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Chemisorption of hydrogen sulfide on halloysite-based porous clay heterostructures modified with potassium permanganate.

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Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
Published online 9 July 2010 in Wiley Online Library
( DOI:10.1002/apj.473
Research article
Chemisorption of hydrogen sulfide on halloysite-based
porous clay heterostructures modified with potassium
Zhenxiang Lu, Zheng-Hong Huang and Feiyu Kang*
Laboratory of Advanced Materials, Department of Material Science and Engineering, Tsinghua University, Beijing 100084, China
Received 30 January 2010; Revised 18 May 2010; Accepted 18 May 2010
ABSTRACT: Hydrogen sulfide gas is harmful to human health and causes corrosion of electronic devices, when it
is present in indoor air. Porous clay heterostructures (PCHs) provide a new type of material for catalysis, adsorptive
separations and as H2 S sensors because their large pores allow access to their active interiors. PCHs posses a large
adsorptive surface area (400–900 m2 g−1 ) and a unique combination of micro- and mesoporosity. In this work, PCHs
were synthesized by the polymerization of tetraethoxysilane (TEOS) in the micelles, which were assembled by mixing
tubular halloysite powders and cetyltrimethylammonium bromide (CTMAB). Both as-synthesized PCHs and pristine
halloysite were impregnated with KMnO4 by equal-volume mixing to obtain chemosorbents. The mass percentages
of KMnO4 ranged from 5 to 30 wt%. The samples were characterized by using N2 adsorption, X-ray diffraction
(XRD), diffuse reflectance ultraviolet–visible (UV–Vis) spectroscopy, transmission electron microscope (TEM) and
infrared spectroscopy. The dynamic adsorption of the chemosorbents for hydrogen sulfide was evaluated with a fixed
bed. The results show that the PCH-based chemosorbents exhibit better H2 S breakthrough performance due to their
rich porous structure, the samples with 15–20 wt% KMnO4 possessing the highest activity. This study shows that
the KMnO4 /PCH chemosorbents can effectively remove H2 S from indoor air at room temperature.  2010 Curtin
University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: chemosorbent; powder characterization; hydrogen sulfide; porous clay heterostructures; halloysite
Hydrogen sulfide gas is especially detrimental to human
health and causes corrosion of electronic devices, when
it is present in indoor air.[1 – 3] Removal of H2 S from
a gas stream could be accomplished by adsorption onto
a solid surface, catalytic oxidation and absorption using
a liquid solution. Various materials have been developed to capture H2 S from a great amount of industrial
gas effluent streams.[4 – 7] However, all of these materials have disadvantages for indoor air purification, even
they possess high removal capacity. For example, activated carbons with high B-E-T (Brunauer, Emmett,
Teller) surface area are costly, and the catalytic oxidation materials[8] and liquid solution could cause secondary pollution after invalidation.
The discovery of porous clay heterostructures (PCHs)
provides a new type of candidate for catalysis, separation and sensor because their large pores enable the
active centers to be accessible. Moreover, PCHs are
*Correspondence to: Feiyu Kang, Department of Material Science
and Engineering, Tsinghua University, Beijing 100084, China.
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Curtin University is a trademark of Curtin University of Technology
alternative adsorbents due to their large external surface
area (400–900 m2 g−1 ) and the unique combination of
micro- and mesoporosity. Zhu et al .[9] used bentonite
to obtain PCH with a BET surface area of 690 m2 g−1
and a total pore volume of 0.27 cm3 g−1 . Tchinda and
Ngameni et al .[10] used smectite clays to obtain PCH
with a BET surface area of 773 m2 g−1 and a total pore
volume of 0.56 cm3 g−1 . As a typical kind of kaolin
clay mineral, halloysite possesses naturally occurring
microtubes, mined in Brazil, China, France, Japan and
Korea.[11] It contains many types of water molecules
within its structure and has a regular tubular morphology. Halloysite occurs mainly in two different polymorphs, the hydrated form with the minimal formula
Al2 Si2 O5 (OH)4 ·2H2 O and the dehydrated form with
the minimal formula Al2 Si2 O5 (OH)4 , being identical to
kaolinite.[12] Due to structural mismatch between the
siloxane and the gibbsite layers, the most common morphology of halloysite is a more or less ordered curled
empty nano scroll, exposing the oxygen planes to the
outer surface.[13] For the particular structure and good
adsorption ability, halloysite has recently been used to
synthesize many nanocomposites.[14,15]
Asia-Pacific Journal of Chemical Engineering
Figure 1. Scheme of H2 S breakthrough testing system: (1) mass flow controller;
(2) one-way valve; (3) isothermal water bath; (4) gas mixer; (5) tubular reactor;
(6) drying chamber; (7) gas MultiCheck 2000 and (8) data logger.
