A Novel CdS/g-C3N4Composite Photocatalyst: Preparation, Characterization and Photocatalytic Performance with Different Reaction Solvents under Visible Light Irradiation

Article abstract of DOI:10.1002/cjoc.201600251

CdS/graphtic carbon nitride (CdS/g-C₃N₄) hybrid materials were fabricated by thermal polymerization and hydrothermal methods using Cd(CH₃COO)₂?2H₂O, thioacetamide, and melamine as precursors. The structural and optical properties of the as-synthesized samples were investigated by X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, etc. A coupled system toward the selective oxidation of benzyl alcohol to benzaldehyde and the reduction of nitrobenzene into aniline was used to estimate the photocatalytic performance of CdS/g-C₃N₄composite photocatalysts under visible light illumination. Results indicate that the CdS/g-C₃N₄sample exhibits an outstanding photocatalytic performance for selective oxidation of benzyl alcohol and reduction of nitrobenzene. Meanwhile, benzotrifluoride is the best reaction medium among the screened solvents. Further research demonstrates that the selective oxidation of benzyl alcohol to benzaldehyde is induced by the photoexcited holes and the reduction of nitrobenzene into aniline is triggered by the photoexcited electrons. Additionally, the catalyst can be recycled several times without noticeable deactivation.

Full text of DOI:10.1002/cjoc.201600251

FULL PAPER
DOI: 10.1002/cjoc.201600251
A Novel CdS/g-C N Composite Photocatalyst: Preparation,
3
4
Characterization and Photocatalytic Performance with
Different Reaction Solvents under Visible Light Irradiation
a
a,b
,b
b
,a,b
Xiangju Ye, Xia Dai, Sugang Meng,* Xianliang Fu, and Shifu Chen*
a
College of Chemistry and Materials Engineering, Anhui Science and Technology University, Fengyang,
Anhui 233100, China
b
College of Chemistry and Materials Science, Huaibei Normal University, Huaibei, Anhui 235000, China
3 4
CdS/graphtic carbon nitride (CdS/g-C N ) hybrid materials were fabricated by thermal polymerization and hy-
drothermal methods using Cd(CH COO) •2H O, thioacetamide, and melamine as precursors. The structural and op-
3
2
2
tical properties of the as-synthesized samples were investigated by X-ray powder diffraction, UV-Vis diffuse reflec-
tance spectroscopy, scanning electron microscopy, transmission electron microscopy, etc. A coupled system toward
the selective oxidation of benzyl alcohol to benzaldehyde and the reduction of nitrobenzene into aniline was used to
estimate the photocatalytic performance of CdS/g-C N composite photocatalysts under visible light illumination.
3
4
Results indicate that the CdS/g-C N sample exhibits an outstanding photocatalytic performance for selective oxida-
3
4
tion of benzyl alcohol and reduction of nitrobenzene. Meanwhile, benzotrifluoride is the best reaction medium
among the screened solvents. Further research demonstrates that the selective oxidation of benzyl alcohol to ben-
zaldehyde is induced by the photoexcited holes and the reduction of nitrobenzene into aniline is triggered by the
photoexcited electrons. Additionally, the catalyst can be recycled several times without noticeable deactivation.
Keywords CdS, g-C N , photocatalyst, selective oxidation, reduction
3
4
Introduction
tributed to the complete oxidation of organic matters
into carbon dioxide, water, and mineral acid. Therefore,
developing appropriate band gap semiconductor photo-
catalysts with higher conduction band (CB) position and
It is commonly accepted that the current environ-
mental pollution and energy crisis have become crucial
issues and have already hindered the development of the
world economy. Photocatalysis has attracted a consider-
able amount of attention among researchers in the past
decades as a renewable, green, and environmentally
friendly technology, mainly because of its extensive
applications in environmental remediation, photolysis of
water into hydrogen and oxygen, organic photosynthesis,
lower valence band (VB), such as In
AgInS may be the preferable option for selective oxi-
dation of alcohols to corresponding aldehydes.
2 3
S , CdS, and
2
[31-33]
Recently, Xu and co-workers have reported the result
that when VB position of a photocatalyst is higher than
2
.1 eV, it may realize effectively the aerobic oxidation
[
34]
of benzyl alcohol to benzaldehyde.
