Synthesis and characterization of BiPO4/g-C3N4 nanocomposites with significantly enhanced visible-light photocatalytic activity for benzene degradation

Article abstract of DOI:10.1039/c5ra01607j

In order to enhance the photocatalytic activity of g-C₃N₄ in the visible light region, BiPO₄/g-C₃N₄ nanocomposites photocatalysts with different BiPO₄ contents were prepared through a hydrothermal method including calcination. Through N₂ adsorption-desorption measurements, BiPO₄/g-C₃N₄ showed a large surface area (172.9 m² g^-1) and small pore diameter and the incorporation of BiPO₄ caused a red-shift of g-C₃N₄ in the visible light region by UV-vis diffuse reflection spectroscopy. The photocatalytic degradation of benzene over BiPO₄/g-C₃N₄ was investigated. Degradation of benzene could be achieved up to 73% in 2 wt% BiPO₄/g-C₃N₄ photocatalysts under optimum reaction conditions, which was 6 times more when compared with pure g-C₃N₄ at the same conditions. The improved photoactivity of BiPO₄/g-C₃N₄ could be ascribed to its effective separation of photogenerated hole-electron pairs between BiPO₄ and g-C₃N₄. Furthermore, the BiPO₄/g-C₃N₄ photocatalysts showed excellent stability. By using an in situ FTIR technique, ethyl acetate, carboxylic acid and aldehyde could be regarded as the intermediate products, and CO₂ and H₂O were produced as the final products. Through electron spin resonance (ESR), OH and O₂^- were examined in the photocatalytic degradation of benzene.

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Synthesis and characterization of BiPO /g-C N
4
3
4
nanocomposites with significantly enhanced visible-
light photocatalytic activity for Benzene degradation
Cite this: DOI: 10.1039/x0xx00000x
a
a
a*
c
a
b*
Xuejun Zou , Yuying Dong , Zhaobo Chen , Dapeng Dong , Dongxue Hu , Xinyong Li ,
Yubo Cui
Received 00th January 2012,
Accepted 00th January 2012
a
DOI: 10.1039/x0xx00000x
In order to enhance the photocatalytic activity of gꢀC N under visible light region, the
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BiPO /gꢀC N nanocomposites photocatalysts with different BiPO contents were
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www.rsc.org/
prepared through hydrothermal with calcination method. Throgh N adsorptionꢀdesorption
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−1
measurement, the BiPO /gꢀC N showed large surface area (234.8 m g ) and small pore
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diameter and the incorporation of BiPO caused a redꢀshift of gꢀC N in visible light
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region by UVꢀvis diffuse reflection spectroscopy. The photocatalytic degradation of
benzene over BiPO /gꢀC N was investigated. The degradation of benzene could get 73%
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in 2 wt% BiPO /gꢀC N photocatalysts under optimum reaction conditions, which was 6
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times compared with pure gꢀC N at the same conditions. The improved photoactivity of
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BiPO /gꢀC N could be ascribed to its effective separation of photogenerated holeꢀ
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electron pairs between BiPO and gꢀC N . Furthermore, the BiPO /gꢀC N photocatalysts
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showed excellent stability. By using the in situ FTIR technique, ethyl acetate, carboxylic
acid and aldehyde could be regarded as the intermediate products, and CO and H O were
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produced as the final products. Through Electron spin resonance (ESR), OH· and O2·
were examined in the photocatalytic degradation of benzene.
1
Introduction
21 since Wang et al. reported that gꢀC N showed a good
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photocatalytic performance for hydrogen or oxygen
product by water splitting under visible light irradiation .
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The effective applications on solar energy conversion
and environmental pollutions removal by semiconductor
photocatalysts have attracted considerable attention in
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For gꢀC N , the catalysts possess high stability respect to
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thermal and chemical attacks due to its triꢀstriazine ring
structure and high condensation. Meanwhile, it features a
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ꢀ4
modern society
.
