be seen from Table 3, the proposed method of the template
removal afforded the SBA-16 samples with much larger pore volumes than those
reported previously.
In summary, this study has demonstrated that a combination of extraction and
temperature-controlled calcination is a successful template removal method. The obtained
cage-like silicas are characterized by high pore volume and pore size as a result of cocondensation process in the presence of sodium chloride at low acid concentrations.
3.2.2. Adsorption studies of thermal stability of SBA-16 mesoporous silica
Figure 5 A and B present the X-ray diffraction patterns for as-synthesized and
extracted cage-like SBA-16 silica samples, respectively. As can be seen, the XRD pattern
for the S-e sample exhibits one major peak and two less intensive peaks associated with
(110), (200) and (211) reflections, respectively, as well as confirms the face-centered
cubic (Fm3m) and body-centered cubic (Im3m) symmetry groups. As can be noticed in
Figure 5 A and B, an increase in the calcination temperature from 350 to 900 °C for assynthesized and extracted silicas led to a gradual decrease in the peak intensities and a
progressive shift of the (110) peak towards higher angles. It shows that the higher
calcinations temperature caused a substantial shrinkage. In addition, the effect of
calcination did not affect the ordering of the cubic mesostructure and preserved the cagelike ordering at higher calcination temperatures, even 800-900 °C.
65
A
S-c700
S-c800
S-c900
0.5
1.0
1.5

2 
S-ec550
S-ec700
S-ec800
S-ec900
2.0
N2
0.2
0.4
0.6
0.8
Relative Pressure
PSD (cm3g-1nm-1)
S-c350
S-c550
S-c700
S-c800
S-c900
E
0.2
0.1
2
1.0
D
500
Amount Adsorbed (cm3 STP g-1)
Intensity (a.u.)
S-ec350
1.5

2 
100
0.0
S-e
1.0
200
0
B
0.5
300
2.0
S-c350
S-c550
S-c700
S-c800
S-c900
0.3
4
6
8
Pore Diameter (nm)
S-e
S-ec350
S-ec550
S-ec700
S-ec800
S-ec900
0.3
400
PSD (cm3g-1nm-1)
S-c550
Amount Adsorbed (cm3 STP g-1)
Intensity (a.u.)
S-c350
C
400
F
0.2
300
200
100
N2
0
0.0
0.2
S-e
S-ec350
S-ec550
S-ec700
S-ec800
S-ec900
0.4
0.6
0.8
Relative Pressure
1.0
0.1
0.0
2
4
6
8
Pore Diameter (nm)
10
Figure 5. X-ray diffraction (XRD) patterns (A and B), nitrogen adsorption isotherms (C
and D) measured at – 196 °C and the corresponding pore size distributions (PSDs) (E
and F) calculated according to the KJS method [279] for the cage-like SBA-16
mesoporous silica calcined at various temperatures for 4 hrs in the flowing air.
66
The structural properties are presented in Table 5. The adsorption parameteres of
the extracted SBA-16 samples exhibit higher values in comparison to the calcined
samples of cage-like silicas. Moreover, the difference in the values is significant for the
samples calcined below 550 °C, whereas for the silica mesostructures treated above the
550 °C, the unit cell values are close to each other.
Nitrogen adsorption-desorption isotherms measured at -196 °C for a series of
calcined template-containing silicas and calcined-extracted silicas is presented in Figure 5
D and E, respectively. All calcined siliceous materials represent typical type IV isotherms
with a pronounced adsorption and sharp desorption branches. These two branches form a
type H2 hysteresis loop associated with mesoporous materials with uniform cage-like
pores and narrow oppenings. As can be seen from the isotherms shown in Figure 5 D and
E, an increase in the calcination temperature from 350 to 900 °C caused a gradual
decrease in the adsorption capacity and offset the capillary condensation step to smaller
values of relative pressures, indicating a decrease in the mesopore cage width. Similar
behaviour was already reported by Kruk et al. [60] for the cubic cage-like FDU-1
materials.
Figure 6 presents the evolution chart showing the changes in the structural
parameters of the samples studied. Panels A nd B present the pore diameters of calcined
and extracted-calcined SBA-16 silicas, respectively. The KJS pore diameters for a series
of the S-cT and S-ecT samples were reduced from 7.42 to 6.14 nm and 8.56 to 6.23 nm,
respectively. Other paramaters such as the specific surface area (Panel C and D), the
pore-wall thickness (Panel E and F) and the total pore volume (Panel G and H) display
67
their evolution with increasing calcination temperature. As can be seen from the Figure 6,
for the samples calcined in the range 350 and 900 °C (Panel C and D) the BET surface
area decrease progressively with increasing temperature and after calcination at 700 °C
and 900 °C the BET surface area is reduced by about 39 % and 31 % as well as 71 % and
63 % for the S-cT and S-ecT series, respectively. Moreover, the pore wall thickness
(Panel E and F) shows a tendency of having a maximum with the highest value of 4.27
and 4.51 nm for S-c700 and S-ec550, respectively.
The total pore volume shown in Figure 6 (Panel G and H), similarly to the BET
surface area, decreases with increasing calcination temperature. However, about 41 %
and 44 % of the volume of primary mesopores (Vo) as well as 26 % and 31% of the
volume of complementary pores (Vc) was retained for the S-cT and S-ecT materials after
calcination at 900 °C.
In summary, the study shows the effect of calcination on the structural properties
of cage-like mesostructures. All SBA-16 silicas possessed high thermal stability.
Moreover, this study confirms the results obtained by Kruk et al. for cage-like FDU-1
silicas [23], and related mesoporous materials reported by others [61].
68
Table 5. Adsorption parameters for the SBA-16 silicas studieda
a
Sample
SBET
m2 g-1
Vc
cc g-1
Vo
cc g-1
Vt
cc g-1
wKJS
nm
wd
nm
b
nm
a
nm
S-c350
1166
0.42
0.32
0.74
7.42
9.78
3.56
15.41
S-c550
941
0.37
0.23
0.60
7.02
8.91
4.10
15.02
S-c700
713
0.26
0.16
0.46
6.70
7.79
4.27
13.93
S-c800
564
0.19
0.19
0.39
6.38
8.23
3.62
13.68
S-c900
341
0.11
0.13
0.25
6.14
7.56
4.06
13.42
S-e
871
0.36
0.37
0.73
8.56
11.51
3.40
17.22
S-ec350
1187
0.45
0.39
0.84
8.56
11.52
3.59
17.44
S-ec550
1044
0.42
0.21
0.63
7.26
8.68
4.51
15.23
S-ec700
816
0.31
0.22
0.56
7.06
8.43
3.78
14.10
S-ec800
708
0.26
0.23
0.49
6.69
8.61
3.51
14.00
S-ec900
434
0.14
0.17
0.32
6.23
7.82
3.52
13.10
Notation: SBET , BET specific surface area; Vc, volume of interconnecting pores (including micropores) of
the diameter below 4 nm; Vo, volume of primary mesopores; Vt, total pore volume; wKJS, mesopore
diameter calculated by the KJS method [18]; wd, pore diameter calculated on the basis of the unit cell
parameter and pore volumes according to the relation derived for the cubic Im3m structure assuming 2.2
g/cc density of silica; b, minimal wall thickness a, unit cell parameter calculated from the observed
characteristic Bragg’s reflection (110) for the silicas studied.
8
A
Mesopore Diameter (nm)
Mesopore Diameter (nm)
69
6
4
2
0
8
6
4
2
0
C
800
600
400
200
0
2 -1
1000
0
BET Surface Area (m g )
BET Surface Area (m2g-1)
400 600 800 1000
o
Temperature ( C)
1200
1200
800
600
400
200
0
3
2
1
0
5
Wall Thickness (nm)
Wall Thickness (nm)
4
E
0
3
2
1
0
G
0.6
0.4
0.2
0.0
400 600 800 1000
o
Temperature ( C)
0
Total Pore Volume (cc g-1)
Total Pore Volume (cc g-1)
200 400 600 800
1000
o
Temperature ( C)
F
4
400 600 800 1000
o
Temperature ( C)
0.8
200 400 600 800 1000
o
Temperature ( C)
D
1000
400 600 800o 1000
Temperature ( C)
5
B
10
200 400 600 800 1000
o
Temperature ( C)
H
H
0.8
0.6
0.4
0.2
0.0
0
200 400 600 800 1000
o
Temperature ( C)
Figure 6. Evolution of the mesopore diameter (A and B), the BET surface area (C and
D), minimal pore-wall thickness (E and F) and the total pore volume (G and H) plotted
against the temperature of calcination for the SBA-16 silicas studied.
70
3.2.3. Effects of hydrothermal treatment and template removal on the adsorption
and structural properties of SBA-16 mesoporous silica
Nitrogen adsorption-desorption isotherms measured at -196 °C for extracted
SBA-16 silicas are shown in Figure 7. Each Panel in Figure 7 presents the series of
samples with increasing duration time of stirring in the self-assembly stage (2-20 h) and
the time of hydrothermal treatment (Panels A, B, C and D for 6h, 12h, 24h and 48h,
respectively). All obtained samples represent typical type IV isotherms with the H2
hysterisis loop, characteristic for cage-like materials with uniform pores. A broad
hysteresis loop confirms these properties by starting at a relative pressure of ~ 0.6 - 0.7
and abruptly ending at ~ 0.45, which indicates the presence of cage-like pores with
openings below 5nm. The high uniformity is also manifested by pore size distributions in
Figure 8. The BET specific surface area, total pore volume, volume of primary
mesopores, as well as the pore diameter for those samples are listed in Table 6. As can be
noticed, the pore size increases significantly with the longer duration of the self-assembly
synthesis stage. In addition, the hydrothermal treatment time affects the uniformity of
cage-like pores and shows the need of longer time of this process to obtain narrow pore
size distributions.
The template removal for cage-like SBA-16 mesostructures was monitored by
high-resolution thermogravimetry (TG). The TG patterns and the corresponding
differential TG (DTG) profiles recorded in nitrogen atmosphere from room temperature
to 800 °C, are displayed in Figure 9. The typical weight loss curves are presented and
show three important weight loss segments confirming the efficient template removal.
71
B
A
800
Amount Adsorbed (cc STP g-1)
Amount Adsorbed (cc-1 STP g-1)
800
600
400
S16-2st-6HT
S16-4st-6HT
S16-6st-6HT
S16-10st-6HT
S16-20st-6HT
200
600
400
200
S16-2st-12HT
S16-4st-12HT
S16-6st-12HT
S16-10st-12HT
S16-20st-12HT
0
0
0.0
0.2
0.4
0.6
Relative Pressure
0.8
0.0
1.0
0.4
0.6
Relative Pressure
0.8
1.0
D
C
1000
Amount Adsorbed (cc STP g-1)
800
Amount Adsorbed (cc STP g-1)
0.2
600
400
S16-2st-24HT
S16-4st-24HT
S16-6st-24HT
S16-10st-24HT
S16-20st-24HT
200
0
0.0
0.2
0.4
0.6
Relative Pressure
0.8
1.0
800
600
400
S16-2st-48HT
S16-4st-48HT
S16-6st-48HT
S16-10st-48HT
S16-20st-48HT
200
0
0.0
0.2
0.4
0.6
Relative Pressure
0.8
1.0
Figure 7. Nitrogen adsorption isotherms at -196ºC for the extracted-calcined SBA-16
samples synthesized by varying duration time of the first stage of synthesis (2-20h) and
hydrothermal treatment step at 100ºC for 6, 12, 24 and 48h, shown in Panels A, B, C and
D, respectively.
72
-1
-1
0.15
-1
-1
B
S16-2st-12HT
S16-4st-12HT
S16-6st-12HT
S16-10st-12HT
S16-20st-12HT
0.20
PSD (cc g nm )
0.15
PSD (cc g nm )
A
S16-2st-6HT
S16-4st-6HT
S16-6st-6HT
S16-10st-6HT
S16-20st-6HT
0.10
0.10
0.05
0.05
0.00
0.00
2
0.10
4
6
Pore Diameter (nm)
8
D
S16-2st-48HT
S16-4st-48HT
S16-6st-48HT
S16-10st-48HT
S16-20st-48HT
0.20
PSD (cc g-1 nm-1)
0.15
2
C
-1
-1
8
S16-2st-24HT
S16-4st-24HT
S16-6st-24HT
S16-10st-24HT
S16-20st-24HT
0.20
PSD (cc g nm )
4
6
Pore Diameter (nm)
0.15
0.10
0.05
0.05
0.00
0.00
2
4
6
Pore Diameter (nm)
8
2
4
6
Pore Diameter (nm)
8
Figure 8. Pore size distributions (PSD) obtained for the extracted-calcined SBA-16
samples synthesized by varying duration time of the first stage of synthesis (2-20h) and
hydrothermal treatment step at 100ºC for 6, 12, 24 and 48h, shown in Panels A, B, C and
D, respectively.
S16-comp-4h-24HT
S16-e-4h-24HT
S16-e-cal3550-4h-24HT
Weight change (%)
100
90
80
70
- Deriv. Weight (% / OC)
73
S16-comp-4h-24HT
S16-e-4h-24HT
S16-e-c350-4h-24HT
0.8
0.6
0.4
0.2
60
B
A
0.0
200
400
600
Temperature (oC)
800
200
400
600
Temperature (oC)
800
Figure 9. Comparison of the TG (A) and DTG (B) curves obtained for the silicapolymer composite, extracted and extracted-calcined at 350ºC representative samples of
SBA-16 prepared for 4h (the first stage of synthesis) and 24h (hydrothermal treatment at
100ºC).
74
Table 6. Adsorption and low angle XRD data obtained for the extacted SBA-16 samples
synthesized by varying duration time of the first stage of the process (2-20h) and
hydrothermal treatment at 100ºC for 6, 12, 24 and 48h.
a
[nm]
SBET
[m2/g]
Vc
[cc/g]
Vt
[cc/g]
wd
[nm]
2 st -6 HT
14.15
721
0.21
0.43
8.77
2 st -12 HT
13.24
760
0.26
0.45
7.75
2 st -24 HT
15.17
694
0.25
0.47
9.26
2 st -48 HT
15.85
788
0.29
0.59
10.30
4 st -6 HT
14.95
506
0.18
0.31
8.16
4 st -12 HT
13.72
1032
0.39
0.70
8.72
4 st -24 HT
14.45
840
0.31
0.56
8.92
4 st -48 HT
16.37
973
0.38
0.71
10.59
6 st -6 HT
13.62
740
0.18
0.36
8.11
6 st -12 HT
14.63
815
0.28
0.50
8.84
6 st -24 HT
14.34
832
0.25
0.52
9.21
6 st -48 HT
14.96
969
0.37
0.73
9.91
10 st -6 HT
12.82
671
0.25
0.48
7.91
10 st -12 HT
11.57
584
0.17
0.36
7.02
10 st -24 HT
13.52
730
0.26
0.51
8.49
10 st -48 HT
13.63
708
0.27
0.58
8.98
20 st -6 HT
14.22
851
0.31
0.52
8.40
20 st -12 HT
15.88
799
0.28
0.46
9.10
20 st -24 HT
15.55
874
0.33
0.54
9.12
20 st -48 HT
16.46
889
0.33
0.55
9.77
Sample
a – unit cell parameter; SBET – BET surface area; Vc – volume of complementary pores calculated from the
PSD curves in the range of 0-5nm; Vt - total pore volume calculated from the PSD curves in the range of 011nm; wd – pore width at the maximum of the PSD curve.
75
The first weight loss region until 100-150 °C exhibits the thermodesorption of
physisorbed water and ethanol. The next weight loss step around 200°C, reflects the
polymer removal. The third weight loss region, above 400 °C, reflects the condensation
of silanol groups. The TG and DTG profiles of the representative SBA-16 samples
confirm the successful removal of the polymer template.
Overall, this study shows the importance of duration of both process stages, the
self-assembly and hydrothermal treatment, in the synthesis of SBA-16 in order to obtain
good quality mesostructures. The optimal time of each stage of the process was
established for the synthesis of good quality SBA-16 samples.
3.3.
Microwave-assisted
synthesis
and adsorption properties
of
cage-like
mesoporous silicas
Nitrogen adsorption isotherms measured at -196 °C for the calcined OMSs are
shown in Figure 10 - Figure 13 together with the corresponding pore size distributions,
which were calculated from adsorption branches of nitrogen adsorption isotherms using
the improved KJS method, and with small angle powder X-ray diffraction (XRD)
patterns. It is noteworthy that each particular series of the OMS samples was obtained by
varying temperature and time of microwave irradiation. The first step of the synthesis
was performed at 40C for 2 to 12 hours. The second step, hydrothermal treatment, was
carried out at 100, 120, 140 or 160C for 2 to 24 hours. The basic parameters for the
samples studied such as the BET specific surface area, the single-point pore volume, the
76
volume of complementary pores, the pore width and the d-spacing are provided in Table
7. Figure 10 - Figure 13 and data summarized in Table 7 show that the temperature and
time of microwave irradiation are essential factors that control the adsorption properties
of the resulting OMS samples.
Figure 10 shows a complete set of nitrogen adsorption isotherms, pore size
distributions and small angle XRD patterns for all OMS samples hydrothermally treated
under microwave irradiation at 100oC. Panels A, B and C contain adsorption isotherms
for the samples obtained by stirring at 40oC for 2, 6 and 12 hours, respectively; each
panel shows a series of isotherms referring to different durations of hydrothermal
treatment at 100oC. The BET specific surface area, the volume of complementary pores,
single-point total pore volume and mesopore diameter for these samples are summarized
in Table 7. As can be seen from Figure 10, all adsorption isotherms are type IV with a
broad hysteresis loop and delayed desorption ending at relative pressure of ~0.45, which
is typical for cage-like mesostructures. The type of the block copolymer used, the shape
of hysteresis loop and the corresponding XRD profiles indicate that all samples have the
SBA-16-type mesostructure. For these SBA-16 samples the BET specific surface area
changes from 626 to 1200 m2/g, the single-point pore volume varies from ~0.40 to 0.86
cc/g; and the pore diameters are in the range of 6-8 nm with a distinctive tendency to
grow with increasing time of the microwave-assisted synthesis. Figure 10 and data in
Table 7 show that the duration of the first synthesis step as well as hydrothermal
treatment (the second step) is an important factor for the overall quality of SBA-16,
especially for the surface area and the volumes of primary (ordered) and complementary
77
Table 7. Adsorption and structural parameters of ordered mesoporous silicas obtained
under microwave irradiation. *
Sample
100-2-1
100-2-3
100-2-4
100-2-6
100-6-1
100-6-3
100-6-4
100-6-6
100-6-9
100-6-12
100-6-24
100-12-6
100-12-8
100-12-12
100-12-24
120-2-1
120-2-3
120-2-4
120-2-6
120-6-1
120-6-3
120-6-4
120-6-6
140-2-1
140-2-3
140-2-4
140-2-6
140-6-1
140-6-3
140-6-4
140-6-6
160-2-1
160-2-3
160-2-4
160-2-6
160-6-1
160-6-3
160-6-4
160-6-6
SBET
m2/g
816
793
830
884
684
745
812
779
866
1104
1061
877
626
798
1200
916
951
951
955
857
942
959
1191
769
758
798
769
888
787
1010
953
812
692
710
637
953
782
803
631
Vc
cm3/g
0.29
0.28
0.28
0.30
0.22
0.26
0.28
0.27
0.31
0.39
0.37
0.30
0.23
0.29
0.42
0.30
0.32
0.31
0.30
0.29
0.32
0.32
0.40
0.07
0.09
0.15
0.07
0.31
0.24
0.33
0.24
0.16
0.08
0.06
0
0.25
0.18
0.12
0.03
Vo
cm3/g
0.22
0.22
0.29
0.32
0.15
0.19
0.24
0.30
0.28
0.41
0.43
0.24
0.17
0.20
0.41
0.32
0.35
0.44
0.60
0.31
0.37
0.44
0.52
1.16
1.03
0.87
1.10
0.29
0.39
0.51
0.77
0.79
0.90
1.12
1.49
0.70
0.64
0.91
1.05
Vt
cm3/g
0.52
0.51
0.59
0.63
0.38
0.47
0.54
0.50
0.61
0.83
0.82
0.55
0.41
0.50
0.86
0.64
0.70
0.77
0.93
0.62
0.72
0.78
0.95
1.25
1.15
1.06
1.35
0.61
0.64
0.88
1.04
0.98
1.01
1.20
1.54
0.98
0.86
1.06
1.11
wKJS
nm
6.62
6.78
7.07
7.43
6.02
6.21
6.36
6.80
6.15
8.32
7.78
6.77
7.26
6.50
7.23
6.92
7.08
7.94
8.92
7.23
7.41
7.77
7.75
9.72
9.36
9.31
9.64
7.24
7.94
8.11
8.58
9.19
9.24
9.61
0.92
8.83
8.82
8.92
9.37
d
nm
8.4
8.5
8.4
8.6
8.3
8.8
8.6
8.8
9.0
9.3
9.2
8.8
8.8
8.5
9.1
8.4
8.1
9.4
8.7
8.6
8.7
9.5
8.9
8.9
9.7
9.4
9.4
8.9
8.9
8.6
9.6
9.7
9.6
9.3
10.3
9.8
9.6
8.7
9.4
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters below
4 nm; Vo, volume of ordered pores; Vt, single-point pore volume; wKJS, mesopore diameter calculated by
the KJS method [279]; d, spacing value for the XRD (110) peak;
a
78
3
0.10
0.05
D
0.00
-1
Amount Adsorbed (cm STP g )
3
400
0.15
0.10
0.05
E
4 6 8 10 12 14
Pore Diameter (nm)
2
300
200
100-12-6
100-12-8
100-12-12
100-12-24
100
0.2 0.4 0.6 0.8
Relative Pressure
0.2
0.1
F
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
4 6 8 10 12 14
Pore Diameter (nm)
I
H
G
1.0
100-12-6
100-12-8
100-12-12
100-12-24
0.3
-1
0.20
0.00
2
C
0
0.0
1.0
100-6-1
100-6-3
100-6-4
100-6-6
100-6-9
100-6-12
100-6-24
0.25
-1
0.15
0.2 0.4 0.6 0.8
Relative Pressure
3
-1
0.20
100
0
0.0
1.0
100-2-1
100-2-3
100-2-4
100-2-6
100-6-1
100-6-3
100-6-4
100-6-6
100-6-9
100-6-12
100-6-24
200
-1
0.2 0.4 0.6 0.8
Relative Pressure
PSD (cm g nm )
100
300
-1
100-2-1
100-2-3
100-2-4
100-2-6
500
3
3
200
0.25
-1
400
3
300
0
0.0
PSD (cm g nm )
B
-1
Amount Adsorbed (cm STP g )
500
PSD (cm g nm )
A
-1
Amount Adsorbed (cm STP g )
400
100-6-1
100-6-4
100-6-6
Intensity (a.u.)
Intensity (a.u.)
100-2-3
Intensity (a.u.)
100-6-3
100-2-1
100-12-6
100-12-8
100-6-9
100-2-4
100-2-6
1.0
1.5
2.0 2.5
o
2( )
3.0
1.0
1.5
100-6-12
100-12-12
100-6-24
100-12-24
2.0 2.5
o
2( )
3.0
1.0
1.5
2.0 2.5
o
2( )
3.0
Figure 10. Nitrogen adsorption isotherms measured at -196 °C (Panels A , B and C) and
the corresponding pore size distributions (PSDs) (Panels D, E and F) calculated by the
KJS method [279] as well as the powder X-ray diffraction patterns (Panels G, H and I)
for the ordered mesoporous silicas obtained under microwave irradiation at 40 °C during
the self-assembly stage and at 100°C in the hydrothermal step.
79
pores (the latter include regular small apertures interconnecting ordered spherical cages
in SBA-16 as well as irregular fine pores present in the mesopore walls due to the
penetration of PEO blocks Kruk et al. [23]). As regards the duration of the first step at
40oC, this study indicates that the optimal time is between 2 and 6h. Although 2h of
initial stirring under microwave irradiation at 40oC seemed to be sufficient for the
synthesis of SBA-16, we preferred to use longer time (6h) for the synthesis of other series
of the samples. However, there was no significant effect on the adsorption parameters of
the samples stirred for 12h.
The duration of microwave-assisted hydrothermal treatment of the SBA-16
samples is extremely important factor. An insufficient time of this treatment leads to
lower quality of samples in terms of the surface area, pore volume and other structural
properties. For instance, two SBA-16 samples, 100-6-1 and 100-6-24 were obtained
under microwave irradiation by stirring for 6h at 40oC and hydrothermal treatment at
100oC for 1 and 24h, respectively. The total pore volume of the sample hydrothermally
treated for 24h doubled in comparison to that for the sample treated for 1h only. Also, its
BET surface area increased from 684 to 1061 m2/g, its pore width increased by ~2nm,
and the volume of complementary micropores enlarged by 40%. This substantial increase
in the surface area and total pore volume is caused by significant increase in the
complementary porosity due to extended time of microwave treatment at 100oC; similar
effect was observed for the cage-like mesostructures prepared under conventional
conditions [61]. Thus, 24h microwave-assisted hydrothermal treatment of SBA-16 is too
long and may lead to the structure deterioration due to the expansion of complementary
80
porosity. Data listed in Table 7 indicate that ~6-9h is an optimal time for microwave
hydrothermal treatment of SBA-16.
The PSD curves corresponding to the adsorption isotherms shown in Figure 10
are bimodal with quite narrow peaks; one reflecting primary mesopores and other
representing complementary pores, which consist of regular apertures and irregular fine
pores in the mesopore walls created by penetration of PEO blocks [23]. Since hysteresis
loops for the isotherms shown in Figure 10 close at the limiting pressure, the size of pore
openings (apertures) is below 5nm, which is confirmed by location of the first PSD peak.
Its maximum is about 2 nm for PSDs shown in Figure 10. The second PSD peak is
located at about 6-8nm and its position shows some tendency to increase with extending
time of hydrothermal treatment. Note that the size of this peak is underestimated about 2
nm [61] because the BJH and KJS methods are applicable for cylindrical pores.
Powder X-ray diffraction (XRD) patterns for the above discussed SBA-16
samples are shown in panels G-I of Figure 10. These XRD patterns show distinct peak at
2 0.85o attributed to (110) reflection and in some cases the further low intensity
reflections are visible; poor resolution of the latter reflections is due to limitation of the
XRD instrument for recording small angle patterns, especially for cage-like OMSs such
as SBA-16. Figure 14 presents the transmission electron microscopy (TEM) and scanning
electron microscopy (SEM) images of the selected ordered mesoporous silicas obtained
under microwave irradiation at 40 °C followed by hydrothermal treatment at 100°C
(sample 100-12-24) and 120°C (sample 120-6-6). STEMs images show ordered porosity
in the samples studied.
81
A
500
-1
400
3
300
200
120-2-1
120-2-3
120-2-4
120-2-6
100
500
400
300
200
0
0.15
3
3
-1
120-2-1
120-2-3
120-2-4
120-2-6
0.20
-1
0.25
0.0
1.0
-1
0.2 0.4 0.6 0.8
Relative Pressure
PSD (cm g nm )
0.0
-1
120-6-1
120-6-3
120-6-4
120-6-6
100
0
PSD (cm g nm )
B
600
Amount Adsorbed (cm STP g )
3
-1
Amount Adsorbed (cm STP g )
600
0.10
0.05
0.2 0.4 0.6 0.8
Relative Pressure
120-6-1
120-6-3
120-6-4
120-6-6
0.3
0.2
0.1
C
0.00
1.0
D
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
2
4 6 8 10 12 14
Pore Diameter (nm)
E
F
120-6-1
120-2-3
120-6-3
Intensity (a.u.)
Intensity (a.u.)
120-2-1
120-6-4
120-2-4
120-6-6
120-2-6
1.0
1.5
2.0 2.5
o
2( )
3.0
1.0
1.5
2.0 2.5
o
2( )
3.0
Figure 11. Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and the
corresponding pore size distributions (PSDs) (Panels C and D) calculated by the KJS
method [279] as well as the powder X-ray diffraction patterns (Panels E and F) for the
ordered mesoporous silicas obtained under microwave irradiation at 40 °C during the
self-assembly stage and at 120°C in the hydrothermal step.
82
The resulting samples possess a well-developed mesoporous network, indicating a good
quality of the silica materials.
Shown in Figure 11 are nitrogen adsorption isotherms, PSDs and XRD patterns
for the SBA-16 samples obtained by microwave-assisted hydrothermal treatment at
120ºC. Similarly as in the case of hydrothermal treatment at 100oC, adsorption isotherms
shown in Figure 11 for the samples treated at 120oC are typical for cage-like OMSs and
can be considered as SBA-16 materials. Moreover, there is a similar tendency of
increasing the pore volume, surface area and pore width with increasing time of
hydrothermal treatment, although the observed changes at 120oC seem to be slightly
smaller than those for the samples treated at 100oC (Table 7). Analysis of the adsorption
parameters for the SBA-16 samples prepared at 120oC under microwave irradiation
indicates that 6h treatment can be too long, especially for the sample initially stirred for
2h only; in this case desorption branch starts to decrease before 0.45 p/po.
In comparison to the SBA-16 samples prepared at 100 and 120ºC under
microwave conditions, the OMS samples obtained at higher temperatures (140 and
160ºC) give nitrogen adsorption isotherms with evolving shape of hysteresis loop from
H2 type observed for cage-like mesostructures to H1 type characteristic for channel-like
materials (Figure 12 and Figure 13). It is extremely interesting that the aforementioned
evolution of the hysteresis loop is more pronounced for the samples initially treated at
40oC for 2h. The well-developed H1 hysteresis loops are observed for the samples
initially treated at 40oC for 2h and hydrothermally treated at 140 or 160oC for 4-6h. It
seems that the short initial treatment at 40oC produces less condensed mesostructures,
83
which are more susceptible to structural transformations at higher temperatures.
