g-C3N4/H3PW4Mo8O40 S-scheme photocatalyst with enhanced photocatalytic oxidation of alcohols and sulfides

Article abstract of DOI:10.1016/j.inoche.2021.108842

In this work, graphitic carbon nitride (g-C₃N₄) decorated with molybdenum-substituted tungstophosphoric acid as a novel photocatalyst (H₃PW₄Mo₈O₄₀/g-C₃N₄) was used to catalyze the oxidation of alcohols and sulfides. H₃PW₄Mo₈O₄₀/g-C₃N₄ (PW₄Mo₈/g-C₃N₄) displays higher photocatalytic activity under visible light irradiation for the oxidation of alcohols and sulfides compared with Keggin/g-C₃N₄ (PW₁₂/g-C₃N₄). To obtain the optimum value, molybdenum substitution contents (H₃PW_12-xMo_xO₄₀) were changed from x = 4 to 12. The results showed that PW₄Mo₈ produces the best yield under visible-light irradiation. The results showed that PW₄Mo₈ was the best sample. The reaction rate increase can be due to the redox and acid properties of PW₄Mo₈/g-C₃N₄. This study provides a new insight for the preparation of highly efficient photocatalysts for the oxidation of organic compounds.

Full text of DOI:10.1016/j.inoche.2021.108842

Journal Pre-proofs
g-C3N4/H3PW4Mo8O40 S-scheme photocatalyst with enhanced photocatalytic
oxidation of alcohols and sulfides
Razieh Nejat, Zohreh Najminejad, Farnaz Fazlali, Somaye Shahraki, Zeynab
Khazaee
PII:
S1387-7003(21)00397-X
DOI:
https://doi.org/10.1016/j.inoche.2021.108842
INOCHE 108842
Reference:
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Inorganic Chemistry Communications
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Accepted Date:
11 May 2021
31 July 2021
1 August 2021
Please cite this article as: R. Nejat, Z. Najminejad, F. Fazlali, S. Shahraki, Z. Khazaee, g-C3N4/H3PW4Mo8O40 S-
scheme photocatalyst with enhanced photocatalytic oxidation of alcohols and sulfides, Inorganic Chemistry
Communications (2021), doi: https://doi.org/10.1016/j.inoche.2021.108842
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g-C3N4/H3PW4Mo8O40 S-scheme photocatalyst with enhanced
photocatalytic oxidation of alcohols and sulfides
Razieh Nejata (PhD), Zohreh Najminejadb (PhD), Farnaz Fazlalic (PhD), Somaye Shahrakid
(PhD), Zeynab Khazaeec (PhD)
a Chemistry Department, Faculty of science, Kosar University of Bojnord, Iran. Bojnord, Iran.
Fax: (+98)-58-3242740, phone: (+98)-58-32262863. P.O. Box 9415615458; Email:
organochem.nejat@kub.ac.ir
b Department of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran.
c Tarbiat Modares University, Department of Chemistry, 14155-4383, Tehran, Iran. Fax: (+98)-
21- 82883455, phone: (+98)-21-82883442, P.O. Box 14155-4838.
Email:Farnaz.fazlali@modares.ac.ir
d Department of Chemistry, University of Zabol, Zabol, Iran, Fax: +98-542-222 6765, phone:
(+98)-54-31232078, P.O. Box 98615-538. E-mail address: s-shahraki@uoz.ac.ir ۰
Corresponding author: Razieh Nejat
E-mail address: organochem_nejat@yahoo.com.
Razieh Nejat:0000-0001-8742-2342
Zohreh Najminejad: 0000-0002-3676-3101
Farnaz Fazlali :0000-0001-6220-4058
Somaye Shahraki: 0000-0002-0597-4459