In the past decade, traditional
photocatalyst TiO has still been extensively investigated
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27 semiconductor band gap of 2.7 eV corresponding to an
owing to its merits, such as the nontoxicity, low cost and
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optical wavelength of 460 nm, which belongs to visible
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excellent stability against photocorrosion . However, it
can only be acivated by the ultraviolet light ( < 400 nm),
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light region . With an attractive electronic structure, gꢀ
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C N is an ideal semiconductor and is valuable for
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which only constitutes about 4% of the solar spectrum, due
to its wide bandgap (anatase 3.4 eV) and have low
seperation efficiency of electronꢀhole pairs formed in
photocatalysis driven applications. According to the
14ꢀ17
literatures
, the conduction band (CB) of gꢀC N is
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located at about ꢀ1.3 V vs. NHE (pH = 7). Whereas its
valence band (VB) top locates at about 1.4 V, resulting in
a small thermodynamic driving force for organic pollutants
oxidation. Furthermore, the photocatalytic efficiency of
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photocatalytic processes . Therefore, it is necessory to
fabricate efficient new types of photocatalysts responed to
visible light in order to improve the utilization of solar
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energy
.
bulk gꢀC N4 is limited due to fast recombination of
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Recently, graphitic carbon nitride (gꢀC N ), which is as
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38 electronꢀhole pairs formed in photocatalytic process. In
organic semiconductor materials, are increasing interest
due to the constructed plastic optoelectronic systems and
the chemical structure of organic semiconductor materials
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order to resolve this problem, several routes have been
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used including nonꢀmetal doping (boron , fluorine and
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sulfur ), optimizing porous structure , and coupling gꢀ
This journal is © The Royal Society of Chemistry 2013
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C N with semiconductor
. In these methods, there is a
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BiPO /gꢀC N with different amount of BiPO4 was
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great interest in heterostructure of semiconductor catalytic
performance. Through the coupling, synergistic effect may
be achieved. High utilization efficiency of solar light can
96 synthesized by calcination method. In a typical procedure,
97 BiPO (0.016, 0.036, 0.048 and 0.065 for sample 1 wt%
4
98 BiꢀCN, 2 wt% BiꢀCN, 3 wt% BiꢀCN and 4 wt% BiꢀCN,
99 respectively) was dissolved in 2 mL of anhydrous ethanol,
100 and then 15.8 mmol melamine was added and dispersed by
101 ultrasonic for 5 min. The mixtures were dried at 85 °C
102 overnight to remove ethanol. Subsequently, the as
103 prepared mixtures were put into a crucible with cover and
104 heated to 500 °C for 2 h with a heating rate of 20 °C min
105 and 520 °C for another 2 h in a muffle furnace. The pure
106 gꢀC N was also prepared for comparison purpose.
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be achieved by the narrow band gap semiconductor
.
Simultaneously, high seperation rate of photoinduced
electronsꢀhole pairs can be realized due to the interaction
of the two semiconductors. Bismuth salt photocatalysts
(such as Bi WO ), which reported by other groups,
exhibited superior photocatalytic activity for the pollutions
24
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1
degradation. BiPO , as one of them, finds applications in
catalysis and can be used for separating radioactive
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3ꢀ
elements
. PO4 , which possesses a large negative
107
charge, is postulated to help the electronꢀhole pairs
separation, which plays an important role in its excellent
photocatalytic activity.
Benzene is regarded as the priority hazardous substance
due to its high toxicity, confirmed carcinogenicity, and
environmental persistence because it is widely used as a
solvent in industrial processes
effectively remove benzene from the ambient environment
is necessary by mild technology.
