Construction and enhanced efficiency of Z-scheme-based ZnCdS/Bi2WO6 composites for visible-light-driven photocatalytic dye degradation

Article abstract of DOI:10.1016/j.jpcs.2021.110075

Novel ZnCdS/Bi₂WO₆ composites have been prepared through a three-step method. The products have proved to be highly effective in the photodegradation of malachite green (MG) under visible light, while also showing outstanding stability. The excellent photocatalytic performance of the composites can be primarily attributed to effective separation and migration of electrons and holes across their tight contact interfaces, which conform to a Z-scheme heterostructure. Free radical capture experiments have verified that hydroxyl radicals (·OH) and superoxide ion radicals (·O₂^?) play decisive roles in the reaction process. A putative photocatalytic mechanism over ZnCdS/Bi₂WO₆ is proposed, providing a rationale for its enhanced photocatalytic activity. This work provides a perspective for the design of ZnCdS/Bi₂WO₆ photocatalysts with a Z-scheme heterostructure that can not only utilize solar energy more effectively, but may also provide a new concept for environmental remediation.

Full text of DOI:10.1016/j.jpcs.2021.110075

Journal of Physics and Chemistry of Solids 154 (2021) 110075
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids
journal homepage: http://www.elsevier.com/locate/jpcs
Construction and enhanced efficiency of Z-scheme-based ZnCdS/Bi2WO6
composites for visible-light-driven photocatalytic dye degradation
,
**
Xiaohan Zhaoa, Yue Xua, Xiaohong Wanga, Qian Lianga, Man Zhoua, Song Xub
,
,b,c,d,*
Zhongyu Lia
a Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, PR China
b Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University, Changzhou, 213164, PR China
c School of Environmental and Safety Engineering, Changzhou University, Changzhou, 213164, PR China
d School of Petrochemical Engineering, Jilin Institute of Chemical Technology, Jilin, 132022, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Novel ZnCdS/Bi2WO6 composites have been prepared through a three-step method. The products have proved to
be highly effective in the photodegradation of malachite green (MG) under visible light, while also showing
outstanding stability. The excellent photocatalytic performance of the composites can be primarily attributed to
effective separation and migration of electrons and holes across their tight contact interfaces, which conform to a
Z-scheme heterostructure. Free radical capture experiments have verified that hydroxyl radicals (⋅OH) and su-
peroxide ion radicals (⋅O2ꢀ ) play decisive roles in the reaction process. A putative photocatalytic mechanism over
ZnCdS/Bi2WO6 is proposed, providing a rationale for its enhanced photocatalytic activity. This work provides a
perspective for the design of ZnCdS/Bi2WO6 photocatalysts with a Z-scheme heterostructure that can not only
utilize solar energy more effectively, but may also provide a new concept for environmental remediation.
Photocatalytic activity
ZnCdS/Bi2WO6 composites
Photocatalytic mechanism
Visible-light photocatalyst
1. Introduction
conversion [17]. Due to their advantages of low cost, good stability, high
light absorption efficiency, narrow band gap, and rapid charge separa-
Organic pollution in the environment is one of the important and
urgent issues currently faced by humanity. Semiconductor photo-
catalysts offer a green, clean technology for degrading organic pollut-
ants, and have great application prospects in the field of environmental
pollution treatment [1,2]. Among numerous photocatalytic materials,
TiO2 has been most widely applied, but it is limited by its wide intrinsic
band gap [3–5]. Although solar energy is a renewable, environmentally
friendly, and clean energy [6,7], rapid recombination of photogenerated
carriers reduces its efficiency. Thus, poor efficiency and low stability
have restricted extensive practical application of photocatalysts [8–10].
A great deal of research effort has been directed towards improving the
performance of photocatalysts by adding co-catalysts or constructing
suitable heterojunctions [11–15]. Metal sulfides constitute a significant
class of semiconductor materials, and have been extensively applied in
photocatalytic, photoelectrochemical, and other fields [16]. They can
utilize solar energy through photochemical and photoelectric
tion, metal sulfides have great potential in the field of photocatalysis
[18–20]. However, their shortcoming of rapid recombination of pho-
togenerated carriers can decrease the photocatalytic efficiency and limit
their further application [21,22]. ZnCdS is an important inorganic
semiconductor material with a suitable band gap, high absorptivity, and
good conductivity, which has potential application prospects [23].
However, ZnCdS solid solution is associated with some defects that
cannot be ignored, such as poor visible light utilization and low carrier
separation efficiency [24,25]. Moreover, ZnCdS particles are small and
tend to significantly accumulate, which severely restricts the hydrogen
production performance of the material. Therefore, it is essential to in-
crease the activity and stability of pure ZnCdS for photocatalytic
hydrogen production. Synthesizing different semiconductor materials to
modify semiconductor morphologies or create heterogeneous structures
for carrier separation to enhance the specific surface area are increas-
ingly popular methods for improving the photocatalytic performances of
* Corresponding author. Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University,
Changzhou, 213164, PR China.
** Corresponding author.
E-mail addresses: cyanine123@163.com (S. Xu), zhongyuli@mail.tsinghua.edu.cn (Z. Li).
https://doi.org/10.1016/j.jpcs.2021.110075
Received 30 July 2020; Received in revised form 18 March 2021; Accepted 19 March 2021
Available online 31 March 2021
0022-3697/© 2021 Elsevier Ltd. All rights reserved.

X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
semiconductor materials [26].
2.3. Preparation of ZnCdS/Bi2WO6 composites
Many efforts have been made to explore Bi-based photocatalysts.
Chen et al. reported that carbon quantum dots (CQDs)/BiOBr composite
showed significantly improved photocatalytic performance after the
introduction of CQDs [27]. Sun et al. reported that the combined effect
of heterojunctions, oxygen vacancies, and surface plasmon resonance of
Bi particles improved the photocatalytic activity of BiOI [28]. Li et al.
reported the photocatalytic performance of Bi metal-deposited Bi2GeO5
(Bi@BiGeO) [29]. The band gap of Bi2WO6 is 2.8 eV as an n-type
semiconductor material [30–32]. The Aurivillius-type layered structure
of Bi2WO6 is composed of alternating corner-sharing [WO6] octahedral
layers and [Bi2O2] layers, and an indirect transition mode can promote
the migration of photo-induced carriers and improve its photoactivity
[31–33]. Nevertheless, the narrow absorption range of Bi2WO6 and the
recombination rate of photo-generated electrons and holes (eꢀ /h+)
seriously hinder its practical application in the field of photocatalysis
[34]. Combining Bi2WO6 with other semiconductors can accelerate the
separation of carriers and frustrate the recombination of eꢀ /h+ pairs,
directly improving the activity of the photocatalytic material [35–37].
In the present study, in order to make the most of the merits of ZnCdS
and Bi2WO6, and to overcome their respective shortcomings, they have
been formed into suitable heterojunctions to acquire better catalytic
performance in the degradation of organic pollutants and hydrogen
evolution. ZnCdS/Bi2WO6 composites were easily prepared by a three-
step method, and exhibited significantly enhanced performance in the
degradation of MG. To further understand the mechanism of MG
degradation, the optical, structural, and electronic properties of the
ZnCdS/Bi2WO6 composites have been measured. The splendid photo-
catalytic performance can be ascribed to efficient migration of photo-
generated carriers across the intimate contact interface. The expeditious
migration of electrons and holes between ZnCdS and Bi2WO6 not only
inhibits the recombination of carriers, but also extends the lifetime of
the reaction. This work put forwards a new design of ZnCdS/Bi2WO6
photocatalyst for the further efficient utilization of sunlight and offers a
new perspective for environmental remediation.