۵۸۳۲۲۶۲۸۶۳
Abstract. In this work, graphitic carbon nitride (g-C3N4) decorated with
molybdenum-substituted tungstophosphoric acid as a novel photocatalyst
(H3PW4Mo8O40/g-C3N4) was used to catalyze the oxidation of alcohols and
sulfides.
H3PW4Mo8O40/g-C3N4
(PW4Mo8/g-C3N4)
displays
higher
photocatalytic activity under visible light irradiation for the oxidation of
alcohols and sulfides compared with Keggin/g-C3N4 (PW12/g-C3N4). To obtain
the optimum value, molybdenum substitution contents (H3PW12-xMoxO40) were
changed from x= 4 to 12. The results showed that PW4Mo8 produces the best yield
under visible-light irradiation. The results showed that PW4Mo8 was the best
sample. The reaction rate increase can be due to the redox and acid properties
of PW4Mo8/g-C3N4.This study provides a new insight for the preparation of
highly efficient photocatalysts for the oxidation of organic compounds.
Keywords: Heteropolyacid, g-C3N4, Photocatalyst, Oxidation.
Running title: molybdenum-substituted tungstophosphoric acid/g-C3N4 as
photocatalyst.

Highlights
 Designing a new set of HPAs as photocatalyst under visible-light.

Proving the promising role of Mo cations in selective photocatalytic oxidation
of alcohols and sulfides.
 The g-C3N4 with electronic structural property as visible-light active
photocatalyst

Introduction
Recently, water pollution treatment has attracted the increasing attention of researchers. There are
many water treatment technologies, like adsorption [1], Microwave [2,3], extraction [4], oxidation
[5], and photo-oxidation [6] which are used to eliminate pollutants. Compared with other advanced
oxidation technologies, photocatalysis was considered to be a more promising technology for
transforming organic pollutants into harmless substances [7].
on the other hand, The Selective Oxidation of alcohols and sulfides to the corresponding carbonyl
compounds and sulfoxides represent key reactions in the field of synthetic organic chemistry [8-
18]. Sulfoxides have received enormous interest as chiral auxiliaries in organic synthesis, as useful
building blocks to produce various chemically, biologically, and medicinally active molecules [19-
21]. Several types of oxidizing agents, such as toxic metal oxides and peroxides, and methods have
been used for the oxidation of alcohols and sulfides in solution and solid phases [22-29]. Many of
these reagents and catalysts suffer from certain drawbacks such as the toxicity of the transition
metals and environmentally harmful waste by‐products, long reaction times, low selectivity, poor
yields of products, and over-oxidation of the sulfoxides and aldehydes to sulfones and Carboxylic
acids as side-reaction [30-32]. Therefore, in order to oxidation of sulfides and alcohols to
sulfoxides and carbonyl compounds without excessive oxidation to sulfones and carboxylic acids,
there is a demand for environmental-economic methods. Over the past few decades, significant
attention has been paid to selective oxidation photocatalysts. Recently, numerous research on
discovering new photocatalytic materials has been undertaken that are both more effectual and
innately active under visible light [33-37]. Visible light has attracted wide attention with its clean
and abundant advantages [38]. In this regard, photocatalysis using semiconductors is as ZnO [39],

TiO2 [40], metal-organic frameworks [41, 42], heteropoly acids (HPAs) [43], and g-C3N4
nanaosheets [44, 45], is an efficient approach for oxidation reactions such. Among these
compounds, heteropoly acids show high efficiency due to the redox and acidity properties. The
dodecatunvgstophosphoric acid, H3PW12O40 could show photocatalytic activity under visible light
[46].
Recently tungesto- and molybo-phosphoric acids draw attention in photocatalytic reactions. For
example, Fazlali et al. [47] explored Keggin hetero polyacid supported on BN and C3N4 as an
efficient catalyst in the methanol photocatalytic dehydration reaction. Also, the ion-exchange in
Keggin type HPAs (W and Mo) lead to improve the catalytic properties of the catalysts because
the substitution of these atoms changes their acid and redox properties [48-50]. Unfortunately, low
charge separation and high solubility in polar media hinder its practical utilization at a large scale.
Recent studies have shown that the recombination of photogenerated electrons and holes can be
controlled by coupling HPAs with an ideal substrate [51, 52]. In this perspective, for the anchoring
of HPAs, graphitic carbon nitride (g-C3N4) can be an appropriate candidate because of the presence
of various functional groups and their unique properties. Graphitic carbon nitrides as the most
stable allotrope of carbon nitride with high chemical and thermal stability and also unique
electronic structure, have been standing in the hot research area for their potential applications in
photocatalysis [53-55]. Also, g-C3N4 has rich surface properties that are attractive for catalysis
applications due to the presence of basic surface sites. Besides, the band gap of g-C3N4 is 2.85 eV,
with valence band (VB) and conduction band (CB) positions respectively at −1.1 and +1.6 eV. The
g-C3N4 with this electronic structural property can be visible-light active photocatalyst [56].
Results show that the pure g-C3N4 almost exhibits no photocatalytic performance during the
photocatalytic process, however, PMO/g-C3N4 composite exhibits excellent photocatalytic

