In situ synthesis of Bi2S3/Bi2SiO5 heterojunction photocatalysts with enhanced visible light photocatalytic activity

Article abstract of DOI:10.1039/c5ra09070a

In order to improve the photocatalytic activity of Bi₂SiO₅ under visible light irradiation, Bi₂S₃/Bi₂SiO₅ heterojunctions were synthesized through a facile in situ ion exchange method. Thioacetamide (TAA) is regarded as the appropriate sulfur source. The as-prepared samples of Bi₂SiO₅ and Bi₂S₃/Bi₂SiO₅ were systematically characterized by XRD, SEM-EDS, TEM, XPS, PL, UV-vis DRS and BET techniques. The photocatalytic activities of the samples were evaluated by degrading rhodamine B (RhB) under visible light and UV-vis light irradiation, respectively. Bi₂S₃/Bi₂SiO₅ heterojunctions show enhanced photocatalytic activities under visible light irradiation. Further investigation reveals that ion exchange reaction time plays an important role in the photocatalytic efficiency. The mechanism of the enhanced photocatalytic activity was proposed.

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In situ synthesis of Bi2S3/Bi2SiO5 heterojunction
photocatalysts with enhanced visible light
photocatalytic activity
Cite this: DOI: 10.1039/x0xx00000x
Xiaolei Liu,a Wenjun Wang,a Yuanyuan Liu,＊a Baibiao Huang,＊a Ying Dai,b
Xiaoyan Qin,a and Xiaoyang Zhanga
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
In order to improve the photocatalytic activity of Bi2SiO5 under visible light irradiation,
Bi2S3/Bi2SiO5 heterojunctions were synthesized through a facile in situ ion exchange method.
Thioacetamide (TAA) is regarded as the appropriate sulfur source. The asꢀprepared samples of
Bi2SiO5 and Bi2S3/Bi2SiO5 were systematically characterized by XRD, SEMꢀEDS, TEM, XPS,
PL, UVꢀvis DRS and BET techniques. The photocatalytic activities of the samples were
evaluated by degrading rhodamine B (RhB) under visible light and UVꢀvisible light irradiation,
respectively. Bi2S3/Bi2SiO5 heterojunctions show enhanced photocatalytic activities under
visible light irradiation. Further investigation reveal that ion exchange reaction time play an
important role in the photocatalytic efficiency. The mechanism of the enhanced photocatalytic
activity was proposed.
www.rsc.org/
to the ultraviolet light due to its wide energy band gap (3.76
eV),12 and the ultraviolet light accounts for as less as about 4%
1. Introduction
of the solar radiation energy. Therefore, low utilization of solar
radiation energy severely restricts the application of Bi2SiO5
into photocatalysis.
Semiconductor photocatalytic technology has received much
attention as one of the most promising technologies in solving
the worldwide energy shortage and environmental degradation.