ZnCdS was dispersed in absolute ethanol (20 mL) for 30 min with the
aid of ultrasound to obtain suspension A. Similarly, Bi2WO6 was also
dispersed in absolute ethanol (20 mL) for 30 min with the aid of ultra-
sound to obtain suspension B. Composite samples were prepared in mass
ratios of 1:1 wt%, 1:1.3 wt%, and 1:1.5 wt%, respectively. Suspension A
was added to suspension B, and the mixture was sonicated for 2 h and
stirred for 24 h. Each ZnCdS/Bi2WO6 composite was collected by
centrifugation and dried in a vacuum drying oven at 70 ◦C for approx-
imately 12 h. A schematic illustration of the preparation of ZnCdS/
Bi2WO6 composites is shown in Fig. 1.
2.4. Photocatalytic activity
The photocatalytic activities of the ZnCdS/Bi2WO6 samples were
evaluated by degrading MG using a 1 kW Xe lamp to simulate visible
light. In these experiments, photocatalyst (30 mg) was added to MG
solution (20 mg/L) in distilled water (50 mL). The mixture was first
stirred for 30 min in the dark to ensure the establishment of an
adsorption–desorption equilibrium, and then the dye was degraded
under visible light. Aliquots (5 mL) of the mixture were removed at
intervals of 10 min and transferred to a centrifuge tube, and the pho-
tocatalyst was removed by centrifugation. The change in the MG con-
centration was determined by monitoring its absorbance at 617 nm on a
UV/Vis spectrophotometer. The degradation of the MG dye was calcu-
lated according to ln(C0/C) = kappt [Eq. (1)], where C0 (mg/L), C (mg/
L), t (min), and kapp denote the initial concentration of MG, the con-
centration of MG at time t, the irradiation time with visible light, and the
reaction rate constant, respectively.
2.5. Characterization
The phase structures and crystallinities of the samples were analyzed
by powder X-ray diffractometry (Rigaku D/Max 2500) employing Cu-Kα
radiation. The morphologies and elemental distributions of the samples
were directly observed by means of a SUPRA55 scanning electron mi-
croscope (SEM) and a JEOL 2100 transmission electron microscope
(TEM). UV/Vis diffuse-reflectance spectra (UV/Vis DRS) were recorded
on a UV-3600 instrument to measure the optical response ranges and
band gaps of the products. Photoluminescence (PL) spectra were
recorded on an Agilent Cary Eclipse instrument at room temperature.
Raman spectra (Horiba Jobin-Yvon, France) were measured by using a
LabRAM XploRA Raman spectrometer with a 542 nm laser concentrated
2. Experimental section
2.1. Preparation of ZnCdS nanoparticles
Cd(NO3)2⋅4H2O (2.0008 g) and Zn(NO3)2⋅6H2O (1.4875 g) were
combined in distilled water (5 mL) and stirred for 30 min to form a
homogeneous mixed solution. A 6 mol/L aqueous NaOH solution (10
mL) was then added dropwise and stirring was continued for 30 min.
Thiourea (20 mmol) was then slowly dropped into the mixture and
stirring was continued for approximately 1 h to obtain a homogeneous
product. The resulting mixture was transferred to a Teflon-lined stain-
less steel autoclave and allowed to react for 12 h at 180 ◦C. After cooling
to room temperature, the yellow ZnCdS was collected by centrifugation
and washed several times with absolute ethanol and distilled water. The
pure ZnCdS was dried in a vacuum oven at 70 ◦C for 12 h.
on a spot about 3 μm in diameter. X-ray fluorescence (XRF) spectrometry
was performed on a Thermo Fisher 3600 instrument. X-ray photoelec-
tron spectroscopy (XPS, PHI-5000 versaprobe) on a Thermo ESCALAB
250XI instrument provided a convenient strategy for analyzing the
energy-state distribution on the surfaces of the samples. Total organic
carbon (TOC) was measured by means of a Shimadzu-GL TOC-L CPH
analyzer.
2.2. Synthesis of Bi2WO6 microspheres
2.6. Electrochemical analysis
Bi(NO3)3⋅5H2O (2.9104 g) and Na2WO4⋅2H2O (0.9896 g) were each
taken up in distilled water (60 mL), the solutions were combined in a
dropwise manner, and stirring was continued for 30 min. The mixture
was transferred to a Teflon-lined stainless steel autoclave and main-
tained at 180 ◦C for 6 h. Thereafter, it was allowed to cool naturally, and
then removed from the reactor. The pure white Bi2WO6 sample was
collected by centrifugation and washed 3–4 times each with absolute
ethanol and distilled water. The pure Bi2WO6 was dried at 60 ◦C over-
night in a vacuum drying oven.
A CHI660D electrochemical workstation was used to measure the
photoelectric properties of the samples. An Ag/AgCl electrode was used
as the reference electrode, with a Pt wire cathode as the counter elec-
trode. The working electrode was a photoanode made up of ZnCdS,
Bi2WO6, or the ZnCdS/Bi2WO6 composites. Each working electrode was
prepared with a total area of 0.5 cm2 and an active area of 0.12 cm2. The
preparation process was as follows: 8 mg of each sample was weighed
and evenly dispersed in N,N-dimethylformamide (DMF; 4 mL) with the
aid of ultrasound. Under irradiation from a simulated natural light
source, the performance of the sample was measured in an electrolyte of
0.1 M Na2SO4 solution over 360 s. The photocurrent response perfor-
mance was measured at a steady potential of +0.7 V vs. Ag/AgCl [8].
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 1. Schematic illustration of the preparation of ZnCdS/Bi2WO6 composites.
3. Results and discussion
Table 1
Comparison of kinetic parameters for photocatalytic degradation over Bi2WO6-
based materials.
3.1. XRD and XRF analysis
Catalysts
Light source
k (minꢀ 1
)
Ref.
The XRD patterns of ZnCdS, Bi2WO6, and the ZnCdS/Bi2WO6 com-
posites are exhibited in Fig. 2. The characteristic diffraction peaks at
28.30◦, 32.79◦, 47.14◦, 55.82◦, 58.54◦, 69.04◦, and 78.35◦ correspond
to the (131), (200), (202), (262), (331), (083), and (402) planes,
respectively, of the hexagonal phase of Bi2WO6 (JCPDS file no.
39–0256). The diffraction peaks at 25.5◦, 27.1◦, 28.8◦, 37.4◦, 44.8◦,
48.9◦, and 52.2◦ correspond to the (100), (002), (101), (102), (110),
(103), and (200) planes, respectively, of the hexagonal phase of ZnCdS
(JCPDS file no. 40–0836) [38,39]. The well-matched strong diffraction
peaks of the composites, apparently free from impurities, prove the high
crystallinity of the materials.
