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j.mcat.2018.07.026

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Molecular Catalysis 458 (2018) 33–42
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
RuC@g-C3N4(H+)/TiO2 visible active photocatalyst: Facile fabrication and
Z-scheme carrier transfer mechanism
T
⁎
Ke Genga, Ye Wub, Guodong Jianga, , Kailai Liua, Linlin Jianga
a
b
College of Materials Science and Engineering, Nanjing Tech University, Nanjing, 210009, China
School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
A R T I C LE I N FO
A B S T R A C T
Keywords:
Heterojunction
Photocatalyst
Ruthenium complexes
Active species
Z-scheme
The protonated g-C3N4 bonded with ruthenium complexes as photosensitizer, and then was loaded on TiO2 to
form RuC@g-C3N4(H+)/TiO2 by solvothermal method. The morphology and structure of photocatalyst were
characterized by high-resolution transmission electron microscopy (HRTEM) with element mapping, X-ray
diffraction (XRD) and (BET) surface area measurements. The chemical composition was analyzed by X-ray
photoelectron (XPS) and Fourier transform infrared (FTIR). Photoluminescence (PL) emission intensity was
employed to determine the separation efficiency of photogenerated electron-hole pairs. The results suggested
that the protonation of g-C3N4 could improve both photocatalytic performance of g-C3N4 and the content of
ruthenium complexes loaded on the g-C3N4(H+) by 1.33 times that for the g-C3N4(without protonation). Thus,
the photocatalytic kinetic constant k of optimal RuC@g-C3N4(H+)/TiO2 (N16-1) was enhanced 1.7 times than
that of RuC@g-C3N4/TiO2 (G12-1) without protonated treatment. Through analyzing three scavengers for BQ, tBuOH, and EDTA-2Na trapping active species of the %O2−, h+ and %OH respectively in MB aqueous solution
during light irradiation, the transfer of photogenerated electron-hole of g-C3N4(H+)/TiO2 hybrids could be
described as classic Z-scheme photocatalytic mechanism, and further confirmed that the ruthenium complexes,
performing as a pump to transfer electron, could improve effectively the separation of photogenerated electronhole. The main significance of this paper is providing analysis of photogenerated electron-hole pairs transfer
through scavenging active species in aqueous solution, and working mechanism of photosensitizer.
1. Introduction
Recently, the semiconductor heterojunction photocatalyst has attracted great attention [1,2]. Especially, the g-C3N4/TiO2 hybrids, as a
non-toxic raw material, easily synthesized, cheap and matched well in
energy level, were explored in the removal of organics in aqueous phase
[3–5]. Several strategies have been employed to improve the separation
of photogenerated electron-hole including fabricating heterojunction
between g-C3N4 and TiO2 [6–8], doping foreign atom in g-C3N4 and
TiO2 [9], and photosensitizer sensitizing [10]. W. A. Daoud et al. [11]
using the copper(II) porphyrin as a photosensitizer synthesized the
Copper(II) Porphyrin/TiO2; W. Lu et al. [12] prepared the zinc phthalocyanine-sensitized g-C3N4; P. Elizondo et al. [13] synthesized the Ru
(II) polyaza complexes modified TiO2 materials; Jiang et al. [14] had
reported a strategy through the minor amount of ruthenium complexes
sensitizing g-C3N4/TiO2 hybrid, which all exhibited the more excellent
photocatalytic characteristics degradation. In addition, Zhang et al.
[15] described the activation of g-C3N4 by a convenient protonation in
⁎
concentrated HCl, which was found that H2 production efficacy of the
protonactivated g-C3N4 in visible light could increase.
All the time, there have been two charge transfer modes for heterojunction photocatalyst. One mode is that the stimulated electrons
jump from the VB to the CB, leaving behind positive holes on the VB. In
the presence of an electric field, there exists a force to drive the electrons from the CB of one semiconductor to a more positive CB of another semiconductor, while holes oppositely move to one with a more
negative VB, such as Kumar et al. [16] synthesized the g-C3N4-CaTiO3
heterojunction photocatalyst. Li et al. [17] prepared the carbon
quantum dots modified porous g-C3N4/TiO2 nano-heterojunctions.
Tonda et al. [18] developed 2D/2D g-C3N4/NiAl-LDH hybrid heterostructures. Wei et al. [19] obtained the TiO2/g-C3N4 hybrid heterostructure thin film and so on. By contrast, another mode (Z-scheme
type) is that the electrons transfer directly from the CB of one semiconductor to the VB of another semiconductor, such as K. Maeda and
co-workers [20–22] constructed the g-C3N4 coupled with a binuclear Ru
(II) complex Z-scheme photocatalyst. Tang et al. [23] reported the Z-
Corresponding author.
E-mail address: gdjiang@njtech.edu.cn (G. Jiang).
https://doi.org/10.1016/j.mcat.2018.07.026
Received 23 June 2018; Received in revised form 25 July 2018; Accepted 26 July 2018
2468-8231/ © 2018 Elsevier B.V. All rights reserved.
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
above reaction mixture and then refluxing methylbenzene for 12 h,
while the formyl chloride would react with the amino groups of g-C3N4.
Finally, the desired [Ru(4,4′-dicarboxy-2,2′-bipyridine)3]Cl2@gC3N4(H+) (RuC@g-C3N4(H+)) was obtained by distillation of the methylbenzene and sequentially washed for several times with water and
ethanol. The schematic of RuC@g-C3N4(H+) is shown in Fig. S2 of
Supplementary material. In addition, the RuC@g-C3N4 without activated treatment was prepared by the same method.
scheme TiO2/g-C3N4 Nanofibers. Tateishi et al. [24] developed a Zscheme g-C3N4/tetrahedral Ag3PO4 hybrid. Wu et al. [25] synthesized
the Z-scheme g-C3N4-RGO-TiO2 and so on. The two kinds of movement
modes all can effectively separate the electrons and holes so as to decrease the recombination rate of the electron-hole pairs [26–29].
However, most of these published papers have insufficient evidence to
confirm why they select one of the modes [30]. Even now there has
been a useful method of electronic spin resonance (ESR) spectroscopy
to detect reactive species with one unpaired electron, it cannot directly
track reactive species of aqueous solution during photocatalytic process
[31]. Some of literatures have reported utilization of some compounds
as detecting molecular of specified reactive species due to extremely
high reactive rate, such as Buxton et al. [32] reported the tert-Butanol
(t-BuOH) as the %OH radical scavenger with high reaction rate constant
of 6.0 × 10−8 M-1S-1. Palominos et al. [33] used the benzoquinone
(BQ) as the scavenger to trap the superoxide radicals (%O2−). Zhu et al.