[
1-19]
and CO reduction via sunlight.
Among these ap-
2
Photocatalytic reduction of nitrobenzene into aniline
using semiconductor materials as photocatalysts has
become an extensively studied topic in the last few
plications, the selective oxidation of alcohols to corre-
sponding aldehydes, as well as the reduction of nitro-
benzene to aniline have recently become a research
[
35-37]
years.
Unfortunately, the reduction system of ni-
[20-25]
hotspot.
2
For example, it has reported that TiO has
trobenzene depends strongly on the aid of hole scaven-
gers, such as methanol and ethanol. In principle, when
the conduction band (CB) potential of a photocatalyst is
lower than 0.486 eV, the formation of aniline can be
achieved from nitrobenzene via photocatalysis technol-
been introduced as a well-known photocatalyst for se-
lective transformation of organic compounds using solar
[26-29]
radiation.
of 3.2 eV (vs. NHE pH 7) and positive valence band of
.7 eV, the reaction system for selective oxidation of
However, due to its wide energy gap (Eg)
[38]
2
ogy.
As we all know, •O2 and h are important oxidants
for selective oxidation of aromatic alcohols to corre-
sponding aldehydes, and photo-induced electrons are
＋
benzyl alcohol to coressponding aldehyde by TiO pho-
tocatalysts is usually limited by its poor selectivity in
the presence of UV light and O
2
[30]
2
.
This is mainly at-
*
E-mail: chshifu@chnu.edu.cn; Tel.: 0086-0561-3806611; Fax: 0086-0561-3090518
Received April 25, 2016; accepted June 22, 2016; published online XXXX, 2016.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201600251 or from the author.
Chin. J. Chem. 2016, XX, 1—9
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1

Ye et al.
FULL PAPER
important reducers for reduction of nitrobenzene into
aniline. Thus, constructing a novel narrow band gap
hybrid photocatalyst with more negative CB values and
appropriate VB position may realize simultaneously the
selective oxidation of aromatic alcohols to correspond-
ing aldehydes, as well as the reduction of nitrobenzene
into aniline in a reaction system. According to the pre-
by washing with water and ethanol 3 times.
(c) Synthesis of CdS/g-C composite: An amount
of g-C powder was dispersed in the solution A under
vigorously stirring for 30 min. Then, using the same
hydrothermal method, a series of X wt% CdS/g-C (X
＝1.0, 5.0, 10, 30, 50, where X represents the percentage
of CdS in the hybrid material) composite photocatalyst
was prepared.
3
N
4
3
N
4
3
N
4
vious reports, we know that the CB and VB of g-C
3 4
N
are 1.13 and 1.57 eV, and the CB and VB of CdS are
XRD measurements were carried out by using a
BRUKER D8 ADVANCE X-ray powder diffractometer
(Cu Kα1 radiation, λ＝1.5406 Å) at a scanning speed of
3 (°)/min. The accelerating voltage and emission current
were 40 kV and 30 mA, respectively. The UV/vis dif-
fuse reflectance spectra (DRS) were performed on a
UV-3600 (SHIMA-DZU, Japan) UV-Vis-NIR spectro-
photometer equipped with an integrating sphere attach-
[39,40]
0.49 and 1.86 eV, respectively.
So, it is predicted
that CdS/g-C hybrid photocatalyst has ability for
3
N
4
selective oxidation of alcohols to aldehydes, as well as
reduction of nitrobenzene to aniline under visible light
illumination. In addition, the photoinduced charge car-
riers can be seperated efficiently by the as-constructed
hybrid photocatalysts, thus resulting in the improvement
[41-43]
of its photocatalytic performance.
In this paper, CdS/g-C composite photocatalysts
4
ment. A white standard of BaSO was used as a refer-
3
N
4
ence sample. The morphology of the as-obtained sam-
ples was investigated by a JEOL JSM-6610LV scanning
electron microscope with 30 kV scanning voltages.