Moreover, the PSD curves (Figure 12 and Figure 13) for the samples initially treated at
40oC for 2h and hydrothermally treated at 140 or 160oC show smaller complementary
porosity in the range of micropores, which was also observed for the SBA-15 samples
synthesized at high temperatures under microwave irradiation [265]. This effect is
especially pronounced for the samples treated at 160oC; in this case, the surface area is
reduced and the pore width and the total pore volume are enlarged with increasing time
of hydrothermal treatment. Again, the effect of the pore width expansion seems to be less
pronounced for the samples prepared at 140 and 160oC with longer initial treatment (6h)
at 40oC. The observed gradual changes in the hysteresis loops for the samples treated at
140 and 160oC under microwave irradiation are very interesting and suggest structural
changes from cage-like to channel-like porous systems.
It is shown that the microwave-assisted synthesis affords good quality SBA-16
samples at lower temperatures of hydrothermal treatment (100-120oC), whereas the
treatment at higher temperatures (140-160oC) may result in the silica mesostructures
resembling channel-like porous systems. This structural change seems to be facilitated for
the samples exposed to a short stirring (2h) at 40oC. Also, this study shows that the
microwave-assisted synthesis was successfully used to screen a wide range of
temperatures and time in order to establish optimal conditions for the synthesis of SBA16. It is noteworthy to mention that the significant time reduction of the process was
achieved in comparison to the conventional method. The duration of traditional process
was shortened from 48 hours to optimal 2-6 h for the self-assembly step and 6-12 h for
84
the hydrothermal treatment in the case of syntheses temperature at 100-120 °C. The
resulting cage-like materials exhibited high surface area, large pore volume and large
pore diameters.
-1
Amount Adsorbed (cm STP g )
A
800
400
140-2-1
140-2-3
140-2-4
140-2-6
200
0
0.2 0.4 0.6 0.8
Relative Pressure
140-6-1
140-6-3
140-6-4
140-6-6
200
0
1.0
C
140-2-1
140-2-3
140-2-4
140-2-6
400
0.0
0.3
1.0
D
140-6-1
140-6-3
140-6-4
140-6-6
0.4
-1
-1
0.2 0.4 0.6 0.8
Relative Pressure
3
3
-1
0.3
PSD (cm g nm )
-1
0.0
0.4
B
600
3
600
PSD (cm g nm )
3
-1
Amount Adsorbed (cm STP g )
85
0.2
0.1
0.2
0.1
0.0
0.0
2
2
4 6 8 10 12 14
Pore Diameter (nm)
4 6 8 10 12 14
Pore Diameter (nm)
F
E
140-2-3
140-6-1
Intensity (a.u.)
Intensity (a.u.)
140-2-1
140-6-3
140-6-4
140-2-4
140-6-6
140-2-6
1.0
1.5
2.0 o 2.5
2( )
3.0
1.0
1.5
2.0 o 2.5
2( )
3.0
Figure 12. Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and the
corresponding pore size distributions (PSDs) (Panels C and D) calculated by the KJS
method [279] as well as the powder X-ray diffraction patterns (Panels E and F) for the
ordered mesoporous silicas obtained under microwave irradiation at 40 °C during the
self-assembly stage and at 140°C in the hydrothermal step.
-1
400
200
A
600
400
200
B
0
0
0.0
1.0
0.5
C
160-2-1
160-2-3
160-2-4
160-2-6
3
0.2 0.4 0.6 0.8
Relative Pressure
-1
0.4
-1
0.3
1.0
D
160-6-1
160-6-3
160-6-4
160-6-6
3
0.3
0.2 0.4 0.6 0.8
Relative Pressure
PSD (cm g nm )
-1
0.4
-1
0.0
PSD (cm g nm )
160-6-1
160-6-3
160-6-4
160-6-6
3
600
160-2-1
160-2-3
160-2-4
160-2-6
Amount Adsorbed (cm STP g )
-1
800
3
Amount Adsorbed (cm STP g )
86
0.2
0.1
0.0
0.2
0.1
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
2
4 6 8 10 12 14
Pore Diameter (nm)
E
F
160-2-3
160-6-1
Intensity (a.u.)
Intensity (a.u.)
160-2-1
160-6-3
160-6-4
160-2-4
160-2-6
1.0
1.5
2.0 o 2.5
2( )
3.0
160-6-6
1.0
1.5
2.0 o 2.5
2( )
3.0
Figure 13. Nitrogen adsorption isotherms measured at -196 °C (Panels A and B) and the
corresponding pore size distributions (PSDs) (Panels C and D) calculated by the KJS
method [279] as well as the powder X-ray diffraction patterns (Panels E and F) for the
ordered mesoporous silicas obtained under microwave irradiation at 40 °C during the
self-assembly stage and at 160°C in the hydrothermal step.
87
A
B
50 nm
C
50 nm
D
50 nm
50 nm
Figure 14. STEM images of the selected ordered mesoporous silicas obtained under
microwave irradiation at 40 °C followed by hydrothermal treatment at 100°C (sample
100-12-24: panels A and B show TEM and SEM images, respectively) and 120°C
(sample 120-6-6: panels C and D show TEM and SEM images, respectively).
IV. Ordered mesoporous materials with organic surface
groups*
The enormous potential of functionalized mesoporous organosilicas in various
applications encouraged many scientists to pursue an intensive research in this field. The
success of microwave irradiation method in the preparation of pure silica materials
provides a good prognosis for the incorporation of organic groups on the surface of silica
pore walls. So far, the microwave-assisted synthesis of ordered mesostructures was not
used much for the modification of channel-like and cage-like materials. The study shows
the usage of microwave-irradiation in the synthesis of organosilicas. First, mono- and
bifunctional 2D-hexagonal and 3D-cubic materials were prepared by conventional
method. Next, these materials were prepared under microwave irradiation (see Scheme
7).
*
This Chapter is based on the following publications:
B.E. Grabicka, D.J. Knobloch, R.M. Grudzien, M. Jaroniec: Adsorption - Progress in Fundamental and
Application Research: Selected Reports at the 4th Pacific Basin Conference on Adsorption Science and
Technology, Tianjin, China 22 - 26 May 2006" (Li Zhou, ed.), World Scientific Publ. Co., Singapore, 2007
189 [109]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec Adsorption 2006 12 293 [107]
R.M. Grudzien, B.E. Grabicka, R. Felix, M. Jaroniec Adsorption 2007 13 323 [141]
B.E. Grabicka, M. Jaroniec: Microwave-assisted synthesis and characterization of mesoporous
organosilicas with ureidopropyl and mercaptopropyl groups. 2010, in preparation [268]
B.E. Grabicka, M. Jaroniec: Microwave-assisted co-condensation synthesis and adsorption properties of
vinyl-modified mesoporous organosilicas. 2010, in preparation [269]
Author’s related articles: R.M. Grudzien, B.E. Grabicka, O. Olkhovyk, M. Jaroniec, J.P. Blitz Nanoporous
Materials (A. Sayari and M. Jaroniec, eds), World Scientific Publ. Co., Singapore, 2008 665 [281]; R.M.
Grudzien, B.E. Grabicka, D.J. Knobloch, M. Jaroniec, Coll. Surfaces A 2006 291 139 [116]; R.M.
Grudzien, B.E. Grabicka, D.J. Knobloch, M. Jaroniec Stud. Surf. Sci. Catal. 2007 165 443 [108]
88
89
The successful introduction of organic groups to the surface of silica pore walls
under conventional and microwave conditions were confirmed by nitrogen adsorption
isotherms, X-ray powder diffraction, thermogravimetric and elemental analysis.
4.1. Experimental
4.1.1. Synthesis of mono- and bifunctional channel-like SBA-15 and cage-like SBA16 materials with ureidopropyl and ureidopropyl-mercaptopropyl surface groups
Syntheses of all channel-like mesoporous SBA-15 silicas were performed in the
presence of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene
oxide) triblock copolymer (P123, EO20PO70EO20) by co-condensation of tetraethyl
orthosilicate (TEOS) and either trialkoxyorganosilanes (R’O)3Si-R (where R denotes
functional group) to introduce the desired surface functionalities. In general,
ureidopropyl-functionalized SBA-15 materials were synthesized by one-pot route using
ureidopropyltrimethoxysilane (U) and TEOS; bi-functional SBA-15 containing
ureidopropyl and mercaptopropyl (SH) surface groups were prepared using
ureidopropyltrimethoxysilane, 3-mercaptopropylsilane and TEOS (see Scheme 7 and
Scheme 8). The adopted procedure was similar to that used for the synthesis of SBA-15
reported by Zhao et al. [70]. In a typical synthesis, 2g of polymer was dissolved in 61.2
ml of 2M HCl and 10.8 ml of deionized water (DW) under vigorous stirring at 40 oC.
After 4-6 hours of stirring a specified volume of TEOS was added dropwise to this
90
solution under vigorous mixing, and then after 15 minutes organosilane was pipetted to
achieve the desired molar composition of both silanes (see Table 8). The resulting
mixture was stirred for 24 hours followed by aging at 100 °C for 48 hours. The white
solid was washed with DW, filtered and dried at 80 °C. The template was removed by
extraction three times with 2 ml of 36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC.
The extracted ureidopropyl-functionalized SBA-15 and ureidopropyl-mercaptopropylfunctionalized SBA-15 samples are denoted as SBA-15-Ux and SBA-15-U1-SHy, where
U and SH refer to ureidopropyl and mercaptopropyl surface groups, respectively. Letters
x and y = 1, 2, 3, 4 refer to the samples with successively growing concentration of
functional groups (see Table 8). The letter t refers to the as-synthesized organicfunctionalized silica. The pure channel-like silica subjected to calcination at 550 °C in
flowing air for 4 hours was denoted as SBA-15.
Cage-like mesoporous SBA-16 silicas with functional surface groups (see Scheme
7 and Scheme 9) were synthesized similarly to SBA-15 by co-condensation of TEOS and
proper organosilanes in the presence of poly(ethylene oxide)-block-poly(propylene
oxide)-block-poly(ethylene oxide) triblock copolymer (Pluronic F127, EO106PO70EO106).
The procedure adopted is a slightly modified recipe reported by Qiu at al. [58]. In a
typical synthesis, 1 g of F127 and 3.527 g of sodium chloride were dissolved in 10 ml of
2M HCl and 30 ml of deionized water at 40 ºC. After 4 hours of stirring a specified
volume of TEOS was pipetted dropwise to this solution under vigorous mixing, and next
after 15 minutes organosilane was added to achieve the desired molar composition of
both silanes (see Table 9). After further stirring for 20 hrs at 40 ºC, the resulting white
91
precipitate was transferred into a polypropylene bottle and subsequently heated at 100 ºC
for 24 hrs. The product was filtered, washed with DW, and dried in the oven at 80 ºC. To
remove the polymeric template from mesopores, the as-synthesized nanocomposites were
extracted three times with 2 ml of 36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC.
The extracted ureidopropyl-functionalized SBA-16 and ureidopropyl-mercaptopropylfunctionalized SBA-16 samples are denoted as SBA-16-Ux and SBA-16-U1-SHy, where
U and SH refer to ureidopropyl and mercaptopropyl surface groups, respectively. Letters
x and y = 1, 2, 3 refer to the samples with successively growing concentration of
functional groups (see Table 2). The letter t refers to as-synthesized sample, i.e., sample
containing polymeric template. The pure silica sample subjected to calcination at 550 °C
in flowing air for 4 hours was denoted as SBA-16.
4.1.2. Synthesis of channel-like SBA-15 organosilicas modified by ureidopropyl
surface group: Effect of organosilane addition at different synthesis stages
Ordered mesoporous organosilicas were synthesized in the presence of
poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer
(P123, EO20PO70EO20) by co-condensation of tetraethyl orthosilicate (TEOS) and
ureidopropyltrimethoxysilane to functionalize the surface. The recipe incorporated here
was analogous to the synthesis of the SBA-15 silica reported by Zhao et al. [70]. In
general, triblock copolymer P123 (2g) was mixed with 2M HCl (61.2 ml) and distilled
water (10.8 ml) under rapid stirring at 40 oC until its complete dissolution was achieved.
92
After 4-6 hours of mixing, either 3.858 ml or 4.07 ml of TEOS was added dropwise to the
P123-HCl-DW mixture under vigorous stirring, and next 0.371 ml of ureidopropyltrimethoxysilane was added after 0, 10, 15, 20, 40, 60 and 120 minutes, respectively. The
slurry was further stirred for 24 hours and aged for 48 hours at 100 °C. The powder was
washed with DW, filtered and dried overnight at 80 °C. The polymeric template was
extracted with 2 ml of 36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The series of
the mesoporous SBA-15 silicas with ureidopropyl surface groups was designated as Ux,
where U and x relate to ureidopropyl surface groups and time of the organosilane
addition (see Table 12).
4.1.3. Microwave-assisted synthesis of mono- and bifunctional channel-like SBA-15
and
cage-like
SBA-16
materials
with
ureidopropyl
and
ureidopropyl-
mercaptopropyl surface groups
Syntheses of channel-like mesoporous SBA-15 organosilicas were performed
in the presence of poly(ethylene oxide)-block-poly(propylene oxide)-blockpoly(ethylene oxide) triblock copolymer (P123, EO20PO70EO20) by co-condensation
of tetraethyl orthosilicate (TEOS) and trialkoxyorganosilanes (R’O)3Si-R (where R
denotes functional group). In general, ureidopropyl-functionalized SBA-15 materials
were synthesized by one-pot route using ureidopropyltrimethoxysilane (U) and
TEOS; bi-functional SBA-15 containing ureidopropyl and mercaptopropyl (SH)
surface
groups
were
prepared
using
ureidopropyltrimethoxysilane,
3-
93
mercaptopropylsilane and TEOS. The adopted procedure was similar to that used for
the synthesis of SBA-15 reported elsewhere [70]. In a typical synthesis, 2g of
polymer was dissolved in 61.2 ml of 2M HCl and 10.8 ml of deionized water (DW)
under vigorous stirring at 40 oC. After 4-6 hours of stirring a specified volume of
TEOS was added dropwise to this solution under vigorous mixing, and then after 15
minutes organosilane was pipetted to achieve the desired molar composition of both
silanes (see Table 13). The obtained mixture was transferred to the teflon vessels,
which were installed in microwave oven (MARS 5; CEM Corp.). Both steps of the
organosilica synthesis, i.e., the self-assembly of organosilane precursors and the
hydrothermal treatment, were carried out in the microwave oven (see Scheme 7). In
the first step, the samples were stirred using magnetic bars for 12h at 40°C. After
initial stage, temperature was increased to 100ºC and kept for 6-24h; magnetic
stirring was off during this stage. The slurry was filtered, washed with DW, filtered
and dried at 80 °C. The template was removed by extraction two times with 2 ml of
36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The extracted ureidopropylfunctionalized SBA-15 and ureidopropyl-mercaptopropyl-functionalized samples are
denoted as SBA-15-U-mx and SBA-15-U-SH-mx, where U and SH refer to
ureidopropyl and mercaptopropyl surface groups, respectively. The letters m and c
refer to the samples obtained under microwave and conventional conditions,
respectively. The letter x refers to the duration of hydrothermal treatment. The pure
channel-like silica, calcined at 550 °C in flowing air for 4 hours, is presented as
SBA-15.
94
Cage-like mesoporous SBA-16 organosilicas with functional surface groups
were synthesized similarly to SBA-15 by co-condensation of TEOS and proper
organosilanes in the presence of poly(ethylene oxide)-block-poly(propylene oxide)block-poly(ethylene oxide) triblock copolymer (Pluronic F127, EO106PO70EO106).
The procedure adopted was a slightly modified recipe reported by Qiu at al. [58]. In
a typical synthesis, 2 g of F127 and 7.054 g of sodium chloride were dissolved in 20
ml 2M HCl and 60 ml deionized water at 40 ºC. After 4 hours of stirring a specified
volume of TEOS was pipetted dropwise to this solution under vigorous mixing, and
next after 15 minutes organosilane was added to achieve the desired molar
composition of both silanes (see Table 14). Next step of experiment was similar to
the aforementioned SBA-15 organosilicas. The resulting mixture was transferred to
the teflon vessels, which were installed in microwave oven. Both steps of the
organosilicas synthesis were proceeded in the microwave oven. In the first step, the
self-assembly of organosilane precursors, the samples were stirred using magnetic
bars for 12h at 40°C. After initial stage, the hydrothermal treatment was continued in
microwave oven and temperature was increased to 100ºC and kept for 6-24h;
magnetic stirring was off during this stage. The product was filtered, washed with
DW, and dried in an oven at 80 ºC. To remove the polymeric template from
mesopores, the as-synthesized nanocomposites were extracted two times with 2 ml of
36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The extracted ureidopropylfunctionalized SBA-16 and ureidopropyl-mercaptopropyl-functionalized samples are
denoted as SBA-16-U-mx, SBA-16-U-SH-mx, where U and SH refer to ureidopropyl
95
and mercaptopropyl surface groups, respectively. The letters m and c refer to the
samples obtained under microwave and conventional conditions, respectively. The
letter x refers to the duration of hydrothermal treatment. The pure cage-like silica,
calcined at 350 °C in flowing air for 4 hours is denoted as SBA-16.
4.1.4. Synthesis of vinyl-functionalized channel-like SBA-15 mesoporous material
via conventional and microwave methods
Synthesis of channel-like mesoporous SBA-15 organosilicas was performed in
the
presence
of
poly(ethylene
oxide)-block-poly(propylene
oxide)-block-
poly(ethylene oxide) triblock copolymer (P123, EO20PO70EO20) by co-condensation
of tetraethyl orthosilicate (TEOS) and triethoxyvinylsilane (V) (see Scheme 10). The
adopted procedure was similar to that used for the synthesis of SBA-15 reported
elsewhere [70]. In a typical synthesis, 2g of polymer was dissolved in 61.2 ml of 2M
HCl and 10.8 ml of deionized water (DW) under vigorous stirring at 40 oC. After 4-6
hours of stirring a specified volume of TEOS was added dropwise to this solution
under vigorous mixing, and then after 15 minutes, organosilane was pipetted to
achieve the desired molar composition. The series of samples with four different
molar compositions, V10, V15, V20 and V30, where the molar concentration of
organosilane in the initial synthesis gel mixture is 10, 15, 20 and 30%, respectively.
The obtained slurry was transferred to the teflon vessels, which were installed in
microwave oven (MARS 5; CEM Corp.). Both steps of the organosilica synthesis,
96
i.e., the self-assembly of organosilane precursors and the hydrothermal treatment,
were carried out in the microwave oven (see Scheme 7). In the first step, the samples
were stirred using magnetic bars for 12h at 40°C. After initial stage, temperature was
increased to 100ºC and kept for 6-24h; magnetic stirring was off during this stage.
The slurry was filtered, washed with DW, filtered and dried at 80 °C.
The template was removed by extraction two times with 2 ml of 36 wt. % HCl and
100 ml of 95 % ethanol at 70 ºC. The extracted vinyl-functionalized SBA-15 samples
are denoted as Vx-MW-y, where V refers to triethoxyvinylsilane surface groups, x
denotes the molar concentration of organosilane, MW refers to the samples obtained
via microwave-assisted synthesis, and y denotes the length time of the hydrothermal
treatment stage. For the comparison purpose, each series of vinyl-modified
organosilicas shows the sample obtained via conventional method which is assigned
as Vx-conv.
97
EO20PO70EO20 or EO106PO70EO106
+
Si(EtO)4
+
surface organosilane
self-assembly
24h at 40 C
hydrothermal
treatment
24h or 48h
at 100 C
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
A
24h at 60-70 C
B
EO20PO70EO20 or EO106PO70EO106
+
Si(EtO)4
+
surface organosilane
self-assembly
6-12h at 40 C
hydrothermal
treatment
6-24h at 100 C
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
A
24h at 60-70 C
B
microwave-assisted synthesis
Scheme 7. Schematic comparison of the synthesis of organosilicas with surface groups
by conventional (top) and microwave-assisted (bottom) methods.
98
A
B
C
Scheme 8. Schematic illustration of mesoporous channel-like structure SBA-15 silica (A)
and interconnected cylindrical channels (large circles with thin channels) containing
ureidopropyl surface ligands (B) (open circles), bifunctional ureidopropyl (open circles),
and mercaptopropyl (filled circles) surface ligands (C).
99
A
B
C
Scheme 9. Schematic illustration of mesoporous cage-like structure SBA-16 silica (A)
and interconnected spherical cages (large circles with straight channels) containing
ureidopropyl surface ligands (B) (open circles), bifunctional ureidopropyl (open circles)
and mercaptopropyl (filled circles) surface ligands (C).
100
Scheme 10. Schematic illustration of vinyl-functionalized SBA-15 organosilica.
101
4.2. Mono- and bifunctional channel-like SBA-15 and cage-like SBA-16 materials
with ureidopropyl and ureidopropyl-mercaptopropyl surface groups
The amounts of ureidopropyl surface groups in SBA-15 and SBA-16, as well as
ureidopropyl and mercaptopropyl surface groups in bi-functional SBA-15 and SBA-16,
were estimated on the basis of elemental analysis data (see Table 8 and Table 9). The
nitrogen and sulfur contents obtained for the resulting OMOs by elemental analysis show
that about 50-85 % of the amount in the initial molar composition was introduced to the
final samples, indicating quite good incorporation efficiency.
Introduction of surface organic groups into channel-like SBA-15 and SBA-16
mesostructures was monitored by high-resolution thermogravimetry (TG). The TG
patterns and the corresponding differential TG (DTG) profiles for ureidopropylfunctionalized SBA-15 and SBA-16 silicas (Panels A and C), ureidopropylmercaptopropyl-functionalized SBA-15 and SBA-16 silicas (Panels B and D) recorded
under nitrogen atmosphere are displayed in Figure 15 for channel-like materials and in
Figure 17 for cage-like materials, respectively. The TGA and DTG patterns show three
TG events. The first event, below 100 °C, reflects thermodesorption of physisorbed water
and ethanol. As can be seen, the complete removal of P123 has been achieved by
extraction process with hydrochloric acid and ethanol solution at 80 °C as confirmed by
the disappearance of the major peak on the DTG curves for mono- and bifunctional
representative samples. In the case of cage-like organosilicas, the template removal was
incomplete and it is especially noticeable for the SBA-16-U1 sample at ~400 °C (see
Figure 17D). It is noteworthy that the removal of polymeric templates from cage-like
102
mesostructures is more difficult in contrary to the channel-like mesostructures, especially
when the cage openings in the former structures are small and the attached surface groups
are relatively large. Moreover, the intensity of the minor decomposition peaks observed
in the range between 200 and 300 °C on the DTG curves for the template-free
organosilicas increases gradually with increasing concentration of ureidopropyl groups
(SBA-15-U1, SBA-15-U2, SBA-15-U3 and SBA-15-U4), which indicates that the
functionalization was effective. The last event above 500 °C, reflects the condensation of
silanol groups and decomposition of some residual organic groups.
Structural characterization of the mono- (Panel A) and bifunctional (Panel B)
SBA-15 and SBA-16 organosilicas was performed on the basis of the XRD patterns
shown in Figure 16 and Figure 18, respectively. The unit cell parameters for the samples
studied are summarized in Table 10 and Table 11, respectively. As can be seen from
Figure 16A, the diffraction profile for the extracted ureidopropyl-functionalized SBA-15
silica exhibits one sharp reflection at 2 ~ 0.75 indexed as (100) and two minor
reflections (110) and (200), characteristic for the channel-like mesostructure (P6mm
symmetry group). The XRD patterns for the ureidopropyl-mercaptopropyl modified
samples (Panel B) were also analyzed according to the P6mm symmetry group.
Furthermore, the XRD study shows the tendency of a gradual deterioration of the
mesostructural ordering with increasing loading of surface groups for both types of
functionalization of the silica material.
103
Table 8. Molar composition of the synthesis gels used and the corresponding elemental
analysis data for the organic-functionalized channel-like SBA-15 mesoporous silicas.a
Molar composition
Sample
Elemental analysis
P, (%)
TEOS
U
SH
C, (mmoles/g)
PN
PS
CU
CSH
P, (%)
P*N
P*S
SBA-15
19.20
SBA-15-U1
18.24
0.96
2.16
0.43
1.20
SBA-15-U2
17.28
1.92
4.04
0.79
2.22
SBA-15-U3
16.32
2.88
5.67
1.27
3.55
SBA-15-U4
15.36
3.84
7.12
0.92
2.57
SBA-15-U1-SH1
17.76
0.96
0.48
2.11
1.21
0.37
0.26
1.03
0.83
SBA-15-U1-SH2
16.80
0.96
1.44
2.01
3.45
0.26
0.81
0.72
2.60
a
nTEOS, number of mmoles of tetraethyl orthosilicate; nU, number of mmoles of
ureidopropyltrimethoxysilane; nSH, number of mmoles of 3-mercaptopropylsilane; PN and PS, nitrogen
and sulfur percentages predicted on the basis of the synthesis gel mixture; CU or CSH concentration of
functional groups in the resulting materials calculated on the basis of nitrogen or sulfur percentages
obtained by elemental analysis; P*N and P*S, nitrogen and sulfur weight percentages obtained from
elemental analysis.
104
Table 9. Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the organic-functionalized cage-like SBA-16 mesoporous
silicas.a
Molar composition
Sample
Elemental analysis
P, (%)
TEOS
U
SH
C, (mmoles/g)
PN
PS
CU
CSH
P, (%)
P*N
P*S
SBA-16
20.16
SBA-16-U1
19.15
1.01
2.17
0.91
2.54
SBA-16-U2
18.14
2.02
4.04
0.92
2.57
SBA-16-U3
17.14
3.02
5.67
1.11
3.10
SBA-16-U1-SH1
18.14
1.01
1.01
2.06
2.36
0.40
0.69
1.11
2.21
SBA-16-U1-SH2
17.14
1.01
2.02
1.96
4.49
0.39
1.32
1.08
4.23
SBA-16-U1-SH3
16.13
1.01
3.02
1.88
6.42
0.42
1.67
1.17
5.35
a
nTEOS, number of mmoles of tetraethyl orthosilicate; nU, number of mmoles of
ureidopropyltrimethoxysilane; nSH, number of mmoles of 3-mercaptopropylsilane; PN and PS, nitrogen
and sulfur percentages predicted on the basis of the synthesis gel mixture; CU or CSH concentration of
functional groups in the resulting materials calculated on the basis of nitrogen or sulfur percentages
obtained by elemental analysis; P*N and P*S, nitrogen and sulfur weight percentages obtained from
elemental analysis.
105
Weight change (%)
100
A
100
90
90
80
80
B
70
70
60
60
50
o
- Deriv. Weight (% / C)
200
400
600
o
Temperature ( C)
SBA-15
SBA-15-U1
SBA-15-U2
SBA-15-U3-t
SBA-15-U3
SBA-15-U4
800
200
400
600
o
Temperature ( C)
800
SBA-15-cal540
SBA-15-U1-SH1
SBA-15-U1-SH2-t
SBA-15-U1-SH2
0.6
0.25
0.5
0.20
0.4
0.15
0.3
0.10
0.2
C
0.05
0.00
0.1
D
0.0
200
400
o600
Temperature ( C)
800
200
400
o600
Temperature ( C)
800
Figure 15. High-resolution TG profiles (top panels) and the corresponding DTG profiles
(bottom panels) recorded in flowing nitrogen for channel-like SBA-15 mesoporous silicas
obtained via co-condensation route using various concentrations of ureidopropyl (U)
ligands (A and C), bifunctional ligands: ureidopropyl (U) and mercaptopropyl (SH) (B
and D), respectively.
106
Weight change (%)
100
100
A
90
B
90
80
80
70
70
60
60
200
400
600
Temperature (oC)
800
50
200
400
600
Temperature (oC)
SBA-16
SBA-16-U1-SH1
SBA-16-U1-SH2-t
SBA-16-U1-SH2
SBA-16-U1-SH3
SBA-16
SBA-16-U1
SBA-16-U2-t
SBA-16-U2
SBA-16-U3
o
- Deriv. Weight (% / C)
800
0.25
0.3
0.20
0.15
0.2
0.10
0.1
0.05
D
C
0.00
0.0
200
400
600
Temperature (oC)
800
200
400
600
Temperature (oC)
800
Figure 17. High-resolution TG profiles (top panels) and the corresponding DTG profiles
(bottom panels) recorded in flowing nitrogen for cage-like SBA-16 mesoporous silicas
obtained via co-condensation using various concentrations of ureidopropyl (U) ligands (A
and C), bifunctional ligands: ureidopropyl (U) and mercaptopropyl (SH) (B and D),
respectively.
107
Table 10. Selected structural parameters of the organic-functionalized channel-like
SBA-15 mesoporous silicasa
Sample
SBET,
m2g-1
Vt,
ccg-1
Vc,
ccg-1
wKJS,
nm
wd,
nm
b,
nm
a,
nm
SBA-15
866
1.38
0.14
11.2
10.4
1.1
11.5
SBA-15-U1
702
1.00
0.12
9.1
9.8
1.4
11.2
SBA-15-U2
731
1.00
0.14
9.1
10.2
1.7
11.9
SBA-15-U3
670
0.87
0.17
8.9
9.5
2.0
11.7
SBA-15-U4
525
0.42
0.16
5.8
7.2
3.4
10.6
SBA-15-U1-SH1
546
0.87
0.10
8.6
9.7
1.6
11.3
SBA-15-U1-SH2
334
0.42
0.07
6.0
7.5
2.5
10.0
a
SBET , BET specific surface area; Vt, single-point pore volume; Vc, volume of micropores and
interconnecting pores of the diameter below 4 nm; wKJS, mesopore cage diameter calculated by the KJS
method [279]; wd, mesopore cage diameter calculated on the basis of the unit cell parameter and pore
volumes according to the relation derived for the hexagonal P6mm structure assuming 2.0 g/cm3 density
of silica; b, pore wall thickness; a, unit cell calculated from the observed characteristic Bragg’s reflection
(100).
