Mixed-calcination synthesis of Bi2MoO6/g-C3N4 heterojunction with enhanced visible-light-responsive photoreactivity for RhB degradation and photocurrent generation

Article abstract of DOI:10.1016/j.materresbull.2016.05.016

Organic-inorganic hybrid photocatalyst Bi₂MoO₆/g-C₃N₄ was synthesized via a mixed-calcination route based on intimate interfacial interaction. The successful combination of g-C₃N₄ and Bi₂MoO₆ was verified by X-ray diffraction (XRD), Fourier-Transform infrared spectra (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping. The optical property of the as-prepared photocatalysts was characterized by UV-vis diffuse reflectance spectra (DRS). The photocatalytic activities were investigated by degradation of Rhodamine B (RhB) and photocurrent generation under visible-light (λ > 420 nm). The results demonstrated that the Bi₂MoO₆/g-C₃N₄ composite exhibits highly enhanced photoreactivity compared to the pristine samples. It should be attributed to the fabrication of a Bi₂MoO₆/g-C₃N₄ heterojunction, thus resulting in the high separation and transfer efficiency of photogenerated charge carriers, as confirmed by the photoluminescence (PL) and electrochemical impedance spectra (EIS). The active species trapping experiments indicated that holes (h⁺) and superoxide radicals (O₂^-) are the main active species in the degradation process.

Full text of DOI:10.1016/j.materresbull.2016.05.016

Accepted Manuscript
Title: Mixed-calcination synthesis of Bi2MoO6/g-C3N4
heterojunction with enhanced visible-light-responsive
photoreactivity for RhB degradation and photocurrent
generation
Author: Ke Xiao Hongwei Huang Na Tian Yihe Zhang
PII:
S0025-5408(16)30220-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.materresbull.2016.05.016
MRB 8784
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Received date:
Revised date:
Accepted date:
20-2-2016
2-5-2016
14-5-2016
Please cite this article as: Ke Xiao, Hongwei Huang, Na Tian, Yihe Zhang, Mixed-
calcination synthesis of Bi2MoO6/g-C3N4 heterojunction with enhanced visible-light-
responsive photoreactivity for RhB degradation and photocurrent generation, Materials
Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2016.05.016
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Highlights
◆ Bi2MoO6/g-C3N4 composites were synthesized by a mixed-calcination method.
◆
The Bi2MoO6/g-C3N4 photocatalyst exhibits much better photocatalytic
performance.
◆ The enhanced photocatalytic activity is attributed to the hetrojunction structure.
◆ Holes (h+) and superoxide radicals (•O2−) serve as the two main active species.
1

Graphical abstract
2

Mixed-calcination
synthesis
of
Bi2MoO6/g-C3N4
heterojunction with enhanced visible-light-responsive
photoreactivity for RhB degradation and photocurrent
generation
Ke Xiao, Hongwei Huang*, Na Tian, Yihe Zhang*
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid
Wastes, National Laboratory of Mineral Materials, School of Materials Science and
Technology, China University of Geosciences, Beijing 100083, China
Corresponding author：hhw@cugb.edu.cn (H.W. Huang); zyh@cugb.edu.cn (Y.H.
Zhang). Tel.: +86-10-82332247.
3

ABSTRACT: Organic-inorganic hybrid photocatalyst Bi2MoO6/g-C3N4 was
synthesized via a mixed-calcination route based on intimate interfacial interaction.
The successful combination of g-C3N4 and Bi2MoO6 was verified by X-ray diffraction
(XRD), Fourier-transform infrared spectra (FTIR), scanning electron microscopy
(SEM) and energy dispersive X-ray (EDX) mapping. The optical property of the
as-prepared photocatalysts was characterized by UV−vis diffuse reflectance spectra
(DRS). The photocatalytic activities were investigated by degradation of Rhodamine
B (RhB) and photocurrent generation under visible-light (λ > 420 nm). The results
demonstrated that the Bi2MoO6/g-C3N4 composite exhibits highly enhanced
photoreactivity compared to the pristine samples. It should be attributed to the
fabrication of a Bi2MoO6/g-C3N4 heterojunction, thus resulting in the high separation
and transfer efficiency of photogenerated charge carriers, as confirmed by the
photoluminescence (PL) and electrochemical impedance spectra (EIS). The active
−
species trapping experiments indicated that holes (h+) and superoxide radicals (•O2 )
are the main active species in the degradation process.
Keywords: A. layered compounds; A. semiconductors; B. chemical synthesis; C.
impedance spectroscopy; D. catalytic properties
4