Phototcatalysis occurs under mild reaction conditions and does
not produce secondary pollution.1,2 In general, improving the
photocatalytic activity is mainly focused on two aspects:
improving the carrier separation efficiency and extending the
spectral response range. Heterojunction is an efficient strategy
to overcome the drawbacks of fast charge recombination and
the limited visibleꢀlight absorption of semiconductor
photocatalysts.3,4,5,6,7
Bismuth silicate (Bi2SiO5) is one of the newly found
compounds within Aurivillius family, which was first reported
in 1996. Bi2SiO5 is composed of (SiO3)2ꢀ pyroxene file layers
and (Bi2O2)2+ layers, which are alternatively stacked. Bi2SiO5
was reported as a material with relatively good dielectric
properties and piezoelectric and nonlinear optical effects.8,9,10 In
addition, Bi2SiO5 has been applied in photocatalytic
degradation of organic compounds during the past several
years. For example, Zhu and coꢀworkers synthesized a phase
junction Bi2SiO5 flowerꢀlike microsphere, which exhibited
superior photocatalytic performance in the degradation of
phenol.9 Chen and his coꢀworkers prepared uniform spongeꢀlike
Bi2SiO5, which is an efficient photocatalyst for Cr(VI)
removal.11 However, the white Bi2SiO5 can only be responsive
Bismuth sulfide (Bi2S3) is a narrow band gap (~1.3eV)
semiconductor which has been widely used as electrochemical
hydrogen storage, thermoelectric, and photoresponsive
materials, etc.13,14,15 Moreover, Bi2S3 can absorb visible light
with wavelength up to 800 nm and exhibit good
photosensitization properties. Therefore, Bi2S3 attracts more
and more attention in photocatalysis.16 Up to now, a large
number of Bi2S3 based heterojunction photocatalysts have been
synthesized for the degradation of organic pollutants and
wastewater treatment, such as Bi2S3/BiOCl, Bi2S3/Bi2O2CO3,
Bi2S3/Bi2WO6, Bi2S3/BiOI, Bi2S3/ZnS and so on.17,18,19,20,21
Thus, Bi2S3 is expected to be a potential candidate which can
combine with Bi2SiO5 forming an effective heterojunction with
enhanced charge separation and visible light responsive
photocatalytic activity. However, the combination of Bi2SiO5
and Bi2S3 to construct novel Bi2S3/Bi2SiO5 heterostructures has
not been reported yet.
In this study, Bi2S3/Bi2SiO5 heterostructures were
synthesized through a facile in situ ion exchange method. A
series of control experiments were carried out to investigate the
influence of the reaction time on the content and size of Bi2S3
and ultimately the photocatalytic activity of Bi2S3/Bi2SiO5
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DOI: 10.1039/C5RA09070A
heterojunctions. The photocatalytic properties were evaluated Spectrometer (EDS). Xꢀray Photoelectron Spectroscopy (XPS)
via the photocatalytic degradation of RhB dye under visible spectra was measured in a Thermo Fisher Scientific Escalab 250
light (λ> 420 nm) and UVꢀvisible light. The enhanced spectrometer with monochromatized Al Kα excitation, and C1s
photocatalytic activity of Bi2S3/Bi2SiO5 was discussed in detail (284.6eV) was used to calibrate the peak positions of the elements.
based on the calculated energy band positions.
The BrunauerꢀEmmettꢀTeller (BET) surface area was measured by a
Micromeritics ASAP 2020 apparatus. The Diffuse Reflectance
Spectroscopy (DRS) of the samples were recorded in the range from
200 to 800 nm using Shimadzu UV 2550 spectrophotometer
equipped with an integrating sphere, using 100% BaSO4 as
reflectance sample. The PL spectra was carried out on a Hitachi
Fꢀ4500 fluorescence spectrophotometer at room temperature
and obtained with excitation wavelength at 300 nm.
2. Experimental section
2.1 Materials
Bismuth nitrate (Bi(NO3)3•5H2O), sodium silicate (Na2SiO3•9H2O),
ethylene glycol methyl ether, sodium hydroxide, thiourea, cystein
and thioacetamide were analytic reagents and were used without
further purification.
2.5 Evaluation of photocatalytic performance
2.2 Synthesis of Bi2SiO5 nanosheets
The RhB was used to evaluate the photocatalytic activity of the
samples at room temperature. The light source is a 500 W Xe arc
lamp (PLSꢀSXE500) equipped with a UV cut off filter (λ> 420 nm).
0.1g photocatalyst was dispersed into 100 mL of 20 mg/L RhB
solution, and the suspensions were first sonicated for 5 min and then
kept in the dark for 60 min to reach the adsorption/ desorption
equilibrium under constant stirring. At the given time interval, 3 mL
of the suspension was taken from the beaker and centrifugated to
separate the photocatalyst and solution. The residual concentration
of RhB was measured by a UVꢀvis spectrophotometer ( Xinmao UVꢀ
7502PC).