[34] reported the ethylenediaminetetraacetic acid disodium salt
(EDTA-2Na) could trap the hole. These methods on real time are really
simple and effective to observe reactive species in aqueous solution,
and can further infer to photocatalytic mechanism.
In the paper, our objectives: further improving the photocatalytic
efficiency of ruthenium complexes sensitizing g-C3N4/TiO2 hybrid basing on our previous study; exploring charge transfer mode for g-C3N4/
TiO2 hybrid; understanding the working mechanism of photosensitizer.
To achieve these goals, the activation of g-C3N4 through protonation
increased the content of ruthenium complexes loaded on the g-C3N4/
TiO2 hybrid; three scavengers for BQ, t-BuOH, and EDTA-2Na were
used to trap active species of the superoxide radicals (%O2−), holes (h+)
and hydroxyl radicals (%OH), respectively in methyl blue (MB) aqueous
solution under light irradiation, and then the charge transfer mode for
g-C3N4/TiO2 and working mechanism of photosensitizer were demonstrated clearly through analyzing the photodegradation kinetic constant
k of MB.
2.1.3. Preparation
of
[Ru(4,4′-dicarboxy-2,2′-bipyridine)3]Cl2@gC3N4(H+)/TiO2 hybrid
[Ru(4,4′-dicarboxy-2,2′-bipyridine)3]Cl2@g-C3N4(H+)/TiO2 hybrid
(RuC@g-C3N4 (H+)/TiO2) could be prepared according to the previous
synthesis procedure [14]. In brief, the designated amount of RuC@gC3N4 (H+) was dispersed into 50 mL of isopropanol with 6.8 g of tetrabutyl titanate (TBT) by ultrasonication for 30 min, and then 1.5 mL
HF (40 wt.%) was dropped into the resulting suspension solution with
stirring for 10 min. After that, the mixture was heated in the PTFE
hydrothermal reactor at 180 °C for 12 h. After the product was centrifuged and dried, the RuC@g-C3N4 (H+)/TiO2 hybrid was obtained.
According to the theory mass ratio of TiO2 to RuC@g-C3N4(H+) of 20:1,
16:1, 12:1, 8:1, and 4:1, they were denoted as N20-1, N16-1, N12-1, N81, and N4-1, respectively. The optimal g-C3N4/TiO2 hybrid without
ruthenium complexes (H12-1) and RuC@g-C3N4/TiO2 hybrid (G12-1)
without protonation of g-C3N4 were prepared according to the theory
mass ratio of TiO2 to g-C3N4 and RuC@g-C3N4 of 12:1 [14,30]. In addition, TiO2 was prepared by the same method.
2.2. Photodegradation test
The photocatalytic performances of the samples were estimated by
the photodecomposition of methyl blue (MB) under light irradiation. A
certain mass of photocatalysts was dispersed in the MB aqueous solution as shown in Fig. S3 of Supplementary Material, and then the suspensions was irradiated by a 500 W Xenon lamp with a 400 nm cut filter
(> 400 nm), whose spectrum is shown in Fig. S4 of Supplementary
material. The average distance between the light source and the liquid
in the reactor is about 3 cm, and the average visible intensity measured
by the optical power meter is about 205 mW/cm2. After every interval
of 15 min of irradiation, the concentration of MB was measured at
620 nm by UV–vis spectrophotometer (UV-3200, Mapada, China). Each
experiment repeated three times and then averaging the data.
2. Experimental
2.1. Preparation of photocatalyst
2.1.1. Protonation of g-C3N4
g-C3N4 was prepared by heating melamine at 520 °C and 550 °C for
3 h and 2 h respectively, and then was milled [30]. Sequentially, the
protonation of g-C3N4 was as follows [15]: 5 g of g-C3N4 was mixed in
50 ml HCl (37 wt.%) and stirred for 12 h at room temperature in order
to make the protonation of nitrogen of g-C3N4, and then a pale-yellow
product was separated by centrifugation. After that, the obtained paleyellow product was dispersed into 50 ml KOH aqueous solution
(0.5 mol/L) with stirring time for 30 min. The above suspension was
further centrifuged, and the precipitate was washed for several times
with deionized water to near neutral, and dried at 90 °C for overnight.
The obtained product was designated as g-C3N4(H+).
2.3. Scavenging experiment
Generally, the main superoxide radicals (%O2−), holes (h+) and
hydroxyl radicals (%OH) would be produced in the semiconductor
photocatalytic solution by light irradiation. Some compounds have
finished scavenging rapidly the %O2−, h+ and %OH before these super
active species have redox reaction with MB due to extremely high reactive rate, such as benzoquinone (BQ), Ethylenediaminetetraacetic
acid disodium salt (EDTA-2Na) and tert-Butanol (t-BuOH) [36–38].
Through a designated scavenger used to trap the corresponding active
species during the photodegradation of MB, we can infer photogenerated electron and hole transfer and working mechanism. Each
experiment was carried out three times and then the obtained data was
averaged.
2.1.2. Preparation
of
[Ru(4,4′-dicarboxy-2,2′-bipyridine)3]Cl2@gC3N4(H+)
RuCl3 containing three crystal water (2.66 mmol) and 4,4′-dicarboxy-2,2′-bipyridine (7.98 mmol) were dissolved in 40 mL aqueous
solution with 13 wt.% of HCl. The mixed solution was added to a
100 ml PTFE hydrothermal reactor at 200 °C and for 5 h. After cooling
to room temperature, a dark red precipitate was obtained, and which
was purified by recrystallization for three times in water. The dark red
precipitate could be proved as [Ru(4,4′-dicarboxy-2,2′-bipyridine)3]Cl2
(designated as RuC) through CCDC crystal library as shown in Fig. S1 of
Supplementary Material [35]. Further, the mixture of 0.1 g of RuC and
excess SOCl2 (60 mL) was refluxed for 24 h under N2 atmosphere for
[Ru(4,4′-diformyl chloride-2,2′-bipyridine)3]Cl2 and then 100 mL methylbenzene was added to the mixed solution. After removal of the
unreacted SOCl2 by distillation, 6 g of g-C3N4(H+) was added into the
3. Results and discussion
3.1. Characterizations
3.1.1. XRD analysis
Fig. 1a shows the full-range XRD patterns of g-C3N4, g-C3N4(H+),
RuC@g-C3N4(H+), N8-1, N16-1, and TiO2 by X-ray diffractometer
(SmartLabTM, Japan). The pure g-C3N4 with two typical diff ;raction
34
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
Fig. 1. XRD patterns of (a) g-C3N4, g-C3N4(H+), RuC@g-C3N4(H+), N8-1, N16-1, and TiO2; (b) enlarging view at 26.5–29.0°.