Herein, we synthesized
BiPO /gꢀC N nanocomposites
hydrothermal with simple calcination method. It was
found the photodegradation activity of BiPO /gꢀC N for
benzene was greatly enhanced under visible light
irradiation comparing with the pure gꢀC N . And the
108 Characterization
109
110
111 Xꢀray diffraction (XRD) using
112 diffractometer (LabXꢀ6000, Shimadzu, Japan, λ = 1.5406
113 Å) with a scan rate of 0.02° s over a 2θ range from 20 to
114 70°. The morphology of the samples was detected by using
115 transmission electron microscopy (TEM; JEOL JEMꢀ2100;
116 accelerating voltage, 200 kV). UV–vis diffuse reflection
The crystal structure of the samples was investigated by
a
powder Xꢀray
–
1
2
7ꢀ30
. Therefore, how to
a
new inorganicꢀorganic
photocatalysts by
117 spectra were recorded on
118 spectrophotometer, using BaSO as reference. The pore
a
Shimadzu UVꢀ500
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119 structure of the obtained sample was characterized by N2
120 adsorption using an adsorption apparatus (Quantachrome
121 NOVA Instruments V 2.2 gas sorption analyzer). Specific
122 surface area of the samples was determined from the
123 BrunauerꢀEmmettꢀTeller (BET) equation, and pore volume
124 was determined from the total amount adsorbed at relative
125 pressures near unity. The photoluminescence (PL) spectra
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BiPO /gꢀC N
4
nanocomposites photocatalyst show
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excellent stability during the photochemical reactions. The
mechanism for this enhanced photocatalytic benzene
degradation can be ascribed to the large surface area,
strong absorption in visible light and excellent charge
transfer between BiPO4 and gꢀC N4 based on the
photoluminescence results.
126 were
surveyed
by
an
Edinburgh
FL/FS900
127 spectrophotometer. The electron spin resonance (ESR)
128 signals of the radicals trapped by 5, 5ꢀdimethylꢀ1ꢀpyrroline
129 Nꢀoxide (DMPO) were detected at ambient temperature
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30 with a Bruker (E500) spectrometer. The irradiation source
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Experimental section
131 was a QuantaꢀRay Nd: YAG pulsed laser system (λ = 532
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32 nm, 10 Hz). The settings for the ESR spectrometer were as
33 follows: center field = 3510 G; sweep width = 200 G;
34 microwave frequency = 9.85 GHz; modulation frequency
35 = 100 kHz and power = 20 mW. To minimize
36 measurement errors, the same quartz capillary tube was
37 used throughout the ESR measurements.
38
39 Photocatalytic activity test
40
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All chemicals were used as received without any further
modification. Bi(NO ) ·5H O, NaH PO ·2H O, Melamine
and anhydrous ethanol were purchased from Tianjin
Kermel Chemical Reagents Development Centre. The
distilled water was used in experimental process.
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Photocatalysts preparation
BiPO4 was synthesized by hydrothermal process.
Typically, 8 mmol of Bi(NO ) ·5H O was soluted into
41
The photocatalytic degradation of gaseous benzene was
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42 carried out under visible light, using a 500W Xe lamp
43 (Shanghai Seagull Colored Optical Glass Co., Ltd.) with a
44 UVꢀcutoff filter (λ > 400 nm). Photocatalytic degradation
45 of benzene was conducted in a Pyrex glass cylindrical
46 reactor with the volume of 120 mL. 0.1 g of the catalysts
47 was put at the bottom of the reactor. Then, benzene vapor
48 was mixed with the air (78% nitrogen, 21% oxygen as
49 reaction gas) and introduced into the reactor at room
50 temperature. Once the concentration of the reactants had
160 mL distilled water under magnetic stirring. Then 28.8
mmol NaH PO ·2H O was added into the mixture and
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stirred for 1 h. The resulting suspension was transferred
into a Teflonꢀlined stainless steel autoclave and maintained
at 160 °C for 24 h. The products were washed three times
with distilled water and anhydrous ethanol respectively
before it dried at 120 °C for 8 h.
2
| J. Name., 2012, 00, 1-3
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51 been stabilized, the inlet and outlet ports were shut off.
52 After adsorption equilibration in the dark for 1 h, the lamp
53 was turned on to allow the photoreaction to proceed. The
54 concentration of benzene was analyzed by gas
55 chromatogram (Agilent7890A) with HPꢀ5 capillary
56 column (30 m×320 ꢁm×0.25 µm).