108
Table 11. Selected structural parameters of the organic-functionalized cage-like
SBA-16 mesoporous silicasa
Sample
SBET,
m2g-1
Vt,
ccg-1
Vc,
ccg-1
wKJS,
nm
wd,
nm
b,
nm
a,
nm
SBA-16
932
0.60
0.35
7.0
9.0
3.6
15.0
SBA-16-U1
494
0.32
0.18
6.5
8.1
4.4
14.8
SBA-16-U2
613
0.41
0.23
6.8
8.4
3.7
14.6
SBA-16-U3
553
0.38
0.20
6.7
8.5
3.6
14.7
SBA-16-U1-SH1
360
0.24
0.14
5.7
7.2
4.5
14.3
SBA-16-U1-SH2
357
0.20
0.09
4.7
7.0
4.4
13.2
SBA-16-U1-SH3
225
0.14
0.07
3.6
6.1
5.1
13.0
a
SBET , BET specific surface area; Vt, single-point pore volume; Vc, volume of micropores and
interconnecting pores of the diameter below 4 nm for SBA-16, SBA-16-U1, SBA-16-U2, SBA-16-U3,
SBA-16-U1-SH1, whereas for other materials Vc was calculated below 3 nm; wKJS, mesopore cage
diameter calculated by the KJS method [279]; wd, mesopore cage diameter calculated on the basis of the
unit cell parameter and pore volumes according to the relation derived for the cubic Im3m structure
assuming 2.0 g/cm3 density of silica; b, pore wall thickness; a, unit cell calculated from the observed
characteristic Bragg’s reflection (110).
109
B
A
SBA-15
Intensity (a.u.)
SBA-15-U1
SBA-15
SBA-15-U1
SBA-15-U2
SBA-15-U1-SH1
SBA-15-U3
SBA-15-U1-SH2
SBA-15-U4
3
1.0
1.5
o
2( )
600
200
200
C
0.0
1.4
-1
3 -1
600
400
1.2
1.0
0.8
E
0.2 0.4 0.6 0.8
Relative Pressure
1.0
SBA 15
SBA-15-U1
SBA-15-U2
SBA-15-U3
SBA-15-U4
1.5
o
2( )
2.0
D
0
0.0
1.4
1.2
1.0
F
0.2 0.4 0.6 0.8
Relative Pressure
1.0
SBA-15
SBA-15-U1
SBA-15-U1-SH1
SBA-15-U1-SH2
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
1.0
SBA-15
SBA-15-U1
SBA-15-U1-SH1
SBA-15-U1-SH2
800
400
0
PSD (cm g nm )
0.5
2.0
SBA 15
SBA-15-U1
SBA-15-U2
SBA-15-U3
SBA-15-U4
800
-1
Amount Adsorbed (cm STP g )
0.5
0.0
5
10
15
Pore Diameter (nm)
20
5
10
15
Pore Diameter (nm)
20
Figure 16. X-ray diffraction (XRD) patterns (A and B), nitrogen adsorption isotherms (C
and D) measured at – 196 °C and the corresponding pore size distributions (PSDs) (E and
F) calculated according to the KJS method [279] for the channel-like SBA-15
mesoporous silicas having various concentrations of ureidopropyl (U) surface ligands (A,
C and E), bifunctional surface ligands: ureidopropyl (U) and mercaptopropyl (SH) (B, D
and F), respectively.
110
B
Intensity (a.u.)
A
SBA-16
SBA-16
SBA-16-U1
SBA-16-U1
SBA-16-U1-SH1
SBA-16-U1-SH2
SBA-16-U1-SH3
SBA-16-U2
SBA-16-U3
1.0
1.5

2 
0.5
2.0
500
SBA-16
400
SBA-16-U1
1.0
1.5

2 
2.0
400
SBA-16
300
SBA-16-U1
3
-1
Amount Adsorbed (cm STP g )
0.5
SBA-16-U2
300
SBA-16-U3
SBA-16-U1-SH2
200
C
0.0
-1
3 -1
0.15
D
0
0.2 0.4 0.6 0.8
Relative Pressure
0.25
0.20
SBA 16-U1-SH3
100
100
0
PSD (cm g nm )
SBA-16-U1-SH1
200
1.0
SBA-16
SBA-16-U1
SBA-16-U2
SBA-16-U3
0.0
0.2 0.4 0.6 0.8
Relative Pressure
0.30
SBA-16
SBA-16-U1
SBA-16-U1-SH1
SBA-16-U1-SH2
SBA-16-U1-SH3
0.25
0.20
0.15
0.10
1.0
0.10
0.05
E
0.00
2
4
6
8 10 12
Pore Diameter (nm)
14
0.05
F
0.00
2
4
6
8 10 12
Pore Diameter (nm)
14
Figure 18. X-ray diffraction (XRD) patterns (A and B), nitrogen adsorption isotherms
(C and D) measured at – 196 °C and the corresponding pore size distributions (PSDs) (E
and F) calculated according to the KJS method [279] for the cage-like SBA-16
mesoporous silicas having various concentrations of ureidopropyl (U) surface ligands (A,
C and E), bifunctional surface ligands: ureidopropyl (U) and mercaptopropyl (SH) (B, D
and F), respectively. The isotherms in Panel C for SBA-16, SBA-16-U1 and SBA-16-U2
were offset vertically by 90, 165 and 50 cc STP g-1. The isotherms in Panel D for SBA16-U1 and SBA-16-U1-SH1 were offset vertically by 75 and 50 cc STP g-1.
111
As can be seen from Figure 18, the diffraction patterns for extracted functionalized SBA16 materials exhibit a strong reflection at 2 ~ 0.8 (110) and some less-resolved minor
reflections, (200) and (211), proving the cubic Im3m symmetry group (body-centeredpacking). Similarly to the modified SBA-15 organosilicas, the change in the XRD profile
suggests a visible structure deterioration in the samples with high concentrations of
surface groups (Figure 18A and B).
Shown in Figure 16 are nitrogen adsorption-desorption isotherms measured at 196 °C (Panels C and D) and pore size distributions (Panels E and F) for the extracted
SBA-15 silicas with ureidopropyl and ureidopropyl-mercaptopropyl groups, respectively.
The summary of structural parameters such as the BET specific surface area, the volume
of complementary pores, the single-point pore volume, the mesopore channel diameter
and pore-wall thickness, are listed in Table 10. In general, all materials synthesized with
the low content of organic groups exhibit type IV adsorption-desorption isotherms. As
can be seen in Panels C and D of Figure 16, the position of capillary condensation step is
shifting towards smaller values of the relative pressures with increasing content of the
introduced functionalities, which reflects a gradual reduction of the diameter of mesopore
channels (see Panels E and F in Figure 16). Also other adsorption parameters such as the
BET specific surface area and single-point pore volume decrease with increasing content
of organics (see Table 10). In the case of ureidopropyl-functionalized and bi-functional
SBA-15 materials, the BET surface area is reduced from 866 m2/g (calcined SBA-15) to
525 m2/g for ureidopropyl-modified SBA-15 and to 334 m2/g for bifunctional SBA-15,
whereas the total pore volume is reduced from 1.38 cm3/g to 0.42 cm3/g (for both types of
112
surface groups). In addition, for all SBA-15 silicas the pore wall thickness increases with
increasing concentrations of U and U1-SH groups and its highest value is obtained for
materials modified with ureidopropyl surface ligands.
Nitrogen adsorption-desorption isotherms measured at -196 °C for ureidopropyl
and ureidopropyl-mercaptopropyl functionalized SBA-16 silicas are shown in Figure 18
(Panels D, E and F, respectively). Table 11 presents the adsorption parameters such as the
BET specific surface area, single-point pore volume, mesopore channel diameter and
pore wall thickness. The SBA-16 silicas with ureidopropyl and bi-functional samples
with the small concentration of these groups, SBA-16-U1 (Panel C) and SBA-16-U1-SH1
(Panel
D),
exhibit
type
IV
adsorption-desorption
isotherms
with
sharp
capillary/evaporation steps and pronounced H2 hysteresis loops. The condensation step
starts at a relative pressure of about 0.7, whereas the evaporation step ends suddenly at
about 0.45, which is typical for mesoporous materials containing cage-like pores and
narrow PSDs (see PSDs in Panels E and F). As can be seen from Figure 18, an increase in
the concentration of organic groups in the material, reduces the steepness of the
evaporation steps (Figure 18D), which is not the case for U-functionalized materials
(Figure 18C).
Similarly to SBA-15-type organosilicas, adsorption parameters such as the BET
surface area and single-point pore volume for the SBA-16-type organosilica samples
decrease with increasing loading of organic groups, except the SBA-16-U1 sample,
which possesses some residue of the template. In the case of mono- and bifunctional
SBA-16, the BET surface area decreases from 932 m2/g (calcined SBA-16) to 553 m2/g
113
and 225 m2/g, respectively, whereas the total pore volume decreases from 0.6 cm3/g to
0.38 cm3/g and 0.14 cm3/g, respectively. Furthermore, the thickness of mesopore walls
shows a tendency to increase with increasing concentrations of U and U1-SH groups.
Overall, the introduction of various surface ligands onto silica pore walls of
SBA-15 and SBA-16 mesostructures was successful. Both functionalized mesoporous
channel-like and cage-like silicas showed similar tendency of decreasing the structural
order with increasing concentration of the introduced functionality. Futhermore, it was
demonstrated that the method of template removal was effective, especially in the case of
channel-like material and P123 template the extraction with hydrochloric acid-ethanol
solution was sufficient. In contrast, the removal of the F127 template from cage-like
SBA-16 organosilicas was more challenging because of the structural nature of these
silica materials. In addition, the results show some possible difficulties in introduction of
surface groups onto surface of cage-like materials in contrary to hexagonal structures.
4.3. Effect of ureidopropyl organosilane addition at different synthesis stages of
channel-like SBA-15 organosilicas
The effect of organosilane addition at different stages of the OMO synthesis on
the structural characteristics of the extracted organosilicas containing ureidopropyl
surface groups was studied by the powder XRD in the range of 2 from 0.5 to 3.5o. The
XRD patterns for the extracted ureidopropyl-functionalized OMOs are shown in Figure
19A, whereas the unit cell parameters calculated using (100) Bragg’s reflection are listed
in Table 12. As can be seen from Figure 19A, an increased delay (from 0 and 120
114
minutes) between the TEOS addition and the addition of reactive organosilane did not
lead to any meaningful changes in the XRD patterns, indicating that the structural quality
of all samples studied is similar. Thus, a delay in adding the reactive organosilane into
the TEOS-polymer gel mixture does not affect the structural ordering of the resulting
OMOs. The XRD patterns fulfill the relations for a 2D hexagonal structure (p6mm
symmetry group). These patterns exhibit one major peak indexed as (100) and two less
intensive peaks indexed as (110) and (200).
Nitrogen adsorption-desorption isotherms measured at -196 °C (B) and the
corresponding pore size distributions (C) calculated from adsorption branches of the
aforementioned isotherms by using the improved KJS (Kruk-Jaroniec-Sayari) method
[279] for the extracted ureidopropyl-functionalized SBA-15 silicas are shown in Figure
19. The BET specific surface area, the volume of complementary pores, the single-point
pore volume and the mesopore diameter are listed in Table 12. All extracted samples
exhibit type IV adsorption-desorption isotherms with a distinct H1 hysteresis loop typical
for the materials with cylindrical mesopores. As can be noticed, a comparison of the
isotherms shown in Figure 19B indicates that an increased delay in the addition of
reactive organosilane did not influence the shape of adsorption isotherms. In addition, the
samples U-15, U-20 amd U-60 show the lack of plateau at higher relative pressures,
which points out the presence of secondary disordered mesopores by elevation of
adsorption branches at pressures approaching the saturation vapor pressure. Moreover, it
is noteworthy that all ureidopropyl-modified SBA-15 samples possess narrow pore size
distributions (Figure 19C) as well as their pore diameters do not change significantly
115
Table 12. Selected adsorption and structural parameters for the SBA-15 silicas with
ureidopropyl groups.a
SBET
m2g-1
Vc,
ccg-1
Vp,
ccg-1
Vt,
ccg-1
wKJS,
nm
a,
nm
U0
520
0.06
0.69
0.81
8.29
11.5
U10
600
0.10
0.75
0.90
8.70
11.3
U15
730
0.12
0.76
0.99
8.47
11.9
U20
625
0.14
0.64
0.90
8.27
11.7
U40
510
0.07
0.66
0.76
8.24
11.3
U60
550
0.11
0.61
0.77
8.10
11.1
U120
505
0.08
0.63
0.77
8.47
10.0
Sample
a
SBET , BET specific surface area; Vc, volume of complementary pores (including micropores) of the
width below 4 nm present in the mesopore walls; Vp, volume of ordered mesopores; Vt, single-point pore
volume; wKJS, mesopore diameter calculated by the improved KJS method [279]; a, unit cell calculated
from the observed characteristic Bragg’s reflection (100).
116
A
C
B
6
U0
U0
U0
1500
5
U10
U15
-1
3
1000
U15
3
Intensity (a.u.)
U15
4
-1
PSD (cm g nm )
U10
-1
Amount Adsorbed (cm STP g )
U10
3
U20
U20
U20
2
U40
U40
U40
500
U60
U60
1
U60
U120
U120
0.5
1.0
1.5 2.0
o
2( )
2.5
3.0
N2
U120
0
0
0.0
0.2
0.4
0.6
0.8
Relative Pressure
1.0
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 19. X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C) calculated
according to the improved KJS method [279] for the channel-like SBA-15 mesoporous
silicas with ureidopropyl surface groups synthesized by delaying the addition of
ureidopropyltrimethoxysilane (U) into the TEOS-polymer mixture from zero to 120
minutes; numbers at the samples codes denote the delay time in minutes. The adsorption
isotherms and PSD curves for U60, U40, U20, U15, U10 and U0 were offset by 210, 440,
615, 800, 1100, 1390 cc STP g-1 and 1.0, 1.8, 2.6, 3.4, 4.2, 5.3 cc g-1 nm-1, respectively.
117
either. It was shown that the time of addition of reactive organosilane to the synthesis gel
does not play such a crucial role in the formation of organosilicas with surface groups.
However, the short delay is sufficient for the formation of the silica-polymer template
mesostructure, which is flexible enough to accommodate organosilane units. A
simultaneous addition of TEOS and organosilane precursors may disturb the formation of
ordered structures. Thus, a delayed addition of reactive organosilane can be positive in
achieving better uniformity of pores and pore openings.
4.4. Microwave-assisted synthesis of mono- and bifunctional channel-like SBA-15
and
cage-like
SBA-16
materials
with
ureidopropyl
and
ureidopropyl-
mercaptopropyl surface groups
The
organic
content
of
ureid-functionalized
and
ureid-mercaptopropyl-
functionalized organosilicas evaluated on the basis of elemental analysis data is listed in
Table 13 and Table 14. As can be noticed, the amounts of introduced surface organic
groups are confirmed by nitrogen and sulfur contents; these values are approximately 5080 % of those estimated on the basis of the initial molar composition of the synthesis
mixture, indicating good incorporation efficiency.
The determination of organic group loadings into channel-like SBA-15 and
cage-like
SBA-16
mesostructures
was
performed
by
high-resolution
thermogravimetry (TG). The TG patterns and the corresponding differential TG
(DTG) profiles for ureidopropyl-functionalized SBA-15 (Panels A and C in Figure
20)
and SBA-16 silicas (Panels A and C in Figure 21), and for ureidopropyl-
118
mercaptopropyl-functionalized SBA-15 (Panels B and D in Figure 20) and SBA-16
silicas (Panels B and D in Figure 21) conducted under nitrogen atmosphere from
room temperature to 800 °C, are displayed in Figure 20 and Figure 21. The typical
weight loss curves exhibit three important weight loss steps and confirm the presence
of organic groups in the final materials. The first weight loss up to 100-150 °C
exhibits the thermodesorption of physisorbed water and ethanol. The next weight
loss, between 180 and 600°C, demonstrates the presence of introduced organic
groups and shows their decomposition. The third weight loss, above 650 °C, reflects
the condensation of silanol groups and the decomposition of some residual organic
groups. The succesfull modification is manifested for channel-like SBA-15 as well as
cage-like SBA-16 organosilica samples. As can be seen, the presence of the major
peak with some minors ones in the range 180 - 600°C, confirms the attachment of
organic groups into silica pore walls.
Nitrogen adsorption–desorption isotherms (Panel A and B) and pore size
distributions (Panel C and D) for mono- and bifunctional channel-like organosilica
SBA-15-type samples are shown in Figure 22, respectively.
The BET specific
surface area, total pore volume, volume of primary mesopores, pore diameter,
elemental analysis results and unit cell parameter for those samples are listed in
Table 15. For the purpose of comparison, nitrogen adsorption isotherms for the
extracted ureidopropyl-functionalized SBA-15 and ureidopropyl-mercaptopropylfunctionalized SBA-15 obtained via conventional process as well as the calcined
SBA-15 sample are shown too.
119
Table 13. Molar composition of the synthesis gels used and the corresponding
elemental analysis data for the organic – functionalized channel-like SBA-15
mesoporous silicasa
Synthesis gel composition
Sample
n, (mmoles)
TEOS
a
U
SH
Elemental analysis
P, (%)
PN
PS
C,
(mmoles/g)
CU
CSH
P*, (%)
P*N
P*S
SBA-15
19.20
SBA-15-U-c
17.28
1.92
4.04
0.79
2.22
SBA-15-U-m6
17.28
1.92
4.04
0.56
1.56
SBA-15-U-m8
17.28
1.92
4.04
0.45
1.25
SBA-15-U-m12
17.28
1.92
4.04
0.53
1.47
SBA-15-U-m24
17.28
1.92
4.04
0.41
1.14
SBA-15-U-SH-c
17.76
0.96
0.48
2.11
1.21
0.37
0.26
1.00
0.83
SBA-15-U-SH-m6
17.76
0.96
0.48
2.11
1.21
0.30
0.28
0.84
0.91
SBA-15-U-SH-m8
17.76
0.96
0.48
2.11
1.21
0.30
0.26
0.84
0.85
SBA-15-U-SH-m12
17.76
0.96
0.48
2.11
1.21
0.31
0.28
0.88
0.90
SBA-15-U-SH-m24
17.76
0.96
0.48
2.11
1.21
0.32
0.29
0.89
0.94
nTEOS, number of mmoles of tetraethyl orthosilicate; nU, number of mmoles of
ureidopropyltrimethoxysilane; nSH, number of mmoles of 3-mercaptopropylsilane; PN and PS, nitrogen and
sulfur percentages predicted on the basis of the synthesis gel mixture; CU or CSH concentration of functional
groups in the resulting materials calculated on the basis of nitrogen or sulfur percentages obtained by
elemental analysis; P*N and P*S, nitrogen and sulfur percentages obtained from elemental analysis.
120
Table 14. Molar composition for the synthesis gels used and the corresponding
elemental analysis data for the organic – functionalized cage-like SBA-16
mesoporous silicasa
Synthesis gel composition
Sample
n, (mmoles)
TEOS
U
Elemental analysis
P, (%)
SH
PN
PS
C, (mmoles/g)
CU
CSH
P*, (%)
P*N
P*S
SBA-16
20.16
SBA-16-U-c
18.14
2.02
4.04
0.92
2.5
SBA-16-U-m6
18.14
2.02
4.04
0.74
2.07
SBA-16-U-m8
18.14
2.02
4.04
0.73
2.04
SBA-16-U-m12
18.14
2.02
4.04
0.68
1.90
SBA-16-U-m24
18.14
2.02
4.04
0.54
1.50
SBA-16-U-SH-c
18.14
1.01
1.01
2.06
2.36
0.40
0.69
1.11
2.21
SBA-16-U-SH-m6
18.14
1.01
1.01
2.06
2.36
0.40
0.52
1.11
1.68
SBA-16-U-SH-m8
18.14
1.01
1.01
2.06
2.36
0.37
0.55
1.03
1.77
SBA-16-U-SH-m12
18.14
1.01
1.01
2.06
2.36
0.34
0.55
0.95
1.76
SBA-16-U-SH-m24
18.14
1.01
1.01
2.06
2.36
0.32
0.56
0.90
1.78
a
nTEOS, number of mmoles of tetraethyl orthosilicate; nU, number of mmoles of
ureidopropyltrimethoxysilane; nSH, number of mmoles of 3-mercaptopropylsilane; PN and PS, nitrogen and
sulfur percentages predicted on the basis of the synthesis gel mixture; CU or CSH concentration of functional
groups in the resulting materials calculated on the basis of nitrogen or sulfur percentages obtained by
elemental analysis; P*N and P*S, nitrogen and sulfur percentages obtained from elemental analysis.
121
100
A
Weight change (%)
95
B
95
90
90
SBA-15
85
85
80
80
75
SBA-15-U-c
SBA-15-U-m12
70
200
400
600
o
Temperature ( C)
0.08
o
- Deriv. Weight (% / C)
100
75
800
SBA-15-U-SH-c
SBA-15-U-SH-m12
200
400
600
o
Temperature ( C)
0.16
SBA-15
SBA-15-U-c
SBA-15-U-m12
0.06
70
SBA-15
800
SBA-15
SBA-15-U-SH-c
SBA-15-U-SH-m12
0.14
0.12
0.10
0.04
0.08
0.06
0.02
C
0.04
D
0.02
0.00
0.00
200
400
o600
Temperature ( C)
800
200
400
o600
Temperature ( C)
800
Figure 20. High-resolution TG (top panels) and the corresponding DTG profiles (bottom
panels) recorded in flowing nitrogen for channel-like SBA-15 mesoporous silicas
obtained via microwaved-assisted synthesis (m) and conventional route (c) with
ureidopropyl (U) surface ligands (A, C), bifunctional surface ligands: ureidopropyl (U)
and mercaptopropyl (SH) (B, D), respectively.
Weight change (%)
122
100
A
95
SBA-16
85
SBA-16-U-c
SBA-16-U-m12
70
200
400
600
Temperature (oC)
0.08
o
- Deriv. Weight (% / C)
SBA-16
80
80
70
B
90
90
75
100
800
SBA-16
SBA-16-U-c
SBA-16-U-m12
0.06
SBA-16-U-SH-c
SBA-16-U-SH-m24
200
400
600
Temperature (oC)
800
SBA-16
SBA-16-U-SH-c
SBA-16-U-SH-m24
0.16
0.14
0.12
0.10
0.04
C
0.02
0.08
0.06
0.04
D
0.02
0.00
0.00
200
400
600
Temperature (oC)
800
200
400
600
Temperature (oC)
800
Figure 21. High-resolution TG (top panels) and the corresponding DTG profiles (bottom
panels) recorded in flowing nitrogen for cage-like SBA-16 mesoporous silicas obtained
via microwaved-assisted synthesis (m) and conventional route (c) with ureidopropyl (U)
surface ligands (A, C), bifunctional surface ligands: ureidopropyl (U) and
mercaptopropyl (SH) (B, D), respectively.
123
All channel-like samples obtained under microwave irradiation possess type
IV isotherms with sharp capillary condensation/evaporation steps and a pronounced
H1 hysteresis loop, which is characteristic for channel-like mesoporous materials. As
can be seen from Figure 22, the both types of functionalized channel-like
organosilicas exhibit the type IV isotherm with a hysteresis loops, indicating the
presence of channel-like pores. Moreover, a comparison of mono- and bifunctional
samples obtained under microwave irradiation with samples prepared via
conventional method, shows very similar or better adsorption properties of the
former (see Table 10). The 12h and 24h ureidopropyl-modified SBA-15 samples
obtained under microwave irradiation show much better mesostructural properties
than ureidopropyl-modified SBA-15 silicas prepared via conventional process. The
SBA-15-U-m12 and SBA-15-U-m24 samples exhibited the BET specific surface
area of 826 and 759 m2 g-1, total pore volume of 1.49 and 1.38 cc g-1, and the pore
width of 9.52 and 9.55 nm, respectively. In contrast, the conventional SBA-15-U-c
has lower BET specific surface area of 731 m2 g-1, total pore volume of 0.81 cc g-1,
and the pore width of 9.1 nm. As can be noticed, microwave-assisted synthesis offers
a time reduction of the experiment from 72 hours in a conventional method to 24
hours, where self-assembly and hydrothermal treatment steps last 12 hours each.
The preparation of samples under microwave conditions is shorter; SBA-15-Um6 and SBA-15-U-m8, possess good mesostructures comparable to SBA-15-U-c,
however the volumes of complementary and ordered pores are significantly reduced.
The pore size reduction is noticeable on the pore size distributions shown in
124
Table 15. Selected structural parameters of the organic-functionalized channel-like
SBA-15 mesoporous silicasa
SBET
m2/g
Vc
cc/g
Vco
cc/g
Vt
cc/g
wKJS
nm
d
nm
SBA-15
866
0.13
1.20
1.38
9.79
9.94
SBA-15-U-c
731
0.14
0.78
1.00
8.47
10.33
SBA-15-U-m6
666
0.11
0.72
0.94
8.51
9.14
SBA-15-U-m8
699
0.11
0.78
1.02
8.62
8.76
SBA-15-U-m12
826
0.11
1.20
1.49
9.52
9.14
SBA-15-U-m24
759
0.08
1.13
1.38
9.55
8.79
SBA-15-U-SH-c
546
0.10
0.72
0.87
8.11
9.78
SBA-15-U-SH-m6
518
0.08
0.68
0.89
8.41
8.67
SBA-15-U-SH-m8
553
0.09
0.72
0.94
8.43
8.83
SBA-15-U-SH-m12
734
0.14
0.94
1.23
8.73
8.84
SBA-15-U-SH-m24
692
0.10
0.91
1.18
8.74
8.74
Sample
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters
below 4 nm; Vco, volume of complementary and ordered pores; Vt, single-point pore volume; wKJS,
mesopore diameter calculated by the improved KJS method for the channel-like mesostructures [279]; d,
spacing value for the XRD (100) peak;
a
125
Table 16. Selected structural parameters of the organic-functionalized cage-like
SBA-16 mesoporous silicasa
SBET
m2/g
Vc
cc/g
Vco
cc/g
Vt
cc/g
wKJS
nm
d
nm
SBA-16
932
0.35
0.20
0.60
7.00
10.21
SBA-16-U-c
613
0.23
0.16
0.41
6.80
10.31
SBA-16-U-m6
639
0.25
0.19
0.46
7.25
10.22
SBA-16-U-m8
593
0.24
0.19
0.43
7.06
10.80
SBA-16-U-m12
878
0.36
0.26
0.64
7.23
9.73
SBA-16-U-m24
600
0.25
0.23
0.49
7.04
10.40
SBA-16-U-SH-c
360
0.14
0.10
0.24
5.70
10.08
SBA-16-U-SH-m6
199
0.08
0.05
0.18
5.59
10.34
SBA-16-U-SH-m8
322
0.12
0.10
0.23
5.82
10.48
SBA-16-U-SH-m12
328
0.12
0.11
0.24
5.83
10.18
SBA-16-U-SH-m24
537
0.23
0.15
0.39
6.24
10.16
Sample
a
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters
below 5 nm; Vco, volume of complementary and ordered pores; Vt, single-point pore volume; wKJS,
mesopore diameter calculated by the KJS method [279] for the cage-like samples; d, spacing value for the
XRD (110) peak;
126
A
Amount Adsorbed (cm STP g )
2500
SBA-15
2000
SBA-15-U-m6
SBA-15-U-m8
1000
SBA-15-U-m12
500
SBA-15-U-m24
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
SBA-15-U-SH-m8
SBA-15-U-SH-m12
500
SBA-15-U-SH-m24
0
1.0
0.0
C
SBA-15-U-m8
2
1.0
D
SBA-15
SBA-15-U-c
SBA-15-U-m6
N2
0.2 0.4 0.6 0.8
Relative Pressure
5
SBA-15
PSD (cm g nm )
3
SBA-15-U-SH-m6
1000
3 -1
3 -1
1500
4
-1
4
SBA-15-U-SH-c
N2
-1
PSD (cm g nm )
5
SBA-15
2000
3
3
SBA-15-U-c
1500
B
-1
-1
Amount Adsorbed (cm STP g )
2500
3
SBA-15-U-SH-c
SBA-15-U-SH-m6
SBA-15-U-SH-m8
2
SBA-15-U-SH-m12
SBA-15-U-m12
1
1
SBA-15-U-SH-m24
SBA-15-U-m24
0
0
2
4 6 8 10 12 14
Pore Diameter (nm)
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 22. Nitrogen adsorption isotherms (A, B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C, D) calculated according to the KJS
method [279] for the channel-like SBA-15 mesoporous silicas obtained via microwaveassisted synthesis (m) and conventional route (c) with ureidopropyl (U) surface ligands
(A, C), bifunctional surface ligands: ureidopropyl (U) and mercaptopropyl (SH) (B, D),
respectively. The isotherms in Panel A for SBA-15, SBA-15-U-c, SBA-15-U-m6, SBA15-U-m8 and SBA-15-U-m12 were offset vertically by 1850, 1550, 1250, 850 and 400 cc
STP g-1. The isotherms in Panel B for SBA-15, SBA-15-U-SH-c, SBA-15-U-SH-m6,
SBA-15-U-SH-m8 and SBA-15-U-SH-m12 were offset vertically by 1750, 1500, 1150,
825 and 400 cc STP g-1. The PSD curves in Panel C for SBA-15, SBA-15-U-c, SBA-15U-m6, SBA-15-U-m8 and SBA-15-U-m12 were offset vertically by 4.5, 3.8, 2.9, 2.2 and
1.0 cm3 g-1 nm-1. The PSD curves in Panel D for SBA-15, SBA-15-U-SH-c, SBA-15-USH-m6, SBA-15-U-SH-m8 and SBA-15-U-SH-m12 were offset vertically by 4.5, 3.6,
2.8, 2.1 and 1.1 cm3 g-1 nm-1.