Transmission electron microscopy (TEM) and high-
resolution transmission electron microscopy (HR-TEM)
images were recorded on a JEM-2100 electron micro-
scope with an acceleration voltage of 200 kV. The X-ray
photoelectron spectroscopy (XPS) data were obtained
with a Thermo Scientific ESCA Lab 250 spectrometer
which consisted of a monochromatic Al Kα as the X-ray
source, a hemipherical analyzer and a sample stage with
multi-axial adjustability to obtain the surface composi-
tion of the samples. All the binding energies were cali-
brated by the C 1s peak of the surface adventitious car-
bon at 284.6 eV.
were prepared by thermal polymerization and hydro-
thermal methods. A synergetic system for the selective
oxidation of benzyl alcohol to benzaldehyde, as well as
the reduction of nitrobenzene into aniline was initiated
by CdS/g-C
atmosphere. Results suggest that CdS/g-C
3
N
4
photocatalysts under visible light and N
composite
2
3
N
4
material shows a superior photocatalytic performance
for selective oxidation of benzyl alcohol to benzalde-
hyde and reduction of nitrobenzene into aniline. Addi-
tionally, direct holes oxidation is responsible for selec-
tive oxidation of benzyl alcohol to benzaldehyde, and
electrons reduction is for the reduction of nitrobenzene
into aniline.
Photocatalytic performance of the as-prepared sam-
ples for selective oxidation of benzyl alcohol to benzal-
dehyde and reduction of nitrobenzene into aniline was
evaluated in a self-designed photochemical reactor
equipped with a pressure gage, which was convenient
Experimental
Melamine (C
3 3 6
H N ) powder, cadmium acetate
Cd(CH COO) •2H O], thioacetamide (TAA), ethanol
3
2
2
(
C H OH), benzyl alcohol, benzaldehyde, nitrobenzene,
2 5
[20]
benzotrifluoride (BTF), aniline and other reagents used
in the experiments were purchased from Sinopharm
Chemical Reagent Co. Ltd. All reagents were of analyt-
ical grade and were used without further purification.
Deionized water was used in this experiment.
for monitoring the pressure in the autoclave. In detail,
0
.1 g photocatalyst was suspended in a benzotrifluoride
2
solution (15 mL) containing benzyl alcohol (2.55×10
3
mol/L) and nitrobenzene (8.5×10 mol/L), and it was
put into a 100 mL reactor of Teflon-lined stainless steel
autoclave. Prior to illumination, the mixture was bub-
bled for 0.5 h to remove the dissolved oxygen and
maintained in the reactor at a pressure of 0.5 MPa, fol-
lowed by stirring in the dark for 1 h to ensure the ad-
sorption-desorption equilibrium between the photocata-
lyst and reactants. The reaction system was stirred at
60 ℃ for 4 h in the dark. To carry out the photo-
chemical reaction, a 300 W Xe arc lamp (PLS-SXE 300,
Beijing Perfect light Co., Ltd.) with a 420 nm cut-off
filter was used as a visible light source for the irradia-
tion of reaction system. At the end of the reaction, the
reaction solution was collected from the reactor and
centrifuged to remove the catalyst completely at 4000
r/min for 20 min, until it was finally filtered through a
0.2-µm millipore filter to remove any residual particles.
The main product of selective oxidation of benzyl
(
a) Preparation of g-C N : g-C N was synthesized
3 4 3 4
according to the following procedure. Melamine powder
was heated in an alumina crucible with a cover at
5
00 ℃ for 2 h, and then heated at 520 ℃ for an addi-
tional 2 h. The heating rate was about 10 ℃/min. Fi-
nally, the obtained sample was cooled naturally to room
temperature.
(
b) Preparation of CdS: CdS was prepared by a hy-
drothermal method using Cd(CH COO) •2H O and thi-
oacetamide as precursors. 3 mmol Cd(CH COO) •2H
3
2
2
3
2
2
O
and 6 mmol TAA were added into 50 mL deionized wa-
ter and stirred for 30 min, thus obtaining solution A. The
suspension was then transferred into a 100 mL teflon-
lined stainless steel autoclave, heated to 180 ℃ and
kept at this temperature for 24 h. After being cooled
naturally to room temperature, the product was collected
2
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3 4
CdS/g-C N Composite Photocatalyst: Preparation, Characterization and Photocatalytic Performance
alcohol and reduction product of nitrobenzene are ben-
zaldehyde and aniline, respectively. The products of the
reactions were analyzed by gas-chromatography (Fuli
may be attributed to the strong interaction between
g-C N and CdS sample.