In a typical procedure, 6mmol (2.91 g) Bi(NO3)3•5H2O was
added into 40 mL ethylene glycol methyl ether with constant stirring
until bismuth nitrate was dissolved, 3mmol (0.852g) Na2SiO3•9H2O
was dissolved into 40 mL deionized water under stirring. Then the
Na2SiO3•9H2O solution was added to the solution of Bi(NO3)3•5H2O
to form a white suspension. Finally, the pH value of the solution was
adjusted to 12 using 2mol/L NaOH. After stirring for 30 min, the
mixture was transferred into a teflonꢀlined autoclave with a capacity
of 100 mL and maintained at 200 °C for 10 h. After cooling down to
room temperature naturally, the product was obtained by filtering
and washed with deionized water and ethanol for three times and
then dried at 60 °C for 12 h.
3. Results and discussion
3.1 The effect of sulfur source on the formation of Bi2S3/Bi2SiO5
heterojunctions
2.3 In situ synthesis of Bi2S3/Bi2SiO5 heterostructures using
different sulfur source
Fig. 1 shows the effect of sulfur source and reaction conditions
on the color of the asꢀprepared samples, and according to which, it
can be directly determined whether Bi2S3 is formed.15 Obviously,
under the same conditions (room temperature and reacted for 30
min), the color of the sample that treated with TAA (d) is gray, while
that treated with thiourea (b) and cysteine (c) is almost the same as
that of pure Bi2SiO5 (a). In addition, negligible Bi2S3 formation is
observed using thiourea and cysteine as sulfur source with increased
reaction time and temperature, the visible light absorption of which
is very low (Fig. S1 in the supporting information). The reason for
above phenomenon is due to the different release rate of S2ꢀ, and
TAA displays the fastest S2ꢀ release speed among three sulfur source.
Therefore, TAA is used as sulfur source for the preparation of
Bi2S3/Bi2SiO5 heterosjunctions. The Ksp of Bi2S3 is much lower than
Bi2SiO5. Consequently, Bi2S3 formed on the surface of Bi2SiO5 once
S2ꢀ was released by TAA. It is noteworthy to point out that in situ
formation enable close interaction between Bi2S3 and Bi2SiO5, which
is advantageous for the separation of photoꢀgenerated charge
carriers.
The prepared Bi2SiO5 sample (0.5mmol, 0.263 g) was
dispersed in into 80 mL three different solutions containing
thiourea (2mmol, 0.152 g), cysteine (2mmol, 0.244 g) or
thioacetamide (2mmol TAA, 0.15 g) with constant stirring for
30 min at room temperature, respectively. And then, the same
prepared Bi2SiO5 samples were dispersed in 80ml solutions
containing thiourea and cysteine with constant stirring for 3 h at
elevated temperature (60 °C) with other experimental
conditions unchanged. The obtained products were filtered,
washed with water and ethanol for four times ,and then dried at
60 °C for 6 h.
The Bi2S3/Bi2SiO5 sample obtained using TAA as sulfur
source under stirring for 15 min, 30 min and 60 min, were
marked as Bi2S3/Bi2SiO5 ꢀ15 min, Bi2S3/Bi2SiO5 ꢀ30 min and
Bi2S3/Bi2SiO5 ꢀ60 min, respectively.
2.4 Characterizations
The crystal structure of asꢀobtained samples was characterized
by Xꢀray powder diffraction recorded on a Bruker AXS D8
diffractometer using Cu Kα radiation. The microstructure and
morphology of the samples were characterized by transmission
electron microscopy (JEOL JEMꢀ2100F) and scanning electron
microscopy (Hitachi Sꢀ4800) equipped with an Energy Dispersive
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The phase structure and crystallinity of the Bi2S3/Bi2SiO5
heterojunctions under different reaction times were determined
by XRD patterns as shown in Fig. 3. All the diffraction peaks
can be indexed to the pure orthorhombic Bi2SiO5 phase (JCPDS
No. 36ꢀ0287, a = 1.5217 nm, b = 0.5477 nm, c = 0.5325 nm,
space group Cmc21). The sharp and intense diffraction peaks
show that the products are well crystallized and contain no
other impurities. No significant diffraction peaks of Bi2S3 can
be detected even for Bi2S3/Bi2SiO5 heterojunctions with stirring
for 60 min. This may be due to the fact that the content of Bi2S3
was very low. The analysis of EDS spectra (part 3 in the
supporting information) suggests the actual molar content of
Bi2S3 in the Bi2S3/Bi2SiO5 heterojunctions synthesized with
different reaction times are 0.110%, 0.247% and 0.427%,
respectively. In addition, the growth of Bi2S3 on Bi2SiO5 lowers
the diffraction intensity of Bi2SiO5.