127
-1
SBA-16-U-c
3
-1
1200
SBA-16-U-m6
1000
SBA-16-U-m8
800
600
SBA-16-U-m12
400
SBA-16-U-m24
200
1400
0.0
0.2 0.4 0.6 0.8
Relative Pressure
SBA-16-U-SH-c
SBA-16-U-SH-m6
1000
SBA-16-U-SH-m8
800
600
SBA-16-U-SH-m12
400
SBA-16-U-SH-m24
200
N2
0
1.0
0.0
C
-1
SBA-16-U-SH-c
1.5
SBA-16-U-SH-m6
3
3
-1
SBA-16-U-m6
1.0
SBA-16
2.0
PSD (cm g nm )
1.5
-1
-1
PSD (cm g nm )
SBA-16-U-c
0.2 0.4 0.6 0.8
Relative Pressure
D
SBA-16
2.0
SBA-16
1200
N2
0
B
3
Amount Adsorbed (cm STP g )
1400
1600
SBA-16
Amount Adsorbed (cm STP g )
A
1600
1.0
SBA-16-U-m8
0.5
SBA-16-U-m12
SBA-16-U-m24
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
1.0
SBA-16-U-SH-m8
0.5
SBA-16-U-SH-m12
SBA-16-U-SH-m24
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 23. Nitrogen adsorption isotherms (A, B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C, D) calculated according to the KJS
method [279] for the cage-like SBA-16 mesoporous silicas obtained via microwaveassisted synthesis (m) and conventional route (c) with ureidopropyl (U) surface ligands
(A, C), bifunctional surface ligands: ureidopropyl (U) and mercaptopropyl (SH) (B, D),
respectively.The isotherms in Panel A for SBA-16, SBA-16-U-c, SBA-16-U-m6, SBA16-U-m8 and SBA-16-U-m12 were offset vertically by 1150, 1000, 750, 500 and 150 cc
STP g-1. The isotherms in Panel B for SBA-16, SBA-16-U-SH-c, SBA-16-U-SH-m6,
SBA-16-U-SH-m8 and SBA-16-U-SH-m12 were offset vertically by 1150, 1000, 900,
600 and 325 cc STP g-1. The PSD patterns in Panel C for SBA-16, SBA-16-U-c, SBA-16U-m6, SBA-16-U-m8 and SBA-16-U-m12 were offset vertically by 2.0, 1.6, 1.2, 0.8 and
0.4 cm3 g-1 nm-1. The PSD patterns in Panel D for SBA-16, SBA-16-U-SH-c, SBA-16-USH-m6, SBA-16-U-SH-m8 and SBA-16-U-SH-m12 were offset vertically by 2.0, 1.65,
1.24, 0.8 and 0.4 cm3 g-1 nm-1.
128
Figure 22, and confirms the need of longer hydrothermal treatment under microwave
irradiation. The similar situation occured for ureidopropyl-mercaptopropyl-modified
channel-like SBA-15 prepared under microwave irradiation. All aforementioned
bifunctional SBA-15-U-SH-m samples possess good porosity, specially SBA-15-USH-m12 in contrast to SBA-15-U-SH-c obtained by conventional method (see Table
15). Not only the KJS pore size is much higher for the SBA-15-U-SH-m12, 8.73 nm
vs. 8.11nm for the SBA-15-U-SH-c sample obtained under conventional conditions,
but also other adsorption parameters such as the BET specific surface area (734 vs.
546 m2 g-1, respectively) and total pore volume (1.23 vs. 0.87 cc g-1, respectively).
The advantage of time reduction of hydrothermal treatment during microwaveassisted synthesis of ureidopropyl-mercaptopropyl-modified SBA-15 appeared not
only in a shorter time of the whole process, from 72 hours to 24 hours, but also in a
better quality of mesoporous ordered networks.
Similarly to the organosilicas SBA-15 type materials, nitrogen adsorption
isotherms (Panel A and B) and pore size distributions (Panel C and D) for a series of
the extracted cage-like SBA-16 organosilicas with ureidopropyl as well as
ureidopropyl and mercaptopropyl organic groups are presented in Figure 23,
respectively. In addition, the analoguos samples were also obtained via conventional
method and shown for the comparison. As expected, the mono- and bifunctional
SBA-16 samples obtained under microwave irradiation showed a good porous
quality and exhibited type IV adsorption-desorption isotherms with sharp capilary
and evaporation steps as well as H2 hysteresis loop. Moreover, the hysteresis loops
129
starts at a relative pressure at ~ 0.65 - 0.7 and abruptly ends at ~ 0.45 - 0.5, which
confirms the cage-like porous network with narrow pore size distribution (see Figure
23). In the case of ureidopropyl-mercaptopropyl functionalized SBA-16 materials,
the capilary step is less steep, which results in the broader pore size distribution,
which is caused by not sufficient time of the hydrothermal treatment, especially for
the SBA-16-U-SH-m6 sample in contrary to SBA-16-U-SH-m24. It is noteworthy
that the adsorption properties of mono- and bifunctional SBA-16 prepared under
microwave irradiation show much better properties in comparison to the SBA-16-U-c
and SBA-16-U-SH-c samples obtained via conventional process. The observed
improvement is reflected by at least 50% increase in the structural parameters (see
Table 16.). A comparison of SBA-16-U-m12 and SBA-16-U-c shows the success of
microwave-assisted synthesis vs. conventional one, where the BET surface area
increased from 613 to 878 m2 g-1, respectively, whereas total pore volume from 0.41
to 0.64 cc g-1, respectively. Moreover, the similar conclusion is valid for bifunctional
cage-like organosilicas. A comparison of the S16-U-SH-m12 and S16-U-SH-m24
samples with S16-U-SH-c material shows better adsorption parameters for the
materials prepared under microwave irradiation and indicates the importance of time
of the hydrothermal treatment. The importance of the latter is noticeable in the
adsorption parameters of S16-U-SH-m12 and S16-U-SH-m24, which for the samples
treated for 24h are significantly higher; for instance the BET specific surface
increased from 328 to 537 m2 g-1, respectively, likewise the total pore volume from
0.24 to 0.39 cc g-1, respectively. In addition, even the sample S16-U-SH-m12 does
130
not represent the best features of the whole series, it still possesses comparable
parameters to S16-U-SH-c.
Powder X-ray diffraction was employed to monitor the structural changes of
mono- and bifunctional channel–like and cage-like mesomaterials under microwave
irradiation. The structural characterization of the samples from each series, together
with organosilicas materials prepared via conventional process, is presented for the
channel- and cage-type mesomaterials on the XRD patterns shown in Figure 24 and
Figure 25, respectively. The d spacing for the samples studied is presented in Table
15 and Table 16. As can be noticed, all channel-like organosilicas prepared under
microwave irradiation are characterized by the presence of one sharp major peak at
2θ = ~ 0.9-1.0 and some minor peaks at 2θ = ~ 1.4-1.8, which confirm the p6mm
symmetry group as that in SBA-15 type materials (see Figure 24). A similar result is
obtained for the mono- and bi-functional cage-like organosilicas. The XRD patterns
of aforementioned mesomaterials exhibit the major reflection at 2θ = ~0.7-0.8 and
some minor peaks in the area of 2θ = ~ 1.1-1.6. Such XRD profiles agree with cubic
Im3m symmetry group, indicating SBA-16 type of organosilicas under microwave
irradiation (see Figure 25). Moreover, all organosilica materials obtained via
microwave-assisted synthesis exhibit high d spacing, which shows good prospects of
this method for the synthesis of ordered mesoporous materials with surface organic
groups.
131
In summary, this study shows that the microwave-assisted synthesis is a useful
method to incorporate functional organic groups on the surface of the silica pore walls in
channel- and cage-like mesoporous materials. It is noteworthy that microwave irradiation
was used succesfully to obtain the mono-functional as well as bi-functional mesoporous
ordered silicas. The resulting materials have good adsorption characteristics such as the
increased pore volume and pore size as well the BET specific surface area in contrary to
the samples manufactured via conventional method. Furthermore, the aforementioned
method offers the significant reduction of synthesis time and simplification of the whole
process. Microwave-assisted synthesis possesses a lot of advantages over conventional
method and is a promising technique for the preparation of mesoporous materials.
132
A
B
SBA-15
Intensity (a.u.)
SBA-15
SBA-15-U-SH-c
SBA-15-U-c
SBA-15-U-m6
0.5
1.0
SBA-15-U-SH-m6
SBA-15-U-m8
SBA-15-U-SH-m8
SBA-15-U-m12
SBA-15-U-m24
SBA-15-U-SH-m12
1.5
o
2( )
2.0
SBA-15-U-SH-m24
0.5
1.0
1.5
o
2( )
2.0
Figure 24. X-ray diffraction (XRD) patterns for channel-like SBA-15 mesoporous
silicas obtained via microwave-assisted synthesis (m) and conventional route (c) with
ureidopropyl (U) surface ligands (A), bifunctional surface ligands: ureidopropyl (U)
and mercaptopropyl (SH) (B).
133
B
Intensity (a.u.)
A
SBA-16
SBA-16
SBA-16-U-c
SBA-16-U-SH-c
SBA-16-U-m6
SBA-16-U-SH-m6
SBA-16-U-m8
SBA-16-U-SH-m8
SBA-16-U-SH-m12
SBA-16-U-m12
SBA-16-U-m24
0.5
1.0
1.5

2 
2.0
SBA-16-U-SH-m24
0.5
1.0
1.5

2 
2.0
Figure 25. X-ray diffraction (XRD) patterns for cage-like SBA-16 mesoporous silicas
obtained via microwave-assisted synthesis (m) and conventional route (c) with
ureidopropyl (U) surface ligands (A), bifunctional surface ligands: ureidopropyl (U)
and mercaptopropyl (SH) (B).
134
4.5. Synthesis of vinyl-functionalized channel-like SBA-15 mesoporous material via
conventional and microwave methods
Nitrogen adsorption–desorption isotherms measured at -196 ºC and the
corresponding pore size distributions (PSD) show the advantage of using microwaveassisted synthesis over conventional method to prepare vinyl-functionalized
organosilicas as well as to study the mesostructural changes that occured upon
gradual introduction of organic ligands into channel-like materials. Figure 26 and
Figure 27 display adsorption isotherms and the PSD curves for vinyl-modified
mesomaterials. The BET specific surface area, total pore volume, volume of primary
mesopores and mesopore diameter for those samples are listed in Table 17.
As can be noticed, the samples obtained under microwave irradiation showed
better adsorption and structural properties in comparison to analogous samples
prepared by conventional method. Moreover, it is important to mention that with
increasing concentration of vinyl groups, the resulting mesostructures changed
gradually. Introduction of higher concentration of organic groups resulted in the
transition from highly ordered channel-like mesoporous materials into organosilicas
material with microporous network and some fraction of small mesopores. Such a
structural change is suggested by the shape of nitrogen adsorption-desorption
isotherms; transformation occured from type IV isotherm with H1 hysteresis loop
into type I-IV isotherm with H4 hysteresis loop in the case of the highest loadings of
A
-1
2000
Amount Adsorbed (cm STP g )
V10-MW-6
B
2000
1500
V10-MW-8
V15-MW-8
1500
V10-MW-12
1000
V15-MW-12
1000
V10-MW-24
500
V10-conv
V15-MW-24
500
0.0
6
0.2 0.4 0.6 0.8
Relative Pressure
V15-conv
N2
N2
0
0
0.0
1.0
C
4
0.2 0.4 0.6 0.8
Relative Pressure
V15-MW-6
3
3
V10-MW-12
2
V10-MW-24
1
3
V15-MW-8
-1
-1
PSD (cm g nm )
-1
V10-MW-8
3
-1
4
2
V15-MW-12
1
V15-MW-24
V10-conv
0
V15-conv
0
2
4 6 8 10 12 14
Pore Diameter (nm)
1.0
D
V10-MW-6
5
PSD (cm g nm )
V15-MW-6
3
3
-1
Amount Adsorbed (cm STP g )
135
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 26. Nitrogen adsorption isotherms (A and B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C and D) calculated according to the KJS
method [279] for the channel-like SBA-15 mesoporous silicas obtained via microwaveassisted synthesis and conventional route (conv) having various concentrations of vinyl
ligands (V).The isotherms in Panel A for V10-MW-6, V10-MW-8, V10-MW-12 and
V10-MW-24 were offset vertically by 1350, 950, 650 and 300 cc STP g-1. The isotherms
in Panel B for V15-MW-6, V15-MW-8, V15-MW-12 and V15-MW-24 were offset
vertically by 1500, 1100, 800 and 400 cc STP g-1. The PSD patterns in Panel C for V10MW-6, V10-MW-8, V10-MW-12 and V10-MW-24 were offset vertically by 3.8, 3.2, 2.1
and 0.9 cm3 g-1 nm-1. The PSD patterns in Panel D for V15-MW-6, V15-MW-8, V15MW-12 and V15-MW-24 were offset vertically by 2.6, 2.3, 1.5 and 0.6 cm3 g-1 nm-1.
136
A
Amount Adsorbed (cm STP g )
3
1400
1200
V20-MW-8
1000
V20-MW-12
800
600
V20-MW-24
400
V20-conv
200
B
-1
V20-MW-6
V30-MW-12
600
200
N2
0
C
0.2 0.4 0.6 0.8
Relative Pressure
1.0
0.0
V20-MW-6
1.0
D
V30-MW-6
-1
-1
PSD (cm g nm )
2.0
V30-MW-8
0.4
3
-1
-1
V20-MW-8
0.2 0.4 0.6 0.8
Relative Pressure
0.6
2.5
3
V30-conv
N2
0.0
PSD (cm g nm )
V30-MW-24
400
0
3.0
V30-MW-6
V30-MW-8
800
3
-1
Amount Adsorbed (cm STP g )
1600
1.5
V20-MW-12
1.0
V30-MW-12
0.2
V30-MW-24
V20-MW-24
0.5
V20-conv
0.0
V30-conv
0.0
2
4 6 8 10 12 14
Pore Diameter (nm)
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 27. Nitrogen adsorption isotherms (A and B) measured at – 196 °C and the
corresponding pore size distributions (PSDs) (C and D) calculated according to the KJS
method [279] for the channel-like SBA-15 mesoporous silicas obtained via microwaveassisted synthesis and conventional route (conv) having various concentrations of vinyl
ligands (V).The isotherms in Panel A for V20-MW-6, V20-MW-8, V20-MW-12 and
V20-MW-24 were offset vertically by 1200, 925, 500 and 200 cc STP g-1. The isotherms
in Panel B for V30-MW-6, V30-MW-8, V30-MW-12 and V30-MW-24 were offset
vertically by 475, 450, 225 and 125 cc STP g-1. The PSD patterns in Panel C for V20MW-6, V20-MW-8, V20-MW-12 and V20-MW-24 were offset vertically by 2.6, 2.1, 1.2
and 0.5 cm3 g-1 nm-1. The PSD patterns in Panel D for V30-MW-6, V30-MW-8, V30MW-12 and V30-MW-24 were offset vertically by 0.5, 0.375, 0.225 and 0.125 cm3 g-1
nm-1.
137
Table 17. Selected structural parameters for the vinyl-functionalized channel-like
SBA-15 mesoporous silicasa
a
Sample
SBET
m2/g
Vc
cc/g
Vco
cc/g
Vt
cc/g
wKJS
nm
d
nm
V10-conv
840
0.19
0.62
0.93
6.84
8.61
V10-MW-6
1013
0.22
0.92
1.27
8.23
9.60
V10-MW-8
1079
0.22
1.03
1.40
8.24
9.32
V10-MW-12
934
0.18
1.00
1.31
8.25
9.37
V10-MW-24
893
0.11
1.00
1.45
8.44
9.76
V15-conv
914
0.21
0.58
1.00
5.71
8.67
V15-MW-6
1031
0.20
1.01
1.38
7.67
9.05
V15-MW-8
1099
0.23
0.98
1.38
7.53
9.19
V15-MW-12
910
0.18
0.84
1.18
7.68
9.18
V15-MW-24
850
0.14
0.90
1.23
7.90
9.62
V20-conv
886
0.29
0.47
0.89
4.96
7.97
V20-MW-6
776
0.17
0.61
0.88
7.15
8.78
V20-MW-8
791
0.18
0.64
0.90
7.12
8.73
V20-MW-12
1017
0.21
1.06
1.35
7.48
9.12
V20-MW-24
1022
0.19
1.03
1.39
7.60
9.32
V30-conv
782
0.22
0.20
0.62
4.14
7.99
V30-MW-6
746
0.34
0.12
0.49
4.15
7.85
V30-MW-8
762
0.34
0.18
0.56
4.33
8.21
V30-MW-12
948
0.40
0.28
0.75
5.19
7.76
V30-MW-24
801
0.32
0.29
0.67
4.96
8.19
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters
below 4 nm; Vco, volume of complementary and ordered pores; Vt, single-point pore volume; wKJS,
mesopore diameter calculated by the improved KJS method [279] for the channel-like mesostructures; d,
spacing value for the XRD (100) peak;
138
organic group. As can be noticed in Figure 26 and Figure 27, the optimal concentration of
introduced vinyl groups is about 15%.
The microwave-assisted synthesis of organosilicas showed good ordered
channel-like structures, likewise the higher loadings of organic groups at 20% caused
some visual changes in the mesostructure and finally, 30% concentration of these
surface group resulted in the material possessing microporous character with some
fration of small mesopores.
The vinyl-functionalized organosilicas with 10 and 15% concentration of
organic groups possess the isotherms of type IV with sharp capillary condensation
and evaporation steps and a pronounced H1 hysteresis loop, which is characteristic
for mesoporous materials like SBA-15. As can be noticed, all samples show high
uniformity of mesopore channels. The corresponding pore size distributions shown
in Figure 26, are centered in the range between 7.53 and 7.9 nm for the series with
10% of vinyl groups and between 8.23 and 8.44 nm for series with 15% vinyl
groups; however, analogous samples obtained by conventional method have smaller
pores, 5.71 and 6.84nm, respectively. In contrary to the samples obtained under
microwave irradiation, the organosilica samples hydrothermally treated in
conventional oven show poorer adsorption parameters such as the BET specific
surface area, 840 m2 g-1 (V10-conv) in comparison to 893 – 1079 m2 g-1 (V10-MW )
as well as the pore volumes 0.93 and 1.27 – 1.45 cc g-1, respectively. The similar
tendency is also observed for 15% of vinyl incorporation. The steep capillary
139
condensation steps for both series of organosilicas prepared under microwave
conditions
indicate narrow pore size distributions, proving the usefulness of
microwave technique for the synthesis of vinyl-modifed OMSs (see Figure 26). An
increase in the concentration of vinyl groups caused a meaningful change in the
mesostructural network of organosilicas (see Figure 27). The 20% loading of organic
groups caused a visible deterioration of channel-like mesostructure. As can be
noticed, time of the hydrothermal treatment under microwave irradiation is also
essential. The shortnen the second step of this process is, the less ordered structure is
obtained (see comparison V20-MW-6 vs. V20-MW-12 sample). Moreover, an
increase in the content of vinyl groups reflects a gradual reduction of the diameter of
mesopore channels from about 8 nm (V10-MW and V15-MW) to about 4 – 5 nm for
the samples with high content of vinyl groups. It is noteworthy that the
mesostructural changes are specially visible for 20 and 30%
loadings of vinyl
groups, which is reflected by a drastic reduction of the KJS pore size as well as other
adsorption parameters. In the case of lower concentrations of vinyl groups, the pore
widths were around 8 nm, and they decreased to ~ 7 nm for the series with 20% vinyl
loadings. A significant difference appeared for the series with 30% vinyl loading, for
which pore size was reduced to ~ 4 nm, the BET surface area droped from 1000 m2
g-1 to 746 m2 g-1 as well as the volume of mesopores decreased significantly (see
PSD inset in Figure 27). As can be seen in Figure 27, the series of the V30-MW
samples is rather microporous with some fraction o small mesopores. An increase in
140
the vinyl-loading caused a significant deterioration of mesostructural network and
transformation into microporous-mesoporous type materials.
Figure 28 shows the X-ray diffraction patterns for the series of vinyl-modified
samples obtained under microwave and conventional conditions; these patterns were
recorded in the small angle region (2θ = 0.4 – 3.5°). As can be noticed, the
diffraction profiles for the materials with smaller ligand loadings (Panels A and B in
Figure 28), exhibit intensive major peak at 2θ = ~ 0.9 and minor less-resolved peaks
at 2θ = ~ 1.25 – 1.75. These XRD patterns are consistent with the profiles obtained
for the SBA-15-type ordered mesoporous materials. Moreover, the XRD spectra
show that an increase in the ligand loadings caused a significant deterioration of
mesostructural network, which is specially visible for the V30-MW series as well as
the V30-conv sample (see Figure 28D). Furthermore, the aforementioned vinylmodified organosilicas exhibit one major peak at = ~ 1.1 – 1.2 with some minors
peaks and such a shift of peaks indicates the significant reduction of the structure. As
can be seen from Table 17, the d spacing parameter gradually decreases with
increasing concentration of vinyl groups present on the surface of silica pore walls,
from 9.76 to 7.76 nm for the samples with lowest and highest vinyl loadings,
respectively.
The vinyl-functionalized channel-like silicas were also analyzed by highresolution thermogravimetry under flowing nitrogen from room temperature to
800°C. The thermogravimetric weight change (TG) and the differential TG curves
Intensity (a.u.)
141
A
B
V10-conv
V15-conv
V15-MW-6
V10-MW-6
V10-MW-8
V15-MW-8
1.0
V15-MW-12
V10-MW-24
V15-MW-24
1.5
o
2( )
Intensity (a.u.)
0.5
V10-MW-12
0.5
2.0
1.0
1.5
o
2( )
2.0
C
D
V20-conv
V30-conv
V30-MW-6
V20-MW-6
V30-MW-8
V20-MW-8
V30-MW-12
V20-MW-12
V30-MW-24
V20-MW-24
0.5
1.0
1.5
o
2( )
2.0
0.5
1.0
1.5
o
2( )
2.0
Figure 28. X-ray diffraction (XRD) patterns for channel-like SBA-15 mesoporous silicas
with various concentrations of vinyl ligands (V) obtained via microwaved-assisted
synthesis (MW) and conventional route (conv).
Weight change (%)
142
100
95
A
90
100
B
95
75
o
- Deriv. Weight (% / C)
0.06
E
0.06
F
200 400 600 800
Temperature (oC)
V30-conv
V30-MW-12
200 400 600 800
Temperature (oC)
V20-conv
V20-MW-12
V15-conv
V15-MW-12
V10-conv
V10-MW-12
0.10
0.08
G
0.06
0.04
0.04
0.06
0.04
0.02
0.02
0.04
0.02
0.02
0.00
0.00
200 400 600 800
Temperature (oC)
H
0.00
0.00
200 400 600 800
Temperature (oC)
D
80
80
200 400 600 800
Temperature (oC)
95
85
80
200 400 600 800
Temperature (oC)
100
90
85
85
80
95
C
90
90
85
100
200 400 600 800
Temperature (oC)
200 400 600 800
Temperature (oC)
Figure 29. High-resolution TG (top panels) and the corresponding DTG profiles (bottom
panels) recorded in flowing nitrogen for channel-like SBA-15 mesoporous silicas with
various concentrations of vinyl ligands (V) obtained via microwaved-assisted synthesis
(MW) and conventional route (conv).
143
(DTG) for the extracted samples obtained under microwave and coventional conditions,
are presented in Figure 29. As can be noticed, several weight loss steps are observed. The
weight change between 35-100°C reflects thermodesorption of physisorbed of water and
ethanol. The next event at 100-600°C represents decomposition of polymeric template
and degradation of organic groups. The decomposition of vinyl groups occured above
300°C, and the maximum peak appears at 400-600°C for particular series of the vinylmodified samples. The presence those peaks confirmed the introduction of vinyl groups
into silica matrix.
This study shows that the microwave-assisted synthesis is afforded vinylfunctionalized ordered mesoporous channel-like SBA-15 materials at lower vinyl
loadings. The microwave technique permitted the synthesis of a good quality
organosilicas with surface groups. Furthermore, the effect of increasing concentration of
organic surface groups was shown, resulting in significant structural changes. Generally,
the addition of surface groups promoted reduction of the pore size reflected by transition
from ordered mesoporous vinyl-silicas to microporous-mesoporous ones. An increase in
the loading of vinyl groups caused a visible deterioration of the mesostructural order and
an increase in the formation of micropores; the latter was observed for the samples with
30% vinyl loadings.
V. Ordered mesoporous materials with ethane bridging
group*
Preparation of nanomaterials under microwave irradiation offers several
advantages; therefore, the aim of this chapter is to explore the microwave technique
approach for the development of PMO materials. Among many reports on the
microwave-assisted synthesis of OMMs, only a few of them refer to mesoporous
organosilicas [226-230]. The detailed studies are presented for ethane-silica ordered
mesostructures prepared under microwave conditions (see Scheme 11); for the purpose of
comparison, this nanomaterial was also synthesized in a conventional way. Incorporation
of bridging groups into the framework and the presence of ordered mesopores were
confirmed by nitrogen adsorption at -196C, elemental and thermogravimetric analysis,
and powder X-ray diffraction.
This chapter is based on the following publications:
B.E. Grabicka, M. Jaroniec Microporous and Mesoporous Materials 2009 119 674 [267]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec Applied Surface Science 2007 253 5660 [93]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Colloids and Surfaces A: Physicochemical and Engineering
Aspects 2007 300 235 [198]
Author’s related articles: R.M. Grudzien, B.E. Grabicka, S. Pikus, M. Jaroniec: Chem. Mater. 2006 18
1722 [146];
144
145
5.1. Experimental
5.1.1. Conventional synthesis of SBA-15 organosilicas with ethane bridging group
The SBA-15-type PMO with ethane bridging groups (see Scheme 12) was
synthesized by hydrolysis and condensation of 1,2-bis(triethoxysilyl)ethane in the
presence of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene
oxide) triblock copolymer Pluronic P123 (EO20PO70EO20) at low acid concentrations.
The recipe adopted here was similar to the procedure reported by Bao et al. [196]. In a
typical synthesis, the specified amount of polymer Pluronic P123 (in the successive
syntheses the amount of polymer was increased by 0.5 g increments from 0.5 to 3 g) was
added to 28 ml of deionized water (DW) under magnetic stirring at 40 °C. After 4 h
stirring a 3.82 ml (3.6622 g) of BTSE was combined with 30.4 ml of DW and 2.4 ml of
2.0 M HCl and stirred for 40 min at 40 °C. Next, the P123-DW solution was slowly
added to the BTSE-DW-HCl mixture under vigorous stirring. The slurry was further
stirred for 24 h at 40 °C and the resulting precipitate was transferred into a polypropylene
bottle, which after tight closing was kept at 100 °C for 48 h. The white product was
recovered by filtration, washed with DW, and dried at 80 °C. The template of this assynthesized nanocomposite was removed by extraction with 2 ml of 37 wt.% HCl and
100 ml of 95% ethanol at 70 °C. The extracted SBA-15-type ethane-silica was denoted as
PMO-x, where x stands for the amount (in grams) of added triblock copolymer to the
synthesis mixture. In addition, the letters c and t in PMO-xc and PMO-xt are used to
denote the materials extracted with ethanol/HCl solution and later subjected to
calcination in flowing air for 3 h at 540 °C and as-synthesized material containing
146
structure directing agent Pluronic P123, respectively. The EO20PO70EO20/BTSE ratio for
each material is listed in Table 18. For example, PMO-1.5t denotes an as-made ethaneSBA-15 material prepared using 1.5 g of Pluronic P123, which for the specified amount
of bridging BTSE precursor gives the EO20PO70EO20-BTSE weight ratio = 2.2.
5.1.2. Conventional synthesis of SBA-16 with ethane bridging groups
The SBA-16-type PMO with ethane bridging groups were synthesized using
poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock
copolymer Pluronic F127 (EO106PO70EO106) and 1,2-bis(triethoxysilyl)ethane (BTSE)
instead of tetraethyl orthosilicate (TEOS). In typical synthesis, 0.75g of polymer F127
was added to 10.5 ml of deionized water (DW) and 4.5ml of 2M HCl and stirred at 40
ºC. After 4 h stirring, a 2.975 ml of BTSE was combined with 12.5 ml of DW and 3.0 ml
of 2.0 M HCl and stirred for 40 min at 40 °C. Next, the F127-DW solution was slowly
added to the BTESE-DW-HCl mixture under vigorous stirring. The slurry was further
stirred for 24 h at 40 °C and resulted precipitate was transferred into a polypropylene
bottle, which after tight closing was kept at 100 °C for 24 h. The white product was
recovered by filtration, washed with DW, and dried at 80 °C. Thus prepared organosilica
was extracted three times with 2 ml of 36 wt.% HCl and 100 ml of 95 % ethanol at 70 º
C. To show the effect of degradation of ethane group in the structure of the samples
studied, the extracted samples were subjected to calcination at 550, 700, 800 and 900 º C
for 4 hours under air atmosphere. The resulting materials are denoted as ES-cT, where
147
ES, c, e and T refer the ethane-bridged silica samples, calcined, extracted–calcined and
temperature of calcination, respectively.
5.1.3. Microwave-assisted synthesis of ethane-bridged channel-like organosilicas
Ethane PMO was synthesized by self-assembly of 1,2-bis(triethoxysilyl)ethane
and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer
(Pluronic 123; EO20PO70EO20) under microwave conditions. The recipe used was
analogous to that reported by Bao at al [196] for the synthesis of hexagonally ordered
mesoporous ethane-silica under conventional conditions. Previous studies on the
synthesis of this type PMO suggest the use of 2g of poly(ethylene oxide)-poly(propylene
oxide)-poly(ethylene oxide) triblock copolymer [198], which added to 28 ml of deionized
water and subjected to magnetic stirring at 40 oC for 4-6 hours. Also, 3.82 ml (3.6622 g)
of 1,2-bis(triethoxysilyl)ethane was combined with 30.4 ml of water and 2.4 ml of 2.0 M
HCl and stirred for 40 minutes at 40 oC. Next, the clear polymer solution was added to
the BTSE solution. The resulting mixture was transferred to the teflon vessels, which
were installed in microwave oven (MARS 5; CEM Corp.). Both steps of the PMO
synthesis, i.e., the self-assembly of organosilane precursors and block copolymer and the
subsequent hydrothermal treatment, were carried out under microwave irradiation (see
Scheme 11). In the first step, the synthesis mixture was stirred using magnetic bars for 224h at 40°C. After initial stage, temperature was increased to 100ºC and kept for 8-48h;
magnetic stirring was off during this stage. The slurry was filtered, washed with
148
deionized water, and dried at 80 °C. An efficient removal of the polymeric template was
achieved by extraction, which was repeated two times with 2 ml of 37 wt. % HCl and 100
ml of 95 % ethanol at 70 ºC. The resulting samples are denoted as ES-x, where ES stands
for PMOs obtained using 1,2-bis(triethoxysilyl)ethane, x refers to the time of
hydrothermal treatment of the ES samples in microwave at 100 °C. The duration of the
first step was 12 hours at 40 °C.