Bi2WO6 (140 ◦C)
150 W Xe lamp
500 W Wolfram lamp
300 W Xe lamp
300 W Xe lamp
1000 W Xe lamp
0.008
[1]
Bi2WO6/porous-g–C3N4–15
PO4-doped Bi2WO6
0.0433
0.0529
0.00397
0.0534
[2]
[3]
3-layered 0.4CeO2/0.6Bi2WO6
1.3-ZnCdS/Bi2WO6
[4]
This study
Furthermore, different elements have different ratios of wavelength and
energy. The number or density of X-rays emitted by a specific element in
a certain period of time can be used to measure the quantity of this
element. It is obvious that no other elements were detected except Zn,
Cd, S, Bi, W and O, which indicates that ZnCdS/Bi2WO6 composite has
been successfully prepared. Furthermore, the contents of elements have
been calculated in the Table 2. The elemental contents of Zn, Cd, and S
were found to be 25.32 wt. %, 42.78 wt. % and 26.33 wt. %, respec-
tively. And the elemental contents of Bi, and W were found to be 32.81
wt. % and 65.14 wt. %, respectively. So, the proportion of n(Bi)/n(W) is
2.25:1 according to Wt%/M (M: Molar mass of the element), which is
close to the value of n(Bi)/n(W) in Bi2WO6.
As is shown in Table 2, chemical composition and element content of
ZnCdS/Bi2WO6 composite was investigated by X‾ray fluorescence im-
aging (XRF). XRF spectroscopy analysis technology can be used to
identify specific elements in substances and quantify them at the same
time. It can determine the specific element according to the emission
wavelength (λ) and energy (E) of the X-ray, and determine the amount of
this element by measuring the density of the corresponding ray.
3.2. SEM and BET analysis
The SEM morphologies of ZnCdS, Bi2WO6, and a ZnCdS/Bi2WO6
composite are shown in Fig. 3. ZnCdS displays an agglomerated granular
structure, whereas Bi2WO6 shows a microsphere structure composed of
numerous nanosheets (Fig. 3a and b). From Fig. 3c, the thickness of the
sheets in the Bi2WO6 microspheres can be estimated as about 20 nm. In
Fig. 3d, it can be seen that Bi2WO6 is evenly covered with granular
ZnCdS. The loading of ZnCdS particles increases the surface area and the
number of active sites of the photocatalytic composites, which is ad-
vantageous for their photocatalytic activity.
BET analyses of pure ZnCdS, Bi2WO6, and the ZnCdS/Bi2WO6 com-
posites in different proportions are displayed in Table 3. With increasing
amounts of ZnCdS, the surface areas of the composites increased, which
is beneficial for exposing more active sites and accelerating the transport
rate of photogenerated carriers.
Fig. 2. XRD patterns of ZnCdS, Bi2WO6, and ZnCdS/Bi2WO6 composites.
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Table 2
Chemical composition of ZnCdS and Bi2WO6 complex catalysts.
Samples
Element (Weight %)
n(Zn)/n(Cd)/n(S)
0.95:0.93:2
n(Bi)/n(W)
2.25:1
Zn
Cd
S
Bi
W
ZnCdS
25.32
42.78
26.33
Bi2WO6
32.81
65.14
Fig. 3. SEM images of ZnCdS (a), Bi2WO6 (b, c), and the 1.3-ZnCdS/Bi2WO6 composite (d).
agglomeration of ZnCdS particles. It can be seen that only Bi, W, O, Cd,
S, and Zn were present on the surface of ZnCdS/Bi2WO6 (Fig. 4e). The
zeta potential of ZnCdS in water was measured as ꢀ 19.6 mV, indicating
that its surface bore negative charges (Fig. 4f). Thus, Bi6+ from Bi2WO6
was easily adsorbed by ZnCdS, and ZnCdS nanoparticles tended to grow
on the Bi2WO6 microspheres [41].
Table 3
Specific surface areas of ZnCdS, Bi2WO6, 1-ZnCdS/Bi2WO6, 1.3-ZnCdS/Bi2WO6,
and 1.5-ZnCdS/Bi2WO6.
No.
Samples
Specific surface area (m2/g)
a
b
c
ZnCdS
25.179
24.709
24.210
24.537
26.633
Bi2WO6
1-ZnCdS/Bi2WO6
1.3-ZnCdS/Bi2WO6
1.5-ZnCdS/Bi2WO6
d
e
3.4. Diffuse-reflectance spectra
The light-response range and energy-band structure of a photo-
catalyst are critical for its efficacy. To assess the photocatalytic activities
of the composites, the photo-absorption properties of Bi2WO6, ZnCdS,
and the ZnCdS/Bi2WO6 composites were measured by DRS. The ab-
sorption edges of ZnCdS and Bi2WO6 are seen at about 580 and 460 nm,
respectively, as shown in Fig. 5. Compared with Bi2WO6, the photo-
absorption of the ZnCdS/Bi2WO6 composites shows an apparent
enhancement owing to the successful coupling of ZnCdS and Bi2WO6
[42]. The spectra of the ZnCdS/Bi2WO6 composites are similar to that of
ZnCdS, implying that ZnCdS plays a leading role in the ZnCdS/Bi2WO6
photocatalysts. Furthermore, the Kubelka–Munk (KM) expression was
3.3. TEM analysis
TEM images of ZnCdS, Bi2WO6, and a ZnCdS/Bi2WO6 composite are
shown in Fig. 4. The ZnCdS nanoparticles have diameters in the range
20–50 nm, whereas the Bi2WO6 microspheres have diameters of 2–3 μm.
An HRTEM image (Fig. 4d) of a ZnCdS/Bi2WO6 composite shows lattice
fringes of 0.315 nm and 0.31 nm, corresponding to the (131) planes of
Bi2WO6 [38] and the (101) planes of ZnCdS [39,40], respectively. The
clear lattice stripe demonstrates good crystallization of the material. The
tight contact of the interface between ZnCdS and Bi2WO6 may
contribute to the rapid transfer of photogenerated carriers, thereby
promoting the separation of photogenerated electron–hole pairs. The
assembly of ZnCdS/Bi2WO6 composites effectively prevented the
used to calculate the band gap:
αh
ν
= A(ℎ
ν
–Eg)n/2, where A,
α, h, and ν
denote a constant, the absorption coefficient, Planck’s constant, and the
light frequency, respectively [43]. The values of n are 1 and 4 [44,45].
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 4. TEM images of pure ZnCdS (a), Bi2WO6 and the 1.3-ZnCdS/Bi2WO6 composite (b, c); HRTEM image of the 1.3-ZnCdS/Bi2WO6 composite (d); EDS image of
the 1.3-ZnCdS/Bi2WO6 composite (e); zeta potential of the as-synthesized ZnCdS dispersed in aqueous solution (f).
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 5. UV/Vis diffuse absorption spectra (a), and Eg of ZnCdS, Bi2WO6, and
ZnCdS/Bi2WO6 composites with different mass ratios (b).
The band gaps (Eg) for ZnCdS, Bi2WO6, and the 1-ZnCdS/Bi2WO6,
1.3-ZnCdS/Bi2WO6, and 1.5-ZnCdS/Bi2WO6 composites were calculated
as 2.20, 2.62, 2.25, 2.24, and 2.22 eV, respectively. The energy band
edges were further calculated according to the equations EVB = X – Ee +
0.5Eg and ECB = EVB + Eg Refs. [46,47]. Here, X denotes the electro-
negativity, and the values of X for ZnCdS and Bi2WO6 are 5.23 and 6.39
eV, respectively. Ee is the free electron energy of hydrogen of 4.5 eV.
Thus, EVB and ECB for ZnCdS are 1.83 and ꢀ 0.37 eV, and EVB and ECB for
Bi2WO6 are 3.2 and 0.58 eV [12]. Kadeer et al. prepared CdS quantum
dots (QDs)/Bi2WO6 with a band gap of 2.32 eV [48]. Safaei et al. syn-
thesized a two-dimensional hierarchical structured photocatalyst based
on Bi2WO6 with ZnS, with a band gap of 2.80 eV [49]. Compared with
these previous studies, our ZnCdS/Bi2WO6 composites have narrow
band gaps, which may promote the photocatalytic activity.