peaks at about 27.4° and 12.9° are ascribed to the (002) and (100)
crystal planes corresponding to the inter-planar stacking of conjugated
nitrogen-containing aromatic ring and in-plane repeated tri-s-triazine
units [39,40], respectively. Further, the XRD pattern of g-C3N4(H+)
shows decreased intensity of the diffraction (002) planes and almost
disappeared intensity of the diffraction (100) planes. As shown in
Fig. 1b, an obvious slightly shift of the (002) plane of g-C3N4(H+) from
27.4° to 27.7°, corresponding to the interlayer distances from 0.325 nm
to 0.320 nm, may be due to the protonation of g-C3N4 strengthening
interlayer interaction [41]. As for the TiO2, the diffraction peaks at
around 25.3°, 37.8°, 48.0°, 53.9°, 55.1°, 62.7° and 70.3° are assigned to
the (101), (004), (200), (105), (211), (204) and (116) crystal planes of
anatase TiO2 (JCPDS 21–1272), respectively [42,43]. For the N8-1and
N16-1, the XRD patterns show the characteristic diffraction peaks of
both anatase TiO2 and g-C3N4, and the very weak peaks around 27.4°
indicate the less g-C3N4 component in theses hybrids.
Table 1
The NAD parameters of g-C3N4, g-C3N4(H+), RuC@g-C3N4(H+) and N16-1.
Specific surface area,
SBET(m2/g)
Total pore volume,
VTotal(cm3/g)
Average pore size, DAv (nm)
g-C3N4
g-C3N4(H+)
RuC@g-C3N4(H+)
N16-1
29.10
29.97
33.82
114.5
0.184
0.133
0.154
0.28
24.99
17.75
18.18
9.80
C3N4(H+) and RuC@g-C3N4(H+) narrows the average pore size due to
the protonated nitrogen bonding with hydroxyl and immobile water.
3.1.3. FTIR analysis
FTIR spectra (Nicolet 6700, USA) of TiO2, RuC, g-C3N4, g-C3N4(H+),
RuC@g-C3N4(H+), and the different RuC@g-C3N4(H+)/TiO2 hybrids
(N4-1, N8-1, N12-1, N16-1, and N20-1) are shown in Fig. 3. The wide
band at 3427 cm−1 is related to the stretching mode of eOH. For RuC, a
strong absorption peak can be found in 1721 cm−1, corresponding to
the carboxyl group stretching vibration mode, which can be used to
react with formyl chloride. For g-C3N4, the peak at 1640 cm−1 is assigned to the stretching vibration of C]N [46], and the broad peak at
3.1.2. NAD analysis
Nitrogen adsorption-desorption (NAD) isotherms of g-C3N4, gC3N4(H+), RuC@g-C3N4(H+) and N16-1 are displayed in Fig. 2, it can
be found that the similar isotherms of g-C3N4 and g-C3N4(H+) exhibit
the typical type IV curve with a H3 hysteresis loop for the loose assemblages of plate like particles forming slit-like pores, revealing the
structure of nanosheet g-C3N4 stacking together [44]. Further, the NAD
isotherm of RuC@g-C3N4(H+) is keeping with g-C3N4’s due to low
content of ruthenium complexes, however the N16-1 is a type IV of
NAD isotherm for mesoporous solid. As shown in Table 1, the specific
surface area of RuC@g-C3N4(H+) is increased by about 12.8% than that
of g-C3N4 and g-C3N4(H+), which may be caused by solvent swelling
during refluxing [45]. In addition, the protonated g-C3N4 including g-
Fig. 3. FTIR spectra of TiO2, RuC, g-C3N4, g-C3N4(H+), RuC@g-C3N4(H+), and
different RuC@g-C3N4(H+)/TiO2 hybrids.
Fig. 2. NAD isotherms of g-C3N4, g-C3N4(H+), RuC@g-C3N4(H+) and N16-1.
35
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
around 3174 cm−1 corresponds to the stretching modes of terminal -NH
and -NH2 groups, the peaks at 1572 cm−1, 1401 cm−1 and 1247 cm−1
can further be assigned to CeN heterocycle stretching vibration modes
[47]. For RuC@g-C3N4(H+), there is almost no absorption peak at
1700-1800 cm−1, which is related to the C]O stretching vibration
mode because the low content of RuC was fixed on g-C3N4(H+), and the
peak at 811 cm−1 can be observed in the spectra of g-C3N4, g-C3N4(H+)
and RuC@g-C3N4(H+), which is assigned to the characteristic breathing
mode of triazine units [48], however the above peak for N4-1, N8-1,
N12-1, N16-1 and N20-1 disappear due to the low content of g-C3N4
and overlapping with TiO2. For TiO2, a broad absorption band can be
observed in 400–700 cm−1, which is associated with the TieOeTi and
TieO stretching [49,50]. For g-C3N4(H+) and RuC@g-C3N4(H+), the
absorption peak at 1632 cm−1 can be assigned to the bending vibration
of generated eOH and immobile water due to protonation of g-C3N4.
For RuC@g-C3N4(H+)/TiO2 hybrids, the absorption peak at 1632 cm−1
can be assigned to the bending vibration of eOH on the sample surface
[51]. Particularly, for N4-1, three peaks at 1778 cm−1, 1752 cm-1 and
1721 cm−1 are attributed to the different ortho-positions of nitrogen on
the carbonyl due to the carbonylation of tri-s-triazine units [30], and
other hybrid have almost no absorption peak at the relevant position
may due to the low content of g-C3N4 in hybrids.
RuC@g-C3N4(H+). As indicated in Fig. 4e, two obvious peaks can be
observed at 458.9 eV (Ti2p3/2) and 464.6 eV (Ti2p1/2), both corresponding to Ti4+ in anatase TiO2 [57]. In addition, there is no found
distinct peak for TieC and TieN in N16-1 sample, indicating that the C
and N atoms are not doped in the lattice of TiO2 after the solvothermal
synthesis process. Namely, the RuC@g-C3N4(H+) is only loaded on the
surface of the square flake-like TiO2, which is consistent with the XRD,
FTIR, TEM analysis.