149
EO20PO70EO20 or EO106PO70EO106
+
1,2-bis(triethoxysilyl)ethane
(BTSE)
selfassembly
hydrothermal
treatment
24h at 40 C
48h at 100 C
A
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
24h at 60-70 C
B
EO20PO70EO20
+
1,2-bis(triethoxysilyl)ethane
(BTSE)
selfassembly
hydrothermal
treatment
6-12h
at 40 C
6-24h
at 100 C
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
24h
at 60-70 C
microwave-assisted synthesis
Scheme 11. Schematic illustration of ethane-bridged silica under conventional conditions
(top; ethane-modified SBA-15 (A) and SBA-16 (B)) and microwave synthesis conditions
(bottom).
150
Si
Si
Scheme 12. Schematic illustration of hexagonally-arranged interconnected cylindrical
channels via irregular micropores (large circle with thin ribbons) of SBA-15-type
periodic mesoporous organosilica containing ethane (-CH2-CH2-) bridging groups
incorporated inside framework.
151
5.2. Results and discussion for ethane-silica mesostructure prepared under
conventional conditions
Structural analysis of the extracted SBA-15-type ethane-silicas synthesized using
different amounts of polymeric template P123 was performed on the basis of the XRD
profiles shown in Figure 30 (Panel A). As can be seen from Figure 30A, the XRD
profiles exhibit one intense peak at 2θ = 0.95°. The intensity of the major peak is
different for particular samples, which is quite broad for PMO-0.5, narrow for PMO-1
and PMO-1.5, and becomes again broad for PMO-2, PMO-2.5 and PMO-3. Furthermore,
for the PMO-1 and PMO-1.5 samples, there are some minor peaks present. Analysis of
these XRD peaks confirms the hexagonal P6mm symmetry group of the resulting
materials. Therefore, major and minor peaks were indexed as (100) and (110) and (200),
respectively. A comparison of the sharpness of the aforementioned reflections, suggests
the poor mesostructural ordering for low (PMO-0.5) and high (PMO-2.5 and PMO-3)
contents of P123 as well as a good ordering for the PMO-1 and PMO-1.5 samples,
whereas the PMO-2 sample possesses some deterioration of the structure in comparison
to the PMO-1 and PMO-1.5 samples, which is reflected by the lack of (200) peak.
Nitrogen adsorption–desorption isotherms measured at −196 °C (Panels B) and
the corresponding pore size distributions calculated from adsorption branches according
to the improved KJS method [279] (Panel C) for the extracted SBA-15 ethane-silica
materials studied are shown in Figure 30. The PMO-1.5, PMO-2 and PMO-2.5 samples
exhibit type IV adsorption–desorption isotherms with very prominent adsorption step at
0.60–0.65 p/po (relative pressure), which reflects capillary condensation of nitrogen in
152
A
B
2.5
C
PMO-3
1400
PMO-3
2.0
1200
-1
PSD (cm g nm )
1000
PMO-2
PMO-1.5
-1
PMO-2
1.5
3
Intensity (a.u.)
3
PMO-2.5
PMO-2.5
PMO-2.5
-1
Amount Adsorbed (cm STP g )
PMO-3
800
PMO-1.5
1.0
600
PMO-2
PMO-1
400
PMO-1
PMO-1.5
PMO-0.5
0.5
200
PMO-1
N2
PMO-0.5
PMO-0.5
0.0
0
0.5 1.0 1.5 2.0
2.5 3.0
o
2( )
0.0
0.2
0.4
0.6
Relative Pressure
0.8
1.0
2 4 6 8 10 12 14
Pore Diameter (nm)
Figure 30. A comparison of X-ray diffraction (XRD) patterns (panel A), nitrogen
adsorption-desorption isotherms measured at – 196 °C (panel B) and the corresponding
pore size distributions (PSDs) calculated according to the improved KJS method [279]
from nitrogen adsorption branches (panel C) for the extracted SBA-15-type periodic
mesoporous ethane-silicas synthesized using various triblock copolymer P123-BTSE
bridged silsesquioxane weight ratios ranging from 0.73 to 4.39. The isotherms and PSDs
for PMO-1, PMO-1.5, PMO-2, PMO-2.5, PMO-3 were offset by 175, 360, 530, 710,
1000 cc STP g-1 and 0.16, 0.5, 0.95, 1.85, 2.35 cc g-1 nm-1, respectively.
153
uniform mesopores. The steep capillary condensation steps for PMO-1.5 and PMO-2
indicate a high uniformity of mesopore diameters, which is also confirmed by narrow
PSDs for these samples (see PSDs in Panel C, Figure 30). For the aforementioned PMOs,
adsorption and desorption curves show H1 hysteresis loop with almost parallel branches,
which is typical for large channel-like mesostructures with narrow PSDs. For the PMO2.5 sample desorption does not close instantly but it shows a tailing before it reaches the
adsorption branch. This indicates some non-uniformity in the size of pore openings. The
PMO-0.5 and PMO-3 mesomaterials show adsorption with broad capillary condensation
steps, which is reflected by broad PSDs (Panel C). Moreover, nitrogen adsorption
isotherms at higher pressures, especially those for PMO-0.5, PMO-1, PMO-1.5 and
PMO-2 demonstrate the lack of plateau and showing a gradual increase, which is
characteristic for the presence of some secondary mesoporosity (textural pores).
Adsorption and structural parameters such as the BET specific surface area, the
volume of complementary pores, the volume of complementary and ordered pores, the
single-point total pore volume, the mesopore width and the pore wall thickness
determined on the basis of nitrogen adsorption isotherms are listed in Table 18. In
addition, the bar charts showing the evolutions of these quantities with increasing amount
of the polymer template in the synthesis gel mixture are displayed in Figure 31. As can be
seen from this figure, the BET specific surface area (Panel A) changes in the range from
965 to 1164 m2 g−1 and exhibits a tendency to increase with each addition of the polymer
reaching the highest value of 1164 m2 g−1 for the sample PMO-2.5.
154
Table 18. Adsorption parameters for SBA-15-type ethane-silicas studieda
Wt
g
Wt
ratio
SBET
m2 g-1
Vc
cc g-1
Vt
cc g-1
wKJS
nm
wd
nm
b
nm
a
nm
TG
%
TG*
%
1
0.73
965
0.28
0.63
5.3
6.0
4.3
10.3
14.6
24.5
1.5
1.46
990
0.28
0.67
6.6
6.3
4.1
10.4
16.5
40.5
2
2.20
981
0.28
0.85
7.5
7.5
3.5
11.0
17.9
49.7
2.5
2.93
1072
0.31
0.97
7.5
7.7
3.3
11.0
16.1
48.1
3
3.66
1164
0.34
1.00
7.2
6.9
3.0
9.9
16.9
56.6
SBA-15-3
3.5
4.39
1006
0.28
0.99
5.7
7.4
2.8
10.2
17.2
58.4
SBA-15-1c
1
1.46
563
0.25
0.35
5.2
4.6
4.4
9.0
1.3
44.0
SBA-15-2c
2
2.93
546
0.11
0.37
5.2
5.1
3.8
8.9
2.1
47.6
SBA-15-3c
3
4.39
635
0.21
0.45
4.5
4.7
4.2
8.9
1.2
58.4
Sample
SBA-15-0.5
SBA-15-1
SBA-15-1.5
SBA-15-2
SBA-15-2.5
i a
Notation: Wt; weight of the polymer P123 used in the synthesis mixture; Wt ratio, weight ratio of the
polymer P123 to BTSE; SBET, BET specific surface area; Vc, volume of complementary pores (including
micropores) of the diameter below 4 nm; Vt, single-point pore volume; wKJS, mesopore diameter calculated
by the improved KJS method [279]; wd, pore width calculated using equation 7; b, pore wall thickness
calculated using equation 9; a, unit cell parameter calculated from the observed characteristic Bragg’s
reflection (100) using equation 11; TG, thermogravimetric weight change for the extracted PMOs studied;
TG*, thermogravimetric weight change for the as-synthesized PMOs studied.
155
5
1000
800
600
400
4
3
2
1
200
0
0
0.1
0.0
0.4
0.2
2
F
0.8
0.6
0.4
0.2
0.0
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
4
1.0
E
-1
-1
0.6
6
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
Total Volume (cc g )
0.2
Mesopore Volume (cc g )
-1
Micropore Volume (cc g )
D
C
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
0.3
B
Mesopore Diamaeter (nm)
A
Wall Thickness
2 -1
BET Surface Area (m g )
1200
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Polymer Mass (g)
Figure 31. Evolution of the BET surface area (A), wall thickness (nm) (B), mesopore
diameter (C), volume of micropores (D), volume of ordered mesopores (E) and the total
pore volume (F) for the extracted SBA-15-type ethane-silicas synthesized using different
triblock copolymer P123-BTSE silsesquioxane weight ratios between 0.73 and 4.39.
156
The values of the pore wall thickness (Panel B) decrease gradually from 4.3 to
2.8 nm with increasing P123-BTSE weight ratio analogously as in the case of other
mesostructures prepared from TEOS in the presence of triblock copolymer P123.
Therefore, it is anticipated that thicker pore walls and greater hydrophobicity originated
from ethane groups may enhance hydrothermal stability. The volume of ordered
mesopores (Panel E) and the single-point total pore volume (Panel F) are dependent on
the amount of polymer used and show a tendency to increase with increasing P123/BTSE
ratio, whereas the volume of complementary pores is about 0.28 cm3 g−1 for almost all
samples excluding PMO-2 and PMO-2.5, which have about 10–20% higher volume of
complementary pores.
The removal of triblock copolymer template P123 by using ethanol/hydrochloric
acid solution from the PMOs studied was monitored by high-resolution thermogravimetry
(TG). The TG profiles and the corresponding differential TG (DTG) patterns for assynthesized (t) and extracted SBA-15-type ethane-silicas measured in flowing air are
displayed in Figure 32 (Panels A–F). As can be seen from this figure, the weight change
shows a tendency to decrease systematically in four different temperature regions: 35–
100 °C, 160–220 °C, 230–550 °C and above 550 °C. The observed changes in these
regions are attributed to the thermodesorption of physisorbed water and ethanol,
thermodesorption/decomposition of polymer, degradation of ethane bridging groups and
condensation of silanols, respectively. A very sharp step around 200 °C on the TG
patterns for as-synthesized samples show a gradual increase in the weight loss (from 40.5
to 58.4% for the samples with increasing amount of polymer from 1 to 3 g) as well
157
6.0
60
PMO-0.5t
40
1.6
PMO-1
1.2
PMO-1t
5.0
3.0
4.0
PMO-1.5t
0.1
0.1
20
B
A
0
0.0
C
0.0
0.1
0.0
10.0
100
6.0
PMO-2
80
Weight change (%)
4.0
PMO-1.5
o
- Deriv. Weight (% / C)
80
PMO-0.5
PMO-2.5
3.0
o
- Deriv. Weight (% / C)
Weight change (%)
100
PMO-3
5.0
2.0
60
40
PMO-2t
20
4.0
0.1
0.2
0.1
PMO-2.5t
PMO-3t
0.1
E
D
0
0.0
200
400
600
800
o
Temperature ( C)
200
400
600
800
o
Temperature ( C)
F
0.0
200
0.0
400
600o
800
Temperature ( C)
Figure 32. High-resolution thermogravimetric (TG) weight change curves with the
corresponding differential TG (DTG) profiles recorded in flowing air for the templatecontaining (dashed line) and template-free (solid line) SBA-15-type periodic mesoporous
ethane-silicas obtained for different triblock copolymer P123-BTSE silsesquioxane
weight ratios ranging from 0.73 to 4.39, respectively.
158
as the lack of the characteristic peak for the P123 polymer template on the DTG patterns
for the extracted materials shows a successful template removal. An insufficient removal
of copolymer P123 was evident for the PMO-0.5 sample, which weight loss was about
twice smaller in contrast to other materials.
The effect of thermal degradation of ethane bridging groups via calcination of the
template-free samples in flowing air at 540 °C was investigated by nitrogen adsorption,
powder X-ray diffraction, and high-resolution thermogravimetry (Figure 33 and Figure
34, respectively). As can be noticed, thermal removal of ethane bridging groups from the
PMOs studied did not cause a substantial deterioration of structural ordering. A complete
elimination of these groups was confirmed by DTG analysis, which is reflected by
disappearance of the characteristic peak reflecting their thermal decomposition in the
temperature range from 200 to 550 °C (Figure 34). Moreover, the structural ordering of
channel-like mesopores was preserved during elimination of ethane bridges although this
process caused a significant decrease in the values of basic adsorption and structural
parameters such as the BET surface area, single-point pore volume, pore diameter and
unit cell parameter (see data in Table 18).
In conclusion, a series of tunable SBA-15-type PMOs with ethane bridging
groups in the framework of cylindrical mesopores was obtained by direct condensation of
the BTSE silsesquioxane in the presence of poly(ethylene oxide)-block-poly(propylene
oxide)-block-poly(ethylene oxide) triblock copolymer Pluronic P123. For the P123/BTSE
weight ratio varying from 0.73 to 1.46, the amorphous plugs were formed inside
400
PMO-2
PMO-2c
PMO-1
PMO-1c
500
600
400
300
400
300
200
200
200
A
100
0
B
1.0
E
PMO-1
PMO-1c
0.0
D
0.0
2 4 6 8 10 12 1.0 2.0 3.0
2 (o)
Pore Diameter (nm)
0.4
-1
3
PMO-2
0.2
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
PMO-3
PMO-3c
I
PMO-3c
0.20
-1
Intensity (a.u.)
-1
0.6
3
0.1
0.0
0.30
PMO-2c
-1
PSD (cm g nm )
Intensity (a.u.)
-1
-1
3
PMO-1
0
0.25
0.8
0.2
1.0
G
PMO-2
PMO-2c
1.0
PMO-1c
0.3
0.2 0.4 0.6 0.8
Relative Pressure
PSD (cm g nm )
0.2 0.4 0.6 0.8
Relative Pressure
C
100
0
0.0
PSD (cm g nm )
PMO-3
PMO-3c
600
Intensity (a.u.)
-1
500
3
Amount Adsorbed (cm STP g )
159
0.15
0.10
PMO-3
H
0.05
F
0.00
2
4
6
8 10 12
Pore Diameter (nm)
1
2 3
2 (o)
2 4 6 8 10 12
Pore Diameter (nm)
1
2 3
2 (o)
Figure 33. A comparison of nitrogen adsorption-desorption isotherms measured at – 196
°C (panel A, B, C), the corresponding pore size distributions (PSDs) calculated according
to the improved KJS method [279] from nitrogen adsorption branches (panel D, F, H), Xray diffraction (XRD) patterns (panel E, G, I) for the SBA-15-type periodic mesoporous
ethane-silicas obtained using various triblock copolymer P123-BTSE bridged
silsesquioxane weight ratios ranging from 0.73 to 4.39, respectively.
160
PMO-1c
0.12
0.08
PMO-2c
0.06
PMO-2
0.10
80
Weight change (%)
PMO-3c
PMO-1
60
A
20
0.04
PMO-3
0.08
0.03
0.06
0.04
40
B
0.02
0.05
- Deriv. Weight (% / oC)
100
0.02
0.04
C
0.01
0.02
0.00
0.00
0
200
400
600
800
o
Temperature ( C)
0.00
200
400
600
800
o
Temperature ( C)
200
400
600o
800
Temperature ( C)
Figure 34. High-resolution TG curves with the corresponding differential TG (DTG)
profiles (panel A, B, C) recorded in flowing air for the extracted (solid line) and the same
material subjected to calcination (dashed line) in air atmosphere at 540 °C during three
hours for the SBA-15-type periodic mesoporous ethane-silicas obtained using various
triblock copolymer P123-BTSE silsesquioxane weight ratios ranging from 0.73 to 4.39,
respectively
161
channel-like mesopores, which led to the plugged hexagonally templated ethane-silicas
with small volume of mesopores, small mesopore width, broad pore size distribution,
thick pore walls and poor mesostructural ordering (PMO-0.5 and PMO-1.0). An increase
in the polymer/precursor ratio affords better quality of syntehsized PMOs, which is
confirmed by the large mesopore widths, narrow PSDs, uniform pore openings and high
mesostructural ordering. The PMO-2 (wt. P123/BTSE 2.93 ratio) exhibited a good
quality in terms of adsorption properties although its mesostructural ordering was
somewhat inferior in comparison to PMO-1.5. However, a further increase in this ratio
(from 3.66 to 4.39) led again to poor quality PMOs, which have broad PSDs, high nonuniformity of pore entrances and low structural ordering. In addition, it was shown that
the mesopore structural ordering of the SBA-15-type PMOs was retained even after a
complete removal of ethane bridging groups by calcination.
5.3. Thermal stability of SBA-16 with ethane bridging groups: thermal stability
The powder X-ray diffraction patterns in Figure 35A show the effect of
calcination of the SBA-16-type ethane-silica on the structural properties. As can be
noticed, the XRD pattern for ES-e features three well-resolved peaks, which can be
indexed as (111), (220) and (311) reflections according to the face-centered cubic
(Fm3m) symmetry group. The elevation of calcination temperature causes the thermal
degradation of ethane spacers (-CH2CH2-) as well as the final calcination at 900 °C
affects the structural contraction, which is observed by the shift of (111) reflection to
higher values of 2θ angle. The calcination of ethane-bridged samples at 550 °C does not
162
manifest a significant structural deterioration. Similar behaviour of this type bridgedPMOs was reported by Grudzien et al. [198] in the case of channel-like SBA-15 periodic
mesoporous organosilicas (PMOs) with ethane and large isocyanurate bridging groups.
However, calcination above 800°C caused a major structural collapse of the bridgedorganosilicas (ES-c800 and ES-c900), which is exhibited by visible changes in the XRD
patterns and nitrogen adsorption isotherms.
Nitrogen adsorption-desorption isotherms measured at -196 °C for a series of
calcined ethane-silicas are presented in Figure 35B. As can be seen, all ES-e samples
represent typical type IV isotherms with a pronounced adsorption and sharp desorption
branches. These two branches form a type H2 hysteresis loop associated with
mesoporous materials with uniform cage-like pores and small pore openings. It is
noteworthy that the nitrogen capillary evaporation at -196 °C is delayed to the lower limit
of adsorption-desorption hysteresis at around 0.45 p/po indicating the pore entrance sizes
to be below about 5 nm, as it was discussed elsewhere by Ravikovitch and Neimark [43]
and by Kruk et al. [277]. It is important to mention that the observed change in the
isotherm curve for the SBA-16-type ethane-silica calcined at 550 °C. Its adsorption
changed dramatically, whereas the additional calcination of the ES-ec700, ES-c800 and
E-c900 samples caused a further lowering of the adsorption capacity until the mesopore
structure collapsed completely. The calculated adsorption parameters from nitrogen
adsorption isotherms are summarized in Table 19. This dramatic change is especially
163
ES-ec550
ES-ec700
C
B
ES-e
ES-ec550
ES-ec700
ES-c800
ES-c900
0.3
300
200
N2
ES-e
ES-ec550
ES-ec700
ES-c800
ES-c900
PSD (cm3g-1nm-1)
ES-e
400
Amount Adsorbed (cm3 STP g-1)
Intensity (a.u.)
A
0.2
0.1
100
ES-c800
ES-c900
0.0
0
0.5
1.0
1.5

2 
2.0
0.0
0.2
0.4
0.6
0.8
Relative Pressure
1.0
2
4
6
Pore Diameter (nm)
8
Figure 35. X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C) calculated
according to the KJS method [279] for the cage-like SBA-16 ethane-silica calcined at
various elevated temperatures for 4 hrs in the flowing air
164
Table 19. Adsorption parameters for SBA-16-type ethane-silicas studieda
SBET
Vc
Vo
Vt
wKJS
wd
b
a
m2 g-1
cc g-1
cc g-1
cc g-1
nm
nm
nm
nm
1026
0.45
0.16
0.61
5.95
9.70
7.48
23.68
ES-ec550
403
0.07
0.07
0.14
4.53
5.82
5.06
15.19
ES-ec700
280
0.10
0.06
0.15
4.22
4.92
5.42
14.46
ES-c800
134
0.05
0.02
0.07
3.06
3.83
6.47
14.57
ES-c900
63
0.03
0.01
0.04
2.43
2.97
6.88
13.92
Sample
ES-e
a
Notation: SBET , BET specific surface area; Vc, volume of micropores and interconnecting pores (including
micropores) of the diameter below 4 nm; Vo, volume of primary mesopores; Vt, total pore volume; wKJS,
mesopore diameter calculated by the KJS method [279]; wd, pore diameter calculated on the basis of the
unit cell parameter and pore volumes according to the relation derived for the cubic Im3m structure
assuming 2.2 g/cc density of silica for ethane-silica samples, except ES-e where the density was assumed
1.5 g/cc; b, minimal wall thickness; a, unit cell parameter calculated from the observed characteristic
Bragg’s reflection (110) for ethane-silicas studied.
165
visible for the KJS pore diameter, which was reduced from 5.95 to 2.43 nm as well as for
the BET surface area, which was reduced with increasing temperature and after
calcination at 700 °C and later at 900 °C the BET surface area was reduced by about 73
% and 94 % for the ES-ecT series of samples, respectively.
Overall, ethane-bridged cage-like SBA-16 PMOs with cubic (Im3m) symmetry
group were calcined from 550 to 900 °C to investigate their thermal properties. The XRD
and nitrogen adsorption data analysis showed that the calcination temperature caused a
structural shrinkage that led to a significant decrease in the BET specific surface area by
about 85 % and a gradual reduction in the KJS pore diameter from 5.95 to 2.43 nm.
Ethane-modified SBA-16 exhibited poor high temperature thermal stability, which was
manifested by the structure collapse at 800-900 °C, caused by the degradation of ethane
organic spacers in the framework.
5.4. Results and discussion for ethane-bridged channel-like organosilicas prepared
under microwave conditions
Powder X-ray diffraction (XRD) patterns were recorded for the extracted
organosilicas and used to monitor the structural changes upon microwave irradiation
(Figure 36). As can be seen from Figure 36, the XRD patterns of ethane-bridged PMOs
with 2D hexagonal arrangement of mesopores exhibit one intense peak at 2  0.95 in
addition to less intense broader peaks located at 2  1.5-1.8. There is a tendency of
enhancing mesostructural ordering of organosilicas with increasing time of the
hydrothermal treatment. The optimal conditions for the ethane-silica samples are 12
166
hours for the first step of synthesis and 24 hours for the hydrothermal treatment at 100C
(ES-24). Time and temperature of each synthesis step are essential parameters in the
synthesis of PMOs. Another combinations of time and temperature were tested too;
although nitrogen adsorption isotherms were acceptable (data not shown), they possessed
much broader condensation steps than those presented in Figure 37. For instance, an
increase in the duration of the first synthesis stage to 24 hours or its reduction to 6 hours
followed by hydrothermal treatment at 100C did not improve structural ordering of
PMOs. Similarly, an increase in the temperature of the hydrothermal treatment from 120
to 160C and at the same time an appropriate reduction of time did not help too. A
significant deterioration of the structural ordering was observed for the samples treated
hydrothermally at temperatures of 120oC or higher.
Nitrogen adsorption isotherms measured at -196 °C for the extracted organosilicas
are shown in Figure 37 (Panel A) together with the corresponding pore size distributions,
which were calculated from adsorption branches of the isotherms according to the
improved KJS method (Panel B). The BET specific surface area, the volume of
complementary pores, total pore volume and mesopore diameter for the samples studied
are summarized in Table 20. All adsorption isotherms for the extracted ethane-silica
samples are type IV with capillary condensation step at ~0.70-0.85 relative pressures. For
the aforementioned PMOs the hysteresis loops are H1 type, which is typical for channellike mesostructures. A comparison of adsorption isotherms for ethane-silica prepared
under microwave and conventional conditions is shown in Figure 38.
167
Intensity (a.u.)
ES-8
ES-12
ES-24
ES-36
ES-48
0.5 1.0 1.5 2.0 2.5 3.0
o
2( )
Figure 36. Powder X-ray diffraction patterns for the extracted ethane - bridged PMOs.
168
A
-1
1.6
1500
ES-24
ES-36
500
ES-8
1.2
-1
3 -1
3
ES-12
1000
B
1.4
ES-8
PSD (cm g nm )
Amount Adsorbed (cm STP g )
2000
ES-12
1.0
0.8
ES-24
0.6
ES-36
0.4
ES-48
N2
0.2
ES-48
0.0
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 37. Nitrogen adsorption isotherms measured at -196 °C (A) and the corresponding
pore size distributions (PSDs) (B) calculated by the improved KJS method [279] for the
extracted ethane-bridged PMOs. The isotherms and PSDs for ES-8, ES-12, ES-24 and
ES-36 were offset by 1200, 900, 600, 300 cm3 STP g-1 and 1.2, 0.9, 0.6, 0.35 cm3 g-1nm-1,
respectively.
169
A quantitative analysis of nitrogen adsorption isotherms for the extracted ethane-silica
samples shows that the BET specific surface areas are between 1070 and 1220 m2/g.
Also, relatively large total pore volumes (~1.5 cc/g) and large pore diameters (~8 nm)
were obtained for these samples. Furthermore, a tendency of sharpening the capillary
condensation step is observed with increasing time of the second stage of synthesis up to
24 hrs (ES-24); a further increase of this time has a detrimental effect on the adsorption
properties (see isotherm for ES-48). The PSD curves for the ethane-silica samples studied
are narrow, especially in the case of ES-24. Also, TEM images for these samples show
the presence of ordered mesopores, although there are some disordered domains (Figure
39).
The high-resolution thermogravimetric (TG) and differential (DTG) profiles were
recorded in air from 35 to 800 °C (Figure 40). As can be seen from this figure, there are
two major ranges of the weight loss. The first one, at temperatures up to ~100°C,
indicates the thermodesorption of water and possibly ethanol. The next two weight losses
occurred at temperatures from 230 to 600°C; it reflects the thermal decomposition of
bridging groups embedded in the framework and the condensation of silanols.
In overall, the ethane-bridged PMOs were successfully synthesized under
microwave irradiation. The aforementioned organosilicas were prepared by cocondensation of 1,2-bis(triethoxysilyl)ethane and poly(ethylene oxide)-poly(propylene
oxide)-poly(ethylene oxide) triblock copolymer (Pluronic 123; EO20PO70EO20).
Reduction of the synthesis time from 72 hours in the case of conventional recipe (24
hours for co-condensation step and 48 hours for hydrothermal treatment) to 36 hours was
170
achieved when the self-assembly process and hydrothermal treatment were performed
under microwave irradiation. The resulting materials exhibited high surface area, large
pore volume and large pore diameters. This study demonstrates the attractiveness of
microwave technique for the synthesis of PMOs.
171
Table 20. Adsorption and structural properties for the ethane-PMOs studied.a
Sample
SBET
m2/g
VC
cc/g
VCO
cc/g
Vt
cc/g
wKJS
nm
wd
nm
a
nm
b
nm
CEA
%
ES-8
1190
0.33
1.18
1.37
7.4
7.7
10.3
2.6
17.81
ES-12
1200
0.33
1.21
1.43
7.8
8.0
10.6
2.6
18.11
ES-24
1220
0.32
1.34
1.54
8.0
8.3
10.6
2.3
16.92
ES-36
1180
0.29
1.33
1.56
7.9
8.4
10.6
2.2
17.39
ES-48
1070
0.26
1.31
1.46
8.1
8.4
10.6
2.1
19.25
ES-C
1072
0.31
0.97
1.17
7.5
7.7
11.0
3.3
-
a
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters below
4 nm; Vco, volume of complementary and ordered pores; Vt, single-point pore volume; wKJS, mesopore
diameter at the maximum of PSD obtained by the improved KJS method [279]; wd, pore width, obtained by
using the theoretical relation for the P6mm structure between the pore width, unit cell and the pore volume;
a, unit cell parameter; b, pore wall thickness obtained by subtraction of the pore width wd for the unit cell;
CEA,carbon percentage obtained by elemental analysis. The data for the ES-C sample were taken for the
comparison from ref. [198].
172
ES-24
ES-C
800
3
-1
Amount Adsorbed (cm STP g )
1000
600
400
200
N2
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
Figure 38. A comparison of nitrogen adsorption isotherms measured at -196 °C for the
extracted ethane-bridged PMOs (obtained by the conventional, ES-C sample and
microwave method, ES-24 sample). The data for the ES-C sample were taken for the
comparison from ref [198].
173
Figure 39. TEM images of the ethane-PMO (sample ES-24).
174
100
95
90
85
ES-24
B
0.10
o
- Deriv. Weight (% / C)
Weight change (%)
A
0.08
0.06
ES-24
0.04
0.02
0.00
80
200
400 o 600
Temperature ( C)
800
200
400
600
o
Temperature ( C)
800
Figure 40. Thermogravimetric weight change (TG) profiles (A) and the corresponding
differential TG (DTG) curve (B) measured in flowing air for the extracted ethane bridged PMOs.
VI. Ordered mesoporous organosilicas with disulfide and
isocyanurate bridging groups
A wide variety of small like ethane and larger organic spacers in the framework,
has been studied to show the effect of organic groups on the chemical, physical and
mechanical properties of PMOs. The goal of this chapter is to present data for PMOs with
disulfide and bulky isocyanurate ligands obtained under microwave irradiation. Here, we
present the study of adsorption for the materials obtained under conventional conditions
followed by preliminary studies under microwave irradiation (see Scheme 13).
Incorporation of the aforementioned bridging groups into the framework and the
presence of ordered mesopores were confirmed by nitrogen adsorption at -196C,
elemental and thermogravimetric analysis and powder X-ray diffraction.