Fig. 6. (a) Raman spectra of ZnCdS, Bi2WO6, and the 1.3-ZnCdS/Bi2WO6
composite; (b) FTIR spectra of ZnCdS, Bi2WO6, and ZnCdS/Bi2WO6.
only exhibit the characteristic peaks of ZnCdS of 310 and 614 cmꢀ 1, but
also display the characteristic peaks of Bi2WO6, indicating that they
contain discrete ZnCdS and Bi2WO6. The main band of Bi2WO6 at 3406
cmꢀ 1 can be attributed to the OH stretching vibration of hydroxyl in
lattice water. A peak at 1634 cmꢀ 1 corresponds to a weak C C vibration
–
–
from the bending of aromatic groups [51]. The bands at about 735 cmꢀ 1
can be attributed to O–W–O bonds [52]. The peak of ZnCdS at 1376
cmꢀ 1 can be attributed to a metal-thiourea complex [53].
3.6. Photocatalytic activity of ZnCdS/Bi2WO6 composites
3.5. Raman and FTIR spectra
The degradation activities of the ZnCdS/Bi2WO6 samples were
evaluated under visible light, as shown in Fig. 7. After irradiation for 50
min, the color of the solution was essentially removed and the absorp-
tion peak of MG disappeared (Fig. 7a). The absorption peak showed a
redshift, its maximum shifting from 617 to 607 cmꢀ 1 [32]. The degra-
dation of MG involves the following reactions:
Fig. 6a shows the Raman spectra of ZnCdS, Bi2WO6, and a ZnCdS/
Bi2WO6 composite. The pure ZnCdS exhibits a Raman peak at 310 cmꢀ 1
,
corresponding to a 1-LO (longitudinal optical) phonon mode, which is
instigated by the vibration of the S atom in the ZnCdS lattice, and a
further peak at 614 cmꢀ 1, corresponding to 2-LO [16]. The pure Bi2WO6
exhibits Raman peaks at 309, 705, 792, and 828 cmꢀ 1. The peak at 309
cmꢀ 1 represents the entirely symmetric stretching mode of WO6 octa-
hedra and the Bi–O stretching mode [34]. The peak at 705 cmꢀ 1 rep-
resents the asymmetric stretching vibration mode of W–O. The peaks at
792 and 828 cmꢀ 1 correspond to antisymmetric and symmetric modes of
terminal O–W–O, respectively [50]. The ZnCdS/Bi2WO6 composites not
catalyst → eꢀ + h+
(1)
(2)
(3)
(4)
e
ꢀ + O2 → ⋅Oꢀ2
h+ + H2O → ⋅OH
h+ + ⋅Oꢀ2 + ⋅OH + MG → products
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 7. (a) Temporal evolution of the spectra during
the photodegradation of MG over the 1.3-ZnCdS/
Bi2WO6 composite; (b) photodegradation of MG
over ZnCdS, Bi2WO6, and ZnCdS/Bi2WO6 compos-
ites with different mass ratios under visible light
irradiation; (c) kinetic data for the degradation of
MG in the presence of ZnCdS/Bi2WO6 composites
with different mass ratios; (d) cycling runs of MG
photocatalytic degradation over 1.3-ZnCdS/
Bi2WO6; (e) XRD patterns of the 1.3-ZnCdS/Bi2WO6
composite before and after the cycle run experi-
ment; (f, g) TEM images of the 1.3-ZnCdS/Bi2WO6
composite before and after the cycle run
experiment.
As shown in Fig. 7b, the 1.3-ZnCdS/Bi2WO6 composite exhibited the
the degradation efficiency of this composite remained at 90% after four
cycles, demonstrating its excellent stability. To further investigate the
stability of the 1.3-ZnCdS/Bi2WO6 composite during the repeated pho-
tocatalytic experiments, the XRD pattern (Fig. 7e) and TEM images
(Fig. 7f and g) of the recovered composite were acquired. As shown in
Fig. 7e, the crystallinity of the 1.3-ZnCdS/Bi2WO6 composite was
slightly reduced after the repeated cycles. Nevertheless, as shown in
Fig. 7f and g, compared with the sample before the degradation cycle
test, the ZnCdS and Bi2WO6 were still closely bound, and the crystal
phase was well maintained after the four cycles. The catalytic efficiency
best activity, giving a degree of degradation of about 94% after 50 min
of visible light irradiation [54]. Bi2WO6 showed no photocatalytic ac-
tivity, whereas ZnCdS exhibited a removal efficiency of 63%. The
degradation rates of the pure materials and composites were combined
according to Eq. (1) (Fig. 7c). Values of k for MG degradation over
1.3-ZnCdS/Bi2WO6, 1.5-ZnCdS/Bi2WO6, 1-ZnCdS/Bi2WO6, and pure
ZnCdS were evaluated as 0.0534, 0.0449, 0.0305, and 0.0161 minꢀ 1
,
respectively. Fig. 7d shows the photocatalytic degradation actions of the
1.3-ZnCdS/Bi2WO6 composite over repeated cycles. It can be seen that
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X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
of ZnCdS/Bi2WO6 is compared with those of other catalysts in Table 1.
3.7. TOC analysis
To further investigate the photocatalytic degradation of MG, the
TOCs of MG solutions after 50 min of photodegradation over Bi2WO6,
ZnCdS, and the ZnCdS/Bi2WO6 composites are shown in Fig. 8. The
principle of high-temperature catalytic combustion oxidation-non-
dispersive infrared detection was used. Among all of the samples, 1.3-
ZnCdS/Bi2WO6 showed the lowest residual amount of TOC (8.306 mg/
L), as compared to Bi2WO6 (148.3 mg/L), ZnCdS (67.42 mg/L), 1-
ZnCdS/Bi2WO6 (9.568 mg/L), and 1.5-ZnCdS/Bi2WO6 (8.968 mg/L),
respectively, when the original MG concentration was 152.8 mg/L [8].
The excellent mineralization efficiency of the 1.3-ZnCdS/Bi2WO6 com-
posite was calculated as 94.56%.
3.8. PL analysis
To further study the recombination of photogenerated carriers,
photoluminescence (PL) spectroscopy is a simple and feasible method.
In general, the higher the PL intensity, the poorer the separation per-
formance of the photogenerated carriers, and hence the lower the
photocatalytic activity of the semiconductor [55]. Fig. 9 shows the PL
spectra of the samples upon excitation at 300 nm. The decrease in in-
tensity shows that the composite of ZnCdS and Bi2WO6 greatly reduced
the recombination of photogenerated carriers. It can be observed that
the PL peak intensity of the 1.3-ZnCdS/Bi2WO6 composite was lower
than those of the other samples, indicating a higher separation ability
and enhanced transfer efficiency of photogenerated carriers.
Fig. 9. PL spectra of ZnCdS, Bi2WO6, and ZnCdS/Bi2WO6 composites.
those of pure ZnCdS (5.5
μ
A/cm2) and Bi2WO6 (0.5
μ
A/cm2). The
increased photocurrent indicates greater separation and migration effi-
ciency of carriers [56,57]. Mott–Schottky (MS) plots for ZnCdS, Bi2WO6,
and ZnCdS/Bi2WO6 composites are shown in Fig. 10b. By comparing the
slopes of the linear parts in these MS plots, it can be seen that the slope
for 1.3-ZnCdS/Bi2WO6 is smaller than those for pure ZnCdS and Bi2WO6,
further confirming the higher carrier density in this composite
photocatalyst.