205 032 cm and 596 cm could be attributed to δ(PO ) and
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206 ν(PO ), respectively . For the gꢀC N , the broad band at 3
4
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ꢀ
1
207 155 cm is attributed to stretching modes of NH and
ꢀ
1
208 NH .The band at 1 325 cm corresponds to C(sp2)–N
209 stretching, and the band at 1 641 cm assigns to C(sp2)=N
210 stretching modes. The 807 cm band is attributed to sꢀ
211 triazine ring vibration modes. The C–NH–C unit is found
212 in melem (1 252 and 1 325 cm ) . It can be clearly seen
213 that the main characteristic peaks of gꢀC N and BiPO all
2
ꢀ
1
ꢀ
1
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The in situ FTIR measurement was carried out in a
ꢀ
1 33
58 homeꢀbuilt IR cell (about 120 mL), equipped with two
59 NaCl windows and a sample holder for the catalyst wafer
60 to analyze the degradation mechanism of benzene.
61 Benzene vapor mixture with the dry air, which pretreated
62 through a drying column packed with desiccant and
63 molecular sieves, was introduced to the IR cell at room
64 temperature. When the sample was saturated with reaction
65 gas, the inlet and outlet ports were shut off. After
66 adsorption equilibration in the dark for 1 h, the 500 W Xe
67 lamp (Shanghai Seagull Colored Optical Glass Co.) with a
68 UVꢀcutoff filter (λ > 400 nm) were used as visible light. A
69 Bruker VERTEX 70 FTꢀIR equipped with a DTGS
70 detector was employed for recording of the FTIR spectra.
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214 appeared in the BiꢀCN photocatalysts.
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71 Results and discussion
226
Fig 2. FTIR spectra of the BiPO , pure gꢀC N and Biꢀ
4 3 4
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27 CN.
28 The existence of BiPO in the gꢀC N was visualized by
29 the TEM observations, as shown in Fig. 3. The gꢀC N
30 shows layer structure (Fig. 3a and b), which is consistent
31 with results reported previously. BiPO nanoparticles with
72 Characterization of the BiPO /g-C N nanocomposites
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XRD pattern is used to investigate the phase structures
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74 of the samples, and the typical diffraction patterns are
75 shown in Fig. 1. The peak at 27.4 in the XRD patterns of
76 the samples is due to the stacking of the conjugated
77 aromatic system, which is indexed for graphitic materials
78 as the (002) peak of the gꢀC N . For BiPO , Evidently,
o
4
32 average size of about 20 nm were well dispersed in the gꢀ
33 C N phase (Fig. 3c). The HRTEM reveals that the fringe
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234 spacing of 0.326 nm can be indexed to the (002) crystal
235 planes of gꢀC N (Fig. 3d), while the lattice spacing of
79 the same diffraction peaks of BiPO (JCPDS 15ꢀ0766)
4
3
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80 have been detected, in which the peaks at 25.5°, 29.5°,
81 31.3°, 41.9° and 48.7° are corresponding to the diffraction
82 peaks of (110), (200), (102), (211) and (212) crystal planes
2
36 0.210 nm can be assigned to the (200) facets of BiPO4.
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83 of BiPO4 . For BiPO /gꢀC N samples, these peaks are
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84 intensified with the increasing amount of BiPO , while the
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85 ones belonging to C N gradually decreased. The intensity
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86 of the peak is decreased which indicated that BiPO4
87 nanoparticles may be wrapped in the interlayer of gꢀC N4
88 and weaken the force of interlayer stacking, accordingly.
89 In addition, no impurity peaks were observed.
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38 Fig 3. TEM images of pure gꢀC N (a and b) and 2 wt%
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39 BiꢀCN (c) and HRTEM image (d) of 2 wt% BiꢀCN.
Fig. 4 shows N adsorptionꢀdesorption isotherms of the
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41 2 wt% BiꢀCN and pure gꢀC N . The 2 wt% BiꢀCN and
42 pure gꢀC N4 were found to be of IVꢀtype isotherms
43 according to the BDDT classification. The hysteresis loops
44 for the 2 wt% BiꢀCN and gꢀC N were similar, which
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01
Fig 1. XRD patterns of the BiPO , pure gꢀC N and Biꢀ
4 3 4
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02 CN.