In this work, halloysite with tubular structure was
used as the raw material to synthesize PCHs. To
improve the chemical adsorption for H2 S, both pristine
halloysite and halloysite-based PCHs were impregnated
with KMnO4 . The H2 S breakthrough test was used to
measure the capability of these materials. As expected,
the KMnO4 /PCH chemosorbents exhibit better performance in removing H2 S.
by mixing the PCH powders with KMnO4 solid. Then
the distilled water was added into the mixture under
continuous stirring. The mixed powders were dried at
room temperature to obtain chemosorbents, which were
designated as PCH-x -y% (y means the percentage of
KMnO4 ).
Similarly, the halloysite-based chemosorbents were
prepared by mixing the halloysite powders with KMnO4
solid, following the same process as described in
the previous paragraph. The products were denoted
as halloysite-y (e.g. halloysite-15% means 15 wt%
KMnO4 ).
Preparation of halloysite-based PCHs
The halloysite powders, which were produced by Hunan
Xiangwei Kaolin Co. Ltd., China and purified according
to the reported process,[11] were stirred in 2 mol l−1
HCl for 3 h, and then the sample was separated from
the solution by filtration and washed three times with
distilled water to pH 7. Subsequently, the powders were
dried at 105 ◦ C and then were grounded sufficiently to
pass a 200 mesh sieve.
The fine powders were then added into the 120 ml
solution composed of tetraethylorthosilicate (as the
solvent), cetyltrimethylammonium bromide (CTMAB)
and dodecylamine (C12 H25 NH2 ) with a mass ratio of
halloysite: CTMAB: dodecylamine of 10: x : 5 (x = 0.5,
1, 2). The mixture was allowed to react for 4 h at 60 ◦ C
under continuous stirring. After reaction, the modified
clay was separated by centrifugation. The powders
were dried at room temperature and then calcined at
550 ◦ C for 6 h. Three kinds of PCH samples were
synthesized and referred to as PCH-0.5, PCH-1 and
PCH-2 according to the amount of CTMAB used. When
x = 1, the samples calcined at 350 and 550 ◦ C for
X-ray diffraction (XRD) and Fourier transform infrared
(FTIR) test were named PCH-1-350 and PCH-1-550.
H2 S breakthrough test
A dynamic lab-scale test was carried out to evaluate
the capacity of chemosorbents for H2 S removal and the
schematic diagram is shown in Fig. 1. A given volume
of samples was packed into a glass reaction tube (outside diameter of 11 mm). A gas mixture (containing 100
ppmv H2 S, balance of N2 ) passed through the reactor
and the gas flow rates were controlled at 500 ml min−1
by a mass flow controller system. The inlet and outlet
gases were analyzed by Gas Monitor MultiCheck 2000
(Quest Technology Co. Miami, Florida, USA). All outlet gases from the reactor were sampled with an online
analysis system at every minute. The test was terminated when the outlet concentration was 10 ppmv. The
breakthrough time was defined as the time from the
beginning of the adsorption process to the time when
the H2 S concentration at the outlet reached 1 ppmv. The
exhausted samples after this test are designated with the
additional letter ‘A’.
Samples characterization
Preparation of chemosorbents
Both PCHs and halloysites-based chemosorbents were
prepared. The PCH-based chemosorbents were prepared
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
The powder XRD patterns were obtained with a Japan
Rigaku D/max-RB diffract meter employing Cu Kα
radiation (λ = 1.5418 Å). The X-ray tube was operated at 40 kV and 120 mA. The continuous scan was
Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
performed at 0.02◦ intervals in the range of 10◦ ≤ 2θ ≤
70◦ with a scanning velocity of 2◦ min−1 . The crystal
phase was identified with the help of the JCPDS cards.
FTIR spectra of halloysite, PCH-1-350 and PCH-1-550
were obtained using 2 cm−1 resolution with a Nicolet Avatar 360 FTIR spectrometer using KBr pellets in
transmission mode. TEM images (JEOL 2010F) were
taken to observe halloysite and halloysite-20%. X-ray
photoelectron spectroscopy (XPS) analysis (PHI Quantera) was taken to observe PCH-1-20%-A.
Measurement of potassium permanganate
The various chemosorbents were evaluated by
absorbance at 522 nm[16] using a UV-2450 (Shimadzu
ultraviolet–visible (UV–Vis) spectrophotometer). Halloysite, PCH-x , PCH-1-C and PCH-1-C-A were measured for calculating the consumption rate of potassium
permanganate on the various carriers.