The atomic content of photocatalyst would also be discussed using
XPS as shown Table 2. In Table 2, the atomic contents of tested g-C3N4
are closed to stoichiometric ratio. According to 0.06 and 0.08 atom % of
Ru in tested RuC@g-C3N4 and RuC@g-C3N4(H+), the mass content of
RuC could be inferred to about 5.7 wt.% and 7.6 wt.%, and further the
mass contents of RuC could be calculated as about 0.50 wt.% of N16-1.
In particular, the atomic% of O1s in g-C3N4(H+) is almost double to
normal g-C3N4 as shown in Table 2, which indicates the part from
hydroxyl groups.
3.1.5. FESEM and HRTEM analysis
Morphological evaluations of (a) g-C3N4, (b) g-C3N4(H+), (c) RuC@
g-C3N4(H+) and (d) RuC@g-C3N4(H+)/TiO2 hybrid (N16-1) are performed by FESEM (ULTRA 55, Germany). In Fig. 5a and b, g-C3N4 and
g-C3N4(H+) display the accumulation of irregular particles. After ruthenium complexes was immobilized in the g-C3N4(H+), the image of
RuC@g-C3N4(H+) presents rough surface as shown in Fig. 5c due to
solvent swelling during refluxing. In Fig. 5d, the structure of N16-1
powder shows that TiO2 nanosheet crystal with the side length
50–60 nm and the thickness of 10–15 nm.
As shown in Fig. 6a–c, the g-C3N4, g-C3N4(H+), and RuC@gC3N4(H+) display the porous structure with about 50 nm. For N16-1 as
shown in Fig. 6d and the inset, g-C3N4 is found between the square
flake-like TiO2 nanocrystallines, which suggests the interface of heterostructure between g-C3N4 and TiO2. Further, the element mapping
could be able to demonstrate the existence of C, N, O, Ti and minor Ru
elements as shown in Fig. 7. In Fig. 7a, C, N, O, and minor Ru elements
uniformly distribute in the profile of RuC@g-C3N4(H+) powder. In
Fig. 7b, the signals of C, N, and minor Ru elements are mainly ascribed
to 0.50 wt.% of RuC@g-C3N4(H+) in the N16-1, and the strong Ti signal
is attributed to TiO2.
3.1.4. XPS analysis
X-ray photoelectron spectroscopy (PHI 5000, Japan) can be performed to investigate the surface chemical states and elemental composition of the samples. The full-range XPS analyses of g-C3N4, gC3N4(H+), RuC@g-C3N4(H+) and N16-1 are shown in Fig. S5 of
Supplementary Material, respectively. Further, the high-resolution
spectra of the different specific elements including C1s (a), N1s (b), O1s
(c), Ru3d5/2 (d) and Ti2p (e) of the N16-1 are shown in Fig. 4, respectively. In Fig. 4a, the C1s region of g-C3N4 and g-C3N4(H+) can be
fit into four main peaks corresponding to four kinds of different carbon
species, the peak at 284.7 eV is exclusively assigned to CeC due to the
formation of amorphous sp2-hybridized carbon in the synthesis of gC3N4, the peaks at 286.3 eV and 288.2 eV can be assigned to CeNeC
and NeCeN backbone in the g-C3N4 [52], respectively, the binding
energy at 288.9 eV can be attributed to the carboxyl, more C1s peak can
be found at 292.9 eV corresponding the CeNH2 in nitrogen-containing
aromatic ring. However, the peak at 289.3 eV for RuC@g-C3N4(H+)
refers to carboxyl with pyridine ring which is different with nitrogencontaining aromatic ring, and the peak at about 285.4 eV corresponding
to Ru3d3/2 cannot be found due to low content of ruthenium. In Fig. 4b,
the N1s region of g-C3N4 could be divided into three obvious peaks at
398.6 eV, 400.1 eV, and 401.4 eV, indicating three types of N bonding,
which can be corresponded to C]NeC, NeH and the central N of
triazine unit, respectively [53]. Specially, for g-C3N4(H+), all of N1s
peaks have a slight shift to lower binding energy due to the hydroxyl
bonding with protonated nitrogen prolonging N bond. However, it is
very interested that all of N1s peaks for g-C3N4(H+) with ruthenium
complexes recovers to g-C3N4’s state again due to substitution of hydroxyl and immobile water for refluxing methylbenzene solvent during
preparation of RuC@g-C3N4(H+). Further, all peaks of N16-1 have the
higher binding energies compared with the RuC@g-C3N4(H+)’s, this is
probably due to the chemical environment change arising from the
tight interface interaction between RuC@g-C3N4(H+) and TiO2 [54].
Fig. 4c shows the high-resolution XPS spectra of O1s, the peaks at
532.1 eV and 533.6 eV of g-C3N4 are attributed to O]C and eOH
groups respectively, and the spectra of protonated g-C3N4(H+) and
RuC@g-C3N4(H+) have the peak at 531.4 eV, which could be assigned
to the immobile water and the carboxyl from ruthenium complexes
[55]. The obvious peak detected at 530.1 eV in N16-1 is attributed to
the oxygen in TiO2. In Fig. 4d, the Ru3d5/2 high-resolution spectrum of
RuC@g-C3N4(H+) is observed at the binding energy of 281.2 eV, which
reveals the valence state of Ru2+ in RuC@g-C3N4(H+) [56]. The N16-1
has almost no peak of Ru2+, this is probably due to low content of
3.2. Optical performance
The photoluminescence (PL, Lumina222, USA) analysis is a very
useful to study the capturing efficiency and recombination of photogenerated electron-hole. Generally, lower PL intensity corresponds to
higher the separation efficiency of photogenerated electron-hole pairs,
and contributing to higher photocatalytic activity [58–60]. As shown in
Fig. 8a, the PL of g-C3N4 performs a strong emission peak around
460 nm under the excitation of 320 nm wavelength, which can be attributed to the rapid recombination of photogenerated electron-hole
pairs, and the PL intensity decreases sharply after g-C3N4 protonating.
As shown in Fig. 8b, comparing with the g-C3N4(H+), the PL intensity
of RuC@g-C3N4(H+) significantly reducing suggests that the addition of
ruthenium complexes can improve the separation efficiency of photogenerated electron-hole. As shown in Fig. 8c, the RuC@g-C3N4(H+)/
TiO2 hybrids exhibit further reduction of emission intensity due to the
forming heterojunction between RuC@g-C3N4(H+) and TiO2, thereinto,
N16-1 shows the lowest intensity, which performs highest photocatalytic activity. In addition, there are two distinctly emission peaks at
about 396 nm and 430 nm, corresponding to the superposition of
emission peaks for TiO2 and g-C3N4, respectively.