03
Fig. 2 shows a comparison of the FTIR spectra of BiPO4,
3
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04 pure gꢀC N and BiꢀCN samples. In the case of BiPO , 1
3
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45 shown the incorporation of BiPO didn’t affect the specific
4
46 surface area of gꢀC N . The BET surface areas of the 2 wt%
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47 BiꢀCN and gꢀC N4 were 234.8 and 232.6 m g ,
3
48 respectively (see Table 1). The large surface area can
49 provide more photocatalytic active sites and will be
50 beneficial for the photocatalytic application. Meanwhile,
51 the pore size of 2 wt% BiꢀCN was calculated as 2.432 nm
52 based on the N2 adsorptionꢀdesorption isotherms,
53 exhibiting a character of mesoporous materials. It has been
54 reported that large pore volume might be beneficial for the
55 catalytic activity, while a small average pore diameter
56 might also be one of the reasons for the increasing
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57 catalytic activity
.
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288 Fig 5. XPS survey spectrum of 2 wt% BiꢀCN (a) and its highꢀ
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89 resolution XPS spectra: (b) Bi 4f, (c) P 2p, (d) O 1s, (e) C 1s
90 and (f) N 1s.
67 Fig 4. N adsorptionꢀdesorption isotherms of 2 wt% BiꢀCN
68 and pure gꢀC N .
69 Table 1 Physical properties of 2 wt% BiꢀCN and gꢀC N .
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291
The absorption range of light plays an important role in
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Average
Pore
Diameter
292 the photocatalysis, especially for the visible light
293 photodegradation of contaminants. Fig 6a shows the UVꢀ
294 vis DRS of the asꢀsynthesized samples. As it can be
Surface
Pore
Catalyst
Area
Volume
2
3
(
m /g)
(m /g)
(nm)
295 observed, BiPO
96 absorbance region is from 257 to 368 nm. However, for
297 pure gꢀC N and BiꢀCN samples, strong absorption in the
4
only can absorb UV light, which
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2
wt% Biꢀ
CN
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0.301
0.286
2.432
2.441
298 visible region can be appeared, which absorbance region is
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99 from 371 to 465 nm and BiꢀCN samples exhibit absorption
00 edge of 571 nm together with an increased light absorption,
01 which has a significant redshift (ca. 106 nm) compared
02 with gꢀC N . The results indicated that loading of BiPO
gꢀC N
232.6
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Fig. 5aꢀ5f shows the XPS spectra of 2 wt% BiꢀCN. Fig.
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71 5a is the XPS survey spectrum of the sample which
72 contains the peaks of Bi 4p, Bi 4d, Bi 4f, Bi 5d, O KLL, O
73 1s, P 2s, P 2p, N 1s, and C 1s. The peaks at 164.9 eV and
74 159.6 eV can be assigned to the binding energies of Bi 4f
75 5/2 and Bi 4f 7/2 (Fig. 5b), which indicates the existence
03 improved the light absorption ability. There are two major
04 reasons to explain the resultd. Firstly, the interaction of
05 heterojunction between BiPO4 and gꢀC N effectively
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06 enhances the separation of electronꢀhole pairs account for
07 the band gap transition of photoꢀgenerated electrons and
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76 of a trivalent oxidation state for Bi . A broad signal peak
77 at about 132.7 eV suggests that the P in the sample exist in
31
08 then enhanced the absorption in the visible light region .
09 Secondly, as a colour change of the composites samples,
10 which become darker, that is, from pale yellow to grey,
5+
33
78 the oxidation state of P (Fig. 5c) . For the O 1s, the peak
79 at 530.9 eV is attributed to the crystal lattice oxygen, while
80 the peak at 532.6 eV is related to adsorbed oxygen (Fig.
81 5d). The binding energy of 288.2 eV can be corresponded
82 to the CꢀNꢀC coordination in the C 1s (Fig. 5e). In the N 1s
83 spectrum several binding energies can be separated (Fig.
84 5f). The main signal shows occurrence of C–N–C groups
11 along with a increasing amount of BiPO was introduced
4
12 into the gꢀC N would also cause the absorbance
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38
13 enhanced . The band gap of the pure gꢀC N is estimated
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14 to be about 2.7 eV (Fig 6b). It is noteworthy that the band
15 gap of BiꢀCN samples, which is from 2.3 to 2.5 eV due to
16 incorporation different amount of BiPO , tends to be
4
85 (398.7 eV) and tertiary nitrogen N–(C) groups (400.7
3
17 smaller than that of pure gꢀC N , indicating that the
3
4
3
7
86 eV) .