performance because the step-scheme heterojunction promotes the separation of photoexcited
electron-hole pairs [57, 58, 64]. In an S-scheme heterojunction, the powerful photogenerated
electrons and holes are reserved in the CB of RP and VB of OP, respectively, while the pointless
photogenerated charge carriers are recombined, introducing a strong redox potential. Also, in these
catalysts, three factors: the internal electric field, band bending, and Coulombic attraction, act as
the driving forces for the recombination of electrons in the CB of oxidation photocatalyst and holes
in the VB of reduction photocatalysts [59-61].
The present work deals with the preparation of PW4Mo8/g-C3N4 as a stable and efficient step-
scheme photocatalyst for the oxidation of sulfides and alcohols to sulfoxides and carbonyl
compounds under visible light. We found that the stability and photocatalytic activity were
significantly improved by PW4Mo8/g-C3N4 compared with PW12/g-C3N4, PW4Mo8, and PW12 in
the oxidation of sulfides and alcohols. This s-scheme photocatalyst has many advantages such as
high activity, high specific surface area, strong oxidizing ability, non-toxicity, and high
recyclability.
2. Experimental
2.1. Materials and Physical Techniques
Chemicals used in this work were purchased from Fluka and Merk chemical companies and used
without purification. FT-IR spectra were obtained over the region 400-4000 cm-1 with NICOLET
IR100 FT-IR with spectroscopic grade KBr. The phase purity and crystalline structure of samples
were analyzed by using Philips X-pert X-ray diffractometer using Cu Kα radiation (α = 0.154056
Å). For specific surface areas, BET (Micromeritics Instrument Corporation TriStar II) was used.
The field emission scanning electron microscopy (FESEM) analysis was carried out using a Philips

XL-300. The UV/Vis diffusive reflectance (UV/Vis DRS) was obtained using Thermo Scientific
Evolution 300/600 UV-Visible spectrophotometer (USA) spectrophotometer. The visible
illumination was provided by a 400 W lamp (high-pressure mercury-vapor lamp and λ=546.8 nm.
2.2. Preparation and characterization of the photocatalyst
The bulk graphitic carbon nitride (g-C3N4) was synthesized by thermal condensation of melamine
following a previously published method [62]. HPAs nanoparticles were prepared according to
reported reference [50]. For the synthesis of PW4Mo8/g-C3N4, the g-C3N4 (0.5 g) was taken in
ethanol (30 ml) and sonicated for 2 h to make the thick slurry. H3PMo8W4O40 (0.8 g) was added to
the slurry and then sealed and stirred for 20 hours. Afterward, the cap was removed and the solid
phase was filtered. Subsequently, it was dried at 75
illustrated in Scheme 1.
̊C. The steps of photocatalyst preparation are
Scheme 1. Schematic representation of the synthesis of magnetic PW4Mo8/g-C3N4.