3.9. Electrochemical measurements
To assess the electrochemical performances of the ZnCdS/Bi2WO6
photocatalysts, PEC measurements were carried out. Photocurrent
densities of ZnCdS, Bi2WO6, and the ZnCdS/Bi2WO6 composites were
measured in 0.1 M Na2SO4 solution with cycles of 30 s under irradiation
with visible light. Electrons in the photocatalyst are excited under illu-
mination, giving rise to a high transient photocurrent. At the same time,
holes will attract electrons and block their transmission. When the
transmission and recombination reach dynamic equilibrium, the
photocurrent curve is stable. It is obvious from Fig. 10a that the
3.10. Photocatalytic mechanism
To determine the main active species of the ZnCdS/Bi2WO6 com-
posites, isopropanol (IPA, 0.0005 g), methanol (MeOH, 1 mL), and p-
benzoquinone (PBQ, 0.0058 g) were used as trapping agents in photo-
catalysis for hydroxyl radical (⋅OH), superoxide radical (⋅Oꢀ 2), and
holes (h+) [58]. The experimental results are presented in Fig. 11. It can
be observed that the three capture scavengers had inhibitory effects on
the degradation. The degradation rate decreased most obviously after
the addition of PBQ, implying that ⋅Oꢀ 2 is the most active species in
the photocatalytic degradation [59]. Nevertheless, the performance of
ZnCdS/Bi2WO6 also showed moderate decreases in the presence of IPA
and MeOH, confirming ⋅OH and h+ to be significant active species.
photocurrent of 1.3-ZnCdS/Bi2WO6 (8.5
μ
A/cm2) was far stronger than
3.11. Photocatalytic reaction mechanisms over ZnCdS/Bi2WO6
The surface chemical states of the semiconductor materials were
measured and compared by X-ray photoelectron spectroscopy. The full-
scan XPS patterns of ZnCdS and Bi2WO6 demonstrated the presence of
Zn, Cd, C, S, Bi, W, and O on the surfaces of the composite (Fig. 12a). A C
1s orbital peak at 285 eV can be discerned in the figure. In Fig. 12b, the
peaks at 1022.57 and 1045.67 eV correspond to Zn 2p1/2 and Zn 2p3/2 of
ZnCdS [60], and two similar peaks are seen at 1022.67 and 1045.87 eV
for the 1.3-ZnCdS/Bi2WO6 composite. In Fig. 12c, the Cd 3d peak of
ZnCdS can be divided into Cd 3d3/2 and Cd 3d5/2 peaks at 411.77 and
404.97 eV, respectively, and the corresponding Cd 3d peaks of the
1.3-ZnCdS/Bi2WO6 composite appear at 404.67 and 411.47 eV [50]. In
Fig. 12d, the peak of ZnCdS at 161.47 eV corresponds to the charac-
teristic orbital peak of S 2p [51]. Fig. 12e shows the high-resolution Bi 4f
XPS pattern of the composite, in which the peaks at 164.57 and 159.37
eV can be attributed to Bi 4f5/2 and Bi 4f7/2, respectively [36]. As shown
in Fig. 12f, the XPS pattern of the W 4f orbital features two main peaks,
corresponding to W 4f7/2 (35.57 eV) and W 4f5/2 (36.67 eV), confirming
Fig. 8. TOCs of MG solutions in the presence of ZnCdS, Bi2WO6, and ZnCdS/
Bi2WO6 composites.
8

X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
the presence of W6+ ions. The binding energies of the W 4f orbital of the
1.3-ZnCdS/Bi2WO6 composite are at 35.67 and 36.77 eV, higher than
those for Bi2WO6, indicating that the W6+ valence is lower in the former
[61]. The XPS pattern of O 1s is shown in Fig. 12g. For the
1.3-ZnCdS/Bi2WO6 composite, two peaks at 530.07 and 531.97 eV can
be ascribed to O atoms in the Bi2WO6 lattice and surface –OH groups,
respectively. The O 1s peaks for Bi2WO6 are seen at 530.17 and 532.07
eV. It can be surmised that the W 4f and O 1s peak intensities of the
1.3-ZnCdS/Bi2WO6 composite are decreased due to surface oxygen atom
vacancies. The O 1s peak moves to higher energy, which also indicates
that the oxygen vacancy concentration on the surface of Bi2WO6 in the
1.3-ZnCdS/Bi2WO6 composite is higher [62–64]. From the XPS patterns,
we conclude that the heterojunction prompts photogenerated electrons
in ZnCdS to migrate to Bi2WO6, while holes in Bi2WO6 transfer to ZnCdS,
thereby achieving Fermi level balance. Strong acceptor coupling at the
contact interface of ZnCdS and Bi2WO6 is established due to the redis-
tribution of free electrons.
A possible migration pathway of photogenerated electron–hole pairs
is that electrons may migrate from the conduction band (CB) of ZnCdS to
the CB of Bi2WO6. Meanwhile, holes may migrate from the valence band
(VB) of Bi2WO6 to the VB of ZnCdS. However, the CB potential (0.58 eV)
of Bi2WO6 is higher than Eθ (O2/⋅Oꢀ 2) (ꢀ 0.13 eV vs. Ag/AgCl), and so
the active species (⋅Oꢀ 2) cannot be produced. Furthermore, the VB
potential (+1.83 eV) of ZnCdS is lower than Eθ (⋅OH/H2O) (+2.68 eV),
and so the active species (⋅OH) cannot be generated [65]. The first hy-
pothesis is impossible to achieve, and this type of photocatalytic per-
formance is not consistent with the experimental results. Alternatively,
the heterojunction between ZnCdS and Bi2WO6 may constitute a
Z-scheme photocatalyst. According to our analysis, the CB (ꢀ 0.37 eV) of
ZnCdS is lower than Eθ (O2/⋅Oꢀ 2) (ꢀ 0.13 eV). Hence, photogenerated
electrons reduce O2 to form the active species (⋅Oꢀ 2). Moreover, the
VB (+3.2 eV) potential of Bi2WO6 is higher than Eθ (⋅OH/H2O) (+2.68
eV), implying that photogenerated holes will produce the active species
(⋅OH) from OHꢀ . Simultaneously, some electrons in the CB of Bi2WO6
will rapidly combine with holes in the VB of ZnCdS. Eventually, ⋅OH and
⋅Oꢀ 2 as active species may engage in photooxidation and degrade
organic pollutants. Ultimately, the heterojunction between Bi2WO6 and
ZnCdS may distinctly strengthen the separation of eꢀ /h+ and improve
charge transfer at the interface. Consequently, compared with pure
ZnCdS and Bi2WO6, the ZnCdS/Bi2WO6 catalyst has excellent photo-
catalytic activity. The mechanism of the Z-scheme in the photocatalytic
degradation process is illustrated in Fig. 13. Besides, the photogenerated
holes on ZnCdS can directly react with MG to form CO2 and H2O [66]. In
this case, the photogenerated carriers may be separated in physical
space, hindering their recombination. In short, the combination of
ZnCdS and Bi2WO6 leads to the effective redox properties, enhancing the
reduction of MG under visible light [67,68].
Fig. 10. (a) Transient photocurrent responses for ZnCdS, Bi2WO6, and ZnCdS/
Bi2WO6 composites with different mass ratios; (b) Mott–Schottky plots of
ZnCdS, Bi2WO6, and the ZnCdS/Bi2WO6 composites.