18 absorption of the BiꢀCN samples is shifted to the lower
19 energy region.
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66 indicating that the photogenerated electronꢀhole pairs
67 recombination was very slow. It is concluded that the
68 heterojunction of BiPO and gꢀC N may act as an active
69 center for decreasing the recombination of photoinduced
70 electronꢀhole pairs. On the other hand, according to the
71 result of the N2 adsorptionꢀdesorption, BiꢀCN showed
72 large specific surface area, which means that its surface
73 can provide more photocatalytic active sites.
74
4
3
4
3
3
3
3
3
3
3
3
3
3
3
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3
3
3
3
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3
3
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3
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3
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3
20
1
/2
21 Fig 6. UVꢀvisible DRS spectra (a) and curves of ( αhν)
22 vs. photon energy (b) of the BiPO , pure gꢀC N and Biꢀ
23 CN with different amount of BiPO4.
4
3
4
24
25 Photocatalytic degradation performance of the
26 BiPO /g-C N photocatalysts
27
28
29 the BiPO /gꢀC N photocatalysts was illustrated in Fig. 7a.
30 As shown in Fig. 7a, the photocatalytic activities of BiPO4
31 and gꢀC N were very low under visible light. The
32 conversion of benzene was only 2% and 11%, respectively.
33 In contrast, BiꢀCN samples presented much higher photo
34 degradation activity for benzene under the same conditions.
35 Especially, the conversion of benzene over 2 wt% BiꢀCN
36 achieved 73% after 4 h under visible light irradiation. The
37 BiꢀCN exhibit a higher photocatalytic activity for the
38 decomposition of gaseous benzene compared to pure gꢀ
39 C N under visible light irradiation, which is due to its
40 strong absorption in visibleꢀlight region (from 571 to 363
41 nm) and excellent charge separation characteristics.
42 However, the removal of benzene decreased with
43 increasing amount of BiPO , which might result from the
44 additional recombination of photo induced electronꢀhole
45 pairs in the excess amount of BiPO4 particles and
46 decreasing the diffraction intensity assigned to gꢀC N4
47 because the crystal had important role in photocatalytic
48 oxidation process
49
4
3
4
The photocatalytic degradation of gaseous benzene over
4
3
4
3
4
375
Fig. 7. (a) Photocatalytic degradation of benzene using
376 the asꢀprepared the BiPO , pure gꢀC and BiꢀCN
377 photocatalysts 1ꢀ5 ([benzene] = 115 ppm, [catalysts]
= 200 mW cm ). (b) The variation of ln (C/C )
0
N
3 4
4
=
0
0
−
2
378 100 mg, I
3
4
0
379 of benzene by different processing routes. (c) Cyclic
380 photodegradation of benzene over 2 wt% BiꢀCN under
381 visible light irradiation. (d) PL spectra of gꢀC
382 CN.
383
384 In situ FTIR study of photodegradation mechanism of
385 benzene
386
387
388 the catalyst during the reaction and the surface adsorbed
389 species, which were detected by in situ FTIR, will give an
390 important insight into the reaction mechanisms. In this
391 work, a set of IR transmittance spectra are obtained during
392 the photocatalytic oxidation of benzene over 2 wt% BiꢀCN
393 (Fig. 8). Prior to light irradiation (t=0), when benzene
394 reached adsorption equilibrium on the surface of the 2 wt%
395 BiꢀCN, strong peaks due to gasꢀphase benzene appeared at
396 3 090, 3 055 and 3 047 cm , which are assigned to the Cꢀ
397 H stretching mode of benzene, respectively (Fig. 8a).
398 The band of 1 483 cm is associated with C=C stretching.
399 The vibrational bands at 1 804, 1 820, 1 951, and 1 966
400 cm are assigned to CꢀH outꢀofꢀplane bending mode (Fig.
N and Biꢀ
3 4
4
3
3
9, 40
.