This Chapter is based on the following publications:
B.E. Grabicka, M. Jaroniec Microporous and Mesoporous Materials 2009 119 674 [267]
R.M. Grudzien, B.E. Grabicka, M. Jaroniec Adsorption 2006 12 293 [107]
R.M. Grudzien, B.E. Grabicka, R. Felix, M. Jaroniec Adsorption 2007 13 323 [141]
R.M. Grudzien, B.E. Grabicka, S. Pikus, M. Jaroniec: Chem. Mater. 2006 18 1722 [146];
B.E. Grabicka, M. Jaroniec: Adsorption properties and characterization of mesoporous organosilicas with
large isocyanurate bridging groups synthesized under microwave irradiation. 2010, in preparation [270]
Author’s related articles: R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Colloids and Surfaces A:
Physicochemical and Engineering Aspects 2007 300 235 [198]; R.M. Grudzien, B.E. Grabicka, O.
Olkhovyk, M. Jaroniec, J.P. Blitz Nanoporous Materials (A. Sayari and M. Jaroniec, eds), World Scientific
Publ. Co., Singapore, 2008 665 [281]; R.M. Grudzien, B.E. Grabicka, M. Jaroniec Applied Surface Science
2007 253 5660 [93];
175
176
6.1. Experimental
6.1.1. Synthesis of disulfide-functionalized SBA-15 and SBA-16
Syntheses of channel-like mesoporous SBA-15 silicas with disulfide groups was
performed in the presence of poly(ethylene oxide)-block-poly(propylene oxide)-blockpoly(ethylene oxide) triblock copolymer (P123, EO20PO70EO20) by co-condensation of
tetraethyl orthosilicate (TEOS) and bis(triethoxysilylpropyl) disulfide (see Scheme 13).
The adopted procedure was similar to that used for the synthesis of SBA-15 reported
elsewhere [70]. In a typical synthesis, 2g of polymer was dissolved in 61.2 ml of 2M HCl
and 10.8 ml of deionized water (DW) under vigorous stirring at 40 oC. After 4-6 hours of
stirring, a specified volume of TEOS was added dropwise to this solution under vigorous
mixing, and then after 15 minutes organosilane was pipetted to achieve the desired molar
composition of silanes (see Table 21). The resulting mixture was stirred for 24 hours
followed by aging at 100 °C for 48 hours. The white solid was washed with DW, filtered
and dried at 80 °C. The template was removed by extraction three times with 2 ml of 36
wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The extracted disulfide-functionalized
SBA-15 samples are denoted as SBA-15-DSx, where DS refers to bridging disulfide
groups and x = 1, 2, 3, 4 refer to the samples with successively growing concentration of
functional groups (see Table 21). The letter t refers to the as-synthesized organicfunctionalized silica. The pure channel-like silica subjected to calcination at 550 °C in
flowing air for 4 hours was denoted as SBA-15.
177
Cage-like mesoporous SBA-16 silicas with bridging groups (see Scheme 13) were
synthesized
similarly
to
SBA-15
by
co-condensation
of
TEOS
and
bis(triethoxysilylpropyl) disulfide in the presence of poly(ethylene oxide)-blockpoly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer (Pluronic F127,
EO106PO70EO106). The procedure adopted is a slightly modified recipe reported by Qiu at
al. [58]. In a typical synthesis, 1 g of F127 and 3.527 g of sodium chloride were dissolved
in 10 ml of 2M HCl and 30 ml of deionized water at 40 ºC. After 4 hours stirring a
specified volume of TEOS was pipetted dropwise to this solution under vigorous mixing,
and next after 15 minutes organosilane was added to achieve the desired molar
composition of silanes (see Table 22). After further stirring for 20 hrs at 40 ºC, the
resulting white precipitate was transferred into a polypropylene bottle and subsequently
heated at 100 ºC for 24 hrs. The product was filtered, washed with DW, and dried in an
oven at 80 ºC. To remove the polymeric template from mesopores, the as-synthesized
composites were extracted three times with 2 ml of 36 wt. % HCl and 100 ml of 95 %
ethanol at 70 ºC. The extracted disulfide-functionalized SBA-16 samples are denoted as
SBA-16-DSx, where DS refers to the bridging disulfide groups and x = 1, 2, 3 refer to the
samples with successively growing concentration of functional groups (see Table 22).
The letter t refers to as-synthesized sample, i.e., sample containing polymeric template.
The pure silica sample subjected to calcination at 550 °C in flowing air for 4 hours was
denoted as SBA-16.
178
6.1.2. Synthesis of disulfide-functionalized SBA-15: addition of organosilanes in
different stages of the process
Ordered mesoporous organosilicas were synthesized in the presence of
poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer
(P123, EO20PO70EO20) by co-condensation of tetraethyl orthosilicate (TEOS) and
bis(triethoxysilylpropyl) disulfide to functionalize the framework. The recipe
incorporated here was analogous to that used for the synthesis of the SBA-15 silica
reported elsewhere [70]. Triblock copolymer P123 (2g) was mixed with 2M HCl (61.2
ml) and distilled water (10.8 ml) under rapid stirring at 40 oC until its complete
dissolution was achieved. After 4-6 hours of mixing, either 3.858 ml or 4.07 ml of TEOS
was added dropwise to the P123-HCl-DW mixture under vigorous stirring, and next 0.22
ml of bis(triethoxysilylpropyl) disulfide was added after 0, 10, 15, 20, 40, 60 and 120
minutes. The slurry was further stirred for 24 hours and aged for 48 hours at 100 °C. The
powder was washed with DW, filtered and dried overnight at 80 °C. The polymeric
template was extracted with 2 ml of 36 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC.
The series of the template-free mesoporous SBA-15 silicas with bridging disulfide groups
was designated as DSx, where DS and x refer to bridging disulfide groups and time of the
organosilane addition, respectively (see Table 23)
179
6.1.3. Microwave-assisted synthesis of bridged SBA-15 with disulfide organic group
In a typical synthesis of disulfide-bridged channel-like structure, 4 g of Pluronic
123 block copolymer (P123, EO20PO70EO20) was dissolved in 144 ml of 1.7 M HCl under
vigorous stirring at 40° C for 4-6 hours [70]. Next, 8.14 ml of TEOS was pipetted
dropwise followed by addition 0.44 ml of bis(triethoxysilylpropyl) disulfide (DS). The
resulting mixture was transferred to the teflon vessels, which were installed in microwave
oven (MARS 5; CEM Corp.). Both steps of the PMO synthesis, i.e., the self-assembly of
organosilane precursors and block copolymer and the subsequent hydrothermal treatment,
were carried out under microwave irradiation (see Scheme 16). In the first step, the
synthesis mixture was stirred using magnetic bars for 2-24h at 40°C. After initial stage,
temperature was increased to 100ºC and kept for 8-48h; magnetic stirring was off during
this stage. The product was filtered, washed with deionized water, and dried in the oven
at 80 ºC.
An efficient removal of the polymeric template was achieved by extraction, which was
repeated two times with 2 ml of 37 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The
resulting samples are denoted as DS-x, where DS stands for PMOs obtained using
bis(triethoxysilylpropyl) disulfide and x refers to the time of hydrothermal treatment of
the DS samples in microwave at 100 °C. The length of the first step in both syntheses
was 12 hours at 40 °C.
180
6.1.4. Synthesis of SBA-15 with ethane and iscoyanurate bridging groups
Bifunctional ethane- and isocyanurate-bridged PMOs were prepared by cocondensation
of
1,2-bis(triethoxysilyl)ethane
(BTSE)
and
tri[3-
(trimethoxysilyl)propyl]isocyanurate (ICS) in the presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123, EO20PO70EO20) at low
acid concentrations (see Scheme 14). In a typical synthesis, 5.7 ml of deionized water
(DW) was combined with 0.5g of triblock copolymer P123 and stirred at 40 °C to form a
clear solution. A specified amount of BTSE was added to a solution containing 1.8 ml of
DW and 0.6 ml of 2 M HCl at 40 °C. The P123-DW solution was then slowly added to
the BTSE-DW-HCl mixture under vigorous stirring, and then after 15 min, ICS was
added dropwise to achieve the desired molar composition of both silanes. After further
stirring for 24 h at 40 °C, the resulting white precipitate was transferred into a
polypropylene bottle and subsequently heated at 100 °C for 48 h. The product was
filtered, washed with DW, and dried in an oven at 80 °C. The molar composition of the
synthesis gel mixture was (1-x):x:0.01:0.2:88 BTSE/ICS/P123/HCl/H2O, where x denotes
the mole fraction of ICS. The amount of BTSE was used to maintain the Si/polymer ratio
at the same level for the samples studied. The as-synthesized composites were extracted
twice with 2 mL of HCl and 100 mL of 95% ethanol at 70 °C to remove the polymeric
template from the mesopores. The extracted PMOs are denoted as EI-z, where E and I
refer to ethane and isocyanurate bridging groups (this is an exception of listing
isocyanurate group as I instead of ICS), respectively; z denotes the sample number. PMO
181
with z = 0 refers to the pure ethane-silica. For the samples with growing z the ICS mole
fraction increases as shown in Table 27.
6.1.5. Microwave-assisted synthesis of SBA-15 with isocyanurate organic group
The isocyanurate-bridged channel-like structure was obtained by using 4 g of
Pluronic 123 block copolymer (P123, EO20PO70EO20) in 144 ml of 1.7 M HCl under
vigorous stirring at 40° C for 4-6 hours (see Scheme 15). Next, 6 ml of TEOS was
pipetted dropwise followed by addition 2.02 ml of tri[3-(trimethoxysilyl)propyl]
isocyanurate (ICS). The choice of high loading (30%) was suggested by previous studies
[101]. The resulting slurry was transferred to the teflon vessels, which were installed in
microwave oven (MARS 5; CEM Corp.). Both steps of the PMO synthesis, i.e., the selfassembly of organosilane precursors and block copolymer and the subsequent
hydrothermal treatment, were carried out under microwave irradiation (see Scheme 15).
In the first step, the synthesis mixture was stirred using magnetic bars for 12h at 40°C.
After initial stage, temperature was increased to 100ºC and kept for 6-12; magnetic
stirring was off during this stage. The product was filtered, washed with deionized water,
and dried in an oven at 80 ºC.
An efficient removal of the polymeric template was achieved by extraction, which
was repeated twice with 2 ml of 37 wt. % HCl and 100 ml of 95 % ethanol at 70 ºC. The
resulting samples are denoted as ICS-x, where ICS stands for PMOs obtained using tri[3(trimethoxysilyl)propyl] isocyanurate and x refers to the time of hydrothermal treatment
182
of the ICS samples in microwave at 100 °C. The duration of the first step was 12 hours at
40 °C.
183
EO20PO70EO20 or EO106PO70EO106
+
Si(EtO)4
+
bridging organosilane
self-assembly
24h at 40 C
hydrothermal
treatment
24h or 48h
at 100 C
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
A
24h
at 60-70 C
B
EO20PO70EO20 or EO106PO70EO106
+
Si(EtO)4
+
bridging organosilane
self-assembly
6-12h at 40 C
hydrothermal
treatment
6-24h
at 100 C
A
filtration,
washing,
drying
extraction in
EtOH/HCl
solution
24h at 60-70 C
B
microwave-assisted synthesis
Scheme 13. A comparison of the synthesis of SBA-15 (A) and SBA-16 (B) organosilicas
by conventional (top) and microwave-assisted (bottom) methods.
184
Scheme 14. Schematic illustration of bifunctional SBA-15 with isocyanurate (A) and
ethane groups (B)
185
Scheme 15. Schematic illustration of SBA-15 with isocyanurate organic groups.
186
Scheme 16. Schematic illustration of disulfide-functionalized SBA-15 (A) and SBA-16
(B).
187
6.2. Results and discussion for SBA-15 and SBA-16 with disulfide groups
Structural characterization of the extracted SBA-15 and SBA-16 organosilicas
containing bridging bis(propyl)disulfide groups was performed on the basis of the XRD
patterns shown as a Panel A in Figure 41 and Figure 42, respectively. The unit cell
parameters for the samples studied are summarized in Table 23. As can be seen from
Figure 41A, the diffraction profile for the extracted disulfide-functionalized SBA-15-DS1
silica exhibits one sharp reflection at 2 ~ 0.75 indexed as (100) and two minor
reflections (110) and (200), which confirms the channel-like structure (P6mm symmetry
group). An increase in the loading of disulfide spacers affected the XRD profiles, which
is manifested by reduction of the major and minor peak intensities suggesting a gradual
deterioration of the mesostructural ordering. Similar situation can be observed for the
disulfide-bridged cage-like mesostructures (Figure 42A). Generally, the diffraction
patterns for extracted SBA-16 materials exhibit a strong reflection at 2 ~ 0.8 (110) and
some less-resolved minor reflections, (200) and (211) (Figure 42), indicating the cubic
Im3m symmetry group (body-centered packing).
Nitrogen adsorption-desorption isotherms measured at -196 °C (B) and the pore
size distributions (C) for the extracted SBA-15 and SBA-16 silicas with disulfide groups
are shown in Figure 41 and Figure 42, respectively. Table 23 shows the BET specific
surface area, the volume of complementary pores, the single-point pore volume, the
mesopore channel diameter and pore-wall thickness. The disulfide-functionalized SBA15 materials synthesized with the low content of all types of organic groups exhibit type
IV adsorption-desorption isotherms.
188
SBA-15
SBA-15-DS1
SBA-15-DS2
SBA-15-DS3
SBA-15-DS4
SBA-15-DS2
SBA-15-DS3
-1
3
400
200
B
SBA-15-DS4
0.5
1.0
1.5
o
2( )
2.0
1.4
-1
-1
3
600
PSD (cm g nm )
SBA-15
SBA-15-DS1
800
Amount Adsorbed (cm STP g )
Intensity (a.u.)
A
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
1.2
1.0
0.8
C
SBA-15
SBA-15-DS1
SBA-15-DS2
SBA-15-DS3
SBA-15-DS4
0.6
0.4
0.2
0.0
5
10
15
Pore Diameter (nm)
20
Figure 41. X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C) calculated
according to the KJS method [279] for the channel-like SBA-15 mesoporous silicas
having various concentrations of bis(propyl)disulfide (DS) bridging groups.
189
400
SBA-16
300
SBA-16-DS1
-1
Amount Adsorbed (cm STP g )
A
0.25
SBA-16-DS1
SBA-16-DS2
200
SBA-16-DS3
100
B
SBA-16-DS3
0.5
1.0
1.5

2 
2.0
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
-1
3 -1
SBA-16
SBA-16-DS2
PSD (cm g nm )
Intensity (a.u.)
3
SBA-16
SBA-16-DS1
SBA-16-DS2
SBA-16-DS3
0.20
0.15
0.10
0.05
C
0.00
1.0
2
4
6
8 10 12
Pore Diameter (nm)
14
Figure 42. X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C) calculated
according to the KJS method [279] for the cage-like SBA-16 mesoporous silicas having
various concentrations of bis(propyl)disulfide (DS) bridging groups. The isotherms in
Panel B for SBA-16-DS1 and SBA-16-DS2 were offset vertically by 50 and 10 cc STP
g-1.
190
Table 21. Molar composition of the synthesis gels used and the corresponding elemental
analysis data for the channel-like SBA-15 with disulfide groups.a
Synthesis gel composition
Sample
n, (mmoles)
TEOS
n, (mmoles)
Elemental analysis
P, (%)
C, (mmoles/g)
P, (%)
DS
PS
CDS
PS
SBA-15
19.20
SBA-15-DS1
18.72
0.24
1.30
0.31
1.99
SBA-15-DS2
17.76
0.72
3.70
0.49
3.16
SBA-15-DS3
17.28
0.96
4.81
0.46
2.69
SBA-15-DS4
16.32
1.44
6.89
0.96
6.15
a
nTEOS, number of mmoles of tetraethyl orthosilicate; nDS, number of mmoles of
bis(triethoxysilylpropyl) disulfide; PS, sulfur percentages predicted on the basis of the synthesis gel
mixture; CDS concentration of functional groups in the resulting materials calculated on the basis of
sulfur percentages obtained by elemental analysis; PS, sulfur weight percentages obtained from
elemental analysis.
191
Table 22. Molar composition of the synthesis gels used and the corresponding elemental
analysis data for the cage-like SBA-16 with disulfide groups.a
Synthesis gel composition
Sample
n, mmoles
TEOS
n, (mmoles)
DS
Elemental analysis
P, (%)
PS
C, mmoles/g
CDS
P, (%)
PS
SBA-16
20.16
SBA-16-DS1
19.66
0.5
2.45
0.45
2.92
SBA-16-DS2
18.65
1.01
4.72
0.83
5.31
SBA-16-DS3
18.14
2.02
8.12
0.98
6.26
a
nTEOS, number of mmoles of tetraethyl orthosilicate; nDS, number of mmoles of
bis(triethoxysilylpropyl) disulfide; PS, sulfur percentages predicted on the basis of the synthesis gel
mixture; CDS concentration of functional groups in the resulting materials calculated on the basis of
sulfur percentages obtained by elemental analysis; PS, sulfur weight percentages obtained from
elemental analysis.
192
Table 23. Adsorption parameters for the channel-like SBA-15 with disulfide groupsa
Sample
SBET,
m2g-1
Vt,
ccg-1
Vc,
ccg-1
wKJS,
nm
wd,
nm
b,
nm
a,
nm
SBA-15
866
1.38
0.14
11.2
10.4
1.1
11.5
SBA-15-DS1
909
1.18
0.19
8.7
10.0
1.5
11.5
SBA-15-DS2
958
1.16
0.22
7.4
8.7
1.6
10.3
SBA-15-DS3
952
0.88
0.27
5.64
6.8
2.9
9.7
SBA-15-DS4
935
0.99
0.20
5.17
7.1
2.2
9.3
a
SBET , BET specific surface area; Vt, single-point pore volume; Vc, volume of micropores and
interconnecting pores of the diameter below 4 nm; wKJS, mesopore diameter calculated by the KJS
method [279]; wd, mesopore diameter calculated on the basis of the unit cell parameter and pore
volumes according to the relation derived for the hexagonal P6mm structure assuming 2.0 g/cm3
density of silica; b, pore wall thickness; a, unit cell calculated from the observed chracteristic Bragg’s
reflection (100).
193
Table 24. Adsorption parameters of the cage-like SBA-16 with disulfide groupsa
a
Sample
SBET,
m2g-1
Vt,
ccg-1
Vc,
ccg-1
wKJS,
nm
wd,
nm
b,
nm
a,
nm
SBA-16
932
0.60
0.35
7.0
9.0
3.6
15.0
SBA-16-DS1
549
0.36
0.18
5.1
8.1
3.9
13.8
SBA-16-DS2
557
0.33
0.20
4.2
6.8
4.3
12.9
SBA-16-DS3
508
0.22
0.13
2.9
6.1
4.6
12.4
SBET , BET specific surface area; Vt, single-point pore volume; Vc, volume of micropores and
interconnecting pores of the diameter below 4 nm; wKJS, mesopore cage diameter calculated by the
KJS method [279]; wd, mesopore cage diameter calculated on the basis of the unit cell parameter and
pore volumes according to the relation derived for the cubic Im3m structure assuming 2.0 g/cm3
density of silica; b, pore wall thickness; a, unit cell calculated from the observed chracteristic Bragg’s
reflection (110).
194
They have sharp capillary condensation steps as well as the narrow pore size
distributions. As can be seen in Figure 41B, an increase in the content of the introduced
functionality caused a slight decrease in the diameter of mesopore channels along with
other adsorption parameters such as the BET specific surface area and single-point pore
volume reduction. Incorporation of disulfide spacers into the framework of channel-like
materials prevented the structure deterioration, which is common for the surface
modification of silica pore walls [107].
The SBA-16 silicas with disulfide spacers exhibit type IV adsorption-desorption
isotherms with sharp capillary condensation steps and pronounced H2 hysteresis loops
(Figure 42B). As can be noticed, the SBA-16-DS1 sample with lowest content of
bridging groups, shows less steep capillary condensation and evaporation steps (B),
indicating broader PSD (C) and larger non-uniformity of pore openings. Moreover, an
increase in the concentration of organic groups reduces the steepness of the evaporation
steps for disulfide-modified SBA-16 silicas (Figure 42B). Table 24 presents the structural
paramaters of disulfide-bridged SBA-16, is indicating their gradual decrease with
increasing loading of disulfide group.
It is interesting to point out the relation between the volumes of complementary
and ordered pores for SBA-15 and SBA-16 organosilicas. Triblock copolymer F127
(EO106PO70EO106) used to synthesize SBA-16 possesses 5.3 times more hydrophilic
ethylene oxide blocks (EO) than the P123 polymer(EO20PO70EO20) used to obtain SBA15, and such a difference causes more extensive penetration of EO blocks into pore walls
of functionalized SBA-16 silicas than in the case of SBA-15. Also, for the cage-like
195
materials, the complementary porosity includes small ordered pores that interconnect
large ordered cages.
The amounts of bridging disulfide groups in SBA-15 and SBA-16 were estimated
on the basis of elemental analysis data (see Table 21 and Table 22, respectively). The
sulfur contents obtained for the resulting PMOs by elemental analysis are around 50-85
% of the values estimated on the basis of the initial molar composition of the synthesis
gel mixture, indicating quite good incorporation efficiency.
The introduction of disulfide group into channel-like SBA-15 and cage-like SBA16 mesostructures was monitored by high-resolution thermogravimetry (TG) and the
corresponding differential TG (DTG) profiles (Panels A and B, respectively) recorded
under nitrogen atmosphere are displayed in Figure 43 and Figure 44, respectively. As can
be seen from Figure 43, there are three major events on the TG patterns. The TG event
below 100 °C reflects thermodesorption of physisorbed water and ethanol. The TG event
above 500 °C shows the condensation of silanol groups and decomposition of some
residual organic groups. The range between the aforementioned regions reflects the
template removal and decomposition of incorporated organic groups. A complete
removal of P123 has been achieved by extraction process with hydrochloric acid and
ethanol solution at 80 °C as confirmed by the disappearance of the major peak (see the
DTG curve for the extracted SBA-15-DS2 sample), while the disulfide organic groups
were remained. The TG study shows that the extraction of the block copolymer F127
template from cage-like SBA-16 organosilicas with acidified ethanol solution was
incomplete.
196
A
90
SBA-15
SBA-15-DS1
SBA-15-DS2-t
SBA-15-DS2
SBA-15-DS3
SBA-15-DS4
80
70
60
50
200
400
o600
Temperature ( C)
800
o
- Deriv. Weight (% / C)
Weight change (%)
100
2.3
2.2
2.1
0.4
0.3
0.2
B
0.1
0.0
200
400
600
o
Temperature ( C)
800
Figure 43. High-resolution TG profiles (A) and the corresponding DTG profiles (B)
recorded in flowing nitrogen for channel-like SBA-15 mesoporous silicas obtained via
co-condensation route using various concentrations of bis(propyl)disulfide (DS) bridging
groups.
197
A
Weight change (%)
90
SBA-16
SBA-16-DS1
SBA-16-DS2
SBA-16-DS3-t
SBA-16-DS3
80
70
60
o
- Deriv. Weight (% / C)
100
0.3
0.2
B
0.1
0.0
50
200
400
600
Temperature (oC)
800
200
400
600
Temperature (oC)
800
Figure 44. High-resolution TG profiles (A) and the corresponding DTG profiles (B)
recorded in flowing nitrogen for cage-like SBA-16 mesoporous silicas obtained via cocondensation using various concentrations of bis(propyl)disulfide (DS) bridging groups.
198
However, it should be noted that the removal of polymeric templates from cage-like
mesostructures is more difficult than in the case of channel-like mesostructures,
especially when the cage openings in the former structures are small and the attached
surface groups are relatively large.
In summary, the synthesis of channel-like SBA-15 and cage-like SBA-16
mesostructures with disulfide bridging groups was achieved. The study of the template
removal by extraction with hydrochloric acid-ethanol solution shows that the P123
template can be removed completely in the case of channel-like mesostructures, but some
difficulties might appear for the removal of the F127 template from cage-like
organosilicas.
Moreover, both channel-like and cage-like mesoporous silicas showed the similar
tendency of decreasing the structural ordering with increasing concentration of
introduced organic groups into silica framework. Since the aforementioned mesoporous
organosilicas possess high affinity toward metal ions such as mercury, lead and cadmium
there are promising adsorbents for removal of these pollutants from aqueous solutions.
6.3. Study of the effect of addition of disulfide organosilane at different stages of the
process
The effect of organosilane addition at different stages of the OMO synthesis (0 120 min) on the structural characteristics of the extracted disulfide-bridged organosilicas
was studied. The XRD patterns for the extracted disulfide-functionalized OMOs are
199
shown in Figure 45 A. As can be seen, an increasing delay (from 0 and 120 minutes)
between the TEOS addition and the addition of disulfide organosilane did not cause a
significant change in the XRD patterns, indicating the similar structural quality of all
samples. The XRD panel of disulfide-bridged mesostructures confirmed a 2D hexagonal
structure (p6mm symmetry group) by presence of one major peak indexed as (100) and
two less intensive peaks indexed as (110) and (200).
Nitrogen adsorption-desorption isotherms measured at -196 °C for the extracted
disulfide-functionalized SBA-15 silicas and the corresponding pore size distributions are
shown in Figure 45B. Table 25 presents the BET specific surface area, the volume of
complementary pores, the single-point pore volume and the mesopore diameter. All
extracted samples exhibit type IV adsorption-desorption isotherms with a distinct H1
hysteresis loop typical for the materials with cylindrical mesopores. A comparison of the
isotherms displayed in Figure 45B shows that an increasing delay in the addition of
disulfide silane does not influence the shape of adsorption isotherms except for the SBA15-DS0 sample, which was synthesized by adding TEOS and bis(triethoxysilylpropyl)
disulfide simultaneously. Moreover, the DS-120 sample presents a lack of plateau at
higher preassures, which is reflected by increasing adsorption branch with pressure
approaching the saturation vapor pressure. Such behaviour shows the presence of
secondary disordered mesopores. The pore size distribution (Figure 45C) shows narrow
distribution for all disulfide-modified SBA-15 silicas except the DS0 sample as well as a
visible change in the pore size with increasing delay of organic spacer addition.
200
Table 25. Selected adsorption and structural parameters for the SBA-15 silicas with
disulfide groups.a
a
Sample
SBET,
m2g-1
Vc,
ccg-1
Vo,
ccg-1
Vt,
ccg-1
wKJS,
nm
a,
nm
DS0
1000
0.26
0.60
1.00
6.76
10.2
DS10
970
0.23
0.78
1.07
7.68
10.0
DS15
865
0.20
0.69
0.99
7.50
9.6
DS20
930
0.22
0.67
1.02
7.00
9.9
DS40
965
0.23
0.78
1.09
7.54
10.0
DS60
750
0.17
0.66
0.90
8.27
10.8
DS120
900
0.12
1.00
1.27
9.49
11.0
SBET , BET specific surface area; Vc, volume of complementary pores (including micropores) with the
widths below 4 nm; Vo, volume of ordered mesopores; Vt, single-point pore volume; wKJS, mesopore
diameter calculated by the improved KJS method [279]; a, unit cell calculated from the observed
characteristic Bragg’s reflection (100).
201
A
A
B
B
C
DS0
2000
DS0
DS0
6
DS10
DS15
-1
-1
DS15
3
Intensity (a.u.)
DS15
PSD (cm g nm )
-1
1500
3
DS10
Amount Adsorbed (cm STP g )
DS10
DS20
1000
4
DS20
DS40
DS20
DS40
DS60
DS40
2
500
DS60
DS60
DS120
N2
DS120
0.5
1.0
1.5 2.0
o
2( )
2.5
3.0
DS120
0
0
0.0
0.2
0.4
0.6
0.8
Relative Pressure
1.0
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 45. X-ray diffraction (XRD) patterns (A), nitrogen adsorption isotherms (B)
measured at – 196 °C and the corresponding pore size distributions (PSDs) (C) calculated
according to the improved KJS method [279] for the channel-like SBA-15 mesoporous
silicas with disulfide bridging groups synthesized by delaying the addition of
bis(triethoxysilylpropyl) disulfide (DS) into the TEOS-polymer mixture from zero to 120
minutes; numbers at the samples codes denote the delay time in minutes. The adsorption
isotherms and PSD curves for DS60, DS40, DS20, DS15, DS10 and DS0 were offset by
420, 550, 820, 1080, 1280, 1520 cc STP g-1 and 1.1, 2.1, 3.6, 4.6, 5.6, 7.0 cc g-1 nm-1,
respectively.
202
As can be noticed, the effect of delay addition of disulfide bridging group at different
synthesis stages does not affect significantly the final organosilicas. However, the
simultaneous addition of disulfide spacer and tetraethyl orthosilicate (TEOS) can result in
poorer structural quality of the bridged-organosilicas in comparison to the samples
obtained with a delay of organic group addition (samples DS0 and DS15, respectively).
The short delay of organic spacer addition after silica source is suggested.
6.4. Results and discussion for SBA-15 with disulfide groups obtained under
microwave irradiation
Powder X-ray diffraction (XRD) patterns were recorded for the extracted
organosilicas and used to monitor the structural changes upon microwave irradiation
(Figure 46). As can be seen from Figure 46, the XRD patterns of disulfide-bridged PMOs
with 2D hexagonal arrangement of mesopores exhibit one intense peak at at 2  1.05 in
addition to less intense broader peaks located at 2  1.8-2.0. There is a tendency of
enhancing mesostructural ordering of organosilicas with increasing time of the
hydrothermal treatment. The optimal conditions for the disulfide-silica samples are 12
hours for the first step of synthesis and 24 hours for the hydrothermal treatment at 100C
(ES-24). Time and temperature of each synthesis step are essential parameters in the
synthesis of PMOs. Another combinations of time and temperature were tested too;
although nitrogen adsorption isotherms were acceptable (data not shown), they possessed
much broader condensation steps than those visible in Figure 47. For instance, an
203
increase of the duration of the first synthesis stage to 24hours or its reduction to 6 hours
followed by hydrothermal treatment at 100C did not improve structural ordering of
PMOs. Similarly, an increase of the temperature of the hydrothermal treatment from 120
to 160C and at the same time an appropriate reduction of time did not help too. A
significant deterioration of the structural ordering was observed for the samples treated
hydrothermally at temperatures of 120oC or higher.
