Preparation of CdS/BiOCl/Bi2O3 double composite system for visible light active photocatalytic applications

Article abstract of DOI:10.1016/j.jphotochem.2018.05.044

An efficient visible-light-harvesting (λ ≥ 420 nm) three component system heterojunction photocatalyst, CdS/BiOCl/Bi₂O₃ was prepared by anchoring of CdS nanoparticles on the surface of BiOCl/Bi₂O₃ composite. The effect of CdS nanoparticles on the surface of BiOCl/Bi₂O₃ composite photocatalyst had been justified in enhancing photocatalytic activity towards the degradation of organic pollutants in gas as well as aqueous phase. With the loading of CdS on to the BiOCl/Bi₂O₃ heterojunction composite photocatalyst, the photocatalytic activity of the CdS/BiOCl/Bi₂O₃ composite structure has been appreciably improved for the decomposition of 2-propanol (IPA) in gas phase and salicylic acid (SA) in aqueous phase under visible light irradiation (λ ≥ 420 nm). The amount of loading of CdS nanoparticles was optimized to 2 mol% CdS/BiOCl/Bi₂O₃. Compare to bare BiOCl/Bi₂O₃ photocatalyst, CdS/BiOCl/Bi₂O₃ heterojunction demonstrated 2 times decomposition of IPA in gas phase and 1.8 times of SA in aqueous phase after 120 min. of visible light irradiation. At the same time, with this composition the evolution of CO₂ from degradation of IPA was 1.9 times higher than that of BiOCl/Bi₂O₃ composite. The enhanced photocatalytic efficiency is deduced from the electron (eˉ) and hole (h⁺) transfer among the component semiconductor nanoparticles Bi₂O₃, BiOCl and CdS due to their relative energy band positions. Several experimental evidences were also provided to confirm the electron-hole transfer among the semiconductors and a mechanistic way has been proposed.

Full text of DOI:10.1016/j.jphotochem.2018.05.044

JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Preparation of CdS/BiOCl/Bi2O3 double composite system for visible light
active photocatalytic applications
Ashok Kumar Chakrabortya,⁎, Sumon Gangulib, Sandipan Berac, Wan In Leec
a
Department of Applied Chemistry and Chemical Engineering, Islamic University, Kushtia, 7003, Bangladesh
Department of Applied Chemistry and Chemical Engineering, University of Chittagong, Chittagong, 4331, Bangladesh
Department of Chemistry and Chemical Engineering, Inha University, Incheon, 402-751, Republic of Korea
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
An efficient visible-light-harvesting (λ ≥ 420 nm) three component system heterojunction photocatalyst, CdS/
BiOCl/Bi2O3 was prepared by anchoring of CdS nanoparticles on the surface of BiOCl/Bi2O3 composite. The
effect of CdS nanoparticles on the surface of BiOCl/Bi2O3 composite photocatalyst had been justified in en-
hancing photocatalytic activity towards the degradation of organic pollutants in gas as well as aqueous phase.
With the loading of CdS on to the BiOCl/Bi2O3 heterojunction composite photocatalyst, the photocatalytic ac-
tivity of the CdS/BiOCl/Bi2O3 composite structure has been appreciably improved for the decomposition of 2-
propanol (IPA) in gas phase and salicylic acid (SA) in aqueous phase under visible light irradiation
(λ ≥ 420 nm). The amount of loading of CdS nanoparticles was optimized to 2 mol% CdS/BiOCl/Bi2O3.
Compare to bare BiOCl/Bi2O3 photocatalyst, CdS/BiOCl/Bi2O3 heterojunction demonstrated 2 times decom-
position of IPA in gas phase and 1.8 times of SA in aqueous phase after 120 min. of visible light irradiation. At the
same time, with this composition the evolution of CO2 from degradation of IPA was 1.9 times higher than that of
Composite photocatalyst
CdS/BiOCl/Bi2O3
Visible light
Organic pollutants
Degradation
CO2 evolution
BiOCl/Bi2O3 composite. The enhanced photocatalytic efficiency is deduced from the electron (eˉ) and hole (h+
)
transfer among the component semiconductor nanoparticles Bi2O3, BiOCl and CdS due to their relative energy
band positions. Several experimental evidences were also provided to confirm the electron-hole transfer among
the semiconductors and a mechanistic way has been proposed.
1. Introduction
photocatalyst [17–20]. The photocatalytic activity of BiOCl towards the
decomposition of organic pollutants have been reported [21–23] under
Heterogeneous photocatalytic system for the removal of environ-
mental pollutants has drawn extensive interest as an environmentally-
benign technique over the last few decades [1–5]. Among the semi-
conductors studied so far, TiO2 is the most promising metal oxide
photocatalyst due to its unique characteristics in band position and
surface structure as well as its extended chemical stability, nontoxicity
and cost management. The limitation of using of TiO2 under visible
light region is of it’s relatively wide band gap (Eg = 3.2 eV). In view of
efficient solar energy conversion utilizing TiO2, several different ap-
proaches have been taken to extend its absorption towards visible light
by band gap engineering. So many reports have been published based
on this combination technique e. g., CdS/TiO2, CdSe/TiO2, Cu2O/TiO2,
WO3/TiO2, FeTiO3/TiO2, Bi2O3/TiO2 and so on [6–16]. These efforts to
enhance the absorption as well as photocatalytic activity to remove
organic pollutants from air and aqueous medium is considered as an
effective method.
UV irradiation as the band gap is in the UV region. Its energy band
positions are excellent matched with a good photocatalyst. The con-
duction band (CB) position (−1.1 V) is well above the reduction po-
tential of hydrogen and valence band (VB) position (+2.45 V) is quite
below the H2O oxidation potential [24]. Due to large band gap, BiOCl
can utilize only the photons in the UV region (≤345 nm), which limits
the practical application of BiOCl in sun light or indoor. Anyway, sev-
eral slants have been undertaken in constructing UV and/or visible light
harvesting BiOCl e. g., C modified BiOCl, facet-dependent BiOCl,
BiOCl/Fe3O4, BiOCl/BiVO4, BiOI/BiOCl, BiOCl/BiVO4 and so on
[25–30]. Yet, the photocatalytic efficiency of BiOCl systems is still
limited. On the other hand, Bi2O3 is considered as a narrow band gap
(2.6–2.8 eV) semiconductor and can absorb up to a certain region of
visible spectrum. It consists of deep VB level compare to BiOCl. How-
ever, photo-decomposition efficiency alone Bi2O3 is limited [31,32].
Researchers have paid attention to remove organic pollutants by uti-
lizing this Bi2O3 under visible light. Some reports have been published
BiOCl is known as wide band gap (3.6 eV) semiconductor
⁎
Corresponding author.
E-mail address: ashok@acct.iu.ac.bd (A.K. Chakraborty).
https://doi.org/10.1016/j.jphotochem.2018.05.044
Received 10 March 2018; Received in revised form 27 May 2018; Accepted 29 May 2018
Availableonline07June2018
1010-6030/©2018ElsevierB.V.Allrightsreserved.

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
on modification of Bi2O3 possessing photocatalytic activity to decom-
pose organics under visible light irradiation e. g., B2O3/TiO2, metal
doped Bi2O3, Bi2O3/BiOI and so on [33–37]. CdS is widely used as to
sensitize wide band gap semiconductors for visible light driven photo-
catalysis as the band gap of CdS is within the visible range (2.6 eV).