1 Introduction
Nowadays, the problems on environmental deterioration and energy shortage
have been bothering people, and green chemistry has become a necessary
requirement for the sustainable development of human society. Among the various
green techniques, semiconductor photocatalysis has emerged as one of the most
promising technologies because the semiconductor photocatalyst can use the solar
energy for degradation of organic contaminants [1-3]. In order to achieve the above
goals, two problems must be resolved, increasing the separation efficiency of
photoexcited electron-hole pairs and extending the excitation wavelength range of
photocatalysts. To extend the absorption-wavelength range, the semiconductor
materials, such as oxides, sulfides and nitrides etc., which can be excited by visible
light, have been investigated extensively. However, a single-phase photocatalyst
exhibits significant limitations in the process of photocatalytic reactions due to the
quick combination of photogenerated electrons and holes. To enhance the
separation efficiency of photoexcited charge carriers, fabrication of heterojunction
photocatalysts have been extensively investigated [4,5].
Recently, a polymer photocatalyst named graphitic carbon nitride (g-C3N4) has
attracted intensive attention for hydrogen gas evolution via water splitting,
photocatalytic degradation of organic pollutants and photosynthesis under visible
light illumination [6-8]. It is known that the band gap of g-C3N4 is about 2.7 eV,
which can absorb visible light with wavelength up to 459 nm. Furthermore, the
conduction band (CB) minimum (-1.13 eV vs. NHE) of g-C3N4 is extremely
5

negative, so photogenerated electrons should have a strong reduction ability.
However, the photocatalytic efficiency of single g-C3N4 is limited due to the
insufficient visible-light absorption and high recombination probability of
photoexcited electron-hole pairs. In order to improve the photocatalytic activity of
g-C3N4, many strategies such as doping and coupling with other semiconductor
materials have been used to modify g-C3N4 [9,10].
Bismuth molybdate compounds are a kind of important catalyst materials,
which have been widely used in the preparation of selective oxidation of propylene
dehydrogenation propylene aldehydes, propylene ammoxidation preparation nitrile,
etc. In addition, these compounds can also serve as ion conductor, audio and video
materials, optical conductor and gas sensor due to its unique physical properties.
Recent studies have shown that Bi2MoO6 possesses excellent visible light
photocatalytic properties [11,12]. Its crystal structure consists of alternating
[Bi2O2]2+ layers and MoO6 octahedral perovskite layers. It has been reported that in
the crystal structure of a layered compound, the separation and migration of charge
carrier are much easier, thus resulting in high photocatalytic activity [13,14].
Recently, Li etc. reported the synthesis of g-C3N4/Bi2MoO6 composites by a
solvothermal method [15]. However, the above composites may fail to achieve
controllable compositing degree and strong interfacial interaction.
In this work, we successfully prepared the heterostructural photocatalyst of
Bi2MoO6/g-C3N4 by a mixed-calcination method, which may provide a more
reliable interfacial interaction between g-C3N4 and Bi2MoO6. The photocatalytic
6