4. Conclusions
In summary, ZnCdS/Bi2WO6 composites have been efficiently pre-
pared by a three-step method and their photocatalytic performances in
the degradation of MG have been investigated under visible light irra-
diation. The ZnCdS/Bi2WO6 composites showed superior photocatalytic
efficiency compared to the individual components. The degree of
degradation of MG over 1.3-ZnCdS/Bi2WO6 composite was 94%, 3.3 and
58.8 times higher those over ZnCdS and Bi2WO6, respectively. This
enhancement of photocatalytic performance can be ascribed to the
effective separation of eꢀ /h+ pairs, limiting their recombination. Thus,
ZnCdS/Bi2WO6 composite may constitute a good photocatalytic mate-
rial for the removal of environmental pollutants.
CRediT authorship contribution statement
Fig. 11. Effects of different scavengers on the degradation of MG in the pres-
ence of the 1.3-ZnCdS/Bi2WO6 composite under visible light irradiation.
Xiaohan Zhao: Methodology, Investigation, Data curation, Formal
analysis, Writing – review & editing. Yue Xu: Investigation, Formal
9

X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 12. XPS survey scans of ZnCdS, Bi2WO6, and the 1.3-ZnCdS/Bi2WO6 composite (a); high-resolution XPS patterns of (b) Zn 2p, (c) Cd 3d, (d) S 2p, (e) Bi 4f, (f) W
4f, and (g) O 1s obtained from ZnCdS, Bi2WO6, and 1.3-ZnCdS/Bi2WO6.
10

X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
Fig. 13. Proposed mechanism for the photocatalytic degradation process by ZnCdS/Bi2WO6 photocatalysts under visible light.
[8] H. Cui, B. Li, Z. Li, X. Li, S. Xu, Z-scheme-based CdS/CdWO4 heterojunction visible
light photocatalyst for dye degradation and hydrogen evolution, Appl. Surf. Sci.
455 (2018) 831–840.
analysis, Writing – review & editing. Xiaohong Wang: Investigation,
Data curation, Formal analysis. Qian Liang: Methodology, Writing –
review & editing, Supervision. Man Zhou: Methodology, Investigation,
Writing – review & editing. Song Xu: Methodology, Investigation, Su-
pervision. Zhongyu Li: Writing – review & editing, Supervision, Fund-
ing acquisition.
[9] J. Wang, L. Tang, G. Zeng, Y. Deng, Y. Liu, L. Wang, Y. Zhou, Z. Guo, J. Wang,
C. Zhang, Atomic scale g-C3N4/Bi2WO6 2D/2D heterojunction with enhanced
photocatalytic degradation of ibuprofen under visible light irradiation, Appl.
Catal., B 209 (2017) 285–294.
[10] A. Zhou, L. Liao, X. Wu, K. Yang, C. Li, W. Chen, P. Xie, Fabrication of a Z-scheme
nanocomposite photocatalyst for enhanced photocatalytic degradation of
ibuprofen under visible light irradiation, Separ. Purif. Technol. 250 (2020)
117241.
Declaration of competing interest
[11] L. Zhang, H. Wang, Z. Chen, P.K. Wong, J. Liu, Bi2WO6 micro/nano-structures:
synthesis, modifications and visible-light-driven photocatalytic applications, Appl.
Catal., B 106 (2011) 1–13.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[12] Y. Zhu, Y. Wang, Q. Ling, Y. Zhu, Enhancement of full-spectrum photocatalytic
activity over BiPO4/Bi2WO6 composites, Appl. Catal., B 200 (2017) 222–229.
[13] H. Liu, Z. Chen, Y. Wang, Plasmonic Ag-coated BiOBr nanosheets grown on
graphene with excellent visible-light photocatalytic activity, J. Photochem.
Photobiol., A 326 (2016) 30–40.
Acknowledgments
[14] N.D. Phu, L.H. Hoang, P. Van Hai, T.Q. Huy, X.-B. Chen, W.C. Chou, Photocatalytic
activity enhancement of Bi2WO6 nanoparticles by Ag doping and Ag nanoparticles
modification, J. Alloys Compd. 824 (2020) 153914.
This work was financially supported by the National Natural Science
Foundation of China (Nos. 21876015 and 21703019).
[15] Y. Huang, X. Zhang, Z. Zhou, S. Shen, A new and facile co-modification by
introducing oxygen vacancies and loading Ag nanoparticles to promote the
photocatalytic activities of Bi2WO6, Mater. Res. Bull. 119 (2019) 110538.
[16] C. Duan, W. Luo, T. Jiu, J. Li, Y. Wang, F. Lu, Facile preparation and
characterization of ZnCdS nanocrystals for interfacial applications in photovoltaic
devices, J. Colloid Interface Sci. 512 (2018) 353–360.
References
[1] W. Wang, J. Fang, S. Shao, M. Lai, C. Lu, Compact and uniform TiO2@g-C3N4 core-
shell quantum heterojunction for photocatalytic degradation of tetracycline
antibiotics, Appl. Catal., B 217 (2017) 57–64.
[17] Y. Guo, J. Zhang, D. Zhou, S. Dong, Fabrication of Ag/CDots/BiOBr ternary
photocatalyst with enhanced visible-light driven photocatalytic activity for 4-
chlorophenol degradation, J. Mol. Liq. 262 (2018) 194–203.
[2] J. Yang, P. Deng, X. Wang, J. Huang, P. Li, Modification and functional
investigation of self-assembled two-dimensional TiO2 nanosheets with abundant
hydroxyl groups, Solid State Sci. 101 (2020) 106151.
[18] S. Fang, M. Sun, Y. Zhou, Q. Liang, Z. Li, S. Xu, Solvothermal synthesis of CdS QDs/
MWCNTs nanocomposites with high efficient photocatalytic activity under visible
light irradiation, J. Alloys Compd. 656 (2016) 771–776.
[3] X. Zhang, G. Zuo, X. Lu, C. Tang, S. Cao, M. Yu, Anatase TiO2 sheet-assisted
synthesis of Ti3+ self-doped mixed phase TiO2 sheet with superior visible-light
photocatalytic performance: roles of anatase TiO2 sheet, J. Colloid Interface Sci.
490 (2017) 774–782.
[19] P. Kulkarni, S.K. Nataraj, R.G. Balakrishna, D.H. Nagaraju, M.V. Reddy,
Nanostructured binary and ternary metal sulfides: synthesis methods and their
application in energy conversion and storage devices, J. Mater. Chem. 5 (2017)
22040–22094.
[4] J. Tyagi, H. Gupta, L.P. Purohit, Cascade structured ZnO/TiO2/CdS quantum dot
sensitized solar cell, Solid State Sci. 102 (2020) 106176.
[20] X. Xia, C. Zhu, J. Luo, Z. Zeng, C. Guan, C.F. Ng, H. Zhang, H.J. Fan, Synthesis of
free-standing metal sulfide nanoarrays via anion exchange reaction and their
electrochemical energy storage application, Small Mol 10 (2014) 766–773.
[21] P. Geng, S. Zheng, H. Tang, R. Zhu, L. Zhang, S. Cao, H. Xue, H. Pang, Transition
metal sulfides based on graphene for electrochemical energy storage, Adv. Energy
Mater. 8 (2018) 1703259.
[5] J. Low, B. Cheng, J. Yu, Surface modification and enhanced photocatalytic CO2
reduction performance of TiO2: a review, Appl. Surf. Sci. 392 (2017) 658–686.