Photons with energies spanning the majority of the incident solar ir-
radiance spectrum are absorbed by CdS. Several couple systems have
been reported to be efficient heterojunction photocatalyst, however, the
eiificency is still unsatisfactory [15,38,39].
sulfur (Sigma-Aldrich, 99.998%) dissolved in 1.5 g of ODE was quickly
injected into the hot reaction flask. The temperature of the mixture
decreased to 250 °C by injection and maintained at this temperature for
the growth of CdS nanocrystals. Aliquots were taken out at different
reaction times to monitor the reaction progress by measuring the
UV–vis absorbance. The reaction was stopped when the desired nano-
crystal size was reached. Afterwards, the reaction flask was removed
from the heating mantle and allowed to cool to room temperature [46].
To make an efficient visible light active photocatalyst, previously,
we have developed BiOCl/Bi2O3 composite heterojunction photo-
catalyst [24]. Compared to pure BiOCl, Bi2O3 and Degussa P25, this
photocatalyst remarkably improved adsorptive and photooxidative
performance on the degradation of IPA in gas phase and terephthalic
acid in aqueous phase under visible light irradiation. The improvement
of photocatalytic activity has been explained by an interparticle hole
transfer mechanism between BiOCl and Bi2O3. It was shown that the
excitation of Bi2O3 which had been coupled with BiOCl resulted in hole
transferring into the higher lying VB of the BiOCl. The holes located at
the VB of BiOCl take part of in the photooxidation reactions. Similar
results have been observed by our other previous composite systems
[14,16,40–42]. However, to make the composite BiOCl/Bi2O3 as an
improved efficient photocatalyst we covered BiOCl/Bi2O3 utilizing WO3
and the photodecomposition efficiency was enhanced remarkably and
published earlier [43]. Recently some of our reports [44,45] show that
if three semiconductors could be aligned to make a double hetero-
junction structure by carefully choosing the appropriate energy band
positions of component semiconductors then the resultant photo-
catalysts give much better efficiency in photocatalytic activity than the
individual two heterojunctions.
2.3. Purification of the nanocrystals
Separation of unreacted cadmium precursors from the nanocrystals
was performed by repeated extraction (thrice for most cases) of the
reaction mixtures. An equal volume mixture of CHCl3/CH3OH (1:1) was
used as the extraction solvent. After extraction, the ODE phase con-
taining CdS nanocrystals was precipitated with excess acetone. The
precipitate was isolated by centrifugation and decantation. The com-
plete removal of cadmium precursors from the final solution was con-
firmed by UV–vis spectroscopy.
2.4. Surface ligand exchange
To change the surface ligand group, the oleate capped CdS nano-
particles were suspended in citric acid solution. In the solution, CdS and
citric acid molar ratio was kept to 1:4. The suspension was stirred for
24 h at 60 °C. Afterwards, CdS was separated by centrifugation and
washed with hexane and ethanol/water (50/50 by volume) several
times. The CdS nanoparticles were then tested in ethanol for suspen-
sion. This citrate coated CdS nanoparticles were used for the develop-
ment of CdS/BiOCl/Bi2O3 heterojunction composite system without
further purification.
In this paper, we have prepared CdS/BiOCl/Bi2O3 double hetero-
junction composite photocatalyst by combining three different semi-
conductors BiOCl, Bi2O3 and CdS that offer a considerably higher
photocatalytic efficiency than BiOCl/Bi2O3 and CdS/BiOCl hetero-
junctions toward the decomposition of IPA in gas phase and SA in
aqueous phase under visible light irradiation. From the photocatalytic
behaviors of CdS/BiOCl/Bi2O3, a detail photocatalytic reaction me-
chanism was established.
2.5. Preaparation of CdS/BiOCl/Bi2O3 heterojunction
To prepare CdS/BiOCl/Bi2O3 photocatalyst, CdS nano particles and
BiOCl/Bi2O3 composite were suspended in absolute ethanol with stoi-
cheometric amount of each particles by stirring and sonication and
dried at 65 °C with stirring under ambient condition. Typically, 2 mol%
CdS/BiOCl/Bi2O3 (2 mol% CdS and 98 mol% BiOCl/Bi2O3) composite
was prepared by suspending 2.0 g of 85/15 BiOCl/Bi2O3 composite in
25 mL of absolute ethanol for 20 min then 20.25 mg of CdS nano-
particles were added to the suspension under stirring condition.
Afterwards, solution was dried at 65 °C under ambient condition. The
photocatalyst samples were then heat-treated at 200 °C for 60 min.
under nitrogen flow due to avoid possible oxidation of sulphides and
have been used without further treatment.
2. Experimental
2.1. Preparation of BiOCl/Bi2O3 composite
The optimized 85/15 BiOCl/Bi2O3 employed in the present study
was prepared according to our previous method [24]. Briefly, Bismuth
(III) oxide (Sigma-Aldrich, 99.9%) was dispersed in ethanol solvent.
The Bi2O3 suspension was exposed to ultrasonic irradiation for 10 min.
HCl was added to the dispersed suspension, which was stirred for 3 h at
room temperature and was exposed to sonication for 60 min. The molar
ratio of Bi2O3 to HCl was 2. After the treatment of Bi2O3 particles with
HCl, pure Bi2O3 tinted with yellow was changed to BiOCl with white
color. The white precipitate obtained was washed several times with
ethanol and was heat treated at 250 °C for 60 min. and was used
without further treatment.
2.6. Characterization
X-ray diffraction patterns for the CdS/BiOCl/Bi2O3 powder samples
were obtained by using a Rigaku Multiflex diffractometer with mono-
chromated high-intensity Cu Kα radiation. XRD scanning was per-
formed over the 2θ region of 10–65° at a rate of 2°/min (30 kV, 20 mA).
UV–vis diffuse reflectance spectra were acquired by a Perkin-Elmer
Lambda 40 spectrophotometer. BaSO4 was used as the reflectance
standard. The transmission electron microscope (TEM) images were
obtained by a Philips CM30 operated at 250 kV. One milligram of CdS/
BiOCl/Bi2O3 was dispersed in 50 mL of ethanol, and a drop of the
suspension was then spread on a holey amorphous carbon film de-
posited on the copper grid and dried under vacuum. BET surface areas
were determined using surface area and porosity analyzer (ASAP 2020,
Micromeritics). N2 was used as adsorption gas.
2.2. Synthesis of CdS nanoparticles
CdS nano crystals can be synthesized using noncoordinating solvent,
1-octadecene (ODE) (Sigma-Aldrich, tech., 90%) and oleic acid
(Aldrich, technical grade, 90%), a natural surfactant. Oleic acid was
chosen as the ligand for stabilizing the nanocrystals and the cationic
precursors. Typically, 0.0128 g of CdO (0.10 mmol) (Sigma-
Aldrich,99.99%), 21.2 mmol oleic acid and technological grade ODE
were loaded in a three-necked round bottom flask and was heated to
300 °C under Argon flow. CdO was completely dissolved and made a
clear solution at this condition. A sulfur solution containing 0.0016 g of
2.7. Measurement of photocatalytic activity
The prepared CdS/BiOCl/Bi2O3 samples were tested as
160

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
photocatalyst in decomposition of IPA in gas phase. For the photo-
catalytic measurements, an aqueous suspension containing 8 mg of
CdS/BiOCl/Bi2O3 was spread on a 2.5 × 2.5 cm2 Pyrex glass in a film
form, which was subsequently dried at room temperature over night.