activity of the Bi2MoO6/g-C3N4 was evaluated by decomposing RhB and
photocurrent generation under visible light irradiation (λ > 420 nm). The
Bi2MoO6/g-C3N4 composite exhibits superior RhB photodegradation rate and
photocurrent response, which should be attributed the efficient separation of
photoinduced charge carriers originated from the Bi2MoO6/g-C3N4 heterojunction
fabrication. The structure, optical property and photocatalytic mechanism of the
as-prepared photocatalysts are investigated in details.
2 Experimental
2.1. Synthesis of heterostructured Bi2MoO6/g-C3N4 photocatalyst
All chemicals were used in analytical grade without further purification. The
g-C3N4 precursor was synthesized through pyrolysis of melamine in a crucible
without a cover under ambient pressure in air [16]. The details are as follows: The
melamine was added in a crucible and heated to 520ꢀ at a heating rate of 3ꢀ min-1
in a tube furnace for 4h. After cooling to room temperature, the yellow product was
collected and milled into powder.
Pure Bi2MoO6 was prepared by hydrothermal method: Firstly, 0.004 mol of
Na2MoO4·2H2O was totally dissolved in 25 mL of distilled water to form solution A.
Secondly, 0.008 mol of Bi(NO3)3·5H2O was dissolved in the A solution. Then, the
resultant mixture was sealed in a 50 mL Teflon-lined stainless steel autoclave, and
heated and maintained at 180 ꢀ for 12 h, then cooling to room temperature. After
funnel separation, the powder was washed with water for several times and then
7

dried at 80 ℃ in a vacuum oven.
The Bi2MoO6/g-C3N4 composites were prepared through a mixed-calcination
method at 400℃. 0.0005 mol g-C3N4 and 0.0015 mol Bi2MoO6 were both dissolved
in 50 ml of ethanol under ultrasonic oscillation for 1 h, and then dried in the oven at
60 ℃. The mixed powder was collected and calcined at 400℃ for 0.5 h to obtain
the 1:3 Bi2MoO6/g-C3N4 photocatalyst. Other Bi2MoO6/g-C3N4 photocatalysts with
the molar ratio of 1:5, 1:1 and 3:1 were prepared by the same method.
2.2. Characterization
The phase structures of photocatalysts were investigated by X-ray powder
diffraction (XRD) analysis at room temperature on a XRD powder diffraction
instrument with monochromatized Cu Kα radiation (λ= 1.5406 nm) at a setting of
40 kV and 40 mA. And the Scanning rate and range were 0.02° (2θ)/s and 10-70°,
respectively. Fourier-transform infrared (FTIR) spectra were obtained using a
Bruker spectrometer in the frequency range of 4000-500 cm−1. The morphologies
and microstructures of the photocatalysts were studied by field emission scanning
electron microscopy (SEM) (Hitachi S-4800). UV-vis diffuse reflectance spectra
(DRS) were recorded on a Cary 5000 (America Varian) spectrophotometer. The
photoluminescence (PL) spectra of the samples were measured using a Hitachi
F-4600 fluorescence spectrophotometer to observe the combination rate of
electron-hole pairs.
2.3. Photocatalytic activity measurements
The photocatalytic activities of the samples were evaluated by the degradation
8

of the RhB under visible light irradiation (300 W xenon lamp, λ > 420 nm). 50 mg
of the as-prepared photocatalyst was dispersed into 50 mL of RhB solution (1×10-5
mol/L). Prior to illumination, the adsorption-desorption equilibrium between
photocatalyst powder and RhB was obtained by vigorously stirred for 1h min. And
then, the light was turned on, and 2 mL of the suspensions were taken into the
centrifuge tubes at selected intervals. The vigorously stirring was maintained
throughout the whole reaction process. After that, the photocatalysts in the mixture
were removed by centrifugation (4500 r/min, 5 min) and the centrifuged solution
was analyzed by recording the maximum absorption band (554 nm for RhB) and
UV-vis spectra were recorded by Shimadzu UV-5500PC spectrophotometer
(Shanghai Wuxiang Company).
2.4. Active species trapping experiments
−
The active species, such as hydroxyl radicals (•OH), superoxide radical (•O2 )
and holes (h+) were detected by adding isopropyl alcohol (IPA), 4-benzoquinone (BQ)
and disodium ethylenediaminetetraacetate (EDTA), respectively [17,18]. The method
was similar to the former photocatalytic activity test with the addition of 1 mmol of
quencher in the presence of RhB.
2.5. Photoelectrochemical Measurements.
Photoelectrochemical measurements are carried out in a three-electrode quartz
cell (CHI-660E electrochemical system). The working electrodes were photocatalyst
films coated on ITO. The saturated calomel electrode (SCE) was the reference
electrode, and platinum wire serves as counter electrode. The electrolyte was 0.1 M
9