In order to further check the formation of Bi2S3, increased
reaction time and temperature were applied to increase the
content of Bi2S3, i.e. Bi2SiO5 reacting with TAA at 80 °C for
3h. As expected, the diffraction peaks of Bi2S3 can be detected
(Fig. S2 in the supporting information). This result further
suggests the presence of Bi2S3 in Bi2S3/Bi2SiO5 heterojunctions
under ambient anion exchange process.
Fig. 1 the color of Bi2SiO5 that reacted with different sulfur source
and under different reaction conditions, (a) pure Bi2SiO5, (b) Bi2SiO5
reacted with thiourea for 30 min at room temperature, (c) Bi2SiO5
reacted with cysteine for 30 min at room temperature, (d) Bi2SiO5
reacted with TAA for 30 min at room temperature, (e) Bi2SiO5
reacted with thiourea for 3 h at 60 °C, (f) Bi2SiO5 reacted with
cysteine for 3 h at 60 °C.
3.2 Characterization
3.2.1 Optical properties of Bi2SiO5 and Bi2S3/Bi2SiO5
heterojunctions
The color of pure Bi2SiO5, Bi2S3/Bi2SiO5ꢀ15 min, Bi2S3/Bi2SiO5ꢀ
30 min, and Bi2S3/Bi2SiO5ꢀ60 min gradually changes from white to
gray, which means that the content of Bi2S3 increases with
increasing reaction time. The UVꢀvis diffuse reflectance spectra
(DRS) were shown in Fig. 2(a). It can be seen that the absorption
edge of pure Bi2SiO5 locates at about 330 nm; while with increasing
Bi2S3 content the visible light absorption is enhanced greatly.
Obviously, the light absorption of the Bi2S3/Bi2SiO5 heterojunction
is broadened from UV to the visible light range. This result is
attributed to the small band gap of Bi2S3, which also confirms the
existence of Bi2S3. Fig. 2(b) shows the plot of (ahν)2 vs hν, from
which the band gap of the samples can be estimated, and the Eg of
Bi2SiO5, Bi2S3 in Bi2S3/Bi2SiO5ꢀ15min, Bi2S3 in Bi2S3/Bi2SiO5ꢀ
30min, Bi2S3 in Bi2S3/Bi2SiO5ꢀ60min are 3.76 eV, 2.96 eV, 2.56 eV
and 2.21 eV, respectively (details are in the supporting information
Table S1). Furthermore, the size of Bi2S3 in Bi2S3/Bi2SiO5
heterojunction photocatalysts with different reaction time were
determined to be 3.41 nm, 3.92 nm and 4.61 nm, respectively (part 4
in the supporting information).
Fig.
3
XRD patterns of the asꢀprepared Bi2S3/Bi2SiO5
heterojunctions and pure Bi2SiO5.
3.2.3 XPS analysis of the Bi2S3/Bi2SiO5 heterojunctions
XPS spectra were further carried out to confirm the chemical
state of the elements in the samples. From Fig. 4a, it can be seen that
Bi, O and Si elements can be detected obviously. The weak peak of
S 2p is covered by strong Bi 4f spectra, therefore S could not be
detected by xps easily. Bi 4f spectra (Fig. 4b) displays two strong
peaks at 164.35 eV and 159.05 eV, which are corresponded to the
4f5/2 and 4f7/2 of Bi3+ in Bi2S3/Bi2SiO5 heterojunctions, respectively.