The gas reactor system was designed in such a way that the photo-
catalyst film remains at the center of the reactor and could be irradiated
directly on to the catalyst film. The whole CdS/BiOCl/Bi2O3 film area
was irradiated by a 300 W Xe lamp through a UV cut-off filter
(< 420 nm, Oriel) and through a water filter to remove IR. After
evacuating the reactor, 1.6 μL of 10% (v/v) IPA was injected into the
reaction chamber. At the beginning, the concentration of IPA in reactor
was maintained at 117ppmv by volume. Thus, the ultimate con-
centration of evolved CO2 after complete degradation of gaseous IPA
would be 351 ppmv according to following Eq. (1)
2(CH3)2CHOH(g) + 9H2O → 6CO2(g) + 8H2O(g)
(1)
The total pressure of the reactor was then controlled to 750 Torr by
filling the oxygen gas. Under these environments, IPA and H2O kept in
vapor phase. Every 30 min, 0.5 mL of the gas sample was automatically
picked up from the reactor, and sent to a gas chromatograph (Agilent
Technologies, Model 6890 N). For the detection of CO2, a methanizer
was installed between the GC column outlet and the FID detector.
Photocatalytic behaviour of composite photocatalyst samples were
carried out for the degradation of SA in solution phase under visible
light illumination. 8 mg photocatalysts were suspended in 50 mL of 50
μM SA solution and irradiated under stirring condition. Aliquots of il-
luminated solution were taken out every after 30 min. to detect the
characteristic absorption peak of remnant SA by measuring the absor-
bance using Perkin-Elmer Lambda 40 UV–vis spectrophotometer. A
blank experiment was also carried out. Before going to test photo-
catalytic efficiency, the samples were stirred in dark for 30 min and
observed the change of concentration of IPA in gas phase or SA in
aqueous phase. The concentration of IPA or SA were not being changed
after 30 min of stirring in dark. Thus, 30 min was enough to reach ad-
sorption equilibrium of IPA or SA. However, all the catalytic samples
were stirred in the dark condition for 30 min to confirm adsorption
equilibrium. To detect hydroxyl radical (%OH) in aqueous medium
20 mg of photocatalyst sample was suspended in 50 mL of aqueous
solution containing 0.01 M NaOH and 3.0 mM terephthalic acid. The
suspension was stirred for 30 min in dark and then suspension was ir-
radiated for 60 min. under visible and/or UV light with stirring and
measured the fluorescence spectra. For the measurement of I3ˉ, 20 mg
of catalyst sample was taken in 50 mL of 0.01 M KI solution. The KI
solution containing catalyst sample was irradiated visible and/or UV
light for 120 min. under stirring condition and measured absorption
spectra.
Fig. 1. TEM and HRTEM images of the CdS/BiOCl/Bi2O3 composites (a) BiOCl/
Bi2O3, (b) CdS nanoparticles, (c) 2 mol% CdS/BiOCl/Bi2O3, (d) High Resolution
TEM of circular part of (c), (e) Fringe pattern of CdS nanoparticle in HRTEM
indicates the presence of CdS nanoparticles on BiOCl/Bi2O3 composite.
showed in Fig. 1e (JCPDS # 65-2887). The enlargement of size of CdS
nanoparticles indicate that during changing surface capping agent with
citric acid the size of individual nanoparticle was enlarged.
TEM EDX mapping for different elements, i.e., Bi, Cl, Cd, of 2 mol%
CdS/BiOCl/Bi2O3 composite photocatalyst are shown in Fig. 2. The Bi-
mapping image shown in Fig. 2b was very like the original TEM image
in Fig. 2a. Fig. 2c shows the Cl-mapping image, indicating that BiOCl is
present all over the heterojunction structure. As HCl can transform
Bi2O3 to BiOCl partially it indicates that Bi2O3 particles were embedded
in the BiOCl structure. Fig. 2d shows the Cd elemental mapping image.
As in Fig. 2d, the Cd signal was weak, but its overall image was like the
original TEM image, indicating that the CdS QDs were uniformly dis-
tributed over the surface of the BiOCl/Bi2O3 composite. Moreover, EDX
elemental analysis spectrum was taken and showed in Fig. 2e. The es-
sential elements of Bi, Cl and Cd were viewed From Fig. 2e. Thus, the
CdS QDs were located on the BiOCl surface, considering that the Bi2O3
surface was fully covered by BiOCl.
3. Results and discussion
3.1. Morphology study
TEM image of BiOCl/Bi2O3 heterojunction, prepared by partial
transformation of Bi2O3 to BiOCl using HCl as described in our previous
report [24], is shown in Fig. 1a. Oleic acid capped CdS was prepared
separately by a solution process and the surface ligand was exchanged
by citric acid in order to facilitate the attachment of CdS over BiOCl in
Bi2O3/BiOCl heterojunction. As shown in Fig. 1b the average size of as
prepared CdS was ∼3.9 nm. TEM and HRTEM images of the CdS/
BiOCl/Bi2O3 heterojunction nanocomposites are shown in Fig. 1c and d.
The CdS nanoparticles in the size of 4.5 nm and cover the BiOCl/Bi2O3
nanostructures uniformly. The high resolution TEM image in Fig. 1d
suggests that a tight contact was formed between the CdS nanoparticles
and the BiOCl/Bi2O3 nanostructures. The size of CdS nanoparticles were
little larger from the original CdS nanoparticles, and its fringe pattern
with the spacing of 0.335 nm clearly indicates the (111) plane of CdS as
3.2. Different phase investigation
Fig. 3 shows the XRD patterns of the CdS nanoparticles, BiOCl/
Bi2O3 and CdS/BiOCl/Bi2O3 composites with different compositions.
The diffraction peaks at 26.44°, 43.87° and 51.96° as shown in Fig. 3g,
correspond to the (111), (220) and (311) plane of the cubic CdS na-
noparticles (JCPDS # 65-2887), respectively, whereas all the diffraction
peaks in Fig. 3a are identified as the BiOCl/Bi2O3 composite phase. The
161

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
Fig. 2. (a) TEM image of CdS/BiOCl/Bi2O3 (CdS: 2 mol%) sample. EDX mapping images were obtained for the same area by monitoring the concentrations of (b) Bi,
(c) Cl and (d) Cd, respectively and (D) EDX elemental analysis.
diffraction peaks in Fig. 3b–f indicate the CdS/BiOCl/Bi2O3 composites
to be a representation of the cubic CdS and BiOCl/Bi2O3 composite
phases without any other impurity phases. This suggests that no ap-
preciable chemical reaction occurred between CdS and BiOCl/Bi2O3
composite during the annealing at 200 °C. The diffraction patterns in
Fig. 3b–f seem to be the pure BiOCl/Bi2O3 composite without any CdS
representative peaks. As it is shown in Fig. 3g that the intensity of CdS
diffraction peak is too weak, thus with a small amount like 10 mol% of
CdS (maximum) with BiOCl/Bi2O3 does not show visible strong peak in
CdS/BiOCl/Bi2O3 composite structures. However, the presence of CdS
nanoparticles in the CdS/BiOCl/Bi2O3 composite photocatalyst has
been evidenced by TEM EDX mapping as shown in Fig. 2d and by re-
flectance spectra in Fig. 4.