Na2SO4 solution All the photoelectrochemical measurements are performed under
visible light irradiation from a 300 W Xe lamp with 420 nm cutoff filters.
3 Results and discussion
3.1. Characterization of Bi2MoO6/g-C3N4 composite photocatalysts
Fig. 1a and 1b depict the crystal structures of g-C3N4 and Bi2MoO6, respectively.
The crystal structure of Bi2MoO6 is composed of alternating (Bi2O2)2+ cationic layers
and interbedded (MoO6)6- tetrahedral layers. Obviously, both g-C3N4 and Bi2MoO6
possess layered crystal configuration. It is believed that the layered crystal structure
can promote the separation of electron-hole pairs and depress the recombination rate
of charge carriers. The X-ray diffraction (XRD) patterns of the as-obtained products
were shown in Fig. 2. For the XRD pattern of pure C3N4, two pronounced diffraction
peaks were observed at 13.2º and 27.5º. The former peak is indexed as the (100) plane
corresponding to the interlayer structural packing motif of tristriazine units, while the
peak at 27.5º can be ascribed to the (002) plane which is the characteristic peak of
inter-planar stacking of conjugated aromatic systems (JCPDS 87-1526) [19]. All the
diffraction peaks of Bi2MoO6 can be indexed into the pure orthorhombic Bi2MoO6
(JCPDS 76-2388) [11]. No impurity peaks were observed, which implies that the final
products of g-C3N4 and Bi2MoO6 were of pure phases. Because of the low intensity of
the g-C3N4, there is no obvious peaks can be detected in Bi2MoO6/g-C3N4 composites.
However, the narrow sharp peaks suggest that the Bi2MoO6/g-C3N4 products are
highly crystalline.
10

Fig. 3 presents FTIR spectra of g-C3N4, Bi2MoO6, and g-C3N4/Bi2MoO6
heterojunctions. In the spectrum of g-C3N4, the band at around 3294 cm−1 can be
assigned as the stretching mode of NH2 or N-H groups. The bands at 1322 cm−1 and
1633 cm−1 correspond to the C–N and C = N stretching mode, respectively [20]. The
peak at 808 cm−1 was assigned to the triazine units, and the bands at 1245 and 1574
cm−1 correspond to the stretching vibration of C–N heterocyclics. For the spectrum of
Bi2MoO6, the peak at 3430 cm−1 was attributed to O–H vibrations [21]. The FTIR
spectrum of the Bi2MoO6 mainly exhibits the absorption peaks around at 400-900
cm−1. Absorption bands at 841 cm−1 and 732 cm−1 are attributed to Mo–O stretching
vibrations, while the Bi–O stretching and deformation vibrations are located at 565
cm−1 and 450 cm−1. All the absorption bands of g-C3N4 and Bi2MoO6 can be observed
in the spectra of g-C3N4/Bi2MoO6 composites with molar ratios of 1:1, 1:3 and 1:5.
This result demonstrated the successful synthesis of g-C3N4/Bi2MoO6 composites.
The morphology of g-C3N4, Bi2MoO6 and 1:3 Bi2MoO6/g-C3N4 were studied
by SEM. From Fig. 4a, the g-C3N4 sample clearly showed a layered structure with
numerous stacking layers, which was in accordance with the literature report. The
Bi2MoO6 sample displayed a plate-like structure with a diameter of 100 ~ 500 nm
(Fig. 4b). Fig. 4c and 4d revealed that the two types of materials were all found in
the sample of 1:3 Bi2MoO6/g-C3N4. In addition, it was observed that a large number
of Bi2MoO6 nanoparticles are assembled on the surface of the g-C3N4 sheets. For
further confirmation, EDX mapping of 1:3 Bi2MoO6/g-C3N4 was performed (Fig. 5).
It is obvious that the C, N, Bi, Mo, and O elements are homogenously distributed in
11