2.3. General procedure for the oxidation reaction of sulfides and alcohols in the
presence of PW4Mo8/g-C3N4 as photocatalyst
A mixture of sulfide or alcohol (1 mmol), 0.5 mL of H2O2 33%, 10 mL of ethanol as solvent, and
0.005 g of PW4Mo8/g-C3N4 as photocatalyst was added. The reaction mixture was then stirred
under visible light irradiation for an appropriate time (Table 2, 3) until the completion of the
reaction was achieved as monitored by TLC. After the photocatalytic reaction, the suspension was
centrifuged at 5000 rpm for 10 min and the supernatant was analyzed by gas chromatography
(GCYonglin 6100; BP-5; 30m×0.25×mm×0.25μm).
3. Results and discussion
3.1 PW4Mo8/g-C3N4 as photocatalyst for oxidation of sulfides to the sulfoxides:
Preliminary, the catalyst effect on the oxidation of thioanisole (1a) as the model substrate was
studied. Various conditions on the yield were investigated using visible light irradiation, reaction
temperature, catalyst loading, various catalysts, oxidants, and solvents. (Table 1)
Table 1. Optimization for the oxidative reaction 1a with oxidanta
O
S
,
Catalyst visible light, oxidant
S
Solvent, T °C,
1a
1b
Entry
Catalyst
Catalyst
amount (g)
-
Solvent
oxidant
Time
(min)
110
T ◦C
Yieldb
(%)
-
1
2
3
4
None
g-C3N4
EtOH
EtOH
EtOH
EtOH
H2O2
H2O2
H2O2
H2O2
45-55
45-55
25-35
45-55
0.002
0.005
0.005
110
110
110
-
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
(Without light)
PW12
45
Trace
5
6
0.003
0.003
EtOH
EtOH
H2O2
H2O2
110
110
45-55
45-55
75
78
PW4Mo8

7
PW12@g-C3N4
PW8Mo4/g-C3N4
PW6Mo6/g-C3N4
PW4Mo8/g-C3N4
PW2Mo10/g-C3N4
PMo12/g-C3N4
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.003
0.007
0.005
0.005
0.005
0.005
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
DMSO
CH3CN
DMF
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
O2
110
110
110
110
110
110
110
110
110
110
110
110
110
110
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
45-55
83
80
88
91
82
74
58
27
85
90
25
27
55
58
8
9
10
11
12
13
14
15
16
17
18
19
20
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
PW4Mo8/g-C3N4
air
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O
aReaction conditions: 1 mmol of 1a, 3 mmol of H2O2, catalyst.
bIsolated yield.
It was found that the reaction did not proceed without a heteropolyacid as a catalyst and no activity
was observed in the presence of bare g-C3N4 (entries 1 and 2). Then, the effect of light irradiation
on the reaction was investigated and it was found that the reaction worked out best under visible
light irradiation. Also, in the absence of light, only trace amounts of the product were formed and
the starting materials remained almost intact (entry 4). Generally, the activity of heteropolyacid/g-
C3N4 in catalytic conditions versus the oxidation was higher than that of the pristine heteropolyacid
(entry 4 and 5) and the catalytic activity of PW4Mo8/g-C3N4 was higher than PW12@g-C3N4,
PW8Mo4/g-C3N4, PW6Mo6/g-C3N4, PW2Mo10/g-C3N4, and PMo12/g-C3N4 (entries 6-11). Also, the
use of H2O2 as an oxidant gave higher yields than O2 and air (entry 12, 13). Reducing the amount
of catalyst leads to a decrease in yield (entry 14). The reaction produces the best yield under

visible-light irradiation, using 0.005 g of catalyst and H2O2 as the oxidant in EtOH. To explore the
scope, the optimized conditions are extended to a variety of sulfides and alcohols. (Table 2, 3).
Table 2. Oxidation of sulfides to the sulfoxides catalyzed by PW4Mo8/g-C3N4
O
PW4Mo8/gC3N4, hv
S
1b-11b
Time (min) Yieldb(%)
S
1a-11a
EtOH, 25-35 0C
H2O2(33%)
R1
R2
R1
R2
Entry
Substrate
1a-11a
Product
1b-11b
O
S
1
110
75
91
88
87
S
O
S
S
2
3
Br
Cl
Br
Cl
O
S
115
S
S
O
S
4
5
105
80
NO2
NO2
O
S
80
93
88
S
O
S
S
6
140
O
S
S
7
8
150
140
68
73
Br
Br
O
S
S
S
S
9
60
85
85
91
O
O
10
S
S
11
S
110
90
S
O