3.3. UV-vis DRS analysis
The UV–vis diffuse reflectance spectra of CdS/BiOCl/Bi2O3 powders
annealed at 200° C with different compositions of CdS are shown in
Fig. 4. For comparison, the spectra of BiOCl/Bi2O3, CdS powders are
also included in Fig. 4. From Fig. 4, it is clear that the junction structure
absorbs energy from the visible region of light source. The presence of
three absorption peaks in the spectra of each junction corresponding,
respectively, to every semiconductor indicate that the junction can be
excited using the light having the appropriate wavelength. We also
observed that with increasing the concentration of each of semi-
conductor increases the absorption peak intensity. The obtained data
signify that the heterojunctions can be excited by visible light.
162

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
Fig. 3. XRD patterns of BiOCl/Bi2O3, CdS and CdS/BiOCl/Bi2O3 composites at
different compositions: (a) BiOCl/Bi2O3, (b) 1 mol% CdS/BiOCl/Bi2O3, (c)
2 mol% CdS/BiOCl/Bi2O3, (d) 4 mol% CdS/BiOCl/Bi2O3, (e) 6 mol% CdS/
BiOCl/Bi2O3, (f) 10 mol% CdS/BiOCl/Bi2O3, (g) CdS nanoparticles.
Fig. 4. UV–vis diffuse reflectance spectra of BiOCl/Bi2O3 composite, CdS na-
noparticles and CdS/BiOCl/Bi2O3 composite structures annealed at 200 °C.
3.4. Photocatalytic efficiency measurement
The photocatalytic activities of the CdS/BiOCl/Bi2O3 composites in
decomposing IPA in gas phase were evaluated under visible light irra-
diation (λ ≥ 420 nm). As shown in Fig. 5a, the photocatalytic activity
of Degussa P25 was very low under visible light irradiation. Only a little
decomposition of IPA was observed for Degussa P25, while no appre-
ciable removal was observed by pure CdS, Bi2O3 and BiOCl. However,
BiOCl/Bi2O3 showed better photocatalytic activity than that of Degussa
P25 and others CdS, BiOCl and Bi2O3. By contrast, the CdS/BiOCl/Bi2O3
heterocomposites in several compositions showed notably high photo-
catalytic efficiency under visible light irradiation. Especially, the com-
posite 2 mol% CdS/BiOCl/Bi2O3 (2 mol% CdS and 98 mol% BiOCl/
Bi2O3) exhibits the highest catalytic activity among the photocatalysts.
That is, 29.3% of IPA was decomposed in 120 min. irradiation. When
the CdS content was changed from 2 mol%, the photocatalytic effi-
ciency of the composites was gradually decreased with increasing or
decreasing CdS concentration in the heterojunction composite, CdS/
BiOCl/Bi2O3.
Fig. 5. Photocatalytic decomposition of (a) gaseous 2-propanol (IPA), (b)
evolution of CO2 and (c) degradation of salicylic acid (SA) as a function of
irradiation time under visible light irradiation (λ ≥ 420 nm): (A) BiOCl/Bi2O3
composite, (B) 1 mol% CdS/BiOCl/Bi2O3 composite, (C) 2 mol% CdS/BiOCl/
Bi2O3 composite, (D) 4 mol% CdS/BiOCl/Bi2O3 composite, (E) 6 mol% CdS/
BiOCl/Bi2O3 composite, (F) 10 mol% CdS/BiOCl/Bi2O3 composite, (G) CdS
nanoparticles, (H) Degussa P25, (I) 2 mol% CdS/Bi2O3, (J) 2 mol% CdS/BiOCl.
The photocatalytic oxidation of IPA goes through several inter-
mediate steps giving partially oxidized species such as acetone and the
final oxidized species is CO2. The photocatalytic activity was evaluated
according to the amount of CO2 evolved during the visible light
irradiation (λ ≥ 420 nm). For the three components system, CdS/
BiOCl/Bi2O3, a similar trend was observed for the evolution of CO2 as
that of decomposition of IPA. As shown in Fig. 5b, the CdS/BiOCl/Bi2O3
composites in several compositions demonstrated notably high
163

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
photocatalytic activity in compare with BiOCl/Bi2O3, whereas pure
CdS, BiOCl, Bi2O3 and Degussa P25 showed very low efficiency. Pre-
viously, we have reported that the photocatalytic efficiency of BiOCl/
Bi2O3 is much better than Degussa P25 in evolution of CO2 [24]. The
highest photocatalytic activity was observed from the 2 mol% CdS/
BiOCl/Bi2O3 composite i.e., the evolved CO2 was 19.5 ppm by the re-
action for 120 min. It is clear, from Fig. 5b, the evolved CO2 with 2 mol
% CdS/BiOCl/Bi2O3 is nearly 2 times higher than that of BiOCl/Bi2O3
composite. Thus, by considering the evolution of CO2, it can be inferred
that the efficiency of this three components heterojunction system,
CdS/BiOCl/Bi2O3 is two times higher than that of two components
system, BiOCl/Bi2O3. The increased evolution of CO2 with time clearly
indicates that the complete decomposition of IPA is possible with the
CdS/BiOCl/Bi2O3 composite under visible light irradiation.
The photocatalytic activity of CdS/BiOCl/Bi2O3, BiOCl/Bi2O3, CdS/
Bi2O3, CdS/BiOCl towards the decomposition of SA in aqueous phase
was carried out under visible light and shown in Fig. 5c. A similar trend
was followed as that of degradation of gaseous IP which was indicated
in Fig. 5a. CdS/BiOCl/Bi2O3 composite photocatalyst with 2 mol% CdS
demonstrated the highest effeciency among the photocatalytic samples.
After 120 min of irraddiation, ∼40% degradation of SA was demon-
strated under visible light irradiation. Our investigated photocatalyst
samples with 2 mol% CdS/BiOCl/Bi2O3 demonstrated best photo-
catalytic efficiency among the prepapred compositions both in gas and
aqueous phase. A plausible reason is that when CdS exceded more than
2 mol% in the composite, the recombinaton of photoexcited electron
(e−)-hole(h+) pairs of CdS/BiOCl/Bi2O3 might be increased.
Fig. 6. Degradation rate constant per unit surface area of gaseous IPA and
aqueous SA in presence of different catalyst under of visible light irradiation
(λ ≥ 420 nm) (A: Surface area of used catalyst; Irradiation time 120 min).
Photochemical stability of the catalyst samples were performed four
times both in aqueous and gas phase. The recycled samples did not
show any appreciable change in photocatalytic efficiency, which em-
phasizes the chemical stability of the samples (data not shown).
3.6. Discussion
In the present study, both the narrow band gap semiconductors CdS
and Bi2O3 demonstrated very low photocatalytic efficiency in gas as
well as solution phase compare to their heterocomposite CdS/BiOCl/
Bi2O3 under visible light illumination. This is presumably due to the
first recombination of photoexcited electrons (e−) and holes (h+). The
role of these two semiconductors CdS and Bi2O3 are sensitizer absorbing
visible energy. We believe that this high activity of CdS/BiOCl/Bi2O3
originates from the relative band positions of the semiconductors. CdS
is a narrow band gap (2.6 eV) semiconductor. Its conduction band po-
sition is −1.2 V [47]. For nanoparticles, with decreasing particle size,
band gap of the nanoparticles increases. However, the shift in the
conduction band energy is significantly greater than the shift in valence
band energy for quantized particles [13,48]. Thus, we expect the con-
duction band of CdS to become more negative with decreasing particle
size. However, CdS may be a good candidate for sensitization of BiOCl,
it’s conduction band position is well above the CB band of BiOCl
(−1.1 V) [24,47]. In addition, Bi2O3 is another excellent photo-
sensitizer possessing narrow band gap of 2.8 eV [24,32] which could be
excited under visible light irradiation. During the photocatalytic reac-
tion, the electrons of VB of CdS and Bi2O3 are excited to their respective
CB by visible light irradiation (Eq. (2)).