Fig. 4c shows the XPS spectra of Si 2p, which displays a binding
energy of 101.95 eV, and is ascribed to Si(IV). Fig. 4d presents the
spectra for O 1s which can be fitted to two peaks. The peak at 530
eV is characteristic of crystal O in Bi2SiO5 and the other at 531.8 eV
is due to the adsorbed H2O on the surface.22
Fig. 2(a) UVꢀvis diffuse reflectance spectra, (b) the plot of (ahν)2 vs
hν of the samples.
3.2.2 XRD analysis of Bi2SiO5 and Bi2S3/Bi2SiO5 heterojunctions
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Fig. 4 XPS spectra of Bi2S3/Bi2SiO5ꢀ30 min : (a) the wideꢀscan XPS
spectra of Bi2S3/Bi2SiO5ꢀ30 min sample, (b) Bi 4f, (c) Si 2p, (d) O
1s.
Fig.
5
SEM images of asꢀprepared pure Bi2SiO5 (a,b) and
Bi2S3/Bi2SiO5ꢀ30 min heterojunctions (c,d).
3.2.4 SEM and TEM analysis of Bi2SiO5 and Bi2S3/Bi2SiO5
heterojunctions
The surface morphologies of pure Bi2SiO5 and
Bi2S3/Bi2SiO5ꢀ30 min were investigated by SEM ( Fig. 5). As
can be seen from Fig. 5a and 5b, pure Bi2SiO5 is constructed by
interlaced nanosheets with a thickness of about 20nm. Fig. 5cꢀd
shows the morphologies of Bi2S3/Bi2SiO5ꢀ30 min. No obvious
change is observed between pure Bi2SiO5 and Bi2S3/Bi2SiO5ꢀ30
min. Bi2S3 can not be distinguished from the SEM images. The
presence of sulfur in Bi2S3/Bi2SiO5ꢀ30 min is detected by EDS
mapping (Fig. 6), which indicates the homogeneous distribution
of bismuth, silicon, oxygen and sulfur.
More detailed information of the microstructures of the pure
Bi2SiO5 and Bi2S3/Bi2SiO5ꢀ30 min were further investigated by
TEM and HRTEM. Fig.7a and 7c confirm the SEM results that
both pure Bi2SiO5 and Bi2S3/Bi2SiO5ꢀ30 min are composed of
nanosheets. In Fig.7b the layered lattice fringes with a spacing
of 0.301 nm matches well with the spacing of the (311) crystal
plane of Bi2SiO5. In Fig. 7d, the lattice fringes with a spacing of
0.199 nm which matches well with the spacing of the (002)
crystal plane of Bi2S3, further confirming the presence of Bi2S3.
In addition, the size of the Bi2S3 particles is approximately 5
nm. Meanwhile, the fringe spacing of 0.243 nm is indexed to
the (021) crystal plane of Bi2SiO5. From Fig. 7d, the intimate
contact between Bi2S3 and Bi2SiO5 can be observed thanks to
the in situ ion exchange method.
Fig. 6 EDS distribution maps for bismuth, silicon, oxygen and sulfur
of Bi2S3/Bi2SiO5ꢀ30 min.
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after 4 cycles, indicating that the heterojunctions are relative
stable.
Fig. 8(a) Photocatalytic activities of the prepared samples under
visible light irradiation, (b) The temporal evolution of the absorption
spectra of RhB solution with Bi2S3/Bi2SiO5ꢀ30 min as a function of
irradiation time under visible light irradiation.
Fig. 7 TEM and HETEM images of asꢀprepared pure Bi2SiO5 (a,b)
and Bi2S3/Bi2SiO5ꢀ30 min (c,d).
3.3 Photocatalytic activity
Fig. 9 (a) Photocatalytic activities of different catalysts under
full light (UVꢀvisible light) irradiation, (b) Cycling tests of
photocatalytic activity of Bi2S3/Bi2SiO5ꢀ30 min heterojunction for
RhB degradation.