The optical absorption behavior of photocatalysts can be investigated by the UV–vis diffused reflectance spectra (UV-3600,
Shimadzu, Japan). As shown in Fig. 9, the absorptions of g-C3N4 and gC3N4(H+) from ultraviolet to visible range up to 460 nm and 488 nm,
and their band gaps are 2.71 eV and 2.54 eV, respectively. Comparing
36
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
Fig. 4. XPS spectra of g-C3N4, g-C3N4(H+), RuC@g-C3N4(H+) and N16-1 including C1s (a), N1s (b), O1s (c), Ru3d5/2 (d) and Ti2p (e)of the N16-1.
with g-C3N4(H+), the appearing peak at 478 nm for RuC@g-C3N4(H+)
is assigned to the ruthenium complexes, and the absorption edge of
RuC@g-C3N4(H+) extends to more than 700 nm. In addition, the absorption edge of g-C3N4(H+) for RuC@g-C3N4(H+) expresses red shift
due to the overlap of the absorption left edge for the ruthenium complexes. TiO2 can absorb light with wavelength up to 403 nm corresponding to 3.08 eV band gap, and the absorption edges of RuC@gC3N4(H+)/TiO2 hybrids further perform red shift to some extent while
37
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
it can be seen, the k of the control sample, g-C3N4, g-C3N4(H+), g-C3N4/
TiO2 (H12-1), RuC@g-C3N4/TiO2 hybrid (G12-1), N4-1, N8-1, N12-1,
N16-1 and N20-1 are 0.00018 min−1, 0.0015 min−1, 0.0037 min−1,
0.0167 min−1,
0.0331 min−1,
0.0251 min−1,
0.0324 min−1,
0.0449 min−1, 0.0561 min−1 and 0.0289 min−1 respectively as shown
in Table S1 of Supplementary Material. This result clearly indicates that
the ruthenium complexes sensitizing can significantly improve the
photocatalytic performance of RuC@g-C3N4(H+)/TiO2 hybrid with increase of RuC@g-C3N4(H+), and the optimal theory mass ratio of TiO2/
RuC@g-C3N4(H+) hybrid is about 16:1. Comparing with g-C3N4, the
kinetic constant k of g-C3N4(H+) raises greatly about 2.5 times, may
due to the hydroxyl bonding with protonated nitrogen prolonging the
bonds between nitrogen and other atom and enhancing delocalization
of electron. Comparing with RuC@g-C3N4/TiO2 hybrid (G12-1) without
the protonation of g-C3N4 [14], the photocatalytic kinetic constant k of
optimal N16-1 enhances 1.7 times. However, a further increasing
content of TiO2 could decrease significantly the photodegradation efficiency of MB probably due to TiO2 shielding light absorption of RuC@
g-C3N4(H+). The photocatalytic stability has been tested at the same
recycling intervals of 150 min. After 5 cycles, the photocatalytic efficiency of H 12-1 was about 70% as high as that of the first cycle. For
N16-1, the photocatalytic efficiency decreased about ∼50% than that
of the first cycle after 4 cycles. The possible reason is that these photocatalysts perform the inevitable photocatalytic degradation of g-C3N4
and ruthenium complexes themselves.
Table 2
The different atomic contents (atom %) of tested samples.
Atom %
g-C3N4
g-C3N4(H+)
RuC@g-C3N4
RuC@g-C3N4(H+)
Stoichiometry
Tested
Tested
Tested
Tested
C1s
N1s
O1s
Ru3d5/2
42.86
44.46
42.08
44.58
45.05
57.14
51.63
49.96
51.33
47.51
3.90
7.96
4.03
7.36
0.06
0.08
increase of g-C3N4(H+). The heterojunction between TiO2 and g-C3N4,
RuC@g-C3N4 or RuC@g-C3N4(H+) has no enough capacity to change
the band gaps of g-C3N4/TiO2, RuC@g-C3N4/TiO2 and RuC@gC3N4(H+)/TiO2 hybrids, which is different from that of introducing
minor amount of other elements into the lattice of semiconductor. So
the red shift of RuC@g-C3N4(H+)/TiO2 hybrids is due to the overlap of
the absorption edges for TiO2 and RuC@g-C3N4(H+). Comparing with
H12-1, the appearing peak at 478 nm for N4-1, N8-1, N12-1, N16-1and
N20-1 suggests that the introduction of ruthenium complexes has a
significant effect on the absorption spectra, which can excite to generate more electron-hole pairs under light irradiation.
3.3. Photocatalytic performance
The photocatalytic performances of g-C3N4, g-C3N4(H+), g-C3N4/
TiO2 (H12-1), RuC@g-C3N4/TiO2 hybrid (G12-1) and the different
RuC@g-C3N4(H+)/TiO2 hybrids (N20-1, N16-1, N12-1, N8-1 and N4-1)
are evaluated by the degradation of MB under xenon light irradiation as
shown in Figs. S6 and S7 of Supplementary Material. The LangmuirHinshelwood apparent first-order kinetics equation can be applied to
describe the kinetics of photocatalytic degradation of MB as follows
[61,62] : ln(C0/Ct) = kt, where C0 is the initial concentration of MB, Ct
is the residual concentration of MB at time t, and k is the kinetic constant. For further describing the photocatalytic properties, the kinetic
constant can be derived from the slope of the linear fitting through the
time-course variation of ln(C0/Ct) as shown in Fig. 10. The greater kinetic constant of photocatalyst can reflect the faster MB degradation. As
3.4. Mechanism discussion
Generally, the main superoxide radicals (%O2−), holes (h+) and
hydroxyl radicals (%OH) have been reported to be produced in the
semiconductor photocatalytic solution by light irradiation [36–38], and
the process can be described as follows:
Photo-catalyzer + hν → Photo-catalyzer (e− + h+)
(1)
e− + O2 → %O2-
(2)
%O2−+ H+ → %HO2
(3)
Fig. 5. FESEM images (a) g-C3N4, (b) g-C3N4(H+), (c) RuC@g-C3N4(H+) and (d) RuC@g-C3N4(H+)/TiO2 hybrid (N16-1).
38
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
Fig. 6. HRTEM images (a) g-C3N4, (b) g-C3N4(H+), (c) RuC@g-C3N4(H+) and (d) RuC@g-C3N4(H+)/TiO2 hybrid (N16-1).
Fig. 7. Element mapping of (a) RuC@g-C3N4(H+) and (b) RuC@g-C3N4(H+)/TiO2 hybrid (N16-1) by HRTEM.