[6] S. Gao, C. Guo, S. Hou, L. Wan, Q. Wang, J. Lv, Y. Zhang, J. Gao, W. Meng, J. Xu,
Photocatalytic removal of tetrabromobisphenol A by magnetically separable
flower-like BiOBr/BiOI/Fe3O4 hybrid nanocomposites under visible-light
irradiation, J. Hazard Mater. 331 (2017) 1–12.
[22] J. Mathew, E.I. Anila, Hydrothermal assisted chemical bath deposition of (Cd:Zn)S
thin film with high photosensitivity and low dark current, Sol. Energy 172 (2018)
165–170.
[7] H. Ji, T. Fei, L. Zhang, J. Yan, Y. Fan, J. Huang, Y. Song, Y. Man, H. Tang, H. Xu,
H. Li, Synergistic effects of MoO2 nanosheets and graphene-like C3N4 for highly
improved visible light photocatalytic activities, Appl. Surf. Sci. 457 (2018)
1142–1150.
11

X. Zhao et al.
Journal of Physics and Chemistry of Solids 154 (2021) 110075
[23] Q. Liang, S. Ploychompoo, J. Chen, T. Zhou, H. Luo, Simultaneous Cr(VI) reduction
and bisphenol A degradation by a 3D Z-scheme Bi2S3-BiVO4 graphene aerogel
under visible light, Biochem. Eng. J. 384 (2020) 123256.
[46] Z.Y. Peng, Y. Jiang, X. Wang, et al., Novel CdIn2S4 nano-octahedra/TiO2 hollow
hybrid heterostructure: in-situ synthesis, synergistic effect and enhanced dual-
functional photocatalytic activities, Ceram. Int. 45 (2019) 15942–15953.
[47] X. Chen, L. Li, W.Z. Zhang, Y.X. Li, Q. Song, L. Dong, Fabricate globular flower-like
CuS/CdIn2S4/ZnIn2S4 with high visible light response via microwave-assisted one-
step method and its multipathway photoelectron migration properties for
hydrogen evolution and pollutant degradation, ACS Sustain. Chem. Eng. 4 (2016)
6680–6688.
[24] S. Peng, Y. Yang, J. Tan, C. Gan, Y. Li, In situ loading of Ni2P on Cd0.5Zn0.5S with
red phosphorus for enhanced visible light photocatalytic H2 evolution, Appl, Surf.
Sci. 447 (2018) 822–828.
[25] S. Kai, B. Xi, Y. Wang, S. Xiong, One-pot synthesis of size-controllable core–shell
CdS and derived CdS@ZnxCd1ꢀ xS structures for photocatalytic hydrogen
production, Chem. Eur J. 23 (2017) 16653–16659.
[48] H. Maimaitizi, K. Kadeer, A. Reheman, D. Talifu, Y. Tursun, A. Abulizi, One-pot
sonochemical synthesis of 3D flower-like hierarchical AgCl microsphere with
enhanced photocatalytic activity, Environ. Sci. Pollut. Res. Int. 26 (2019)
26883–26892.
[26] H. Gong, X. Zhang, G. Wang, Y. Liu, Y. Li, Z. Jin, Dodecahedron ZIF-67 anchoring
ZnCdS particles for photocatalytic hydrogen evolution, J. Mol. Catal. 485 (2020)
110832.
[27] R. Chen, Z. Chen, M. Ji, H. Chen, Y. Liu, J. Xia, H. Li, Enhanced reactive oxygen
species activation for building carbon quantum dots modified Bi5O7I nanorod
composites and optimized visible-light-response photocatalytic performance,
J. Colloid Interface Sci. 532 (2018) 727–737.
[49] E. Safaei, S. Mohebbi, Boosted photocatalytic performance of uniform hetero-
nanostructures of Bi2WO6/CdS and Bi2WO6/ZnS for aerobic selective alcohol
oxidation, J. Photochem. Photobiol., A 371 (2019) 173–181.
[50] D. Xu, B. Cheng, W. Wang, C. Jiang, J. Yu, Ag2CrO4/g-C3N4/graphene oxide
ternary nanocomposite Z-scheme photocatalyst with enhanced CO2 reduction
activity, Appl. Catal., B 231 (2018) 368–380.
[28] Y. Sun, J. Liao, F. Dong, S. Wu, L. Sun, A Bi/BiOI/(BiO)2CO3 heterostructure for
enhanced photocatalytic NO removal under visible light, Chin, J. Catal. 40 (2019)
362–370.
[51] R. Singhal, M. Datta, Development of nanocomposites of bentonite with
polyaniline and poly(methacrylic acid), J. Appl. Polym. Sci. 103 (2007)
3299–3306.
[29] X. Li, W. Zhang, W. Cui, J. Li, Y. Sun, G. Jiang, H. Huang, Y. Zhang, F. Dong,
Reactant activation and photocatalysis mechanisms on Bi-metal@Bi2GeO5 with
oxygen vacancies: a combined experimental and theoretical investigation,
Biochem. Eng. J. 370 (2019) 1366–1375.
[52] Z. Lin, J. Li, Z. Zheng, J. Yan, P. Liu, C. Wang, G. Yang, Front cover picture: an
efficient route to isochromene derivatives via cascade radical cyclization and
radical-radical coupling, ACS Nano 9 (2015) 7256.
[30] X. Wang, J. Chen, X. Guan, L. Guo, Enhanced efficiency and stability for visible
light driven water splitting hydrogen production over Cd0.5Zn0.5S/g-C3N4
composite photocatalyst, Int. J. Hydrogen Energy 40 (2015) 7546–7552.
[31] T. Wang, G. Xiao, C. Li, S. Zhong, F. Zhang, One-step synthesis of a sulfur-doped
Bi2WO6/Bi2O3 composite with enhanced visible-light photocatalytic activity,
Mater. Lett. 138 (2015) 81–84.
[53] C. Duan, W. Luo, T. Jiu, J. Li, Y. Wang, F. Lu, Facile preparation and
characterization of ZnCdS nanocrystals for interfacial applications in photovoltaic
devices, J. Alloys Compd. 512 (2019) 353–360.
[54] Q. Liang, J. Jin, M. Zhang, C. Liu, S. Xu, C. Yao, Z. Li, Construction of mesoporous
carbon nitride/binary metal sulfide heterojunction photocatalysts for enhanced
degradation of pollution under visible light, Appl. Catal., B 218 (2017) 545–554.
[55] C. Zhang, Y. Zhu, Synthesis of square Bi2WO6 nanoplates as high-activity visible-
light-driven photocatalysts, Chem. Mater. 17 (2005) 3537–3545.
[32] L. Chen, H. Hua, Q. Yang, C. Hu, Visible-light photocatalytic activity of Ag2O-
coated Bi2WO6 hierarchical microspheres assembled by nanosheets, Appl. Surf. Sci.
327 (2015) 62–67.
[33] J. Zhang, T. Chen, H. Lu, Z. Yang, F. Yin, J. Gao, Q. Liu, Y. Tu, Hierarchical Bi2WO6
architectures decorated with Pd nanoparticles for enhanced visible-light-driven
photocatalytic activities, Appl. Surf. Sci. 404 (2017) 282–290.
[56] Q. Liang, J. Jin, C. Liu, S. Xu, C. Yao, Z. Li, Fabrication of the ternary
heterojunction Cd0.5Zn0.5S@UIO-66@g-C3N4 for enhanced visible-light
photocatalytic hydrogen evolution and degradation of organic pollutants, Inorg.
Chem. Front. 5 (2018) 335–343.