aAll reactions were carried out using 1-11 (1 mmol) and 0.005 gr of catalyst in 10 mL
of ethanol under visible light irradiation.
bIsolated yields.
a
Table 3. Oxidation of alcohols with hydrogen peroxide catalyzed by PW4Mo8/g-C3N4
O
PW4Mo8/gC3N4, hv
OH
CH
C
R1
R2
EtOH, 45-55 0C
H2O2(33%)
R1
R2
R2: H, CH3,Ph, C6H13
R1: CH3, Ph
Entry
1
Substrate
1c-8c
Product
Time (min) Yieldb(%)
1d-8d
H
75
88
OH
O
H
O
2
100
90
OH
Cl
Cl
H
O
120
140
160
80
78
83
OH
OH
Me
3
4
Me
H
O
MeO
MeO
OH
O
5
6
OH
O
115
85
OH
O
7
8
150
60
62
87
O
OH
NO2
NO2
aAll reactions were carried out using 1-8 (1 mmol) and 0.005 gr of catalyst in 10 mL of ethanol under visible light
irradiation.
bIsolated yields.
3.2 Possible mechanism for the photocatalytic oxidations

The accepted mechanism for the oxidation of alcohols and sulfides in the presence of PW4Mo8/g-
C3N4 and H2O2 under visible light is described in Scheme 2.
O
OH
R2
PW4Mo8/gC3N4, hv
R1
R2
R1
EtOH, 45-55 0
H2O2(33%)
C
hv
eV/NHE
e- h+
PW4Mo8/gC3N4 (
+
)
H2O2
e-
e-
e-
e-
e- - e-
e
CB
OH
R2
.
-
( OH + OH)
-
R1
+
+
-
-
+
h+
h+
VB
h+
-
e-
O
.
h+
h+
OH
O
h+
VB
R2
R1
H O
R
R2
+
2
1
.
O
R2
R1
Scheme 2. The photocatalytic mechanism diagram of PW4Mo8/g-C3N4 under visible light irradiation.
3.2.1 Scavengers for determination of active species
To understand the key reactive species in the sunlight driven sulfides and alcohols oxidation
process by PW4Mo8/g-C3N4, a series of control reactions were performed by adding different
radical scavengers into the system. In this study, 1 mmol of KI, AgNO3, and t-BuOH was added
into the reaction mixture for h+, e− and .OH trapping, respectively. As illustrated in Figure 1. The
addition of KI significantly suppressed the efficiency of the oxidation reaction and a relatively
smaller effect was observed when AgNO3, t-BuOH were added to the reaction system. These
observations confirmed that photogenerated holes, e-, and .OH were the main oxidative species in
the oxidation of alcohols and sulfides in the presence of PW4Mo8/g-C3N4 as a photocatalyst.

Figure 1. Effects of radical scavengers on the oxidation yields of Thioanisole and 1-phenylethanol in the
presence of PW4Mo8/g-C3N4.
3.2.2 Possible oxidation mechanism
Combining our experiment results with related studies [63-67], a postulated mechanism for the
oxidation of alcohols and sulfides in the presence of PW4Mo8/g-C3N4 and H2O2 under visible light
is described in Scheme 3. At first, under the irradiation, the electrons (e-) are excited from the VB
to the CB of the catalyst leaving behind (h+). The electrons are very active, so, can be easily trapped
and transferred to the H2O2 promoting the (–OH) and (.OH) formation. Then alcohols undergo a
deprotonation reaction with -OH to produce alkoxide anions. In the oxidative reaction, the alkoxide
anions react with the positive holes (h+) and produce alkoxide radicals. It is observed that the
dehydrogenation reaction with (.OH) produced the carbonyl compounds. Also, the oxidation
mechanism of sulfides is proposed in Scheme 3.