the bulk structure, confirming that the Bi2MoO6 nanosheets are uniformly
assembled on the surface of g-C3N4.
The UV-Vis diffuse reflectance spectra of the as-prepared samples were presented
in Fig. 6, from which the optical absorption edges of the pure g-C3N4 and Bi2MoO6
were roughly estimated from the absorption onset to be 450 and 479 nm, respectively.
After the combination of g-C3N4 and Bi2MoO6, the absorption band edges of the
composites gradually shift to that of pure Bi2MoO6 with the increase of Bi2MoO6
contents, which indicates that Bi2MoO6 was a good visible-light sensitizer to g-C3N4.
The band gap (Eg) can be determined by the formula [22]:
αhv=A(hv–Eg)n/2
(1)
Where α, h, m, Eg and A are absorption coefficient, Planck constant, light frequency,
band gap energy, and a constant, respectively. Among them, n is determined by the
type of optical transition of a semiconductor (n = 1 for direct transition and n = 4
for indirect transition). As previous literature reported, the n value of g-C3N4 was 4,
and the n value of Bi2MoO6 was 1. From the plot of (αhv) 1/2 or (αhv) 2 versus (hv)
in the inset of Fig. 6, the Eg of g-C3N4 and Bi2MoO6 were estimated to be 2.70 eV
and 2.59 eV, respectively.
3.2. Photocatalytic reactivity for RhB degradation and photocurrent generation
The photocatalytic activities of the Bi2MoO6/g-C3N4 composite photocatalysts
were examined by degradation of RhB molecules in aqueous solution and
photocurrent generation under visible light irradiation (λ > 420 nm). Fig. 7a shows
the photocatalytic degradation of RhB with the prepared photocatalysts under
12

visible light irradiation for 6 h. It can be seen that both the pure g-C3N4 and pure
Bi2MoO6 display relatively poor visible-light induced degradation efficiency. The
Bi2MoO6/g-C3N4 photocatalyst with molar ratio of 1:3, displayed the highest
degradation efficiency, and about 72% RhB could be removed within 6 h. Besides,
the 1:5 Bi2MoO6/g-C3N4 photocatalyst also exhibits a higher photocatalytic activity
than those of pure g-C3N4 and pure Bi2MoO6. The time-resolved absorption spectra
were depicted in Fig. 7b. It can be seen that the maximum absorbance of the
solution in the visible region shifted from 554 to 530 nm after 6 h irradiation,
suggesting that N-demethylation and de-ethylation processes occurred during the
photocatalytic reaction.
Photocurrent response can be utilized to monitor the generation and transfer of
the photoexcited charge carriers and elucidate the interfacial charge transfer dynamics
of a photocatalyst [23,24]. Fig. 8 shows the curves of photocurrent density versus
irradiation time over the pristine Bi2MoO6, g-C3N4 and 1:3 Bi2MoO6/g-C3N4
photocatalysts. Under visible light, prompt photocurrent responses are all observed on
the three photocatalyst electrodes. Compared with the two single phases, the
Bi2MoO6/g-C3N4 composite exhibits evidently enhanced photocurrent intensity,
indicating the higher separation efficiency of photoinduced electrons and holes. Thus,
the formation of Bi2MoO6/g-C3N4 composite can effectively facilitate the separation
efficiency of charge carriers in contrast to the pristine photocatalysts.
3.3. Mechanism investigation on the enhanced photocatalytic reactivity
The conduction band (CB) and valence band (VB) positions of g-C3N4 and
13