3.5. BET measurement
BET surface areas were determined using surface area and porosity
analyzer (ASAP 2020, Micromeritics) and shown in Table 1. The surface
area of 2 mol% CdS/BiOCl/Bi2O3 composite is 11.13 m2/g, which is
larger than that of BiOCl/Bi2O3 (6.74 m2/g). The enlarged BET is at-
tributed to introducing the nanoparticles CdS on the surface of BiOCl/
Bi2O3. Yet their BET values are nearly of the same magnitude, both of
which are still very low as compared to that of nanoparticles, TiO2.
After 120 min. of visible light irradiation the rate constants per unit
catalytic surface area of the composite systems were measured and
shown in Table 1 and Fig. 6. It is revealed from the Table 1 and Fig. 6
that the degradation rate constant with 2 mol% CdS/BiOCl/Bi2O3 is
higher than other composite systems both in gas and aqueous phase.
Thus, the enhanced photocatalytic activity demonstrated by the CdS/
BiOCl/Bi2O3 composite may not be attributed due to surface area of the
composite photocatalysts.
Table 1
BET surface area, degradation rate constant and constant per unit surface area of gaseous IPA (KIPA) and aqueous SA (KSA) for different catalysts under visible light
irradiation (A: Surface area of catalysts; Irradiation time: 120 min).
Photocatalyts
BET surface area (m2.g−1
)
2-Propanol (IPA)
KIPA ×10−3
Salicylic acid (SA)
KSA ×10−3
KIPA/A
KSA/A
(h−1
)
(h−1.m-2
)
(h−1
)
(h−1.m-2
)
BiOCl/Bi2O3
13.20
15.33
17.45
21.71
2.0
3.1
3.9
2.7
0.01868
0.02552
0.02794
0.01555
2.9
4.0
5.2
3.7
0.02746
0.03262
0.03725
0.02131
1 mol% CdS/BiOCl/Bi2O3 composite
2 mol% CdS/BiOCl/Bi2O3 composite
4 mol% CdS/BiOCl/Bi2O3
composite
2 mol% CdS/Bi2O3
2 mol% CdS/BiOCl
Degussa P25
14.52
18.05
53.70
1.1
0.7
0.5
0.00947
0.00506
0.00116
1.4
1.0
0.6
0.01205
0.00693
0.00141
164

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
Scheme 1. Schematic diagram of charge transfer in CdS/BiOCl/Bi2O3 compo-
site system under visible light irradiation (λ ≥ 420 nm).
hν + (CdS and Bi2O3) → h+ + eˉ ; hν > Eg (CdS, Bi2O3)
(2)
Thus, in the CdS/BiOCl/Bi2O3 heterojunction composite, the excited
electrons of CB of CdS could transfer to the CB of BiOCl, as the CB of
BiOCl is sufficiently lower than the CB of CdS which is schematically
illustrated in Scheme 1.
The accumulated electrons in CB of BiOCl can generate superoxide
radical (%O2ˉ) and HO2% by reacting with molecular oxygen and can
produce H2O2 or H2O by multielectron process (Eqs. (3)–(6))
[44,49,50].
O2 + eˉ → %O2ˉ, E° = -0.284 V (vs. NHE)
(3)
(4)
(5)
(6)
O2 + H+ + eˉ → HO2%, E° = -0.046 V (vs. NHE)
O2 + 2H+ + 2eˉ → H2O2 E° = +0.682 V (vs. NHE)
O2 + 4H+ + 4eˉ → 2H2O, E° = +1.23 V (NHE)
HO2% can act as an oxidant to initiate the oxidation reaction of or-
ganic compound. On the other hand, Bi2O3 is a semiconductor (2.8 eV)
whose valence band position is +3.15 V [32,24,51]. As indicated in
Scheme 1, the VB of Bi2O3 is sufficiently lower than that of BiOCl
(+2.45 V). The VB electrons of Bi2O3 of CdS/BiOCl/Bi2O3 composite
are excited by visible light (≤443 nm) irradiation to its CB (Eq. (2)) and
thereby, the VB of Bi2O3 is rendered partially vacant, and the electrons
in the VB of BiOCl could be transferred to that of Bi2O3, since the VB
position of Bi2O3 semiconductor is situated lower than that of BiOCl.
Thus, the holes are generated in the VB of BiOCl [24,52]. The holes in
VB of BiOCl can form hydroxyl radical (%OH) by reacting with adsorbed
OH− or H2O on the catalyst surface (Eqs. (7) and (8)). Then those
chemical species initiate various oxidation or reduction reactions to
mineralize various organic pollutants.
Fig. 7. Comparison of the photocatalytic efficiency of 2 mol% CdS/BiOCl/
Bi2O3, BiOCl/Bi2O3 and 2 mol% CdS/BiOCl as a function of irradiation time
under visible light irradiation (λ ≥ 420 nm): (a) decomposition of IPA, (b)
evolution of CO2.
cause photocatalytic reduction reactions.
It is generally considered that the photodecomposition reaction
takes place in the heterogeneous photocatalysis system direct with the
photoinduced hole (h+), electron (eˉ) and/or through superoxide anion
radicals (%O2ˉ) and hydroxyl radicals (%OH). In order to know the detail
photodegradation mechanism in our system, an experiment has been
carried out to confirm the existence of hole (h+) in reaction medium
utilizing KI aqueous solution [45] as shown in Fig. 8. Generally, KI has
been utilized as electrolyte to facilitate charge transfer in dye-synthe-
sized solar-cell, where Iˉ ion accept hole (h+) from the HOMO of the
dyes [53,54]. In aqueous medium, KI gives Iˉ ion. During irradiation
visible and/or UV light, this ionized Iˉ is expected to react with pho-
togenerated hole (h+) in BiOCl/Bi2O3, CdS/BiOCl/Bi2O3 or TiO2 and
form I3ˉ(Eq. (9)). Hence, the redox potential of Iˉ/I3ˉ is +0.536 V,
which is much higher than the VB levels of Bi2O3 (+3.15 V) or BiOCl
(+2.45 V) [52].
OHˉ + h+ → %OH, E0 = +1.99 V (vs. NHE)
(7)
(8)
H2O + h+ → %OH + OHˉ, E0 = +2.70 V (vs. NHE)
In order to test the electron transfer mechanism between CdS and
BiOCl, we have prepared CdS/BiOCl composite system and measured
the photocatalytic activity under visible light irradiation (λ ≥ 420 nm)
at the same experimental condition. As shown in Fig. 7, both CdS and
BiOCl showed a little photocatalytic degradation efficiency towards the
removal of IPA (Fig. 7a) and also evolution of CO2 (Fig. 7b). Whereas,
CdS/BiOCl demonstrated a better photocatalytic efficiency than that of
CdS, BiOCl and Degussa P25 for the removal of IPA and evolution of
CO2. These results suggest that during photocatalytic reduction reaction
on CdS/BiOCl composite surface, the electrons of VB of CdS are excited
to its CB and then these excited electrons are transferred to the lower
leveled CB of BiOCl. Thus, these electrons have sufficient life time to
3I ˉ (aq) + 2 h+ → I3 ˉ (aq)
(9)
This I3ˉ generate characteristic absorption peaks at 286 and 345 nm
in UV–vis spectra [45] after 120 min. of irradiation as illustrated in
Fig. 8. It is divulged from the Fig. 8 that intensity of spectra of the
photocatalysts are different even all the experiments were done under
identical condition. The highest intensified peaks come from TiO2 na-
noparticles when it was irradiated with UV light which means that in
165

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
Fig. 9. Fluorescence spectra of hydroxyl ion (%OH) initiated photocatalytic
decomposition of terephthalic acid with different photocatalysts after 60 min.