Nitrogen adsorption isotherms measured at -196 °C for the extracted organosilicas are
shown in Figure 47 (A) together with the corresponding pore size distributions (B), which
were calculated from adsorption branches of the isotherms according to the improved
KJS method. The BET specific surface area, the volume of complementary pores, total
pore volume and mesopore diameter for the samples studied are summarized in Table 26.
All adsorption isotherms for the extracted disulfide-silica samples are type IV with
capillary condensation steps at ~0.65-0.75 relative pressures. For the aforementioned
PMOs the hysteresis loops are H1 type, which is typical for channel-like mesostructures.
Adsorption and structural parameters for disulfide-bridged SBA-15 samples exhibit high
BET specific surface area (between 1070 and 1220 m2/g) and large total pore volume. As
can be seen from Panel B of Figure 47, the PSD curves for disulfide- bridged samples are
narrower and uniform as well as the diameter for all the samples is about 8 nm. A
comparison of adsorption isotherms for disulfide-bridged PMOs prepared under
microwave and conventional conditions is shown in Figure 48. The high-resolution
thermogravimetric (TG) and differential (DTG) profiles were recorded in air from 35 to
204
Table 26. Adsorption and structural properties for the disulfied-bridged PMOs studied.a
Sample
SBET
m2/g
VC
cc/g
VCO
cc/g
Vt
cc/g
wKJS
nm
wd
nm
a
nm
b
nm
DS-6
1040
0.25
1.09
1.14
7.9
7.1
9.3
2.2
DS-8
1040
0.24
1.11
1.17
7.7
7.5
9.7
2.2
DS-12
1020
0.18
1.19
1.27
8.1
7.8
9.6
1.8
DS-24
960
0.19
1.24
1.32
8.4
7.9
9.7
1.8
DS-C
865
0.20
0.94
0.99
7.5
7.2
9.6
2.4
Notation: aSBET, BET specific surface area; Vc, volume of the interconnecting pores of the diameters below
4 nm; Vco, volume of complementary and ordered pores; Vt, single-point pore volume; wKJS, mesopore
diameter at the maximum of PSD obtained by the improved KJS method [279]; wd, pore width, obtained by
using the theoretical relation for the P6mm structure between the pore width, unit cell and the pore volume;
a, unit cell parameter; b, pore wall thickness obtained by subtraction of the pore width wd for the unit cell;
The data for the DS-C sample were taken for the comparison from ref. [107].
a
205
Intensity (a.u.)
DS-6
DS-8
DS-12
DS-24
1.0
1.5
2.0 o 2.5
2 ( )
3.0
Figure 46. Powder X-ray diffraction patterns for the extracted disulfide - bridged PMOs.
206
-1
DS-8
3
DS-8
3 -1
1000
D
DS-6
DS-6
PSD (cm g nm )
1500
B
4
3
-1
Amount Adsorbed (cm STP g )
B
A
DS-12
2
DS-12
500
1
DS-24
N2
DS-24
0
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
2
4 6 8 10 12 14
Pore Diameter (nm)
Figure 47. Nitrogen adsorption isotherms measured at -196 °C (A) and the corresponding
pore size distributions (PSDs) (B) calculated by the improved KJS method [279] for the
extracted disulfide-bridged PMOs. The isotherms and PSDs for DS-6, DS-8, DS-12 were
offset by 1050, 700, 350 cm3 STP g-1 and 3.5, 2.7, 1.25 cm3 g-1 nm-1, respectively.
207
-1
Amount Adsorbed (cm STP g )
800
600
3
DS-24
DS-C
400
200
N2
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
1.0
Figure 48. A comparison of nitrogen adsorption isotherms measured at -196 °C for the
extracted disulfide-bridged PMOs obtained by the conventional (DS-C sample) and
microwave methods (DS-24 sample). The data for the DS-C sample were taken for the
comparison from ref [107].
208
100
95
90
85
DS-24
B
0.10
o
- Deriv. Weight (% / C)
Weight change (%)
A
0.08
0.06
DS-24
0.04
0.02
0.00
80
200
400 o 600
Temperature ( C)
800
200
400
600
o
Temperature ( C)
800
Figure 49. Thermogravimetric weight change (TG) profiles (A) and the corresponding
differential TG (DTG) curves (B) measured in flowing air for the extracted disulfidebridged PMO (DS-24).
209
800 °C (Figure 49). As can be seen from this figure, there are three major ranges of the
weight loss.
The first one, at temperatures up to ~100°C, indicates the thermodesorption of
water and possibly ethanol. The next weight loss occurrs at temperatures from 230 to
550°C; it reflects the thermal decomposition of bridging groups embedded in the
framework. The third weight loss reflects the condensation of silanols and appears above
600 °C.
The disulfide-bridged PMOs were successfully synthesized under microwave
irradiation. Moreover, the significant reduction of the synthesis time was accomplished.
36 hours was used for the synthesis under microwave conditions (the self-assembly
process and hydrothermal treatment) instead of 72 hours needed for the conventional
synthesis. The resulting materials possess high surface area, large pore volume and large
pore diameters.
6.5. Results and discussion for channel-like SBA-15 with ethane and iscoyanurate
bridging groups
The SAXS profiles of the extracted bifunctional PMOs are shown in Figure 50.
The SAXS patterns prove a two-dimensional hexagonal structure (P6mm symmetry
group) of the resulting samples by presence of three characteristic reflections indexed as
(100), (110), and (200). It is noteworthy that there is a noticeable change in the symmetry
group with increasing concentration of ICS in PMO. A comparison of EI-1 and EI-3
bifunctional samples shows some differences in the SAXS patterns, specially decreasing
210
intensity of the (110) peak. The lack of the (110) peak characteristic for the P6mm
symmetry group and the presence of a (321) peak does not permit to determine precisely
the symmetry group of the last two bifunctional samples. Similar situation was already
reported by Olkhovyk et al. [191]. The presence of (110), (220), and (321) suggests the
I4132 cubic symmetry group, however it cannot be completely determined.
Nitrogen adsorption isotherms measured at -196 °C for the bifunctional PMOs
studied are shown in Figure 51A with the corresponding pore size distributions (PSD)
presented in Figure 51B. These isotherms are type IV with steep capillary
condensation/evaporation steps and H1 hysteresis loops. Table 28 shows the BET
specific surface area, volume of fine pores, volume of primary mesopores, and mesopore
diameter. All bifunctional SBA-15 samples possess narrow pore size distribution,
indicating high uniformity of ordered mesopores. Moreover, there is a noticeable
tendency of reducing the structural parameters of these samples with increasing
concentration of isocyanurate bridging groups. As can be seen from Figure 51, the
isotherm curves and the corresponding PSDs change gradually for the PMOs studied
from EI-0 to EI-3. In addition, the condensation/evaporation steps become less sharp with
increasing concentration of ICS, which suggests a gradual deterioration of the
mesoporous structure with higher loading of bulky ICS bridging groups in the mesopore
walls. In addition, the appearence of a distinct peak in the pore range below 4 nm on the
PSD curves indicates the presence of micropores and small mesopores created by
penetration of some polyethylene (EO) blocks into the silica wall. This penetration can be
somewhat limited by large size of ICS organic spacer in the mesopore walls of ethane-
211
silica, which results in the reduction of space available for the aforementioned EO blocks.
The reduction of micropore volume with increasing loading of ICS group is observed
(see Table 28).
The incorporation of large heterocyclic groups to the ethane-silica was monitored
by high-resolution thermogravimetry (TG) for the EI-0, EI-3, and EI-3-P123 samples.
The TG profiles and the corresponding differential TG (DTG) curves recorded in flowing
air are shown in Figure 52. The TG weight loss data for the extracted bifunctional PMOs
are presented in Table 27. The three major weight loss peaks confirmed a successful
synthesis of bifunctional mesostructures as well as a propitious template removal (the
representative sample EI-3-P123). The latter was achieved by extraction, which is
confirmed by the disappearance of the characteristic decomposition peak at about 160 °C
(see the DTG curve for the EI-3-P123 sample in Figure 52B). The DTG curves for the
extracted bifunctional PMOs (see curve for EI-3 in Figure 52B) exhibit two
decomposition peaks appearing in the temperature ranges of 180-250 °C and 250-400 °C,
indicating the thermal degradation of cross-linked heterocyclic isocyanurate rings and
ethane bridging groups, respectively. The concentration of incorporated isocyanurate
rings in the mesopore walls of ethane-silica was estimated by elemental analysis (see %N
and %C values in Table 27).
A comparison of nitrogen and carbon percentages obtained from elemental
analysis for the EI-3 sample, %N (4.37) and %C (26.73), and the values estimated on the
basis of the synthesis gel composition, %N (4.83) and %C (26.21), confirms a good
incorporation of a large bridging ICS group to the ethane-silica framework.
212
110
EI-3
x22
220
321
110
EI-2
x5
Intensity
220
321
100
200
110
210
100 110 200
0.4
0.8
1.2
-1
q (nm )
EI-1
x14
EI-0
x14
1.6
2.0
Figure 50. A comparison of small angle X-ray scattering patterns for a series of the
extracted PMOs studied.
213
Amount Adsorbed (cm3STPg-1)
1000
EI-0
EI-1
EI-2
EI-3
EI-0
EI-1
EI-2
EI-3
2.0
1.5
800
600
1.0
PSD (cm3g-1nm-1)
1200
400
0.5
200
A
0
0.0
0.2 0.4 0.6 0.8
Relative Pressure
B
1.0 2
0.0
4 6 8 10 12 14
Pore Diameter (nm)
Figure 51. a) A comparison of nitrogen adsorption-desorption isotherms at – 196 °C for
a series of the extracted PMOs; the isotherms for EI-2, EI-1 and EI-0 were offset
vertically by 86, 263 and 437 cc STP g-1, respectively, and b) the corresponding pore size
distributions (PSDs) calculated according to the KJS method [279]; PSDs for EI-2, EI-1
and EI-0 were shifted by 0.3, 0.88 and 1.58 cc g-1 nm-1, respectively.
Weight Change (%)
90
EI-0
EI-3
EI-3-P123
80
P123
EI-0
1.0
EI-3
EI-3-P123
0.8
ICS
70
0.6
BTSE
0.4
60
50
0.2
A
200 400 600 800 100
Temperature (°C)
-Deriv. Weight (%/°C)
214
B
0.0
200 300 400 500
Temperature (°C)
Figure 52. a) Comparison of the thermogravimetric weight change (TG) curves
measured in flowing air for as-synthesized (EI-3-P123) and extracted (EI-0 and EI-3)
PMOs, and b) the corresponding DTG curves.
215
Table 27. Synthesis gel compositions, elemental analysis data and thermogravimetric
weight loss data for the PMOs studied.a
Sample
a
Synthesis gel
mixture
Elemental
analysis
TG wt. loss
(%)
nBTESE
nICS
%C
%N
EI-0
5.164
0
19.12
0
17.42
EI-1
4.647
0.344
22.28
2.42
26.85
EI-2
4.131
0.688
23.94
2.74
28.22
EI-3
3.615
1.038
26.73
4.37
34.96
The weight loss values were estimated in the range from 100 to 950°C from the TG profiles recorded in
flowing air.
216
Table 28. Adsorption properties of PMOs determined from nitrogen adsorption data.a
SBET
Vm
Vp
WKJS
(m2 g-1)
(cc g-1)
(cc g-1)
(nm)
EI-0
1068
0.33
0.77
9.43
EI-1
997
0.30
0.72
8.86
EI-2
933
0.27
0.64
7.56
EI-3
773
0.21
0.54
7.44
Sample
a
SBET, BET specific surface area; Vm, volume of pores below 4nm; Vp, volume of primary mesopores; wKJS,
mesopore diameter.
217
In summary, this work shows that bifunctional PMOs can be synthesized by
incorporation of large bridging groups such as isocyanurate rings into ethane-silica. The
high quality PMOs with relatively large concentration of bulky bridging groups were
obtained in terms of the framework periodicity as well as in terms of high pore volume
and high surface area.
6.6. Results and discussion for SBA-15 with isocyanurate groups prepared under
microwave irradiation
Nitrogen adsorption isotherms measured at -196 °C for the isocyanurate-bridged
SBA-15 are shown in Figure 53 and Figure 54 together with the corresponding pore size
distributions, which were calculated from adsorption branches of isotherms using the
improved KJS method. It is noteworthy that each particular series of the samples was
obtained by varying temperature and time of microwave irradiation. The first step of the
synthesis was performed at 40C for 6 and 12 hours. The second step, hydrothermal
treatment, was carried out at 100 and 120C for 12 and 24 hours. For the purpose of
comparison, nitrogen adsorption isotherms measured on isocyanurate-functionalized
SBA-15 sample via conventional method are also shown. The basic parameters for the
samples studied such as the BET specific surface area, the single-point pore volume, the
volume of complementary pores and the pore width are provided in Table 29. As can be
seen, the structural parameters summarized in Table 29 and Figure 53 demonstrate that
the temperature and time of microwave irradiation play a key role in fabrication of good
218
quality organosilicas materials with bulky isocyanurate spacers.
Figure 53 shows a complete set of nitrogen adsorption isotherms (A) and the pore
size distributions (B) for isocyanurate-modified PMOs samples hydrothermally treated
under microwave irradiation at 100oC for 12 and 24 h. As can be seen from Figure 53 all
adsorption isotherms are type IV with distinct capillary condensation/evaporation steps
and H1 hysteresis loops, which is typical for channel-like mesostructures. All channellike PMOs show comparable and even higher values of structural parameters in
comparison to the ICS-modified SBA-15 sample obtained via conventional synthesis. It
is noteworthy that all samples possess high concentration of ICS groups. The BET
specific surface area changes from 505 to 831 m2/g, the single-point pore volume varies
from ~0.43 to 0.77 cc/g and the pore diameters are about 7 nm with an apparent tendency
to grow with increasing time of the microwave-treatment (see Figure 53 B and Table 29).
The pore size distributions show clearly an increase in the pore size of ICS-containing
samples with increasing time of hydrothermal treatment (Figure B) as well as the steeper
capillary condensation steps and the narrower pore size distributions. Moreover, the ICS100-12-12 and ICS-100-12-24 samples present similar adsorption parameters, indicating
that the optimal time of hydrothermal treatment under microwave irradiation is 12h at
100oC.
An increase in the temperature of hydrothermal treatment step to 120oC had a
positive effect on the resulting PMOs. Figure 54 shows nitrogen adsorption isotherms (A)
and the pore size distributions (B) of isocyanurate-functionalized mesostructures
hydrothermally treated under microwave irradiation at 120oC for 12 and 24 h. Similarly
219
to the aforementioned samples obtained at 100oC, the adsorption isotherms of the ICSPMOs samples prepared at higher temperature, are type IV with distinct capillary
condensation/evaporation steps and H1 hysteresis loops. The adsorption and structural
parameters are higher in comparison to those for the ICS-c sample obtained via
conventional method.
Moreover, a comparison of the ICS-100-12-24 and ICS-120-12-24 materials
shows similar results for the structural properties as well as higher BET specific surface
area (831 vs. 1047 m2/g) and single-point pore volume (0.77 vs. 1.01 cc/g) in a favor of
hydrothermal treatment at 120oC. As can be noticed, the duration of microwave-assisted
hydrothermal treatment and temperature of the isocyanurate-bridged SBA-15 samples are
important factors. An insufficient time of this treatment led to lower quality of samples in
terms of the surface area, pore volume and other structural properties. In addition, it is
noteworthy that the samples prepared under microwave irradiation possess better quality
in comparison to the sample synthesized via conventional method. Furthermore, the
isotherms of all ICS-modified samples manifest the lack of plateu at higher pressures
(especially, for the samples exposed to longer hydrothermal treatment). Nitrogen
branches increase with pressure reaching the saturation vapour pressure, which indicates
the presence of secondary disordered mesopores.
It was shown that the introduction of bulky isocyanurate bridging group into the
framework of channel-like organosilicas was successful by employing the microwaveassisted synthesis. The resulting hexagonal materials with high loadings of
aforementioned organic spacer (30%) exhibited high surface area, large pore volume and
220
large pore diameters. Moreover, a significant time reduction of the process was achieved
in comparison to the conventional method, from 72 hours to 24-36 hours, respectively.
This study shows the benefit of using microwave irradiation in the synthesis of
organosilicas, especially those with large groups as well as with high loading of organic
groups.
221
Table 29. Selected adsorption and structural parameters for the SBA-15 silicas with
isocyanurate groups.a
a
Sample
SBET,
m2g-1
Vc,
ccg-1
Vo,
ccg-1
Vt,
ccg-1
wKJS,
nm
ICS-c
505
0.12
0.30
0.43
6.92
ICS-100-6-12
597
0.18
0.41
0.54
7.39
ICS-100-6-24
672
0.11
0.45
0.57
7.40
ICS-100-12-12
823
0.16
0.59
0.75
7.38
ICS-100-12-24
831
0.16
0.59
0.77
7.34
ICS-120-6-12
645
0.10
0.50
0.61
7.11
ICS-120-6-24
694
0.11
0.54
0.66
7.10
ICS-120-12-12
776
0.13
0.59
0.73
7.40
ICS-120-12-24
1047
0.18
0.82
1.01
7.39
SBET , BET specific surface area; Vc, volume of complementary pores (including micropores) of the
width below 4 nm present in the mesopore walls; Vo, volume of ordered mesopores; Vt, single-point
pore volume; wKJS, mesopore diameter calculated by the improved KJS method [279];
222
-1
Amount Adsorbed (cm STP g )
1000
ICS-c
ICS-100-6-12
ICS-100-6-24
ICS-100-12-12
ICS-100-12-24
1.4
1.2
3
800
1.6
A
PSD (cm3g-1nm-1)
ICS-c
ICS-100-6-12
ICS-100-6-24
ICS-100-12-12
ICS-100-12-24
600
400
B
1.0
0.8
0.6
0.4
200
N2
0
0.0
0.2
0.4
0.6
0.8
Relative Pressure
1.0
0.2
0.0
2
4
6
Pore Diameter (nm)
8
Figure 53. Nitrogen adsorption isotherms measured at -196 °C (A) and the corresponding
pore size distributions (PSDs) (B) calculated by the improved KJS method [279] for the
extracted isocyanurate-bridged PMOs obtained under microwave irradiation at 40 °C
during the self-assembly stage and at 100°C in the hydrothermal step. The isotherms and
PSDs for ICS-100-6-12, ICS-100-6-24, ICS-100-12-12, ICS-100-12-24 were offset by
50, 150, 250, 400 cm3 STP g-1 and 0.2, 0.45, 0.70, 1.00 cm3 g-1 nm-1, respectively.
1500
A
ICS-c
ICS-120-6-12
ICS-120-6-24
ICS-120-12-12
ICS-120-12-24
1.5
PSD (cm3g-1nm-1)
ICS-c
ICS-120-6-12
ICS-120-6-24
ICS-120-12-12
ICS-120-12-24
3
-1
Amount Adsorbed (cm STP g )
223
1000
500
B
1.0
0.5
N2
0
0.0
0.2
0.4
0.6
0.8
Relative Pressure
1.0
0.0
2
4
6
Pore Diameter (nm)
8
Figure 54. Nitrogen adsorption isotherms measured at -196 °C (A) and the corresponding
pore size distributions (PSDs) (B) calculated by the improved KJS method [279] for the
extracted isocyanurate-bridged PMOs obtained under microwave irradiation at 40 °C
during the self-assembly stage and at 120°C in the hydrothermal step. The isotherms and
PSDs for ICS-120-6-12, ICS-120-6-24, ICS-120-12-12, ICS-120-12-24 were offset by
150, 400, 600, 700 cm3 STP g-1 and 0.25, 0.50, 0.80, 1.10 cm3 g-1 nm-1, respectively.
VII. Conclusions
This dissertation reports the synthesis of ordered mesoporous organosilicas with
surface and bridging groups obtained under microwave conditions. The study was
concentrated on the usage of microwave irradiation to synthesize the good quality
organosilica mesostructures, and to monitor their adsorption and surface properties by
varying chemical composition as well as time and temperature of hydrothermal synthesis.
The particular topics studied include: (i) improvement of the synthesis of ordered cagelike mesosilicas under conventional and microwave conditions, (ii) fabrication of ordered
functionalized cage-like and channel-like mesosilicas with various organic surface
ligands via traditional and microwave methods and (iii) synthesis
of ordered
mesostructures with various bridging groups by using conventional and microwave
techniques.
It is shown that the efficient template removal from as-synthesized cage-like
SBA-16 organosilicas should include a combination of extraction by acidified ethanolic
solution and temperature-controlled calcination. Moreover, it is demonstrated that such
calcination is effective at lower temperature (350 ºC or below) in flowing nitrogen. The
resulting cage-like silicas are characterized by high pore volume (~0.85 cm3g-1), large
pore size (~8.5nm) and high surface area (~1200 m2g-1) when co-condensation process is
carried out in the presence of sodium chloride at low acid concentrations. In addition, it is
shown that the duration of both process stages, the self-assembly and hydrothermal
treatment, is important in the synthesis of SBA-16-type organosilicas. Varying the time
224
225
of self assembly (2 – 20h) and hydrothermal treatment (6-48h) gives the ability of
tailoring the parameters for of the resulting cage-like organosilicas.
Importantly, the microwave-assisted synthesis afforded good quality SBA-16
samples at lower temperatures of hydrothermal treatment (100-120oC), whereas the
hydrothermal treatment at higher temperatures (140-160oC) resulted in the silica
mesostructures resembling channel-like porous structures. This structural change seems
to be facilitated for the samples exposed to a short stirring (2h) at 40oC. Also, the
microwave-assisted synthesis was successfully used to screen a wide range of
temperatures and time in order to establish optimal conditions for the synthesis of SBA16. It is noteworthy that a significant time reduction of the microwave-assisted synthesis
was achieved in comparison to the conventional method. The duration of conventional
synthesis was shortened from 48 hours to optimal 2-6 h for the co-condensation step and
6-12 h of hydrothermal treatment at 100-120 °C. The resulting cage-like materials
exhibited high surface area, large pore volume and large pore diameters. The study of the
microwave irradiation effect on the properties of pure silica mesostructures was essential
for the next part of this dissertation, which is devoted to mesoporous organosilicas.
The introduction of triethoxyvinylsilane (vinyl), ureidopropyltrimethoxysilane
(ureidopropyl) and 3-mercaptopropyltrimethoxysilane (mercaptopropyl) surface ligands
onto silica pore walls of SBA-15 and SBA-16 mesostructures was successful under
conventional and microwave conditions. Mono- and bifunctional channel-like and cagelike silicas showed similar tendency of decreasing the structural ordering with increasing
concentration of the introduced functionality. An effective method of the template
226
removal, especially in the case of channel-like materials, appeared to be the extraction
with hydrochloric acid-ethanol solution. In the case of SBA-16 organosilicas, the removal
of the F127 template is more challenging because of the cage-like nature of this silica
material. The obtained results show some possible difficulties in introduction of organic
groups onto surface of cage-like materials in contrary to hexagonal structures.
The resulting materials showed good adsorption properties, reflected by large
pore volume and pore size as well high BET specific surface area in contrary to the
samples manufactured via conventional method. It is important to mention that the
microwave-assisted synthesis offers a significant reduction of time of the whole process.
Similar results were obtained for vinyl-functionalized SBA-15 ordered mesoporous
materials, showing a good quality of those channel-like organosilicas. Furthermore, the
influence of increasing concentration of organic functional groups and the resulting
structural changes associated with incorporation of high loadings of vinyl groups are
presented. Also, an increase of vinyl group loading caused a gradual deterioration of the
mesostructural ordering and enhanced the formation of micropores at high (30%)
concentrations of this group.
The study of incorporation the ethane bridging group in the framework of SBA15-type mesostructures was aimed at the optimization of the synthesis conditions. The
polymer/organosilica weight ratio was used to tune the properties of PMOs in order to
obtain the large mesopore widths, narrow PSDs, uniform pore openings and high
mesostructural ordering. A good quality samples in terms of adsorption properties were
obtained for the polymer/organosilica ratio about 3. Moreover, it was demonstrated that
227
the template can be removed by extraction with acidified ethanol solution.
The microwave-assisted synthesis of ethane-bridged PMOs was reduced to 36
hours in comparison to 72 hours under conventional conditions. The resulting materials
exhibited high surface area, large pore volume and large pore diameters. This study
demonstrates the attractiveness of microwave technique for the synthesis of PMOs.
Also, the channel-like SBA-15 and cage-like SBA-16 mesostructures with
disulfide bridging group were obtained under microwave conditions. The tendency of
decreasing the structural ordering with increasing concentration of introduced organic
spacers into silica framework was shown.
Moreover, it was shown the bifunctional PMOs can be synthesized by
incorporation of large isocyanurate bridging groups into ethane-silica framework under
microwave conditions. The aforementioned organosilicas possessed high concentration of
bulky bridging groups and a good framework periodicity as well as large pore volumes
and high surface areas. Microwave-assisted synthesis of organosilicas, especially those
with large organic groups and with high loading of these groups, gives good quality
PMOs. These materials are of great importance for various applications ranging from
adsorption
and
catalysis
to
environmental
and
energy-related
processes.
References
1.
C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 1992 359
710
2.
J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt,
C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L.
Schlenker, J. Am. Chem. Soc. 1992 114 10843
3.
T. Asefa, M.J. MacLachlan, N. Coombos, G.A. Ozin, Nature 1999 402 867
4.
O. Olkhovyk, M. Jaroniec, J. Am. Chem. Soc. 2005 127 60.
5.
R.M. Grudzien, B.E. Grabicka, S. Pikus, M. Jaroniec, Chem. Mater. 2006 18 1722
6.
R.M. Grudzien, S. Pikus, M. Jaroniec, J. Phys. Chem. B 2006 110 2972
7.
M.H. Lim, A. Stein, Chem. Mater. 1999 11 3285
8.
V. Antochshuk, M. Jaroniec, J. Phys. Chem. B 1999 103 6252
9.