Figure 2. XRD spectra of halloysite PCH-1-350 and PCH1-550.
N2 adsorption measurements
The N2 adsorption–desorption isotherms of halloysite,
PCH-x and PCH-x -y were measured at −196 ◦ C by
using an ASAP 2020 automated gas adsorption system.
The surface areas were calculated using the BET
equations. The pore-size distributions and pore volume
were obtained using the adsorption branch of the N2
isotherms based on the B-J-H (Barrett, Joyner, Halenda)
Characterization of various samples
The structure change of halloysite after heat treatment is shown in Fig. 2. Actually, the halloysite is
a mineral that contains some Al(OH)3 ·3H2 O to be
helpful for tubular structure formation. The dehydration of Al(OH)3 ·3H2 O crystal in clay started at 300 ◦ C
and completed at 550 ◦ C. The disappearance of (002)
diffraction peak in halloysite and PCH-1-350 is an
indicator of the dehydration of Al(OH)3 ·3H2 O. With
increasing heat treating temperature, the diffraction
peaks of PCH-1-550 disappeared, revealing an amorphous structure in PCH-1-550.[18] It should be pointed
out that all the PCH materials tested have amorphous
structures. Dehydration destroyed tubular structure of
halloysite,[19] thus resulting in a higher BET surface
area of the PCH-1-550. FTIR spectra (Fig. 3) confirmed
the organo-silica nature of the materials.[20] Peaks at
around 1630–1650 cm−1 and 3408–3468 cm−1 are
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 3. FTIR spectra for halloysite PCH-1-350 and PCH1-550.
assigned to H–O–H and O–H vibrations due to the
presence of water molecules. In addition, νSiOSi , νSiOAl
and νAlOAl modes in the range of 800–1200 cm−1 give
reliable information on the local structure of PCH-1-350
and PCH-1-550.[20]
On the other hand, PCHs are constructed by selfassembly of silica framework around surfactant micelles
intercalated within the galleries of the phyllosilicate
host. CTMAB intercalated in the interlayer region after
the addition of the silicate source tetraethoxysilane
(TEOS),[21] which play a role of surfactant and template in the synthesis process.As the amount of CTMAB
could affect the dispersity of halloysite, an increase
of CTMAB on the clay surface would form a higher
density bound organic phase above the monolayer
Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Table 1. Pore structure parameters of halloysite, PCH,
PCH-1-20% and PCH-1-20%-A.
area (m2 g−1 )
pore volume
(cm3 g−1 )
The exhausted samples after H2 S adsorption.
Figure 5. Pore-size distributions of various chemosorbents.
Figure 4. TEM images of halloysite (a) and halloysite-20%
coverage.[22] When the initial surfactant concentration was higher than the critical micelle, in the clay
interlayer, the available space to accommodate the
organic sorbates (such as TEOS) reduced greatly, the
densely packed surfactants could not expand as freely as
the loosely packed ones.[23] As a result, the organic sorbates (TEOS) could not penetrate into the dense organic
phase easily.[23] Hence, it is reasonable that the PCH-0.5
achieved a lower BET surface area of 126 m2 g−1 . For
PCH-2, the surfactants were excessive, so that it got a
BET surface area of 612 m2 g−1 , which was lower than
the surface area of PCH-1 (672 m2 g−1 ).
There are similar changes for the pore structure
of PCH-based chemosorbents after H2 S adsorption/
oxidation. The typical samples are summarized in
Table 1. The BET surface area and the total pore
volume of PCH-1 are 672 m2 g−1 and 1.04 cm3 g−1 ,
respectively, which are much higher than those of
halloysite (67 m2 g−1 and 0.25 cm3 g−1 ). The increase
of BET surface area and total pore volume is caused by
the chemical modification with surfactants and TEOS on
halloysite.[20] The higher surface area and pore volume
can give a good opportunity for KMnO4 to load on
PCH-1. The loading of KMnO4 results in a sharp
decrease of surface area and pore volume of PCH-1
in comparison with halloysite. It is seen from TEM
observation (Fig. 4) that KMnO4 particles were loaded
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
in the nanometer-sized tubular structure of halloysite,
which was different from PCH. Moreover, PCH-based
chemosorbent exhibits a sharp decrease of pore volume
after reaction, revealing a high activity of KMnO4
loaded on PCHs.
Because of the neutral amines with long chain (dodecylamine), the PCHs prepared from halloysite possess
a large pore size (with an average pore diameter of
11.9 nm).[24] However, the pores of 3–4 nm play an
important role in KMnO4 dispersion, as shown in Fig. 5.