Bi2MoO6 can be calculated by the following empirical formulas [25,26]:
EVB = X − Ee + 0.5Eg
(2)
(3)
ECB = EVB – Eg
where EVB is the VB edge potential; X is the electronegativity of the semiconductor,
which is the geometric average of the absolute electronegativity of the constituent
atoms (X values of g-C3N4 and Bi2MoO6 are 4.67 eV and 6.31 eV, respectively); Ee
is the energy of free electrons on the hydrogen scale (Ee = 4.5 eV); and Eg is the
band gap energy of the semiconductor. The band gap energies of g-C3N4 and
Bi2MoO6 are adopted as 2.70 eV and 2.59 eV, respectively. Calculated by Eq. (1)
and (2), the positions of the CB and VB of g-C3N4 are -1.13 and 1.57 eV, while
those values for Bi2MoO6 are 0.52 and 3.11 eV, respectively.
The migration and transfer processes of photogenerated charge carriers in a
semiconductor can be investigated via electrochemical impedance spectra (EIS)
[23,24]. The arc in the EIS spectra usually indicates the interface layer resistance
occurred at the surface of electrode. Fig. 9 presents the Nyquist plots of the Bi2MoO6,
g-C3N4 and 1:3 Bi2MoO6/g-C3N4 photocatalysts under visible light. It can be found
that the arc radius of Bi2MoO6/g-C3N4 electrode is obviously smaller than pure
Bi2MoO6 and g-C3N4, which demonstrates a higher charge transfer rate occurred in
Bi2MoO6/g-C3N4 composite electrode.
The separation efficiency of the photogenerated electrons and holes for the
Bi2MoO6/g-C3N4 composite was investigated by photoluminescence (PL) [4,25]. It is
well known that the lower PL emission intensity indicates the lower recombination
14

efficiency of photogenerated charge carriers and thus the higher photocatalytic
activity. Fig. 10 shows the PL spectra of the g-C3N4, Bi2MoO6 and 1:3
Bi2MoO6/g-C3N4 composites. Pure g-C3N4 exhibits the highest emission intensity,
centering at about 459 nm, which is approximately equal to its optical band gap. It is
important to note that the emission intensity of the 1:3 Bi2MoO6/g-C3N4
heterostructure is obviously lower than that of the pure g-C3N4 and Bi2MoO6 samples,
indicating that the recombination rate of photogenerated charge carriers is truly lower
in the Bi2MoO6/g-C3N4 composite. The PL results confirm the importance of the
heterojunctions between Bi2MoO6 and g-C3N4 in hindering the recombination of
electrons and holes.
In order to ascertain the active species in the degradation process and verify
the supposed photocatalytic mechanism, some sacrificial agents, such as isopropyl
alcohol (IPA), disodium ethylenediaminetetraacetate (EDTA) and 4-benzoquinone
(BQ) were used as the hydroxyl radical (•OH) scavenger, hole (h+) scavenger and
−
superoxide radical (•O2 ) scavenger [17,18]. As shown in Fig. 11, the photocatalytic
degradation of RhB was slightly affected by the addition of 1 mM IPA (a quencher
of •OH). However, when 1 mM of BQ is added, obvious decrease of degradation
−
rate is observed, which indicated that the existence of •O2 species. In addition, the
degradation of RhB was also significantly depressed with the addition of 1 mM of
EDTA, suggesting that the holes also play a crucial role in the process of RhB
−
oxidation. The active species trapping experiments demonstrated that the •O2 and
h+ are the two main active species in the degradation process of RhB, which
15