Realꢀtime monitoring of transient events occurring on
The photocatalytic reaction followed a pseudoꢀfirstꢀ
50 order reaction, and the rate constant of benzene
51 decomposition over 2 wt% BiꢀCN, which was estimated to
52 be about 0.316 h , was faster than the other samples (Fig.
53 7b). Furthermore, the photochemical stability of 2 wt% Biꢀ
54 CN was tested. As shown in Fig. 7c, the benzene
55 degradation efficiency declines only about 8% after four
−
1
56 consecutive runs. Therefore, the asꢀsynthesized BiPO /gꢀ
57 C N photocatalyst exhibits excellent stability in the
4
−
1
3
4
4
3
58 visible light photochemical degradation reactions.
The PL spectroscopy is usually utilized to investigate
60 the seperation of the photogenerated electronꢀhole pairs
ꢀ
1
59
4
1, 42
ꢀ1
44
61 during photocatalytic process
62 spectra of gꢀC N and BiꢀCN. The PL spectrum of gꢀC N
4
63 shows a strong emission, which indicates the electrons and
64 holes recombine rapidly. By contrast, for BiꢀCN
65 photocatalysts, there was weak PL peak observed,
. Fig. 7d shows the PL
ꢀ
1
401 8c). The bands at 1 050, 1 038 and 1 025 cm could be
402 ascribed to CꢀH inꢀplane deformation vibrations (Fig. 8d).
403 After reaction, the intensity of bands at 3 090, 3 055 and 3
3
4
3
4
3
ꢀ
1
404 047 cm decreased significantly with increasing reaction
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4
4
05 time. After 4 h, most of benzene was decomposed.
06 Meanwhile, the bands at 2 360 and 2 342 cm (Fig. 8b)
ꢀ
1
07 corresponding to CO increased as the reaction proceeded,
2
08 and some new surface species, which appeared at 1 109,
ꢀ1
09 949 and 791 cm , were evidenced by the FTIR spectra in
ꢀ
1
10 Fig. 8d. Among them, bands at 1 109 cm is assigned to
4
5
11 the CꢀOꢀC stretching vibration which existed in ester .
ꢀ
1
12 The 949 cm band is assigned to OꢀH outꢀofꢀplane
ꢀ
1
13 deformation vibration of carboxylic acid, and 791 cm is
4
6
446 Fig. 9. ESR spectra of radical adducts trapped by DMPO
14 assigned to CꢀH deformation vibration of aldehyde . On
15 the basis of the previous reports and the results,
16 ethylacetate, carboxylic acid and aldehyde are the
17 intermediate products during the photocatalytic
18 degradation of benzene, CO and H O are produced as the
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
47 in 2 wt% BiꢀCN dispersions after 60 s visibleꢀlight
48 irradiation (λ > 400 nm): (a) DMPOꢀOH· formed in
−
49 irradiated aqueous dispersions; (b) DMPOꢀO · formed in
2
50 irradiated methanol dispersions.
2
2
51
Based on the above results, the photocatalytic
19 final product.
52 mechanism may be proposed in Scheme 1. Under visible
ꢀ
53 light irradiation, electrons (e ) are excited from the VB of
+
54 gꢀC N and created holes (h ) in the VB. Normally, these
3
4
55 charge carriers quickly recombine and only a fraction of
56 electrons could participate in the photocatalytic reaction.
57 However, when gꢀC N is connected with BiPO to form
3
4
4
58 composites, these photoinduced electrons on the CB of gꢀ
59 C N tend to transfer to BiPO4 particles due to their
3
4
60 excellent electronic conductivity, improving to holeꢀ
61 electron separation. The transferred electrons will
62 accumulate on the BiPO nanoparticles and presumably as
4
63 interface bound exciton pairs to capture the adsorbed O
2
−
64 and H O on gꢀC N surface to form OH· and O · , and
2
3
4
2
65 then participate in photocatalytic oxidation reaction.
66 Meanwhile, on the VB of gꢀC N , the high separation
3
4
67 efficiency of photogenerated electron–hole pairs is result
68 in the increase of the number of holes, which could
69 directly enhance the moderate performance of
70 mineralization ability.