39
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
Fig. 10. Linear transform ln(C0/C) of the kinetic curves of photocatalytic degradation of MB for control sample, g-C3N4, g-C3N4(H+), g-C3N4/TiO2 hybrid
(H12-1), RuC@g-C3N4/TiO2 hybrid (G12-1), and different RuC@g-C3N4(H+)/
TiO2 hybrids (N20-1, N16-1, N12-1, N8-1 and N4-1) under xenon light irradiation.
be trapped by EDTA-2Na with the pairs of electrons, %O2− can be
scavenged by transferring an electron to BQ [63], and t-BuOH as the
radical scavenger could suppress OH radical-mediated process [64] as
follows:
Fig. 8. PL spectra of different RuC@g-C3N4(H+)/TiO2 hybrids (N20-1, N16-1,
N12-1, N8-1 and N4-1), g-C3N4, g-C3N4(H+), TiO2 and RuC@g-C3N4(H+).
(4)
e− +H2O2 → %OH + OH−
(5)
h++ OH− → %HO
(6)
h + H2O → %HO+H
+
+
(7)
%O2−,
(8)
%OH+ t-BuOH → H2O+%CH2C(CH3)2OH
(9)
The products of scavengers have low activity and cannot further
degrade MB, thus, BQ, EDTA-2Na, and t-BuOH can be used as detected
molecules responding to •O2−, h+, and OH%, respectively.
After adding separately the 0.1 mmol/L of EDTA-2Na, BQ and tBuOH, the degraded rate constants k are shown in Fig. 11. It is generally
know that the redox ability of photo-exited species is dependent upon
the redox potential. According to our previously published work [30],
the CB (conduction band) potentials of g-C3N4 (−1.11 eV, vs. NHE) is
more negative than E0(O2/%O2− = −0.33 eV, vs. NHE), and that of
TiO2 (-0.23 eV, vs. NHE) is more positive, the photo-generated electrons
of g-C3N4 can reduce O2 to form %O2−, however TiO2’s cannot work.
Thus, BQ added entirely suppresses photo-degradation of MB indicates
that the significance of the superoxide radicals %O2− for the gC3N4(H+) and RuC@g-C3N4(H+). On the contrary, the photo-degradation of MB is suppressed deeply after the injection of EDTA-2Na,
which indicates that h+ is the main oxidative species for the anatase
TiO2 and oxidizes directly MB due to the high VB (valence band) potentials of TiO2 (2.85 eV, vs. NHE). Besides the important active species
%OH could be produced by %O2- as shown in Eqs. (3)–(5), the photogenerated holes of TiO2 can also oxidize OH− or H2O to form %HO
because the VB potential of TiO2 (2.85 eV, vs. NHE) is more positive
than E0(%HO/OH−= + 1.99 eV, vs. NHE) and E0(%HO/H2O
= + 2.73 eV, vs. NHE). However, the VB potential of g-C3N4 (1.60 eV,
vs. NHE) is more negative, so cannot work. Actually, the photo-degradation of MB is not suppressed deeply after the addition of t-BuOH as
shown in Fig. 11a, which indicates that %HO is not the main effective
species because forming %HO needs to undergo multistep reactions.
As for the g-C3N4/TiO2 hybrids with H12-1 and N16-1, the photodegradations of MB are comparably suppressed after the addition of
either EDTA-2Na or BQ as shown in Fig. 11b, which suggests that both
h+ and %O2− are the main reactive species, and stem from VB of TiO2
and CB of g-C3N4, respectively. Thus, the transfer of photogenerated
electron-hole in the heterojunction between g-C3N4 and TiO2 could be
described as classic Z-scheme photocatalytic mechanism, in which the
electron of TiO2 is excited to CB under light irradiation, and then
Fig. 9. UV–vis diffuse reflectance spectra of g-C3N4, g-C3N4(H+), TiO2, RuC@gC3N4(H+), RuC@g-C3N4(H+)/TiO2 hybrids (N4-1,N8-1, N12-1, N16-1, N20-1
and H12-1) and inset of band-gaps of g-C3N4,g-C3N4(H+) and TiO2.
e− + %HO2 + H+ → H2O2
BQ+%O2− → %BQ-+ O2
As a result, by the generated
%HO and h , the MB molecules
produce CO2 and H2O as final products. Actually, some compounds
have finished scavenging rapidly the %O2−, h+ and %OH due to extremely high reactive rate before these super active species have redox
reaction with MB, such as BQ, EDTA-2Na, and t-BuOH. Herein, h+ can
+
40
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
Fig. 11. The plots of photodegraded rate constants k of MB under trapping the different photogenerated activated species of (a) g-C3N4(H+), RuC@g-C3N4(H+), TiO2
and (b) H12-1 and N16-1.
(-1.11 eV, vs. NHE) is more negative than excited Ru(bpy)32+*, the
excited Ru(bpy)32+* only can transfer electron into VB of the gC3N4(H+). However, as seen in Table 3, the relative k ratios of MB
under trapping the different photogenerated activated species for
RuC@g-C3N4(H)/g-C3N4(H+) and N16-1/H12-1 all raise in varying
degrees, which implies that the ruthenium complexes can improve the
separation of photogenerated electron-hole. Based on our previous report [30] and UV–vis DRS analysis results, the wavelength of light
absorbed by the g-C3N4 sample reaches 460 nm, TiO2 has a wide band
gap (3.08 eV) and absorbs ultraviolet (UV) light at wavelengths shorter
than 403 nm. As shown in Fig. 12, the Ru(bpy)32+ is excited to Ru
(bpy)32+* under light below 600 nm [65], and the obtained Ru
(bpy)32+* transfers one electron into VB of the g-C3N4(H+), and then
changes to Ru(bpy)33+, while the photogenerated electron in CB of the
TiO2 transfers one electron into Ru(bpy)33+ and then is reduced to Ru
(bpy)32+. Herein, the ruthenium complexes can be similar to a pump
with absorbing light as a source of energy to transfer electron, thereby
the separation efficiency of photogenerated electron-hole is improved
effectively.
Table 3
The relative k ratio of MB under trapping the different photogenerated activated species.
RuC@g-C3N4(H+)/g-C3N4(H+)
N16-1/H12-1
h+
%O2−
%HO
1.40
2.84
1.56*
1.704
1.64
1.56
* Measurement in 0.05 mmol/L of BQ.
transfers to VB of g-C3N4 through the heterojunction between g-C3N4
and TiO2.