Visible and/or UV light irradiation. (a) TiO2-Visible; (b) TiO2-UV; (c) BiOCl/
Bi2O3-Visible; (d) 2 mol% CdS/BiOCl/Bi2O3-Visible (λ ≥ 420 nm).
Fig. 8. UV–vis absorption spectra of aqueous KI solution with different catalyst
after 120 min. of visible and/or UV light irradiation. (a) KI-Visible; (b) KI
combined with TiO2-Visible; (c) KI combined with TiO2 -UV; (d) KI combined
with BiOCl/Bi2O3-Visible; (e) KI combined with CdS/BiOCl/Bi2O3-Visible
(λ ≥ 420 nm).
known that TiO2 having band gap of 3.2 eV could not be excited under
visible light and no hole (h+) as well as %OH radical was formed and
1,4-terephthalic acid was not decomposed to 2-hydroxy terephthalic
acid. However, 2 mol% CdS/BiOCl/Bi2O3 demonstrated notably higher
intensified peak at 426 nm compare to BiOCl/Bi2O3 composite photo-
catalyst under visible light (Fig. 9) which indicate that large quantity
hole (h+) and electron (eˉ) was formed and those subsequently trans-
form to hydroxyl radical (%OH) reacting with H2O, OHˉ and/or O2 by
reactions mentioned above.
presence of UV light TiO2 produce a lot of hole (h+) and subsequently
I3ˉ (Eq. (9)) as the band gap of TiO2 is 3.2 eV and it could be excited by
UV irradiation. That’s why any absorption peaks were not observed
when it was irradiated under visible light. However, 2 mol% CdS/
BiOCl/Bi2O3 photocatalyst combination with KI shows much higher
intensified absorption peak in UV–vis spectra (Fig. 8) than that of
BiOCl/Bi2O3 composite under visible light. This means that large
number of holes (h+) were generated which could induce I3ˉ when
2 mol% CdS/BiOCl/Bi2O3 was irradiated with visible light compare to
BiOCl/Bi2O3 and electron (eˉ)-hole (h+) recombination was strongly
inhibited. The photoexcited electrons (eˉ) from any photocatalyst
samples (TiO2, CdS/BiOCl/Bi2O3, BiOCl/Bi2O3) in KI aqueous medium
were not embezzled through the reduction reaction of
(12)
I3ˉ + 2eˉ cb(TiO2, CdS/BiOCl/Bi2O3, BiOCl/Bi2O3) → 3Iˉ
(10)
However, the VB holes and CB electrons of BiOCl have little or no
chance to recombine. They are spatially separated. In the composite
CdS/BiOCl/Bi2O3 system, Bi2O3 exist inside the BiOCl and CdS remains
outside of BiOCl. Therefore, in these three components composite het-
erojunction photocatalysts, VB holes and CB electrons can simulta-
neously take part in the redox reactions to degrade pollutants which are
pre-adsorbed on the surface of CdS/BiOCl/Bi2O3 composite catalyst.
Even though, BiOCl is a wide band gap semiconductor, the oxidation-
reduction reactions are taking place on the surface of BiOCl in presence
of visible light. By this photocatalytic mechanism, the organic pollu-
tants can be completely mineralized. Moreover, these three components
double composite heterojunction systems will open a new idea in the
field of photocatalytic reaction system for using direct solar energy to
remove pollutants from the environment.
presumably since the reaction in Eq. (9) was faster than the any
other reactions. Thus, this result provides strong evidence that the
visible light photocatalytic activity of the heterojunction system origi-
nates from intersemiconductor hole (h+) transfer.
On the other hand, photoinduced electrons (eˉ) in the CB of Bi2O3
and BiOCl (Scheme 1) is expected to react with O2 to form superoxide
anion radical (%O2ˉ) (Eqs. (3)–(6)). According to Eq. (11), this %O2ˉ
react with H2O and form %OH [55].
2%O2ˉ + 2H2O → 2%OH + 2OHˉ + O2
(11)
To confirm the presence of %OH radical likewise induced through
reaction with hole (h+) according to Scheme 1 and Eqs. (7) and (8) in
the photocatalysis system, 1,4-terephthalic acid has been used as a
probe compound. %OH normally reacts with 1,4-terephthalic acid and
form 2-hydroxy terephthalic acid (equation 12) which is characterized
by the unique fluorescence peak at 426 nm as given in Fig. 9. This is a
common method to detect %OH in aqueous medium [45]. Fig. 9 shows
decomposition of 1,4-terephthalic acid to 2-hydroxy terephthalic acid
in presence of 2 mol% CdS/BiOCl/Bi2O3, BiOCl/Bi2O3 and TiO2 under
UV and/or Visible irradiation and the catalyst samples were irradiated
for 60 min. As shown in Fig. 9 the TiO2 under UV irradiation gave the
highest intensified peak at 426 nm which indicates that under UV ir-
radiation large quantity of hydroxyl radical (%OH) was formed as that of
hole (h+) formation in Iˉ/I3ˉ system (equation 9). No fluorescence peak
was observed when TiO2 was illuminated under visible light. It is well
4. Conclusion
A new class of photocatalyst was formed from the heterojunction
between CdS, BiOCl and Bi2O3. The 2 mol% CdS/BiOCl/Bi2O3 compo-
site exhibited a notably high photocatalytic efficiency in the complete
mineralization of pollutants under visible light irradiation. It is ex-
pected that the high efficiency of the CdS/BiOCl/Bi2O3 composite ori-
ginates from the unique relative band positions of these three semi-
conductors. Since the VB position of Bi2O3 (+3.15 V) is below to that of
BiOCl (+2.45 V), the hole transfer from the VB of Bi2O3 to that of BiOCl
will be possible. On the other hand, CB of CdS (−1.2 V) is well above
166

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
the CB of BiOCl (−1.1 V), the photo excited electron will be trapped by
BiOCl from CdS. Bi2O3 is inside the BiOCl and CdS remains out side of
BiOCl. Thus, radiative recombination will not be possible between holes
and excited electrons. Therefore, the visible light absorption by Bi2O3
and CdS induce the generation of holes on VB of BiOCl and trapped of
electrons on CB, and this can lead to the complete decomposition of
organic compounds. Hence, this double composite might provide a new
model for efficient visible light absorption and charge separation in the
field of photofunctional materials.
assembly of BiOCl nanostructure and their photocatalytic properties,
CrystEngComm 11 (2009) 1857–1862.
[23] M. Li, J. Zhang, H. Gao, F. Li, S.E. Lindquist, N. Wu, R. Wang, Microsized BiOCl
square nanosheets as ultraviolet photodetectors and photocatalysts, ACS Appl.