Especially, an obvious difference in the pore sizes
of PCH-1-20% and PCH-1-20%-A is found, suggesting that the pore entrances and the pores are partially
blocked by KMnO4 loaded on the support. Similarly,
the mesopores in SBA-15 were plugged by FeO particles, which caused the decrease in surface area and
pore volume.[25] In addition, from the sharp decrease of
pore volume after reaction (from 0.58 to 0.06 cm3 g−1 )
and the decrease of pore volume in pores of 3–4 nm
(Fig. 5), it could be inferred that KMnO4 particles in the
pores of 3–4 nm have an effect on the removal of H2 S.
H2 S breakthrough in the bed packed with
Various chemosorbents, halloysite-20%, PCH-0.5-20%,
PCH-1-20% and PCH-2-20% were used for the removal
of H2 S. The breakthrough curves are shown in Fig. 6
(each measurement was done at least twice). The
PCH chemosorbents exhibit better H2 S breakthrough
performance than the halloysite chemosorbent due to
their high BET surface areas. Similarly, PCH-0.5-20%
exhibits lower activity of H2 S removal than PCH-120% and PCH-2-20% due to its lower BET surface area.
Hence, the porous structure of the carrier is important
for H2 S removal.
Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Figure 6. H2 S breakthrough curves of 20 wt% KMnO4 /
PCH-x (x = 0.5, 1, 2) mass of the adsorbents were 0.5 g,
the height of samples from PCH-0.5 to PCH-2 were 1.2 cm,
the halloysite sample was 0.6 cm.
Apart from the BET surface area, the oxidant character is another important factor affecting the performance
of the chemosorbents. The gas–solid reactions at room
temperature mainly occur in a thin hydrated lattice of
metal oxides. It is reported that the removal of H2 S by
metal ions modified sludge-derived materials happens
not only on the surface of porous carbon but also on
the surface of metal oxides or carbonates.[26 – 29] H2 S
oxidation reactions occur simultaneously on the carriers and oxides surfaces, with the formation of elemental
sulfur, metal sulfides and sulfuric acid. When using
the KMnO4 -impregnated-PCHs for the removal of H2 S,
the potassium permanganate functions as the oxidizing
agent and the PCHs could give the site for chemical
reactions between potassium permanganate and hydrogen sulfide. As a carrier to support oxidant, PCHs are
more stable than carbon materials.[29]
After H2 S adsorption/oxidation, the surface areas and
the pore volumes of the chemosorbents are significantly
decreased. For example, the PCH-1-20% sample now
has a surface area of 260 m2 g−1 and a pore volume
of 0.58 cm3 g−1 ; whilst the PCH-1-20%-A sample has
a surface area of 26 m2 g−1 and a pore volume of
0.06 cm3 g−1 after the adsorption/oxidation (Table 1).
This indicates that the pores are active centers during
the adsorption/oxidation process. It should be noted
that the pore volume of halloysite-20% dropped not
so significantly after H2 S adsorption. This is because
halloysite has fewer pores than PCH, resulting in less
KMnO4 loading in the pores (Table 1). Assuming that
sulfur is the oxidation product deposited in these pores,
Bagreev et al .[27] calculated the volume of deposited
sulfur (density assumed to be 2 g cm3 ) based on the
amount of hydrogen sulfide adsorbed and found that
the decrease in the micropore volume (and the total
pore volume) was less than the calculated volume of
sulfur. This indicates that not all the pores of this sample
were completely filled with the oxidation product. It is
clearly seen (Fig. 5) that after H2 S adsorption almost all
the micropores disappeared; the volume of mesopores
decreases but not as dramatically as the micropores.
In fact, the reaction with the oxidant can be confirmed
by the XPS characterization for PCH-1-20%-A (Fig. 7).
The binding energies of Mn 2p3/2 and Mn 2p1/2 are
643.5 and 655.4 eV, indicating the Mn2+ and Mn4+
state. And the binding energy of S 2p is 169.5 eV
indicating definitely the SO4 2− , which indicates that
H2 S gas is oxidized to SO4 2− . The reaction with the
oxidant could be described as 2(KMnO4 ) + (H2 S) =
(K2 SO4 ) + (MnO) + (MnO2 ) + 2(H2 O).[26]
Furthermore, the content of KMnO4 also affects the
H2 S breakthrough capacity, as shown in Fig. 8. The
samples with 15–20 wt% KMnO4 exhibit higher capacity, which is attributed to the well dispersion of KMnO4 ,
compared to the samples with 5, 10 wt% KMnO4
which show lower capacity due to the less KMnO4
content. KMnO4 can also be detrimental to the H2 S
Figure 7. XPS spectra of Mn 2p (a) and SO42− (b) for PCH-1-20%-A.