In order to further discuss the effect of photosensitizer on gC3N4(H+), the dosage of BQ is halved to 0.05 mmol/L, and then the
obtained degraded rate constants for g-C3N4(H+) and RuC@gC3N4(H+) are shown in the inset of Fig. 11a. It is usually considered
that the photosensitizer is excited from Ru(bpy)32+ to Ru(bpy)32+*,
responding to the change of redox potentials from E0(Ru2+/Ru3+
= + 1.26 eV, vs. NHE) to E0(Ru2+*/Ru3+ = -0.86 eV, vs. NHE) in H2O
under light irradiation [65]. Because the CB potential of g-C3N4
Fig. 12. The degradation mechanism of RuC@g-C3N4(H+)/TiO2 hybrid.
41
Molecular Catalysis 458 (2018) 33–42
K. Geng et al.
4. Conclusions
[18] S. Tonda, S. Kumar, M. Bhardwaj, P. Yadav, S. Ogale, ACS Appl. Mater. Interface 10
(2018) 2667–2678.
[19] Z. Wei, F. Liang, Y. Liu, W. Luo, J. Wang, W. Yao, Y. Zhu, Appl. Catal. B Environ.
201 (2017) 600–606.
[20] R. Kuriki, H. Matsunaga, T. Nakashima, K. Wada, A. Yamakata, O. Ishitani,
K. Maeda, J. Am. Chem. Soc. 138 (2016) 5159–5170.
[21] R. Kuriki, K. Maeda, Phys. Chem. Chem. Phys. 19 (2017) 4938–4950.
[22] R. Kuriki, M. Yamamoto, K. Higuchi, Y. Yamamoto, M. Akatsuka, D. Lu, S. Yagi,
T. Yoshida, O. Ishitani, K. Maeda, Angew. Chem. Int. Ed. 56 (2017) 4867–4871.
[23] Q. Tang, X. Meng, Z. Wang, J. Zhou, H. Tang, Appl. Surf. Sci. 430 (2018) 253–262.
[24] I. Tateishi, H. Katsumata, T. Suzuki, S. Kaneco, Mater. Lett. 201 (2017) 66–69.
[25] F. Wu, X. Li, W. Liu, S. Zhang, Appl. Surf. Sci. 405 (2017) 60–70.
[26] M.A. Mohamed, J. Jaafar, M.F.M. Zain, L.J. Minggu, M.B. Kassim, M.N.I. Salehmin,
M.S. Rosmi, W.N.W. Salleh, M.H.D. Othman, Scr. Mater. 142 (2018) 143–147.
[27] S. Selvarajan, A. Suganthi, M. Rajarajan, Ultrason. Sonochem. 41 (2018) 651–660.
[28] N. Tian, H. Huang, Y. He, Y. Guo, T. Zhang, Y. Zhang, Dalton Trans. 44 (2015)
4297–4307.
[29] X. Yu, X. Fan, L. An, G. Liu, Z. Li, J. Liu, P. Hu, Carbon 128 (2018) 21–30.
[30] G. Jiang, X. Yang, Y. Wu, Z. Li, Y. Han, X. Shen, Mol. Catal. 432 (2017) 232–241.
[31] C.J. Rhodes, Annu. Rep. Prog. Chem. Sect. C Phys. Chem. 100 (2004) 149–193.
[32] G.V. Buxton, C.L. Greenstock, W.P. Helman, A.B. Ross, J. Phys. Chem. Ref. Data 17
(1988) 513–886.
[33] R. Palominos, J. Freer, M.A. Mondaca, H.D. Mansilla, J. Photochem. Photobiol. A
Chem. 193 (2008) 139–145.
[34] H. Zhang, Y. Zhu, J. Phys. Chem. C. 114 (2010) 5822–5826.
[35] E. Eskelinen, S. Luukkanen, M. Haukka, M. Ahlgrén, T.A. Pakkanen, J. Chem. Soc.
Dalton Trans. (2000) 2745–2752.
[36] D. Chaudhary, V.D. Vankar, N. Khare, Sol. Energy 158 (2017) 132–139.
[37] M.A. Mohamed, J. Jaafar, M.F.M. Zain, L.J. Minggu, M.B. Kassim, M.S. Rosmi,
N.H. Alias, N.A. Mohamad Nor, W.N.W. Salleh, M.H.D. Othman, Appl. Surf. Sci. 436
(2018) 302–318.
[38] Y. Park, H. Kim, R.C. Pawar, S. Kang, C.S. Lee, Mater. Chem. Phys. 203 (2018)
118–124.
[39] Q. Han, B. Wang, J. Gao, Z. Cheng, Y. Zhao, Z. Zhang, L. Qu, ACS Nano 10 (2016)
2745–2751.
[40] X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J.M. Carlsson, K. Domen,
M. Antonietti, Nat. Mater. 8 (2008) 76–80.
[41] J. Xu, L. Zhang, R. Shi, Y. Zhu, J. Mater. Chem. A 1 (2013) 14766.
[42] F. Deng, X. Luo, H. Shu, X. Tu, S. Luo, Res. Chem. Intermed. 39 (2013) 2857–2865.
[43] K.J. Lee, M.S. Maqbool, P.A. Kumar, K.H. Song, H.P. Ha, Res. Chem. Intermed. 39
(2013) 3265–3277.
[44] K. Sing, D.H. Everett, R. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol,
T. Siemieniewska, Pure Appl. Chem. 57 (1985) 603–619.
[45] J. Ji, J. Wen, Y. Shen, Y. Lv, Y. Chen, S. Liu, H. Ma, Y. Zhang, J. Am. Chem. Soc. 139
(2017) 11698–11701.
[46] Y.C. Zhao, D.L. Yu, H.W. Zhou, Y.J. Tian, O. Yanagisawa, J. Mater. Sci. 40 (2005)
2645–2647.
[47] S.C. Yan, Z.S. Li, Z.G. Zou, Langmuir 25 (2009) 10397–10401.
[48] Y. Wang, R. Shi, J. Lin, Y. Zhu, Energy Environ. Sci. 4 (2011) 2922.
[49] J. Cai, Y. Wang, Y. Zhu, M. Wu, H. Zhang, X. Li, Z. Jiang, M. Meng, ACS Appl.
Mater. Interface 7 (2015) 24987–24992.
[50] Q. Kang, X. Wang, X. Ma, L. Kong, P. Zhang, D. Shen, Sens. Actuators B Chem. 230
(2016) 231–241.
[51] M. Yang, J. Liu, X. Zhang, S. Qiao, H. Huang, Y. Liu, Z. Kang, Phys. Chem. Chem.