3
4
9
790, AC20, SE-30 0.53 mm×30 m capillary column)
with FID detector. Conversion of benzyl alcohol, yield
of benzaldehyde, and selectivity for benzaldehyde were
[20,44]
calculated by the following express-ions:
Conversion＝[(C ]×100%
0
Calcohol)/C
0
(1)
(2)
(3)
0
Yield＝Caldehyde/C ×100%
Selectivity＝[Caldehyd/(C Calcohol)]×100%
0
where C is the initial concentration of benzyl alcohol in
0
the solution before illumination; Calcohol is the concen-
tration of benzyl alcohol in the solution after illumina-
tion for 4 h; Caldehyde is the concentration of benzalde-
hyde in the solution after illumination for 4 h.
Figure 1 XRD patterns of pure g-C
3 4
N , CdS and 10 wt%
CdS/g-C samples
3
N
4
Reduction of the nitrobenzene during the photocat-
alytic reaction was defined as follows:
UV-Vis DRS analysis In order to obtain the opti-
cal properties of the samples, the UV-Vis diffuse reflec-
tance spectroscopy was performed. Figure 2(a) shows
Conversion＝[(C
×100%
CNB)]×100%
0
CNB)/C
0
]×100%
(4)
(5)
(6)
the UV-Vis DRS of pure CdS, g-C
CdS/g-C samples. It is seen that pure CdS sample
reveals an absorption edge at about 528 nm, and pure
g-C shows its fundamental absorption edge at 460
nm. Meanwhile, the spectrum of CdS/g-C
3 4
N and 10 wt%
Yield＝Caniline/C
0
3
N
4
Selectivity＝[Caniline/(C
0
3
N
4
where C is the initial concentration of nitrobenzene in
0
4
N sample
3
the solution; CNB is the concentration of nitrobenzene in
the solution after illumination for 4 h; Caniline is the con-
centration of aniline in the solution after illumination for
displays two absorption band edges, which implies that
the hybrid samples contain two semiconductors of CdS
and g-C
28 nm are ascribed to g-C
contrast with pure g-C , the absorption band edge of
CdS/g-C N sample appears red shift. It may be favora-
3
N
4
. The absorption band edges at about 460 and
4
h.
5
3 4
N
and CdS, respectively. In
3
N
4
Results and Discussion
3
4
ble for the utilization of the solar energy, thereby result-
ing in an improvement of its photocatalytic performance.
For a crystalline semiconductor, the optical absorption
Characterization of photocatalysts
XRD analysis XRD analysis was used to deter-
mine the crystal phases of the as-obtained samples. Fig-
ure 1 shows the X-ray diffraction patterns of g-C N ,
[
20,48]
near the band edge follows the formula:
3
4
n/2
ahv＝A(hvE
g
)
(7)
CdS and 10 wt% CdS/g-C N composite samples, re-
3
4
spectively. Notably, it is observable that the g-C N has
two typical peaks at 2θ＝13.1° and 27.4°. The diffrac-
tion intensity of the former is weak and it is indexed as
3
4
where a, h, v, A and E are the absorption coefficient,
g
Planck constant, light frequency, proportionality coeffi-
cient, and band gap energy, respectively. n keys the
properties of the transition in a semiconductor (n＝1 for
direct transition, and n＝4 for indirect transition). The
(
100) diffraction plane, which corresponds to a distance
of d＝0.676 nm. The later is attributed to the character-
istic (002) plane of graphitic, layered structure with an
values of n for g-C
The E of g-C
obtained from the plots of (ahν) or (ahν) versus pho-
ton energy (hν). As shown in Figure 2 (b) and (c), the E
of g-C N and CdS are about 2.7 and 2.35 eV, respec-
3
N
4
and CdS are 4 and 1, respectively.
[
45-47]
interlayer distance d＝0.325 nm.
The CdS prepared
g
3 4
N and CdS photocatalysts can thus be
1
/2
2
in this experiment is a mixture of cubic phase (JCPDS
card no. 41-1049) and hexagonal phase (JCPDS card no.
g
1
0-0454). The unique planes (100), (002) and (101) are
3
4
indexed to the hexagonal phase, and the characteristic
diffraction plane (200) is assigned to the cubic phase.