RhB was used as the pollutant to evaluate the photocatalytic
activity of the samples under visible light (λ > 420 nm) and
UVꢀvisible light irradiation. Fig. 8(a) exhibits the results of
photocatalytic
decomposition of
RhB
over
different
photocatalysts under visible light irradiation. As well known,
RhB is quite stable, and its selfꢀdegradation without
photocatalyst can be ignored (Fig. 8(a)). Only 35% RhB is
decomposed under irradiation for 3 h over pure Bi2SiO5, due to
the selfꢀsensitization effect. However, the photocatalytic
activity is greatly improved after in situ formation of Bi2S3 on
Bi2SiO5. Among the different Bi2S3/Bi2SiO5 heterojunctions,
Bi2S3/Bi2SiO5 ꢀ30 min displays the best photocatalytic activity
with 87% RhB is decomposed. The photocatalytic activity of
Bi2S3/Bi2SiO5 heterojunctions decreases with further increasing
Bi2S3 content. Fig. 8(b) shows the absorption profile of RhB in
the presence of Bi2S3/Bi2SiO5ꢀ30 min under different
irradiation time. The intensity of the maximum absorption
decreases gradually, suggesting the decolorization of RhB. In
addition, a blue shift of the maximum absorption is observed,
which is consistent with the previously reported results and
means the conjugated structure was destructed (deꢀethylation of
RhB).23
3.4 PL spectra
The recombination of free photogenerated carriers can
cause photoluminescence (PL) emission. Therefore, PL
spectroscopy is an effective technique to investigate the the
separation efficiency of the photogenerated charge carriers in a
semiconductor. The PL spectra of Bi2SiO5 and Bi2S3/Bi2SiO5
heterojunctions are presented in Fig. 10. From Fig. 10, pure
Bi2SiO5 displays the highest intensity of PL emission,
indicating that the photogenerated carriers recombine quickly.
The PL intensity of Bi2S3/Bi2SiO5 heterojunctions are lower than
pure Bi2SiO5, and with the increase of reaction time, the PL
intensity gradually decreases. This phenomenon demonstrates
that the Bi2S3/Bi2SiO5 heterojunctions can deeply suppress the
recombination of photogeneration carriers and lead to lower PL
intensity. Therefore, the photocatalytic activity enhanced.
The enhanced photocatalytic activity of these
heterojunctions was further investigated under UVꢀvis light
irradiation. The results are shown in Fig. 9(a). As expected,
Bi2S3/Bi2SiO5ꢀ30 min heterojunction displays the best
photocatalytic activities, and nearly 100% of RhB (20 mg/L)
are decomposed within 90 min. In addition, stability is
significant for catalysts to be used in practical applications. In
order to evaluate the stability of the Bi2S3/Bi2SiO5
heterojunctions, cycling test of Bi2S3/Bi2SiO5ꢀ30 min have been
done( Fig. 9(b)). The photocatalytic activity reduced a little
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Fig. 10 PL spectra of Bi2SiO5 and Bi2S3/Bi2SiO5 heterojunctions promote the recombination of photoinduced electrons and holes to
reduce the photocatalytic activity.25 Consequently, it is the combined
(λexc = 300 nm).
effect of visible light absorption and the CB and VB position that is
responsible for the best photocatalytic activity of Bi2S3/Bi2SiO5ꢀ30
3.5 Photocatalytic mechanism
min.
The band positions of the samples can be calculated by the
empirical formula EVB = X
－ －Eg.
Ee + 0.5 Eg,24 and ECB = EVB
Where EVB is valence band (VB) edge potential, ECB is
conduction band (CB) edge potential, X is the electronegativity
of the semiconductor, Eg is the band gap energy of the
semiconductor that is the geometric mean of the absolute
electronegativity of the constituent atoms and Ee is the energy
of free electrons on the hydrogen scale (4.5 eV). The positions
of ECB and EVB of Bi2SiO5 and Bi2S3/Bi2SiO5 heterojunctions
were calculated in supporting information (Table S1).