Phys. 17 (2015) 17887–17893.
[52] L. Ge, C. Han, J. Liu, Y. Li, Appl. Catal. A Gen. 409-410 (2011) 215–222.
[53] S.J. Yang, J.H. Cho, G.H. Oh, K.S. Nahm, C.R. Park, Carbon 47 (2009) 1585–1591.
[54] X. Song, Y. Hu, M. Zheng, C. Wei, Appl. Catal. B Environ. 182 (2016) 587–597.
[55] X. She, L. Liu, H. Ji, Z. Mo, Y. Li, L. Huang, D. Du, H. Xu, H. Li, Appl. Catal. B
Environ. 187 (2016) 144–153.
[56] S. Sayan, S. Suzer, D.O. Uner, J. Mol. Struct. 410 (1997) 111–114.
[57] L.C. Sim, K.H. Leong, P. Saravanan, S. Ibrahim, Appl. Surf. Sci. 358 (2015)
122–129.
[58] R. Velmurugan, M. Swaminathan, Res. Chem. Intermed. 41 (2015) 1227–1241.
[59] X. Zhou, B. Jin, L. Li, F. Peng, H. Wang, H. Yu, Y. Fang, J. Mater. Chem. 22 (2012)
179–1795.
[60] S.G. Kumar, K.S.R.K. Rao, Appl. Surf. Sci. 391 (2017) 124–148.
[61] Y. Mizukoshi, N. Ohtsu, S. Semboshi, N. Masahashi, Appl. Catal. B Environ. 91
(2009) 152–156.
[62] X.H. Wang, J.G. Li, H. Kamiyama, Y. Moriyoshi, T. Ishigaki, J. Phys. Chem. B 110
(2006) 6804–6809.
[63] R. Palominos, J. Freer, M.A. Mondaca, H.D. Mansilla, J. Photochem. Photobiol. A
Chem. 193 (2008) 139–145.
[64] G.V. Buxton, C.L. Greenstock, W.P. Helman, A.B. Ross, J. Phys. Chem. Ref. Data 17
(1988) 513–886.
[65] K. Kalyanasundaram, Coord. Chem. Rev. 46 (1982) 159–244.
After the activation of g-C3N4 protonating, the appearing hydroxyl
bonding with protonated nitrogen can prolong the N bonds between
nitrogen and other atom, resulting in both photocatalytic performance
of g-C3N4 increasing, and the increase of ruthenium complexes loaded
on g-C3N4. Thus the kinetic constant k of g-C3N4(H+) through the activation of g-C3N4 protonating raises greatly about 2.5 times than that
of g-C3N4, and the optimal RuC@g-C3N4(H+)/TiO2 (N16-1) further
enhances 1.7 times than that of the optimal RuC@g-C3N4/TiO2 (G12-1).
Through analyzing three scavengers for BQ, t-BuOH, and EDTA-2Na
trapping active species of the %O2−, h+ and %OH respectively in MB
aqueous solution during xenon light irradiation, the transfer of photogenerated electron-hole in the heterojunction between g-C3N4 and TiO2
could be described as classic Z-scheme photocatalytic mechanism, in
which the electron of TiO2 is excited to CB under light irradiation, and
then transfers to VB of g-C3N4 through the heterojunction between gC3N4 and TiO2. Further, the working mechanism of photosensitizer can
be demonstrated that the ruthenium complexes similar to a pump with
absorbing light as a source of energy to transfer electron, can improve
effectively the separation efficiency of photogenerated electron-hole.
Acknowledgements
This work was supported by Advantage Discipline Construction
Foundation of Jiangsu, the Priority Academic Program Development of
Jiangsu Higher Education Institutions (PAPD), and National Natural
Science Foundation of China through Grant No. 51506095.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2018.07.026.
References
[1] M.R. Hoffmann, S.T. Martin, W.Y. Choi, D.W. Bahnemann, Chem. Rev. 95 (1995)
69–96.
[2] M.N. Chong, B. Jin, C.W.K. Chow, C. Saint, Water Res. 44 (2010) 2997–3027.
[3] R. Hao, G. Wang, H. Tang, L. Sun, C. Xu, D. Han, Appl. Catal. B Environ. 187 (2016)
47–58.
[4] Z. Lu, L. Zeng, W. Song, Z. Qin, D. Zeng, C. Xie, Appl. Catal. B Environ. 202 (2017)
489–499.
[5] Y. Li, K. Lv, W. Ho, F. Dong, X. Wu, Y. Xia, Appl. Catal. B Environ. 202 (2017)
611–619.
[6] L. Zhang, D. Jing, X. She, H. Liu, D. Yang, Y. Lu, J. Li, Z. Zheng, L. Guo, J. Mater.
Chem. A 2 (2014) 2071–2078.
[7] L. Sim, W. Tan, K. Leong, M. Bashir, P. Saravanan, N. Surib, Materials 10 (2017) 28.
[8] Z. Jiang, C. Zhu, W. Wan, K. Qian, J. Xie, J. Mater. Chem. A 4 (2016) 1806–1818.
[9] Z. Li, G. Jiang, Z. Zhang, Y. Wu, Y. Han, J. Mol. Catal. A Chem. 425 (2016)
340–348.
[10] B. Yao, C. Peng, W. Zhang, Q. Zhang, J. Niu, J. Zhao, Appl. Catal. B Environ. 174175 (2015) 77–84.
[11] S. Afzal, W.A. Daoud, S.J. Langford, ACS Appl. Mater. Interface 5 (2013)
4753–4759.
[12] W. Lu, T. Xu, Y. Wang, H. Hu, N. Li, X. Jiang, W. Chen, Appl. Catal. B Environ. 180
(2016) 20–28.
[13] J.F. Góngora, P. Elizondo, A. Hernández-Ramírez, Photochem. Photobiol. Sci. 16
(2017) 31–37.
[14] G. Jiang, K. Geng, Y. Wu, Y. Han, X. Shen, Appl. Catal. B Environ. 227 (2018)
366–375.
[15] Y. Zhang, A. Thomas, M. Antonietti, X. Wang, J. Am. Chem. Soc. 131 (2009) 50.
[16] A. Kumar, C. Schuerings, S. Kumar, A. Kumar, V. Krishnan, Beilstein J.
Nanotechnol. 9 (2018) 671–685.
[17] J. Pan, M. You, C. Chi, Z. Dong, B. Wang, M. Zhu, W. Zhao, C. Song, Y. Zheng, C. Li,
Int. J. Hydrogen Energy 43 (2018) 6586–6593.
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