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
total area for reaction with H2 S. It can be seen in
Fig. 9 that the halloysite-5% behaves worse than others, but the difference between halloysite-10% and 15%
is not obvious because the 15 wt% KMnO4 on halloysite is excessive. Note that not all the capacities
of KMnO4 /PCHs (Fig. 8) are higher than those of
KMnO4 /halloysite (Fig. 9). This is because the weight
of KMnO4 /PCHs is only 0.5 g but KMnO4 /halloysite is
1 g at the same bed height due to the lighter PCHs.
The consumption rate of potassium
permanganate in chemosorbents
Figure 8. H2 S breakthrough curves of C wt% KMnO4 /
PCH-1 (C = 30, 20, 15, 10, 5) mass of the adsorbents were
0.5 g, the height of samples was 1.2 cm.
Figure 9. H2 S breakthrough curves of C wt% KMnO4 /
halloysite (C = 15, 10, 5) mass of the adsorbents were 1 g,
the height of samples was 1.2 cm.
breakthrough capacity if its content is too high. For
example, the PCH-1-30% behaves not so effectively
because the excessive oxidants restrain the adsorption
of H2 S onto chemosorbents, which could be confirmed
by the pore-size distributions of PCH-1-30% before
and after reaction as shown in Fig. 5. Nguyen et al .[30]
compared different oxidants for removing H2 S on clay
materials. Their results showed that the excessive oxidants resulted in the destruction of micropores and the
formation of large clusters. Similarly, in the modifiedPCH samples, an excessive quantity of potassium permanganate in PCHs has negative effect on removing
H2 S. Too much potassium permanganate reduced the
 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
To understand the role of KMnO4 in chemosorbents,
the consumption rate was calculated from the KMnO4
content change in the chemosorbents after reaction.
The KMnO4 consumption rate and H2 S breakthrough
time are summarized in Table 2. The KMnO4 contents
by testing in various chemosorbents are also listed in
Table 2. The performances of these samples are influenced by the initial KMnO4 content and the consumption rate. The PCH-1-20% possessed the longest breakthrough time depending on its higher consumption rate
and the KMnO4 initial content. However, the PCH-130% has a lower capacity with the highest KMnO4
initial content due to its lower consumption rate. Thus,
there is a balance between the KMnO4 initial content
and the consumption rate, which could affect the H2 S
removal performance. The optimum loading range of
KMnO4 was 15–20 wt% in the present study. Similarly,
for zinc oxide modified aluminum-substituted SBA-15
with a different Zn content from 0.8 to 15.8 wt%, 2.1
wt% is the suitable amount but excessive additive content is detrimental to the performance.[31]
Generally, if the KMnO4 content is lower and the
BET surface area of carrier is higher, the consumption
rate is higher. The KMnO4 particles on carrier can
be smaller. Nano-sized oxidant particles can bring a
catalytic effect besides a high active oxidation, which
explains why samples with a lower KMnO4 content,
such as the PCH-15% sample, also shows a remarkable
activity in H2 S removal.
PCHs with higher BET surface areas and total pore volumes can be obtained based on mineral halloysite. The
as-synthesized PCHs and halloysite were modified with
KMnO4 to obtain chemosorbents for the removal of
H2 S. The loading of KMnO4 causes a marked decrease
of surface area and pore volume but increases the breakthrough capacities of samples. KMnO4 particles in the
pores play an important role in removing H2 S. Thus, the
Asia-Pac. J. Chem. Eng. 2011; 6: 879–885
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
Table 2. The consumption rate of KMnO4 on various chemosorbents and H2 S breakthrough time.
KMnO4 (wt%)
(before reaction)
KMnO4 (wt%)
(after reaction)
Consumption rate
of KMnO4 (%)a
H2 S breakthrough
time (min)
Consumption rate of KMnO4 = 1 – wt% KMnO4 (after reaction)/wt% KMnO4 (before reaction).
KMnO4 /PCHs show higher H2 S breakthrough capacity for their rich porous structure. Nevertheless, excessive KMnO4 are unfavorable for removing H2 S and
thus there is a balance between KMnO4 initial content
and consumption rate. It suggests that the PCH-based
chemosorbents with 15–20% KMnO4 are effective for
indoor H2 S removal.
The authors thank the Financial Support of National
High Technology Research and Development Program
of China (863 Program) (No. 2007AA061405), and the
help and suggestion from Professor Xiuyun Chuan of
Peking University in China.
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DOI: 10.1002/apj
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base, hydrogen, porous, sulfide, potassium, permanganate, clay, halloysite, modified, heterostructures, chemisorption
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