V. Antochshuk, M. Jaroniec, Chem. Mater. 2000 12 2496
10. C.P. Jaroniec, M. Kruk, M. Jaroniec, A. Sayari, J. Phys. Chem. B 1998 102 5503
11. S.L. Burkett, S.D. Sims, S. Mann, Chem. Commun. 1996 1367
12. M. Kruk. T. Asefa, N. Coombs, M. Jaroniec, A.G. Ozin, J. Mater. Chem. 2002 12
3452
13. Y.J. Gong, Z.H. Li, D. Wu, Y. H. Sun, F. Deng, Q. Luo, Y. Yue, Microporous
Mesoporous Mater. 2001 49 95
14. T. Yanagisawa, T. Shimizu, K. Kuroda, C. Kato, Bull. Chem. Soc. Japan 1990 63
988
228
229
15. Q. Huo, D.I. Margolese, U. Ciesla, D.G. Demuth, P. Feng, T.E. Gier, P. Sieger, A.
Firouzi, B.F. Chmelka, F. Schüth, G.D. Stucky, Chem. Mater. 1994 6 1176
16. Q. Huo, D.I. Margolese, G.D. Stucky, Chem. Mater. 1996 8 1147
17. M. Jaroniec, M. Kruk, H.J. Shin, R. Ryoo, Y. Sakamoto, O. Teresaki, Microporous
Mesoporous Mater. 2001 48 127
18. A. Stein, Adv. Mater. 2003 15 763
19. M. Kruk, M. Jaroniec, A. Sayari, Langmuir 1997 13 6267
20. M. Kruk, M. Jaroniec, Langmuir 1999 15 5279
21. V. Meynen, P. Cool, E.F. Vansant, Microporous Mesoporous Mater. 2009 125 70
22. M. Kruk, M. Jaroniec, J. Phys. Chem B 1999 103 4590
23. M. Kruk, M. Jaroniec, R. Ryoo, J.M. Kim, Chem. Mater. 1999 11 2586
24. F.M. Bobonich, S.A. Kovalenko, Y.G. Voloshina, A.S. Korchev, V.N Solomakha,
A.P. Philippov, V.G Iln, Adsorpion Sci. Technol. 2002 20 595
25. Q.S. Huo, D.I. Margolese, G.D. Stucky, Chem. Mater. 1996 8 1147
26. U. Ciesla, F. Schueth, Microporous Mesoporous Mater. 1999 27 131
27. S. Battacharyya, G. Lelong, M.-L. Saboungi, J. Exp. Nanosci. 2006 1 375
28. P. Selvam, S.K. Bhattia, Ch.G. Sonwane, Ind. Eng. Chem. Res. 2001 40 3237
29. X.S. Zhao, G.Q.M. Lu, G.J. Millar, Ind. Eng. Chem. Res. 1996 35 2075
30. A. Sayari, M. Kruk, M. Jaroniec, I.L. Moudarowski, Adv. Mater. 1998 10 1376
31. A. Sayari, Angewandte Chem. Int. Ed. 2000 39 2920
32. A. Anandan, M. Okazaki, Microporous Mesoporous Mater. 2005 87 77
230
33. E. Climent, M.D. Marcos, R. Martinez-Manoz, F. Sancenon, J. Soto, K. Rurack, P.
Amoros, Angewandte Chem. Int. Ed. 2009 48 8519
34. D. Pai, P. Yuan, L. Zhao, N. Liu, L. Zhou, G. Wei, J. Zhang, Y. Ling, Y. Fan, B.
Wei, H. Liu, Ch. Yu, X. Bao, Chem. Mater. 2009 21 5413
35. F. Fajula, D. Brunel, Microporous Mesoporous Mater. 2001 48 119
36. B.F.G. Johnson, S.A Raynor, D.B. Brown, D.S Shephard, T. Mashmeyer, J. Meurig
Thomas, S. Hermanns, R. Raja, G. Sankar, J. Molecular Catal. A 2002 182 89
37. D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D.
Stucky, Science 1998 279 548
38. P. Van Der Voort, C. Vercaemst, D. Schaubroeck, F. Verpoort, Phys. Chem. Chem.
Phy. 2008 10 347
39. A. Sayari, S. Hamoudi, Chem. Mater. 2001 13 3151
40. A. Taguchi, F. Schueth, Microporous and Mesoporous Mater. 2005 77 1
41. A. Stein, Adv. Mater, 2003 15 763
42. M. Kruk, M. Jaroniec, C.H. Ko, R. Ryoo, Chem. Mater. 2000 12 1961
43. P.I. Ravikovitch, A.V. Neimark, J. Phys. Chem. B 2001 105 6823
44. P.Yang, D. Zhao, D.I. Margolese, B.F. Chmelka, G.D. Stucky, Chem. Mater. 1999
11 2813
45. P.F. Fulvio, S. Pikus, M. Jaroniec, J. Mater. Chem. 2005 15 5049
46. G. Oye, J. Sjoblom, M. Stocker, Adv. Colloid and Interface Sci. 2001 89 439
47. J. Cejka, S. Mintova, Cat. Rev. Sc. Eng. 2007 49 457
48. C. Ispas, I. Sokolov, S. Andreescu, Anal. Bioanal. Chem. 2009 393 543
231
49. I. Izqierdo-Barba, M. Colilla, M. Valett-Regi, J. Nanomater. 2008 106970
50. C.P. Jaroniec, M. Kruk, M. Jaroniec, A. Sayari, J. Phys. Chem. B 1998 102 5503
51. I. Nowak, M. Ziolek, M. Jaroniec, J. Phys. Chem. B. 2004 108 3722
52. M. Kruk, V. Antochshuk, J.R. Matos, L.P. Mercuri, M.J. Jaroniec, J. Am. Chem.
Soc. 2002 124 768
53. P.V.D. Voort, M. Benjelloun, E.F. Vansant, J. Phys. Chem. B 2002 106 9027
54. Y. Sakamoto, M. Keneda, O. Teresaki, D.Y. Zhao, J.M. Kim, G. Stucky, H.J. Shin,
R. Ryoo, Nature 2000 408 449
55. L. Wang, J. Fan, B. Tian, H. Yang, Ch. Yu, B. Tu, D. Zhao, Microporous
Mesoporous Mater. 2004 67 135
56. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, J. Mater. Chem. 2006 16 819
57. T.-W. Kim, R. Ryoo, M. Kruk, K.P. Gierszal, M. Jaroniec, S. Kamiya, O. Teresaki,
J. Phys. Chem. B 2004 108 11480
58. L. Zhao, G. Zhu, D. Zhang, Y. Di, O. Teresaki, Sh. Qiu, J. Phys. Chem. B 2004 109
764
59. C. Yu, Y. Yu, D. Zhao, Chem. Commun. 2000 575
60. M. Kruk, V. Antochshuk, J.R. Matos, L.P. Mercuri, M. Jaroniec, J. Am. Chem. Soc.
2002 124 168
61. J.R. Matos, M. Kruk, L.P. Mercuri, M. Jaroniec, L. Zhao, T. Kamiyama, O.
Teresaki, T.J. Pinnavaia, Y. Liu, J. Am. Chem. Soc. 2003 125 821
62. R.M. Grudzien, M. Jaroniec, Chem. Commun. 2005 1076
63. R.M. Grudzien, M. Jaroniec, Stud. Surface Sci. Catal. 2005 156 105
232
64. R.M. Grudzien, B.E. Grabicka, M. Kozak, S. Pikus, M. Jaroniec, New J. Chem.
2006 30 1071
65. M. Kruk, E.B Celer, M. Jaroniec, Chem. Mater. 2004 16 698
66. R. Srivastava, D.Srinivas, P. Ratnasamy, Microporous Mesoporous Mater. 2006 90
314
67. L. Zhang, W. Zhang, J. Shi, Z. Hua, Y. Li, J. Yan, Chem. Commun. 2003 210
68. O. Olkhovyk, M. Jaroniec, Adsorption 2005 11 205
69. M.J. Kim, R. Ryoo, Chem. Mater. 1998 11 487
70. D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 1998 120
6024
71. R. Ryoo, C.H. Ko, M. Kruk, V. Antochshuk, M. Jaroniec J. Phys. Chem. B 2000
104 11465
72. B.L. Newalkar, S. Komarneni, U.T. Turaga, H. Katsuki J. Mater. Chem. 2003 13
1710
73. C. Yu, Y.Yu, D. Zhao, Chem. Commun. 2000 575
74. P. Feng, X. Bu, D. Pine, Langmuir 2000 16 5304
75. W-H. Zhang, L; Zhang, J. Xiu, Z. Shen, Y. Li, P. Ying, C. Li, Microporous
Mesoporous Mater. 2006 89 179
76. D. Zhao, J. Sun, Q. Li, G.D. Stucky, Chem. Mater. 2000 12 27
77. Ch.-F. Cheng, Y.-Ch. Lin, H.-H. Cheng, Sh.-M. Liu, H-Sh. Sheu. Chem. Lett. 2004
33 262
78. F. Kleitz, T.W. Kim, R. Ryoo Langmuir 2006 22 440
233
79. Y.K. Hwang, J.-S. Chang, Y.-U. Kwon, S.-E. Park, Microporous Mesoporous
Mater. 2004 68 21
80. P.E. Fulvio, B.E. Grabicka, R.M. Grudzien, M. Jaroniec, Adsorption Sci. Technol.
2007 25 439
81. E. Kramer, S. Forster, C. Goltner, M. Antonietti, Langmuir 1998 14 2027
82. L. Zhao, Y. Yu, L. Song, M. Ruan, X. Hu, A. Larbot, Applied Catalysis A: General
2004 263 171
83. C.M. Yang, B. Zibrowius, F. Schüth, Chem. Commun. 2003 1772
84. J. Patarin, Angew. Chem. Int. Ed. 2004 43 3878
85. C.M. Yang, B. Zibrowius, W. Schmidt, F. Schüth, Chem. Mater. 2003 15 3739
86. C.M. Yang, B. Zibrowius, W. Schmidt, F. Schüth, Chem. Mater. 2004 16 2918
87. K.W. Gallis, C.C. Landry, Adv. Mater. 2001 13 23
88. B. Tian, X. Liu, C. Yu, F. Gao, Q. Luo, S. Xie, B. Tu, D. Zhao, Chem. Commun.
2002 1186
89. A. Hozumi, Y. Yokogawa, T. Kameyama, K. Hiraku, H. Sugimura, O. Takai, M.
Okido, Adv. Mater. 2000 12 985
90. M. Mesa, L. Sierra, J. Patarin, J.-L. Guth, Solid State Sci. 2005 7 990
91. L. Huang, C. Poh, S.C. Ng, K. Hidajat, S. Kawi Langmuir 2005 21 1171
92. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, J. Mater. Chem . 2006 16 819
93. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Applied Surface Sci. 2007 253 5660
94. A. Walcarius, Electroanalysis 2008 20 711
234
95. M. Kruk. T. Asefa, N. Coombs, M. Jaroniec, A.G. Ozin, J. Mater. Chem. 2002 12
3452
96. S. Hamoudi, S. Kaliaguine, Microporous Mesoporous Mater. 2003 59 195
97. M. Jaroniec, Nature 2006 442 638
98. X. Feng, G.E. Fryxell, L.Q. Wang, A.Y. Kim, J. Liu, K. Kemner, Science 1997 276
923
99. C.P. Jaroniec, M. Kruk, M. Jaroniec, A. Sayari, J. Phys. Chem. B 1998 102 5503
100. O. Olkhovyk, M. Jaroniec, Adsorption 2005 11 205
101. R.M. Grudzien, B. E. Grabicka, S. Pikus, M. Jaroniec, Chem. Mater. 2006 18 1722
102. R.M. Grudzien, S. Pikus, M. Jaroniec, J. Phys. Chem. B. 2006 1102972
103. T. Asefa, M.J. MacLachlan, N. Coombos, G.A. Ozin, Nature 1999 402 867
104. C. Yoshina-Ishii, T. Asefa, N. Coombos, M.J. MacLachlan, G.A. Ozin, Chem.
Commun. 1999 2539
105. S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna, O. Teresaki, J. Am. Chem. Soc.
1999 121 9611
106. B.J. Melde, B.T. Holland, C.F. Blandford, A. Stein, Chem. Mater. 1999 11 3302
107. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Adsorption 2006 12 293
108. R.M. Grudzien, B.E. Grabicka, D.J. Knobloch, M. Jaroniec, Stud. Surface Sci.
Catal. 2007 165 443
109. B.E. Grabicka, R.M. Grudzien, D.J. Knobloch, M. Jaroniec, PBAST World
Scientific Publ. Co. 2007 189
235
110. S. Huh, J.W.Wiench, J-Ch. Yoo, M. Pruski, V.S.-Y. Lin, Chem. Mater. 2003 15
4247
111. R.P. Hodkings, A.E. Garcia-Bennett, P.A. Wright, Microporous Mesoporous
Mater. 2005 79 241
112. D. Margolese, J. A. Melero, S. C. Christiansen, B. F. Chmelka, G. D. Stucky,
Chem. Mater. 2000 12 2448
113. W. M. Van Rhijn, D. E. De Vos, B. F. Sels, W. D. Bossaert, P. A. Jacobs, Chem.
Commun. 1998 317
114. V. Ganesan, A. Walcarius, Langmuir 2004 20 3632
115. C.E. Fowler, S.L. Burkett, S. Mann, Chem. Commun. 1997 1769
116. R.M. Grudzien, B.E. Grabicka, D.J. Knobloch, M. Jaroniec, Colloids & Surfaces A
2006 291 139
117. T. Kang, Y. Park, K. Choi, J.S.Lee, J. Yi, J. Mater. Chem. 2004 14 1043
118. R. Srivastava, D.Srinivas, P. Ratnasamy, Microporous Mesoporous Mater. 2006 90
314
119. B. Gadenne, P. Hasemann, J.J.E. Moreu, Chem. Comm. 2004 1768
120. Y.Q. Wang, C.M. Yang, B. Zibrowius, B. Spliethoff, M. Linden, F. Schuth, Chem.
Mater. 2003 15 5029
121. H.M. Kao, J.-D. Wu, Ch.-Ch. Cheng and A.S.T. Chiang, Microporous Mesoporous
Mater. 2006 88 319
122. M. H. Lim, C. F. Blanford, A. Stein, J. Am. Chem. Soc. 1997 119 4090
123. L. Mercier, T. J. Pinnavaia, Chem. Mater. 2000 12 188
236
124. M.H. Lim, A. Stein, Chem. Mater. 1999 11 3285
125. M. Kruk, T. Asefa, M. Jaroniec, G.A. Ozin, J. Am. Chem. Soc 2002 124 6383
126. Y.Q Wang, B. Zibrowius, C.M. Yang, B. Spliethoff, F. Schüth, Chem. Commun.
2004 46
127. R.M. Grudzien, S. Pikus, M. Jaroniec, J. Phys. Chem. B 2006 110 2972
128. M. Kruk, T. Asefa, N. Coombs, M. Jaroniec, A.G. Ozin, J. Mater. Chem. 2002 12
3452
129. S. Fiorilli, B. Ondia, B. Bonelli, E. Garrone, J. Phys. Chem. B 2005 109 16725
130. Ch.-M.Yang, Y. Wang, B. Zibrowius, F. Schueth, Phys. Chem. 2004 6 2461
131. X. Wang, K.S.K. Lin, J.C.C. Chan, S. Cheng, J. Phys. B 2005 109 1763
132. D. J. Macquarrie, D. B. Jackson, Chem. Commun. 1997 1781
133. D. J. Macquarrie, D. B. Jackson, S. Tailland, K. A. Utting, J. Mater. Chem. 2001 11
1843
134. M.H. Lim, C.F. Blanford, A. Stein, J. Am. Chem. Soc. 1997 119 4090
135. D.J. Macquarrie, Chem. Commun. 1996 1961
136. S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunieda, O. Terasaki, T.
Tatsumi, Nat. Mater. 2003 2 801
137. T. Yokoi, H. Yoshitake, T. Tatsumi, J. Mater. Chem. 2004 14 951
138. A. S. M. Chong, X. S. Zhao, J. Phys. Chem. B 2003 107 12650
139. L. Zhang, J. Liu, J. Yang, Q. Yang, C. Li, Microporous Mesoporous Mater. 2008
109 172
237
140. M.C. Burleigh, M.A. Markowitz, M. S. Spector, B.P. Gaber, J. Phys. Chem. B.
2001105 9935
141. R.M. Grudzien, B.E. Grabicka, R. Felix, M. Jaroniec, Adsorption 2007 13 323
142. D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 1998 120
6024
143. Y.A.I. Abu-Lebdeh, P.M. Budd, V.M. Nace, J. Mater. Chem, 1998 8 1839
144. P.F. Fulvio, S. Pikus and M. Jaroniec, J. Mater. Chem. 2005 15 5049
145. X. Wang, Y.-H. Tseng, J.C.C. Chan, S. Cheng Microporous Mesoporous Mater.
2005 8537 241
146. R.M. Grudzien, B.E. Grabicka, S. Pikus, M. Jaroniec, Chem. Mater. 2006 18 1722
147. B. Hatton, K. Landskron, W. Whitnall, D. Perovic, G.A. Ozin, Acc. Chem. Res.
2005 38 305
148. G.A. Fryxell, Inorg. Chem. Commun. 2006 9 1141
149. O. Olkhovyk, M. Jaroniec, J. Am. Chem. Soc. 2005 127 60
150. O. Olkhovyk, M. Jaroniec, Adsorption 2005 11 685
151. V. Antochshuk, O. Olkhovyk, M. Jaroniec, I.-S. Park, R. Ryoo, Langmuir 2003 19
3031
152. L. Zhang, W. Zhang, J. Shi, Z. Hua, Y. Li, J. Yan, Chem. Commun. 2003 210
153. M.C. Dujardin, C. Caze, I. Vroman, React. Functional Polymers 2000 43 123
154. S. Chiarle, M. Ratto, M. Rovatti, Water Research 2000 34 2971
155. M.J.Zamzow, B.R. Eichbaum, Sep. Sci Technol. 1990 25 1555
156. K. Ranganathan, Carbon, 2003 41 1087
238
157. P.K. Jal, S. Patel, B.K. Mishra, Talanta 2004 62 1005
158. A.G.S. Prado, L.N.H. Araki, C. Airoldi, Green Chem. 2002 4 42
159. O. Olkhovyk, V. Antochshuk, M. Jaroniec, Colloids and Surfaces A 2004 236 69
160. O. Olkhovyk, V. Antochshuk, M. Jaroniec, Analyst 2004 130 104
161. V. Antochshuk, M. Jaroniec, Chem. Commun. 2002 258
162. T. Kang, Y. Park, K. Choi, J.S. Lee, J. Yi, J. Mater. Chem. 2004 14 1043
163. Q. Wie, Z. Nie, Y. Hao, Z. Chen, J. Zou, W. Wang, Mater. Lett. 2005 59 3611
164. X. Wang, K.S.K. Lin, J.C.C. Chan, S.J. Cheng, J. Phys.Chem. B 2005 109 1763
165. R.P. Hodgkins, A.E. Garcia-Bennett, P.A. Wright, Microporous Mesoporous
Mater. 2005 79 241
166. A. Ghosh, C.R. Patra, P. Mukherjee, M. Sastry, R. Kumar, Microporous
Mesoporous Mater. 2003 58 201
167. S. Huh, J.W. Wiench, J.Ch. Yoo, M. Pruski, V.S.-Y. Lin, Chem. Mater. 2003 15
4247
168. Q. Wie, L. Liu, Z.-R. Nie, H.-Q. Chen, Y.-L. Wang, Q.-Y. Li, J.-X. Zou,
Microporous Mesoporous Mater. 2007 101 381
169. O. Dag, G.A. Ozin, Adv. Mater. 2001 13 1182
170. J.R. Matos, M. Kruk, L.P. Mercuri, M. Jaroniec, T. Asefa, N. Coombos, G.A. Ozin,
O. Teresaki, Chem. Mater. 2002 14 1903
171. X.Y. Bao, X.S. Zhao, X. Li, P.A. Chia, J. Li, J. Phys. Chem. B 2004 108 4684
172. X.Y. Bao, X.S. Zhao, J. Phys. Chem. B 2005 109 10727
173. A. Stein, Adv. Mater. 2003 15 763
239
174. M. Kruk, M. Jaroniec, A. Sayari, Langmuir 1997 13 6267
175. M. Kruk, M. Jaroniec, Langmuir 1999 15 5279
176. M. Kruk, M. Jaroniec, J.Phys. Chem B 1999 103 4590
177. M. Kruk, M. Jaroniec, R. Ryoo, J.M. Kim, Chem. Mater. 1999 11 2586
178. D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D.
Stucky, Science 1998 279 548
179. M. Kruk, M. Jaroniec, C.H. Ko, R. Ryoo, Chem. Mater. 2000 12 1961
180. P.I. Ravikovitch, A.V. Neimark, J. Phys. Chem. B 2001 105 6823
181. P.F. Fulvio, S. Pikus, M. Jaroniec, J. Mater. Chem. 2005 15 5049
182. P.Yang, D. Zhao, D.I. Margolese, B.F. Chmelka, G.D. Stucky, Chem. Mater. 1999
11 2813
183. P.V.D. Voort, M. Benjelloun, E.F. Vansant, J. Phys. Chem. B 2002 106 9027
184. Y. Sakamoto, M. Keneda, O. Teresaki, D.Y. Zhao, J.M. Kim, G. Stucky, H.J. Shin,
R. Ryoo, Nature 2000 408 449
185. S. Inagaki, S. Guan, T. Ohsuna, O. Teresaki, Nature 2002 416 304
186. Y. Liang, M. Hanzlik, R. Anwander, Chem. Commun. 2005 525
187. X. Zhou, S. Qiao, N. Hao, X. Wang, Ch. Yu, L. Wang, D. Zhao, G.L. Lu, Chem.
Mater. 2007 19 1870
188. W. Guo, I. Kim, C.-S. Ha, Chem. Commun. 2003 2692
189. M.P. Kapoor, S. Inagaki, Chem. Mater. 2002 14 3509
190. A. Sayari, W. Wang, J. Am. Chem. Soc. 2005 127 12194
191. O. Olkhovyk, S. Pikus, M. Jaroniec, J. Mater. Chem. 2005 15 1517
240
192. T. Asefa, M. Kruk, M.J. MacLachlan, N. Coombos, H. Grondey, M. Jaroniec, G.A.
Ozin, J. Am. Chem. Soc. 2001 123 8520
193. M.C. Burleigh, M.S. Markowitz, M.S. Spector, B.P Gaber, Langmuir 2001 17 7923
194. S. Hamoudi, Y. Yang, I. L. Moudrskovski, S. Lang, A. Sayari, J. Phys. Chem. B
2001105 9118
195. T. Ren, X. Zhang, J. Suo, Microporous Mesoporous Mater. 2002 54 139
196. X. Y. Bao, X. S. Zhao, X. Li, P. A. Chia, J. Li, J. Phys. Chem. B 2004 108 4684
197. X. Bao, X. S. Zhao, X. Li, J. Li, Appl. Surf. Sci. 2004 237 380
198. R.M. Grudzien, B.E. Grabicka, M. Jaroniec, Colloids & Surfaces A 2007 300 235
199. E.B. Cho, K. Char, Chem. Mater. 2004 16 270
200. W. Guo, I. Kim, C.-S. Ha, Chem. Commun. 2003 2692
201. J. R. Matos, M. Kruk, L. P. Mercuri, M. Jaroniec, T. Asefa, N. Coombs, G. A. Ozin,
T. Kamiyama, O. Terasaki, Chem. Mater. 2002 14 1903
202. L. Zhao, G. Zhu, D. Zhang, Y. Di, Y. Chen, O. Terasaki, S. Qiu, J. Phys. Chem. B
2005 109 765
203. L. Zhang, W. Zhang, J. Shi, Z. Hua, Y. Li, J. Yan, J. Chem Commun. 2003 210
204. J. Liu, Q. Yang, M.P. Kapoor, N. Setoyama, S. Inagaki, J. Yang, L. Zhang, J. Phys
Chem. 2005 109 12250
205. R. Gedye, F.S mith, K. Westaway, H. Ali, L. Badisera, L. Laberge, J. Rousell,
Tetrahedron Lett. 1986 27 279
206. R.J. Giguere, T.L. Bray, S.M. Duncan, G. Majetich, Tetrahedron Lett. 1986 27
4945
241
207. A.K. Bose, B.K. Banik, N. Lavlinskaia, M. Jayaraman, M.S. Manhas, Chemtech
1997 27 18
208. Y. Li, W. Yang, J. Membrane Sci. 2008 316 3
209. C.S. Cundy, Collect. Chech. Chem. Commun. 1998 63
210. A. Arafat, J.C. Jansen, A.R. Ebaid, H. Vanbekkum, Zeolites 1993 13 162
211. Ch. G. Wu, T. Bein, Chem. Comm. 1996 925
212. M. Bandyopadhyay, H. Gies, C. R. Chimie 2005 8 621
213. T. Jiang, Y. Tang, Q. Zhao, H. Yin, Colloids & Surfaces A 2008 315 299
214. H. Mi, S.-S. Dae, S. Kim, Y.-K. Park, S.-E. Park, Res. Chem. Intermediates 2000 26
283
215. L.F. Yin, F.F. Wang, J.Q. Fu,, Materials Letters 2007 61 3119
216. B. L. Newalkar, S. Komarneni, H. Katsuki, Chem. Comm. 2000 2389
217. B.L. Newalkar, S. Komarneni, Chem. Mater. 13 2001 4573
218. B. L. Newalkar, S. Komarneni, Chem. Comm. 2002 1774
219. K. Szczodrowski, B. Prélot, S. Lantenois, J. Zajac, M. Lindheimer, D. Jones, A.
Julbe, A. van der Lee, Microporous Mesoporous Mater. 2008 110 111
220. Y. K. Hwang, J.-S. Chang, Y.-U. Kwon, S.-E. Park, Microporous Mesoporous
Mater. 2004 68 21
221. S. Eko, A. Prasetyanto, S.-Ch. Lee, S.-E. Park, Microporous Mesoporous Mater.
2009 118 134
222. M.C.A. Fantini, J.R. Matos, L.C. Cides da Silva, L.P. Mercuri, G.O. Chiereci, E.B.
Celer, M. Jaroniec, Mater. Sci.Eng B 2004 112 106
242
223. G.A. Tompsett, W.C. Conner, K.S. Yngvesson, Chem. Phys. Chem 2006 7 296
224. H.I. Lee, J.H. Kim, S.H. Joo, H.Chang, D. Seung, O.-S. Joo, D.J. Suh, W.-S. Ahn,
Ch. Pak, J.M. Kim, Carbon 2007 45 2851
225. T. Jiang, W. Shen, Y. Tang, Q. Zhao, M. Li, H. Yin, Applied Surface Science 2008
254 4797
226. S.-E. Park, J.-S. Chang, Y. K. Hwang, D.S. Kim, S. H. Jhung, J.S. Hwang,
Catalysis Surveys Asia 2004 8 91
227. D.-J. Kim, J.-S. Chang, W.-S. Ahn, G.-W. Kang, W.-J. Cheong, Chem. Letters 2004
33 422
228. S. Guan, S. Inagaki, T. Ohsuna, O. Terasaki, J. Am. Chem. Soc. 2000 122 5660
229. S.S. Yoon, W.-J. Son, K. Biswas, W.-S. Ahn, Bull. Korean Chem. Soc. 2008 29 609
230. G. Smeulders, V. Meynen, G. Van Baelen, M. Mertens, O.I. Lebedev, G. Van
Tendeloo, B.U.W. Maes, P. Cool, J. Mater. Chem. 2009 19 3042
231. S.G. Deng, Y.S. Lin, J. Mater. Sci. Letters 1997 16 1291
232. K.J. Rao, B. Vaidhyanathan, M. Ganguli, P.A. Ramakrishnan, Chem. Mater. 1999
11 882
233. B. Tian, X. Liu, Ch. Yu, F. Gao, Q. Luo, S. Xie, B. Tu, D. Zhao, Chem. Comm
2002 1186
234. M. Nuechter, U. Mueller, B. Ondruschka, A. Tied, W. Lautenschlaeger, Chem. Eng.
Technol., 2003 26 1207
235. B. L. Newalkar, S. Komarneni, U.T. Taruga, H. Katsuki, J. Mater. Chem. 2003 13
1710
243
236. M. Nuechter, B. Ondruschka, Molecular Diversity 2003 7 253
237. N.S. Wilson, G.P. Roth, Current Opinion in Drug Discovery & Development 2002
5 620
238. M. Nuechter, B. Ondruschka, W. Bonrath, A. Gum, Green Chem. 2004 6 128
239. K. Adachi, T. Iwamura, Y. Chujo, Polymer Bulletin 2005 55 309
240. W. Guo, X. Li, X.S. Zhao, Microporous Mesoporous Mater. 2006 93 285
241. R. Hoogenboom, U.S. Schubert, Macromolecular Rapid Commun. 2007 28 368
242. S.-E. Park, Sujandi, Current Applied Physics 2008 8 664
243. S.-E. Park, E.A. Prasetyanto, Topics in Catalysis 2009 52 91
244. K. Walczak, I. Nowak, Catalysis Today 2009 142 293
245. M. Inada, A. Nishinosono, K Kamada, N. Enomoto, J. Hojo, J. Mater Sci. 2008 43
2362
246. A. Lew, P.O. Krutzik, M.E. Hart, A.R. Chamberlin, J. Comb. Chem. 2002 4 95
247. K. Kacprzak, Synthetic Commun. 2003 33
248. G. Chen, W. Wang, A.S. Mujumdar, Chemical Eng. Sci. 2001 56 6823
249. D. V. Kuznetsov, V. A. Raev, G. L. Kuranov, O. V. Arapov, R. R. Kostikov,
Russian J. Org. Chem. 2005 41 1719
250. C. O. Kappe, Angewandte Chemie 2004 43 6250
251. A. de la Hoz, A. Díaz-Ortiz, A. Moreno, Chem Soc Rev. 2005 34 164
252. M. Larhed, A. Hallberg, Drug Discovery Today 2001 6 406
253. F. Mavandadi, P. Lidstrom, Current Topics in Medicinal Chemistry 2004 4 7 773
254. B. Wathey, J. Tierney, P. Lidström, J. Westman, Drug Discovery Today 2002 7 373
244
255. R. Hoogenboom, T.F.A. Wilms, T. Erdmenger, U.S. Schubert, Australian J. Chem.
2009 62236
256. V. Polshettiwar, R.S. Varma, Acc. Chem. Res. 2008 41 629
257. V. Polshettiwar , M.N. Nadagouda, R.S. Varma, Australian J. Chem. 2009 62 16
258. S.-E. Park, J.-S. Chang, Y.K. Hwang, D.S. Kim, S.H. Jhung, J.S. Hwang, Catalysis
Surveys Asia 2004 8 91
259. K.Orrling, P. Nilsson, M.Gullberg, M.Larhed, Chem. Commun. 2004 790
260. B.N. Pramanik, U.H. Mirza, Y.H. Ing, P.L. Bartner, P.C. Weber, A.K. Bose, Protein
Science 2002 11 2676
261. T. Maugard, D.Gaunt, M.D. Legoy, T. Besson, Biotechnology Letter 2003 25 623
262. Y.C Tsai, B.A.Coles, R.G. Compton, F. Marken, J. Am. Chem. Soc. 2002 124
9784
263. A. Khan, S.Hecht, Chem. Commun. 2004 300
264. D. Bogdal, P. Penczek, J.Pielichowski, A. Prociak, Adv. Polymer Sci. 2003 163 193
265. E.B. Celer, M. Jaroniec, J. Am. Chem. Soc. 2006 128 14409
266. B.E. Grabicka, M. Jaroniec, Adsorption 2010 16 385
267. B.E. Grabicka, M. Jaroniec, Microporous Mesoporous Mater. 2009 119 674
268. B.E. Grabicka, M. Jaroniec, Microwave-assisted synthesis and characterization of
mesoporous organosilicas with ureidopropyl and mercaptopropyl groups. 2010, in
preparation
245
269. B.E. Grabicka, M. Jaroniec, Microwave-assisted co-condensation synthesis and
adsorption properties of vinyl-modified mesoporous organosilicas. 2010, in
preparation
270. B.E. Grabicka, M. Jaroniec, Adsorption properties and characterization of
mesoporous organosilicas with large isocyanurate bridging groups synthesized
under microwave irradiation. 2010, in preparation
271. K.S.W. Sing, D.H. Everett, R.A. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol, T.
Siemieniewska, Pure Appl. Chem. 1985 57 603
272. S.J. Gregg, K.S.W. Sing, Adsorption, Surface Area and Porosity. Academic Press,
London, 1982
273. J. Roquerol, D. Avnir, C.W. Fairbridge, D.H. Everett, J.H. Hayness, N. Pernicone,
J.D.F. Ramsay, K.S.W. Sing, K.K. Unger, Pure Appl. Chem. 1994 66 1739
274. S. Brunauer, P.H. Emmet, E. Teller, J. Am. Chem. Soc. 1938 60 09
275. M. Kruk,M. Jaroniec, A. Sayari, Langmuir 1997 13 6267
276. E.P. Barrett, L.G. Joyner, P.P. Halenda, J. Am. Chem. Soc. 1951 73 373
277. M. Kruk, V. Antochshuk, J.R. Matos, L.P. Mercuri, M. Jaroniec, J. Am. Chem.
Soc. 2002 124 168
278. J.R. Matos, M. Kruk, L.P. Mercuri, M. Jaroniec, L. Zhao, T. Kamiyama,O.
Terasaki, T.J. Pinnavaia,Y. Liu, J. Am. Chem. Soc. 2003 125 821
279. M. Jaroniec, L.A. Solovyov, Langmuir 2006 22 6757
280. P.F. Fulvio, R.M. Grudzien, B.E. Grabicka, M. Jaroniec, to be submitted
246
281. R.M. Grudzien, B.E. Grabicka, O. Olkhovyk, M. Jaroniec, J.P. Blitz, Nanoporous
Materials (A. Sayari and M. Jaroniec, eds), World Scientific Publ. Co., Singapore,
2008 665
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