Fig. 11 show the energy level of Bi2S3/Bi2SiO5
heterojunctions and the possible charge transfer process of the
heterojunctions under visible light irradiation. The
photocatalytic mechanism was suggested as follows. Under
visible light irradiation, Bi2S3 absorb photons giving rise to
electrons and holes. The photogenerated electrons transfer to
the conduction band of Bi2SiO5; while the photogenerated holes
left at the valence band of Bi2S3. Therefore, the photoꢀinduced
electrons and holes are separated spatially. The photogenerated
Fig. 11 Diagram for energy level of Bi2S3/Bi2SiO5 heterojunctions
and the possible charge transfer process of the heterojunctions under
visible light irradiation.
ꢀ
electrons react with adsorbed O2 to produce O2 , meanwhile,
photogenerated holes left at the valence band of Bi2S3. Then
photogenerated holes and O2 initiate the oxidative reaction of
4. Conclusions
ꢀ
RhB.
In this study, a novel Bi2S3/Bi2SiO5 heterojunctions was
synthesized by a simple in situ ion exchange method. The
Bi2S3/Bi2SiO5 heterojunctions exhibited enhanced visible light
absorption and photocatalytic activity compared with pure Bi2SiO5.
With the ion exchange time increasing, the content and size of Bi2S3
in Bi2S3/Bi2SiO5 heterojunctions increased but less than 10 nm, and
the photocatalytic activity increased first and then decrease.
Bi2S3/Bi2SiO5ꢀ30 min heterojunction displays the best photocatalytic
activity that can degrade 87% of RhB within 3h under visible light
irradiation. The quantum size confinement of Bi2S3 nanoparticles
cause the tunable energy band so that the suitable heterojunction can
be formed. The enhanced photocatalytic activity can attribute to the
extended spectral response range, the effective separation of
photoinduced electrons and holes and the photosensitization of
Bi2S3.
Under UVꢀvisible light irradiation, both Bi2SiO5 and Bi2S3
can absorb photons giving rise to electrons and holes. The
photogenerated electrons from the conduction band of Bi2S3
transfer to the conduction band of Bi2SiO5; meanwhile, the
photogenerated holes from the valence band of Bi2SiO5 transfer
to the valence band of Bi2S3. Therefore, the photogenerated
holes and electrons can be separated effectively, the
photocatalytic activity enhanced a lot.
As mentioned above, Bi2S3/Bi2SiO5ꢀ30 min displays the best
photocatalytic activity. The BET surface areas of all the samples are
almost the same (Table S2 in the supporting information), therefore,
surface area is not the main factor for the different photocatalytic
activity. The reason may be attributed to the quantum size effect of
Bi2S3. When the ion exchange reaction time is 15 min, the size of
Bi2S3 is small. Therefore, the band gap is larger (Eg = 2.96 eV) and
the conduction band (CB) position is more negative, which means
the driving force for electrons transfer from the CB of Bi2S3 to the
CB of Bi2SiO5 is stronger and the photogenerated holes at the
valence band have higher oxidation capacity, but larger band gap
cause less visible light absorption. With increasing the ion exchange
reaction time up to 60 min, the size of Bi2S3 increase significantly
(up to 4.61 nm). According to quantum size effect, the band gap of
Bi2S3 decreased (Eg = 2.21 eV) which means more visible light can
be absorbed. However, the CB position of Bi2S3 shifts to positive
and the VB position of Bi2S3 shifts to negative, which mean both the
driving force for electrons transfer from the CB of Bi2S3 to the CB of
Bi2SiO5 and the oxidation capacity of photogenerated holes at the
VB of Bi2S3 are decreased. The overmuch content of Bi2S3 can
Acknowledgements
This work is financially supported by the Shandong Province Natura
l Science Foundation (ZR2014JL008), National Basic Research Prog
ram of China (the 973 Program: No. 2013CB632401), and the Natio
nal Natural Science Foundation of China (No. 21333006, 11374190
and 51021062 ).
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

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Journal Name
RSC Advances
View ArticAle ROnTliInCeLE
DOI: 10.1039/C5RA09070A
Notes and references
a
State key lab of crystal materials, Shandong university, Jinan, China,
250100. Email: bbhuang@sdu.edu.cn, yyliu@sdu.edu.cn
b School of physics, Shandong university, Jinan, China, 250100.
†
Electronic Supplementary Information (ESI) available: See
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