hv
PW4Mo8/gC3N4
PW4Mo8/gC3N4 (e-+ h+)
OH
OH
+
H2O2
+
eCB
OH
CH
O
OH
+
R2
h+
S
CH
+
S
VB
R1
R1
H
R2
H2O
R1
R1
R2
R1
R2
+
O
O
O
CH
OH
+
hVB
S
S
CH
R2
R1
R2
R1
R2
R1
R1
R2
H
O
C
O
O
O
C
+
H2O
H2O
+
R2
S
+
OH
S
OH
+
R2
R1
R2
R1
R2
R1
H
Scheme 3. Possible passway for oxidation of alcohols and sulfides with hydrogen peroxide catalyzed by
PW4Mo8/g-C3N
3.3. Characterization of the catalyst
The Fourier transform infrared (FT-IR) spectroscopy of (a) the PW4Mo8 and (b) PW4Mo8 /g-
C3N4 were also investigated in the range of 500–4000 cm-1. The chief peaks of PW4Mo8/g-C3N4
located at 1048 and 1020 cm−1 (ν P-O), 930–945 cm−1 (ν metal=O), 850–890 cm−1 (ν metal-O-
metal) and 769 cm−1 (ν metal-O-metal) were observed (Figure 2a). For PW4Mo8/g-C3N4, the
peaks between 3100 and 3300 cm-1 are assigned to N-H and OH stretching vibrations. As well
as, the bands at 1150-1750 cm-1 regions are attributed to aromatic C-N heterocycles. The
intensity of the specific bands of H3PW4Mo8O40 is low, due to the presence of a small amount of
HPA on the g-C3N4 (Figure 2b) [68].

Figure 2. The FT-IR spectra of (a) the PW4Mo8 and (b) PW4Mo8 /g-C3N4.
The XRD measurements were implemented to investigate the presence as well as the crystallinity
degree and purity of g-C3N4, PW4Mo8, and PW4Mo8/g-C3N4 catalysts (Figure 3). The XRD pattern
of g-C3N4 showed diffraction peaks at 2θ = 13.1 and 27.5 correspondings to the reflection planes
(100) and (002), respectively (JCPDS No. 87-1526) [69, 70]. The intensity of the (100) plane is
quite good which confirms the presence of a graphite-like structure. The sample of PW4Mo8
exhibits peaks at 7º~10º, 16º~23º, 25º~31º, and 36º~43º corresponding to the peaks of the
Keggin structure, which demonstrated that heteropoly acid with Keggin structure had been
prepared [71]. Whole these diffraction peaks have remained in the XRD patterns of PW4Mo8/g-
C3N4 compound but with reduced intensity, which can result from the decrease crystallite size.
The XRD pattern of both the g-C3N4 and PMo8W4 /g-C3N4 showed a strong diffraction peak at 2θ
=27.5°, which indicated the characteristic interlayer stacking of aromatic systems. Thus the XRD
pattern of the PW4Mo8/g-C3N4 exhibits the typical Keggin-type diffraction peaks and g-C3N4
diffraction peaks which indicated that PW4Mo8 was loaded on g-C3N4 successfully.

Figure 3. XRD of g-C3N4, PW4Mo8, and PW4Mo8/g-C3N4.
The SEM images of g-C3N4 support and PW4Mo8/g-C3N4 catalyst are reported in Figure 4. As
seen in Fig. 4b, the g-C3N4 were covered by some crystals that indicate an acid-base reaction
between PW4Mo8 and the NH/NH2 groups present in the g-C3N4 materials has occurred.
Figure 4. SEM image of (a) g-C3N4 and (b) PW4Mo8/g-C3N4
The DRS spectra were recorded to study the optical properties of the PW4Mo8 and PW4Mo8/g-
C3N4 (Figure 5). The band gap energy of PW4Mo8 and PW4Mo8/g-C3N4 was estimated to be 3.53
and 2.54 eV respectively. The reduced band gap energy of PW4Mo8/g-C3N4 could lead to better