Interestingly, for 10 wt% CdS/g-C N composite, the
tively.
The valence band edge and conduction band edge of
a semiconductor at the point of zero charge (pHZPC) can
be calculated by the following empirical formulas:
3
4
(
100) diffraction peaks of g-C N disappear in the pat-
3 4
tern, suggesting that CdS particles are evenly dispersed
on the surface of g-C N and restrain the growth of the
E
E
VB＝X＋0.5E
CB＝EVBE
g
E
e
(8)
(9)
3
4
in-plane structural repeating motifs of the aromatic sys-
tem. Notably, the (002) plane diffraction angle of
g-C N shifts to higher angle from 27.3° to 28.1°, which
g
In this equation, X is the absolute electronegativity of a
3
4
Chin. J. Chem. 2016, XX, 1—9
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3

Ye et al.
FULL PAPER
semiconductor, E
hydrogen scale (~4.5 eV), and E
of a semicondutor. Through these equations, the CB and
VB of g-C
e
is the energy of free electrons on the
nanoparticles are distributed evenly on the surface of
g
is the band gap energy
g-C
CdS particles deposited on the surface of g-C
strate is smaller than those of pure CdS particles. It is
probably because the introduction of g-C sample
3
N
4
sample. It is worth noting that the size of the
3
N
4
sub-
3
4
N are 1.13 and 1.57 eV, and the CB and
VB of CdS are 0.49 and 1.86 eV, respectively.
3 4
N
controls the growth of CdS particles during the hydro-
thermal process. Additionally, the chemical composition
of 10 wt% CdS/g-C N samples can be studied by EDX.
3 4
It is obvious from Figure 3 (d) that the sample is com-
posed of C, N, Cd and S elements, which is in good
consistent with the composition of the as-synthesized
sample.
3 4
Figure 3 SEM images of g-C N (a), CdS (b), 10 wt%
CdS/g-C N samples (c) and the corresponding EDS of 10 wt%
3
4
CdS/g-C N sample (d).
3
4
TEM analysis In order to investigate the surface
morphology of 10 wt% CdS/g-C N sample, TEM and
3
4
HRTEM were performed. Figure 4 (a) shows the overall
image of the composite material. It indicates that the
pure CdS particles with a mean size of 0.2－0.5 μm are
deposited on the surface of alveolate g-C N sample,
3
4
which is in good agreement with the result of SEM im-
age. It is obvious that the heterostructure of 10 wt%
CdS/g-C N samples is favorable for the efficient sepa-
3
4
ration and migration of photoexcited carriers, thus re-
sulting in improving the photocatalytic activity. Figure 4
(
b) displays the HRTEM image of 10 wt% CdS/g-C N
3 4
Figure 2 UV-Vis diffuse reflectance spectra of g-C N , CdS,
sample. The lattice-fringe spacing of 0.325 nm matches
3
4
and 10 wt% CdS/g-C
CdS (c).
3
N
4
samples (a), and E
g
of g-C
3
N
4
(b) and
SEM analysis Figure 3 depicts the morphology of
g-C , CdS and 10 wt% CdS/g-C samples. As
showed in Figure 3 (a), pure g-C exhibits aggrega-
3
N
4
3 4
N
3
N
4
tion, which consists of block-based flakiness and parti-
cles. Figure 3 (b) displays the morphology of CdS sam-
ple. It is evident that the as-synthesized sample is com-
posed of small spherical particles with a diameter of less
than 0.5 μm. From Figure 3 (c), we can find that CdS
Figure 4 TEM (a) and HRTEM (b) images of 10 wt%
CdS/g-C N sample.
3 4
4
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CdS/g-C
3
N
4
Composite Photocatalyst: Preparation, Characterization and Photocatalytic Performance
Figure 5 XPS spectra of 10 wt% CdS/g-C N : C 1s (a); N 1s (b); Cd 3d (c) and S 2p (d).
3
4
2
−
the (002) crystallographic plane of hexagonal carbon
nitride (JCPDS card No. 87-1526). The lattice fringes
with spacing about 0.336 and 0.358 nm are assigned to
the (111) plane of cubic CdS (JCPDS card No. 10-0454)
and (100) plane of hexagonal CdS (JCPDS card No.