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
20
Fig. 8. (aꢀd) Infrared spectra recorded as a function of
21 irradiation time following the photooxidation of toluene
22 over 2 wt% BiꢀCN photocatalyst.
23
In order to detect the reactive species evolved during the
24 photocatalytic reaction process, such as hydroxyl radical
25 and superoxide radical species, the electron spin resonance
4
7
26 (ESR) technique was usually used . As shown in Fig. 9a,
27 four characteristic peaks of DMPOꢀOH· with intensity
28 1:2:2:1 can be observed with visible light irradiated
29 aqueous dispersions of 2 wt% BiꢀCN. Similarly, the
−
30 stronger six characteristic peaks of the DMPOꢀO2·
31 adducts are also observed with visible light irradiated
32 methanol dispersions of 2 wt% BiꢀCN in Fig 9b. ESR
−
33 results indicate that the generation of OH· radical and O2·
34 radical species is crucial during the reaction and it is
471
−
35 confirmed that both OH· and O · radicals are produced on
472 Scheme. 1. Schematic diagram showing the possible
473 mechanism for the photocatalytic degradation of benzene
2
36 the surface of 2 wt% BiꢀCN and OH· radicals with strong
37 oxidation capability act as the predominant species.
474 over the BiPO
/gꢀC N .
4 3 4
38
39
40
41
42
43
44
45
475 Conclusions
4
4
76
In summary, we have successfully synthesized BiPO /gꢀ
4
77 C N by hydrothermal with calcination method for
3 4
478 efficient photocatalytic degradation of gaseous benzene
479 under visible light irradiation. The photocatalytic activities
4
4
80 of BiPO /gꢀC N on benzene degradation under visible
4 3 4
81 light irradiation increase to about 6.0 times as high as
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

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ARTICLE
DOI: 10.1039/C5RA01607J
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82 those of pure gꢀC N . The significant enhancement on
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83 photocatalytic performance was ascribed to strong
84 absorption in visible light and rapid photogenerated
85 electron transfer rate and charge separation efficiency in
86 BiPO /gꢀC N . Through in situ FTIR technique, phenol,
48
50
4
3
4
87 carboxylic acid and aldehyde could be regarded as the
88 intermediate products, and CO and H O are determined as
2
2
552
89 the final product during the reaction process. Through ESR,
−
90 OH· and O2· are examined in the photocatalytic
554
5
5
5
5
5
5
91 degradation
of
benzene.
Such
BiPO /gꢀC N
4 3 4
56
58
60
92 nanocomposites with high photocatalytic performances
93 may provide an alternative of traditional catalysts to
94 address energy conversion, green chemistry, and
95 environmental issues.
96
97
561 17. S. Cao and J. Yu, The Journal of Physical Chemistry Letters, 2014,
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98 Acknowledgements
99
This work was supported financially by the National
65
Chemistry of Materials, 2010, 22, 5119ꢀ5121.
00 Nature Science Foundation of China (No. 21477001, No.
01 21301023, No. 51208131 and No. 51278088), Liaoning
02 province high school program for excellent talents (second
03 levels), Dalian Science and Technology Fund
04 (2013J21DW016), National rural areas supporting scienceꢀ
05 technology project of China (No. 2013BAJ12B02) and
06 special grand national scienceꢀtechnology project (No.
07 2014ZX07204ꢀ005, 2012ZX07201003ꢀ002). The authors
08 are grateful to the Institute of Environmental
09 Biotechnology in Dalian Nationalities University for their
10 technical and logistic assistance.
66 20. G. Liu, P. Niu, C. H. Sun, S. C. Smith, Z. G. Chen, G. Q. (Max) Lu,
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12 Notes and references
a
13
Department of Environmental Science and Technology, Dalian
81
14 Nationalities University, Dalian, 116600, China. Email:
15 zhaobochen@dlnu.edu.cn; Tel: +86-8765-6347; Fax: +86-8765-
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18 Industrial Ecology and Environmental Engineering, School of
19 Environmental Sciences and Technology, Dalian University of
20 Technology, Dalian, 116024, China. E-mail address:
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