absorption of light in the visible region favoring more e-h+ pair formation, thus probably resulting
in improved photoactivity.
Figure 5. a) Diffuse reflectance spectra and band gaps of (a) PW4Mo8 and (b) PW4Mo8/g-C3N4.
To investigate the band-edge potentials of g-C3N4 and PW4Mo8 photocatalyst, Mott-Schottky
plots were used at frequency of 500 Hz (Fig. 6). In Figure 6, which illustrates the plots, the
positive slope of the curves indicates that both g-C3N4 and PW4Mo8 have typical n-type
semiconductor nature [72]. The flat band potentials (EFB) of the samples are estimated to be − 1.3
and − 1.0 V (vs Ag/AgCl, pH=7), based on the tangent of their Mott-Schottky curves. As is well
known, the conduction band edge (ECB) is about 0.1− 0.2 eV below the EFB for an n-type
semiconductor [73]. Thus, by considering it as 0.2, the CB edges for g-C3N4 and PW4Mo8 are
calculated as − 1.5 eV and − 1.2 eV. The VB positions of g-C3N4 and PW4Mo8 are calculated to
be 1.35 and 2.33 eV, respectively. Based on the results from Mott-Schottky plots, the conduction
band edge of g-C3N4 is clearly more negative than the conduction band of PW4Mo8, whereas the
valance band of g-C3N4 is less positive than the VB of PW4Mo8. A more negative EVB suggests a
higher photoelectrochemical and photocatalytic oxidative activity [74]. The diagrams of the band
energy of the g-C3N4 and PW4Mo8 are presented in Scheme 2.

Figure 5. Mott - Schottky plots of g-C3N4 and PW4Mo8 at 500 Hz.
To describe the textural properties of the catalyst, the nitrogen adsorption-desorption isotherm was
measured and the results are presented in Figure 7. In general, the sample had an IV isotherm with a type
of H3 hysteresis loop. The hysteresis loops at a relative pressure (P/P0) range of 0.4-0.95 indicated the
mesoporous structure of PW4Mo8/g-C3N4. Pristine g-C3N4 had a low BET surface area of 10.1 m2/g,
which was consistent with the reported value. [75, 76] After g-C3N4 was decorated with PW4Mo8,
the specific surface area increased to 25.22 m2/g. Accordingly, the specific surface area was
increased. The improved textural property of g-C3N4 can be ascribed to the hydrothermal treatment
as the specific surface area of POMs is generally as low as g-C3N4.

Figure 7. N2 sorption isotherms of photocatalyst.
Conclusion
In summary, graphitic carbon nitride (g-C3N4) is a promising visible-light photocatalyst due to its
unique electronic structure. The visible-light photocatalytic efficiency of g-C3N4 is relatively low
and far from the requirements of practical applications. Therefore, it has been decorated with
molybdenum-substituted tungstophosphoric acid (PW4Mo8/g-C3N4) to develop a higher
performance photocatalyst, and then it has been employed as an effective photocatalyst in the
presence of visible light and H2O2 to effect the oxidation of alcohols and sulfides. In the present
work, we have examined five different H3PW12-yMoyO40/g-C3N4 photocatalysts in our reactions
among which the PW4Mo8/g-C3N4 is found the best. We have used the Keggin/g-C3N4 (previously
reported by us) in this work for the purpose of comparison with (PW4Mo8/g-C3N4) to verify that
(PW4Mo8/g-C3N4) was superior in terms of yields as well as reaction times. The catalyst is able to
oxidize sulfides and alcohols with excellent yields, and without over-oxidation or the formation of
other by-products.

Acknowledgements
The financial support of this work, by Kosar University of Bojnord is gratefully
acknowledged.
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6
(2014) 16745-

g-C3N4/H3PW4Mo8O40 S-scheme photocatalyst
with enhanced photocatalytic oxidation of alcohols
and sulfides
Razieh Nejata, Zohreh Najminejadb, Farnaz Fazlalic,
Somaye Shahrakid, Zeynab Khazaeec
e- e-
H2O2
e-
graphitic carbon nitride (g-C3N4) decorated with
molybdenum-substituted tungstophosphoric acid
(H3PW4Mo8O40) as a novel photocatalyst (and used to
catalyze the oxidation of alcohols and sulfides. Increasing
of the reaction rate in the photo-assisted catalytic reaction
under visible light illumination can be due to the redox and
the acidity properties of PW4Mo8/g-C3N4.
e- e-
e-
.
-
( OH + OH)
O
R2
R2
R1
R1
OH
R2
O
S
R1
S
h+
h+
h+
R1
R2
h+
h+ h+

Highlights
 Designing a new set of HPAs as photocatalyst under visible-light.

Proving the promising role of Mo cations in selective photocatalytic oxidation
of alcohols and sulfides.
 The g-C3N4 with electronic structural property as visible-light active
photocatalyst