161.6 eV for the sample is in good agreement with S
[50,51]
in CdS particles. Thus, it is reasonable to conclude
4
that CdS/g-C N photocatalyst is successfully synthe-
3
sized in our system.
Photocatalytic activities and stability
4
1-1049), respectively, which are all consistent with the
polycrystalline structure reflected by XRD patterns of
CdS/g-C samples.
In order to evaluate the photocatalytic performance
of the resulting samples, a synergetic system for selec-
tive oxidation of benzyl alcohol to benzaldehyde and
reduction of nitrobenzene to aniline was carried out in
different reaction solvents with visible light (λ＞420 nm)
3
N
4
XPS analysis XPS analysis was used to investi-
gate the surface chemical composition and element
states of the as-synthesized samples. Figure 5 shows the
high-resolution XPS spectra of the elements C 1s, N 1s,
for 4 h under N
2
protection. From Figure 6 and Figure 7,
, 10 wt% CdS/g-C
Cd 3d and S 2p for 10 wt% CdS/g-C
s peaks of CdS/g-C compound in Figure 5a can be
separated into two peaks at the binding energies of
84.6 and 287.8 eV, which are attributed to C－C and C
N－C bonding (CN network), respectively. Figure 5b
3
N
4
sample. The C
it can be observed that for g-C
3
N
4
3 4
N
1
3
N
4
and CdS samples, the selective oxidation of benzyl al-
cohol to benzaldehyde and the reduction of nitroben-
zene to aniline can be realized when BTF, toluene, ace-
tonitrile, and water are used as solvents, respectively.
2
－
shows that the N 1s spectra can be deconvoluted into
three peaks, which are centered at 398.4, 399.9 and
3 4
Moreover, 10 wt% CdS/g-C N samples exhibit superior
photocatalytic performance for the formation of ben-
zaldehyde from benzyl alcohol and the production of
4
04.8 eV, respectively. Among these, the peak with
lower binding energy at 398.4 eV is assigned to nitrogen
atoms bonded with the graphite carbon atoms (C＝N－
C), the weak peak at 399.9 eV correponds to bridging
nitrogen atoms N－(C3), and the peak with higher
binding energy at 404.8 eV is originated from the amino
aniline from nitrobenzene to sole CdS and g-C
3 4
N cata-
lysts except for using H O as a solvent. Further studies
2
reveal that when BTF is used as a solvent, the conver-
sion and selectivity are the highest among the screened
solvents. This may be attributed to the relatively high
[
49]
[52]
functional groups with a hydrogen atom (C－H－N).
inert behavior of BTF solvent. For example, for se-
Additionally, characteristic binding energies of 404.8
and 411.7 eV for Cd 3d are detected, suggesting that the
lective oxidation of benzyl alcohol to benzaldehyde, the
conversion and selectivity of 10 wt% CdS/g-C N sam-
3 4
chemical state of Cd element in CdS/g-C
Cd ( Figure 5c). In Figure 5d, the S 2p broad peak at
3
N
4
sample is
ples in BTF solvent are 48.0% and 93%, respectively.
However, the conversion and selectivity for g-C N and
2
＋
3
4
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5

Ye et al.
FULL PAPER
CdS samples in BTF solvent are 9.3%, 83% and 16.3%,
CdS/g-C
3
N
4
as a probe sample for simultaneously selec-
9
2%, respectively. Meanwhile, for reduction of nitro-
benzene to aniline in BTF solvent, the conversion and
selectivity of 10 wt% CdS/g-C samples are 49.2%
and 52.8%, respectively. As we expected, the trends of
conversion and selectivity for g-C and CdS samples
tive oxidation of benzyl alcohol and reduction of nitro-
benzene in toluene medium. After each reaction, the
catalyst was separated from the reaction system, washed
with deionized water several times, recovered, and then
re-dispersed in a new reaction mixture. The results are
shown in figure 8. It indicates that in the 5-cycle ex-
periments, the conversion of benzyl alcohol and yield of
benzaldehyde are about 28.5% and 23.7% under visible
light, respectively, and no obvious deactivation is ob-
served in toluene solvent. Meanwhile, no noticeable
3
N
4
3
N
4
correspond with those of the oxidation of benzyl alcohol.