[34] C. Li, G. Chen, J. Sun, J. Rao, Z. Han, Y. Hu, W. Xing, C. Zhang, Doping effect of
phosphate in Bi2WO6 and universal improved photocatalytic activity for removing
various pollutants in water, Appl. Catal., B 188 (2016) 39–47.
[57] X. Zheng, C. Li, M. Zhao, Z. Zheng, L. Wei, F. Chen, X. Li, Photocatalytic
degradation of butyric acid over Cu2O/Bi2WO6 composites for simultaneous
production of alkanes and hydrogen gas under UV irradiation, Int. J. Hydrogen
Energy 42 (2017) 7917–7929.
[35] R. Wu, H. Song, N. Luo, Y. Sheng, G. Ji, Microwave-assisted preparation and
enhanced photocatalytic activity of Bi2WO6/BiOI heterojunction for organic
pollutants degradation under visible-light irradiation, Solid State Sci. 87 (2019)
101–109.
[58] H. Cui, B. Li, Y. Zhang, X. Zheng, X. Li, Z. Li, S. Xu, Constructing Z-scheme based
CoWO4/CdS photocatalysts with enhanced dye degradation and H2 generation
performance, Int. J. Hydrogen Energy 43 (2018) 18242–18252.
[36] Y. Su, G. Tan, T. Liu, L. Lv, Y. Wang, X. Zhang, Z. Yue, H. Ren, A. Xia,
Photocatalytic properties of Bi2WO6/BiPO4 Z-scheme photocatalysts induced by
double internal electric fields, Appl. Surf. Sci. 457 (2018) 104–114.
[37] D.O. Charkin, D.N. Lebedev, S.Y. Stefanovich, S.M. Kazakov, Uranium substitution
for tungsten in the Bi2WO6–Bi2UO6 system: Formation of a broad high-temperature
solid solution, Solid State Sci. 12 (2010) 2079–2085.
[59] S. Fang, C. Ding, Q. Liang, Z. Li, S. Xu, Y. Peng, D. Lu, In-situ precipitation synthesis
of novel BiOCl/Ag2CO3 hybrids with highly efficient visible-light-driven
photocatalytic activity, J. Alloys Compd. 684 (2016) 230–236.
[60] H. Liu, Z. Jin, Z. Xu, Hybridization of Cd0.2Zn0.8S with g-C3N4 nanosheets: a visible-
light-driven photocatalyst for H2 evolution from water and degradation of organic
pollutants, Dalton Trans. 44 (2015) 14368–14375.
[38] F. Deng, Y. Liu, X. Luo, D. Chen, S. Wu, S. Luo, Enhanced photocatalytic activity of
Bi2WO6/TiO2 nanotube array composite under visible light irradiation, Separ.
Purif. Technol. 120 (2013) 156–161.
[61] X. Jia, M. Tahir, L. Pan, Z.-F. Huang, X. Zhang, L. Wang, J.-J. Zou, Direct Z-scheme
composite of CdS and oxygen-defected CdWO4: an efficient visible-light-driven
photocatalyst for hydrogen evolution, Appl. Catal., B 198 (2016) 154–161.
[62] X. Sun, J. Wu, Q. Li, Q. Liu, Y. Qi, L. You, Z. Ji, P. He, P. Sheng, J. Ren, W. Zhang,
J. Lu, J. Zhang, Fabrication of BiOIO3 with induced oxygen vacancies for efficient
separation of the electron-hole pairs, Appl. Catal., B 218 (2017) 80–90.
[63] Y. Yan, H. Yang, Z. Yi, T. Xian, R. Lia, X. Wang, Construction of Ag2S@CaTiO3
heterostructure photocatalysts for enhanced photocatalytic degradation of dyes,
Desalin. Water Treat. 170 (2019) 349–360.
[39] W.-J. Ong, J.-J. Yeong, L.-L. Tan, B.T. Goh, S.-T. Yong, S.-P. Chai, Synergistic effect
of graphene as a co-catalyst for enhanced daylight-induced photocatalytic activity
of Zn0.5Cd0.5S synthesized via an improved one-pot co-precipitation-hydrothermal
strategy, RSC Adv. 4 (2014) 59676–59685.
[40] X. Guo, D. Wu, X. Long, Z. Zhang, F. Wang, G. Ai, X. Liu, Nanosheets-assembled
Bi2WO6 microspheres with efficient visible-light-driven photocatalytic activities,
Mater. Char. 163 (2020) 110297.
[41] H. Wang, H. Ye, B. Zhang, F. Zhao, B. Zeng, Synthesis of ZnIn2S4/CdS
heterostructure based on electrostatic interaction mechanism for indirect
photoelectrochemical detection of dopamine, J. Phys. Chem. C 122 (2018)
20329–20336.
[64] Y. Yan, H. Yang, Z. Yi, X. Wang, R. Li, T. Xian, Evolution of Bi nanowires from
BiOBr nanoplates through a NaBH4 reduction method with enhanced
photodegradation performance, Environ. Eng. Sci. 37 (2020) 64–77.
[65] J. Luo, X. Zhou, L. Ma, L. Xu, X. Xu, Z. Du, J. Zhang, Enhancing visible light
photocatalytic activity of direct Z-scheme SnS2/Ag3PO4 heterojunction
photocatalysts, Mater. Res. Bull. 81 (2016) 16–26.
[42] Y. Wang, A. Zhang, D. Zhang, P. Zhou, R. Wang, J. Xiang, X. Zhang, S. Su, Ag2CO3
anchored on BiOI/CoFe2O4 composites with p-n-p heterojunctions: highly
enhanced activity for photocatalytic oxidation of Hg0 under fluorescent light
irradiation, Colloids Surf., A 579 (2019) 123654.
[66] X. Yin, X. Li, W. Gu, F. Wang, Y. Zou, S. Sun, Z. Fu, Y. Lu, Enhanced photocatalytic
activities of g-C3N4 via hybridization with a Bi–Fe–Nb-containing ferroelectric
pyrochlore, ACS Appl. Mater. Interfaces 9 (2017) 19908–19916.
[43] Y. Yang, F. Teng, Y. Kan, L. Yang, Z. Liu, W. Gu, A. Zhang, W. Hao, Y. Teng,
Investigation of the charges separation and transfer behavior of BiOCl/BiF3
heterojunction, Appl. Catal., B 205 (2017) 412–420.
[67] Y. Zhou, S. Fang, M. Zhou, G. Wang, S. Xue, Z. Li, S. Xu, C. Yao, Fabrication of
novel ZnFe2O4/BiOI nanocomposites and its efficient photocatalytic activity under
visible-light irradiation, J. Alloys Compd. 696 (2017) 353–361.
[44] J. Hu, W. An, H. Wang, J. Geng, W. Cui, Y. Zhan, Synthesis of a hierarchical BiOBr
nanodots/Bi2WO6 p–n heterostructure with enhanced photoinduced electric and
photocatalytic degradation performance, RSC Adv. 6 (2016) 29554–29562.
[45] Y. Chen, X. Jin, Preparation of Fe3O4@SiO2@BiO1.8⋅0.04H2O/Ag3PO4 magnetic
nanocomposite and its photocatalytic performance, Ceram. Int. 45 (2019)
1283–1292.
[68] Q. Liang, S. Cui, J. Jin, C. Liu, S. Xu, C. Yao, Z. Li, Fabrication of BiOI@UIO-66
(NH2)@g-C3N4 ternary Z-scheme heterojunction with enhanced visible-light
photocatalytic activity, Appl. Surf. Sci. 456 (2018) 899–907.
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