contributed to the enhancement of photocatalytic activity of the Bi2MoO6/g-C3N4
composite.
According to the above results, the schematic band energy levels and charge
transfer processes of the Bi2MoO6/g-C3N4 composites can be illustrated as Fig. 12.
Coupling two or several semiconductors with matchable band structures has been
widely considered as one of the most promising methods to construct a
high-performance photocatalyst system. Many researchers attributed the synergetic
effect to the efficient charge transfer at the interface of two semiconductors or
multiple semiconductors, which would lead to an effective photoexcited electron-hole
separation and promote the photocatalytic activity [27-29]. As revealed in Fig. 11, as
the CB potential of g-C3N4 is more negative than that of Bi2MoO6, the photogenerated
electrons (e-) in the CB of g-C3N4 are easier to move to the CB of Bi2MoO6 owing to
the interfacial interactions between the two components. Then, the e- further reacted
with oxygen molecules absorbed in the surface of photocatalyst to generate
−
superoxide radical (•O2 ). Meanwhile, the photoinduced holes (h+) in the VB of
Bi2MoO6 will transfer to the VB of g-C3N4. Thus, the photogenerated electrons and
holes were effectively separated in the Bi2MoO6/g-C3N4 heterojunction, which
−
allowed the •O2 and h+ to play photooxidated roles in photocatalytic reactions.
4. Conclusions
Visible-light-driven heterostructured photocatalysts Bi2MoO6/g-C3N4 were
successfully synthesized by a mixed-calcination method. The homogenous
compositing of Bi2MoO6 nanosheets on g-C3N4 was confirmed by XRD, FTIR, SEM
16

and EDX mapping. The photodegradation and photoelectrochemical experiments
revealed that the Bi2MoO6/g-C3N4 composite exhibits enhanced photocatalytic
reactivity for RhB degradation and photocurrent response than the two individual
components under visible light irradiation. EIS and PL results demonstrated that the
high separation and fast transfer of photogenerated charge carriers resulted from the
Bi2MoO6/g-C3N4 heterojunction fabrication are responsible for the high photocatalytic
performance of Bi2MoO6/g-C3N4. The detailed radicals trapping experiments revealed
−
that superoxide radicals (•O2 ) and holes (h+) play dominated roles in the
photooxidation process.
Acknowledgements
This work was supported by the National Natural Science Foundations of
China (Grant No. 51302251), the Fundamental Research Funds for the Central
Universities (2652013052 and 2652015296)
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Figures caption
Fig. 1 Crystal structures of g-C3N4 and Bi2MoO6.
Fig. 2 XRD pattern of g-C3N4, Bi2MoO6 and Bi2MoO6/g-C3N4 photocatalysts with
molar ratios of 1:5, 1:3, 1:1 and 3:1.
Fig. 3 FTIR spectra of g-C3N4, Bi2MoO6 and Bi2MoO6/g-C3N4 with molar ratios of
1:5, 1:3, 1:1 and 3:1.
Fig. 4 SEM images of the as-obtained samples: (a) g-C3N4, (b) Bi2MoO6, (c,d) 1:3
Bi2MoO6/g-C3N4.
Fig. 5 (a) SEM image and (b-f) SEM-EDX mapping images.
Fig. 6 UV-vis diffuse reflectance spectra of g-C3N4, Bi2MoO6, Bi2MoO6/g-C3N4
photocatalysts with malar ratios of 1:5, 1:3, 1:1 and 3:1.
Fig. 7 (a) Photocatalytic degradation curves of RhB over the as-prepared g-C3N4,
Bi2MoO6 and Bi2MoO6/g-C3N4 samples under the irradiation of
visible-light (λ > 420 nm). (b) UV-visible spectra of RhB at different
visible irradiation time in the presence of 1:3 Bi2MoO6/g-C3N4.
Fig. 8 Comparison of transient photocurrent responses of g-C3N4, Bi2MoO6 and1:3
Bi2MoO6/g-C3N4 photocatalysts under visible light irradiation (λ > 420
nm, [Na2SO4] = 0.1 M).
Fig. 9 EIS Nynquist plots of g-C3N4, Bi2MoO6 and 1:3 Bi2MoO6/g-C3N4 electrodes
under the irradiation of visible light (λ > 420 nm, [Na2SO4] = 0.1 M).
Fig. 10 Photoluminescence spectra of the g-C3N4, Bi2MoO6 and 1:3
Bi2MoO6/g-C3N4 composite.
Fig. 11 Photocatalytic degradation of RhB over 1:3 Bi2MoO6/g-C3N4 photocatalyst
21

alone and with the addition of IPA, EDTA, or BQ.
Fig. 12 Schematic diagram of the possible mechanism over the 1:3 Bi2MoO6/g-C3N4
photocatalyst under visible light irradiation.
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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