However, when water is used as a solvent, the yield is
very poor, although the conversion is the highest. The
reason is unknown, although there is research into the
reason.
The conversion and yield of the benzyl alcohol to
3 4
decay of 10 wt% CdS/g-C N for reduction of nitroben-
zene into aniline is observed in the five-run tests (nitro-
benzene conversion of 39.8% and aniline yield of
18.1%). So, it demonstrates that 10 wt% CdS/g-C N is
3 4
a chemically stable heterocatalyst for selective oxidation
of benzyl alcohol and reduction of nitrobenzene in tol-
benzaldehyde for CdS and g-C
3
N
4
samples are the same
as those of the samples when toluene and acetonitrile
are used as solvents. However, when water is used as a
solvent, the selectivities are poor, although the conver-
sions are higher for selective oxidation of benzyl alco-
hol to benzaldehyde and reduction of nitrobenzene to
aniline. This is mainly because many by-products are
continuously produced during the reaction process,
2
uene solvent under N atmosphere and visible light irra-
diation.
[20,31]
Control experiments
which have been investigated by our group.
The
above results are mainly attributed to the polarity of the
solvents, that is, the selectivities decrease with the in-
crease of solvent’s polarity (polarity: water＞aceto-
nitrile＞toluene).
2
It is known that under N atmosphere and visible
light irradiation, the real contributing role in this reac-

＋
tion system is photogenerated e and h . To further val-
[
20]
idate the previous reaction mechanism,
a series of
In order to verify the stability of the photocatalyst,
the cycle tests were conducted using 10 wt%
control experiments were performed. The results are
shown in Figure 9. It is clear that when oxalic acid (OA)
Figure 6 Performance of photocatalytic selective oxidation of benzyl alcohol to benzaldehyde under visible light irradiation (λ＞420 nm)
for 4 h with N purge condition.
2
6
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3 4
CdS/g-C N Composite Photocatalyst: Preparation, Characterization and Photocatalytic Performance
Figure 7 Performance of photocatalytic selective reduction of nitrobenzene into aniline under visible light irradiation (λ＞420 nm) for 4
h with N condition.
2
3 4
Figure 8 Cyclic experiments of 10 wt% CdS/g-C N sample for selective oxidation of benzyl alcohol to benzaldehyde (a) and reduction
of nitrobenzene into aniline (b) under the toluene solvent.
Figure 9 The conversion and yield for selective oxidation of benzyl alcohol (a) and reduction of nitrobenzene (b) using 10 wt%
CdS/g-C N photocatalyst by adding different scavengers (OA: oxalic acid) and CCl under visible light.
3
4
4
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© 2016 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
7

Ye et al.
FULL PAPER
is added to the reaction system to eliminate the holes,
the conversion of benzyl alcohol and yield of benzalde-
hyde decrease significantly, suggesting that the photo-
generated holes are the major oxidation species for the
selective oxidation of benzyl alcohol to benzaldehyde.
Meanwhile, it appears a slight improvement in the con-
version of nitrobenzene and yield of aniline. The addi-
tion of electron scavenger (tetrachloromethane) can
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3 4
In summary, CdS/g-C N hybrid materials were
synthesized by thermal polymerization and hydro-
thermal methods using Cd(CH COO) •2H O, thioacet-
[
[
[
3
2
2
amide, and melamine as precursors. The as-prepared
photocatalyst exhibits an excellent photocatalytic per-
formance for simultaneously selective oxidation of
benzyl alcohol, as well as the reduction of nitrobenzene
under mild conditions (60 ℃, N atmosphere), and BTF
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used as a medium shows the best photocatalytic perfor-
mance. Furthermore, it suggests that photogenerated
holes and electrons play significant roles in this reaction
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3
strated to be a very stable catalyst in this photocatalytic
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Acknowledgement
This study was financially supported by the National
Natural Science Foundation of China (NSFC, Nos.
5
1472005, 21103060 and 51272081), the Natural Sci-
ence Foundation of Anhui Province, China (No.
608085QB37), the Talent Foundation of Education
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Department of Anhui Province, China (No. gxfx
ZD2016176), and the Materials Science and Engineer-
2
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Key
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