Mater. Interfaces 8 (2016) 6662–6668.
[24] S.Y. Chai, Y.J. Kim, M.H. Jung, A.K. Chakraborty, D. Jung, W.I. Lee,
Heterojunctioned BiOCl/Bi2O3, a new visible light photocatalyst, J. Catal. 262
(2009) 144–149.
[25] J. Di, J. Xia, M. Ji, B. Wang, S. Yin, Q. Zhang, Z. Chen, H. Li, Carbon quantum dots
modified BiOCl ultrathin nanosheets with enhanced molecular oxygen activation
ability for broad spectrum photocatalytic properties and mechanism insight, ACS
Appl. Mater. Interfaces 7 (2015) 20111–20123.
[26] J. Jiang, K. Zhao, X. Xiao, L. Zhang, Synthesis and facet-dependent photoreactivity
of BiOCl single-crystalline nanosheets, J. Am. Chem. Soc. 134 (2012) 4473–4476.
[27] F. Xu, G. Cheng, S. Song, Y. Wei, R. Chen, Insights into promoted adsorption cap-
ability of layered BiOCl nanostructures decorated with TiO2 nanoparticles, ACS
Sustain. Chem. Eng. 4 (2016) 7013–7022.
[28] H. Chen, X. Wang, W. Bi, Y. Wu, W. Dong, Photodegradation of carbamazepine with
BiOCl/Fe3O4catalyst under simulated solar light irradiation, J. Colloid Interface Sci.
502 (2017) 89–99.
[29] L. Sun, L. Xiang, X. Zhao, C.J. Jia, J. Yang, Z. Jin, X. Cheng, W. Fan, Enhanced
visible-light photocatalytic activity of BiOI/BiOCl heterojunctions: key role of
crystal facet combination, ACS Catal. 5 (2015) 3540–3551.
[30] L. Song, Y. Pang, Y. Zheng, C. Chen, L. Ge, Design, preparation and enhanced
photocatalytic activity of porous BiOCl/BiVO4 microspheres via a coprecipitation-
hydrothermal method, J. Alloy Compd. 710 (2017) 375–382.
[31] Y. Lu, Y. Zhao, J. Zhao, Y. Song, Z. Huang, F. Gao, N. Li, Y. Li, Induced aqueous
synthesis of metastable β-Bi2O3microcrystals for visible-light photocatalyst study,
Cryst. Growth Des. 15 (2015) 1031–1042.
[32] L. Zhang, W. Wang, J. Yang, Z. Chen, W. Zhang, L. Zhou, S. Liu, Sonochemical
synthesis of nanocrystallite Bi2O3as a visible-light-driven photocatalyst, Appl. Catal.
A: Gen. 308 (2006) 105–110.
[33] M.K. Hossain, G.F. Samu, K. Gandha, S. Santhanagopalan, J.P. Liu, C. Janáky,
K. Rajeshwar, Solution combustion synthesis, characterization, and photocatalytic
activity of CuBi2O4and its nanocomposites with CuO and α-Bi2O3, J. Phys. Chem. C
121 (2017) 8252–8261.
[34] S. Zhu, L. Lu, Z.W. Zhao, T. Wang, X.Y. Liu, H. Zhang, F. Dong, Y. Zhang,
Mesoporous Ni-doped δ-Bi2O3 microspheres for enhanced solar-driven photo-
catalysis: a combined experimental and theoretical investigation, J. Phys. Chem. C
121 (2017) 9394–9401.
Acknowledgements
The authors are gratefully acknowledged the Dept of Applied
Chemistry and Chemical Engineering, Islamic University, Kushtia 7003,
Bangladesh, Dept of Applied Chemistry and Chemical Engineering,
University of Chittagong, Chittagong-4331, Bangladesh and Dept of
Chemistry and chemical Engineering, Inha University, Republic of
Korea.
References
[1] T. Inoue, A. Fujishima, S. Konishi, K. Honda, Photoelectrocatalytic reduction of
carbon dioxide in aqueous suspensions of semiconductor powders, Nature 277
(1979) 637–638.
[2] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann, Environmental applica-
tions of semiconductor photocatalysis, Chem. Rev. 95 (1995) 69–96.
[3] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-light photocatalysis in
nitrogen-doped titanium oxides, Science 293 (2001) 269–271.
[4] J. Kou, C. Lu, J. Wang, Y. Chen, Z. Xu, R.S. Varma, Selectivity enhancement in
heterogeneous photocatalytic transformations, Chem. Rev. 117 (2017) 1445–1514.
[5] A. Kubacka, M. Fernández-García, G. Colón, Advanced nanoarchitectures for solar
photocatalytic applications, Chem. Rev. 112 (2012) 555–1614.
[6] S.A.K. Leghari, S. Sajjad, F. Chen, J. Zhang, WO3/TiO2, composite with morphology
change via hydrothermal template-free route as an efficient visible light photo-
catalyst, Chem. Eng. J. 166 (2011) 906–915.
[7] J. Wang, B. Wei, L. Xu, H. Gao, W. Sun, J. Che, Multilayered MoS2coated
TiO2hollow spheres for efficient photodegradation of phenol under visible light
irradiation, Mater. Lett. 179 (2016) 42–46.
[8] L. Le, Y. Wu, Z. Zhou, H. Wang, R. Xiong, J. Shi, Cu2O clusters decorated on flower-
like TiO2 nanorod array film for enhanced hydrogen production under solar light
irradiation, J. Photochem. Photobiol. A: Chem. 351 (2018) 78–86.
[9] A.K. Chakraborty, M.R. Islam, M.H. Uddin, M.M. Rhaman, Novel visible-light-
driven photocatalyst Co3O4/FeWO4 for efficient decomposition of organic pollu-
tants, J. Clust. Sci. 29 (2018) 67–74.
[10] X. Xu, Z. Gao, Z. Cui, Y. Liang, Z. Li, S. Zhu, X. Yang, J. Ma, Synthesis of Cu2O
Octadecahedron/TiO2quantum dot heterojunctions with high visible light photo-
catalytic activity and high stability, ACS Appl. Mater. Interfaces 8 (2016) 91–101.
[11] K. Wenderich, G. Mul, Methods, mechanism, and applications of photodeposition in
photocatalysis: a review, Chem. Rev. 116 (2016) 14587–14619.
[12] M. Sboui, S. Bouattour, L.F. Liotta, V.L. Parola, S. Boufi, Paper-TiO2 composite: an
effective photocatalyst for 2-propanol degradation in gas phase, J. Photochem.
Photobiol. A: Chem. 350 (2018) 142–151.
[35] J. Yang, X. Wang, J. Dai, J. Li, Efficient visible-light-driven photocatalytic de-
gradation with Bi2O3 coupling silica doped TiO2, Ind. Eng. Chem. Res. 53 (2014)
12575–12586.
[36] Y. Cong, Y. Ji, Y. Ge, H. Jin, Y. Zhang, Q. Wang, Fabrication of 3D Bi2O3-BiOI
heterojunction by a simple dipping method: highly enhanced visible-light photo-
electrocatalytic activity, Chem. Eng. J. 307 (2017) 572–582.
[37] A.K. Chakraborty, M.E. Hossain, M.M. Rhaman, K.M.A. Sobahan, Fabrication of
Bi2O3/TiO2 nanocomposites and their applications to the degradation of pollutants
in air and water under visible-light, J. Environ. Sci. 26 (2014) 458–465.
[38] G.S. Li, L. Wu, F. Li, P.P. Wu, D.Q. Zhang, H.X. Li, Photoelectrocatalytic degradation
of organic pollutants via a CdS quantum dots enhanced TiO2 nanotube array elec-
trode under visible light irradiation, Nanoscale 5 (2013) 2118–2125.
[39] L. Zou, H. Wang, X. Wang, High efficient photodegradation and photocatalytic
hydrogen production of CdS/BiVO4heterostructure through Z-Scheme process, ACS
Sustain. Chem. Eng. 5 (2017) 303–309.
[40] A.K. Chakraborty, M.S. Akter, M.A. Haque, G.M.A. Khan, M.S. Alam, Synthesis of
Co3O4/WO3 nanoheterojunction photocatalyst for the decomposition of organic
pollutants under visible light irradiation, J. Clust. Sci. 24 (2013) 701–713.
[41] A.K. Chakraborty, M.A. Kebede, Preparation and characterization of WO3/Bi3O4Cl
nanocomposite and its photocatalytic behavior under visible light irradiation,
React. Kinet. Mech. Catal. 106 (2012) 83–98.
[42] A.K. Chakraborty, M.A. Kebede, Efficient decomposition of organic pollutants Over
In2O3/TiO2 nanocomposite photocatalyst under visible light irradiation, J. Clust.
Sci. 23 (2012) 247–257.
[43] A.K. Chakraborty, S.B. Rawal, S.Y. Han, S.Y. Chai, W.I. Lee, Enhancement of visible-
light photocatalytic efficiency of BiOCl/Bi2O3by surface modification with WO3,
Appl. Catal. A: Gen. 407 (2011) 217–223.
[44] S.B. Rawal, A.K. Chakraborty, Y.J. Kim, H.J. Kim, W.I. Lee, Double-heterojunction
structure of SbxSn1-xO2/TiO2/CdSe for efficient decomposition of gaseous 2-pro-
panol under visible-light irradiation, RSC Adv. 2 (2012) 622–630.
[45] S. Bera, S.B. Rawal, H.J. Kim, W.I. Lee, Novel coupled structures of FeWO4/TiO2and
FeWO4/TiO2/CdS designed for highly efficient visible-light photocatalysis, ACS
Appl. Mater. Interfaces 6 (2014) 9654–9663.
[46] W.W. Yu Dr, X. Peng Dr, Formation of high-quality CdS and other II–VI semi-
conductor nanocrystals in noncoordinating solvents: tunable reactivity of mono-
mers, Angew. Chem. Int. Ed. 41 (2002) 2368–2371.
[13] A. Kongkanand, K. Tvrdy, K. Takechi, M. Kuno, P.V. Kamat, Quantum dot solar
cells. Tuning photoresponse through size and shape control of
CdSe−TiO2architecture, J. Am. Chem. Soc. 130 (2008) 4007–4015.
[14] B. Gao, Y.J. Kim, A.K. Chakraborty, W.I. Lee, Efficient decomposition of organic
compounds with FeTiO3/TiO2 heterojunction under visible light irradiation, Appl.
Catal. B: Environ. 83 (2008) 202–207.
[15] N. Qin, Y. Liu, W. Wu, L. Shen, X. Chen, Z. Li, L. Wu, One-dimensional CdS/
TiO2nanofiber composites as efficient visible-light-driven photocatalysts for selec-
tive organic transformation: synthesis, characterization, and performance,
Langmuir 31 (2015) 1203–1209.
[16] Y.J. Kim, B. Gao, S.Y. Han, M.H. Jung, A.K. Chakraborty, T. Ko, C. Lee, W.I. Lee,
Heterojunction of FeTiO3 nanodisc and TiO2 nanoparticle for a novel visible light
photocatalyst, J. Phys. Chem. C 113 (2009) 19179–19184.
[17] K.L. Zhang, C.M. Liu, F.Q. Huang, C. Zheng, W.D. Wang, Study of the electronic
structure and photocatalytic activity of the BiOCl photocatalyst, Appl. Catal. B:
Environ. 68 (2006) 125–129.
[18] WO3/BiOCl, a novel heterojunction as visible light photocatalyst, J. Colloid
Interface Sci. 356 (2011) 465–472.
[19] A.M. Ganose, M. Cuff, K.T. Butler, A. Walsh, D.O. Scanlon, Interplay of orbital and
relativistic effects in bismuth oxyhalides: BiOF, BiOCl, BiOBr, and BiOI, Chem.
Mater. 28 (2016) 1980–1984.
[20] Q. Li, Z. Guan, D. Wu, X. Zhao, S. Bao, Baozhu, Z-Scheme BiOCl-Au-CdS hetero-
structure with enhanced sunlight-driven photocatalytic activity in degrading Water
dyes and antibiotics, ACS Sustain. Chem. Eng. 5 (2017) 6958–6968.
[21] H. Li, J. Shang, H. Zhu, Z. Yang, Z. Ai, L. Zhang, Oxygen vacancy structure asso-
ciated photocatalytic water oxidation of BiOCl, ACS Catal. 6 (2016) 8276–8285.
[22] Y. Lei, G. Wang, S. Song, W. Fan, H. Zhang, Synthesis, characterization and
[47] A.J. Nozik, R. Memming, Physical chemistry of semiconductor−liquid interfaces, J.
Phys. Chem. 100 (1996) 13061–13078.
[48] D.J. Norris, M.G. Bawendi, Measurement and assignment of the size-dependent
optical spectrum in CdSe quantum dots, Phys. Rev. B 53 (1996) 16338–16346.
[49] A.G. Agrios, P. Pichat, State of the art and perspectives on materials and applica-
tions of photocatalysis over TiO2, J. Appl. Electrochem. 35 (2005) 655–663.
[50] R. Abe, H. Takami, N. Murakami, B. Ohtani, Pristine simple oxides as visible light
driven photocatalysts: highly efficient decomposition of organic compounds over
platinum-loaded tungsten oxide, J. Am. Chem. Soc. 130 (2008) 7780–7781.
[51] Y. Xu, M.A.A. Schoonen, The absolute energy positions of conduction and valence
167

A.K. Chakraborty et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry364(2018)159–168
[54] M. Wang, N. Chamberland, L. Breau, J.E. Moser, R.H. Baker, B. Marsan,
S.M. Zakeeruddin, M. Grätzel, An organic redox electrolyte to rival triiodide/iodide
in dye-sensitized solar cells, Nat. Chem. 2 (2010) 385–389.
[55] K. Katsumata, R. Motoyoshi, N. Matsushita, K. Okada, Preparation of graphitic
carbon nitride (g-C3N4)/WO3 composites and enhanced visible-light-driven photo-
degradation of acetaldehyde gas, J. Hazard. Mater. 260 (2013) 475–482.
bands of selected semiconducting minerals, Am. Min. 85 (2000) 543–556.
[52] N. Serpone, P. Maruhamuthu, P. Pichat, E. Pelizzetti, H. Hidaka, Exploiting the
interparticle electron transfer process in the photocatalysed oxidation of phenol, 2-
chlorophenol and pentachlorophenol: chemical evidence for electron and hole
transfer between coupled semiconductors, J. Photochem. Photobiol. A: Chem. 85
(1995) 247–255.
[53] M. Grätzel, Photoelectrochemical cells, Nature 414 (2001) 338–344.
168