Synthesis of Bi2O3-Bi4V2O11 heterojunctions with high interface quality for enhanced visible light photocatalysis in degradation of high-concentration phenol and MO dyes

Article abstract of DOI:10.1039/c8ce00101d

One-dimensional Bi₂O₃-Bi₄V₂O₁₁ heterostructures with enhanced visible light photocatalytic performance were synthesized by high temperature calcination of Bi(OHC₂O₄)·2H₂O-Bi₂VO_5.5 precursors. The Bi₄V₂O₁₁ nanosheets uniformly grew on the Bi₂O₃ porous rods by crystallographic-oriented epitaxial growth, which increased the interface quality and then provided the smallest penetration barrier for electron-hole pair transfer between Bi₂O₃-Bi₄V₂O₁₁ interfaces. The photocatalytic performance of the obtained products was evaluated by degradation of phenol and methyl orange (MO) with high concentration under visible light irradiation. The results show that the Bi₂O₃-Bi₄V₂O₁₁ heterostructure displays higher photocatalytic activity than pure phase Bi₂O₃ and Bi₄V₂O₁₁, and more encouragingly, 40 mg L^-1 of phenol can be completely degraded in 30 min under visible light irradiation using the Bi₂O₃-Bi₄V₂O₁₁ (DS-2) heterostructure as the photocatalyst. This enhanced photocatalytic performance is ascribed to the synergistic effect of the suitable band alignment of the Bi₂O₃ and Bi₄V₂O₁₁, high interface quality and one-dimensionally ordered nanostructure. Radical scavenger experiments indicate that holes (h⁺) and superoxide radicals (O₂^-) were the main active species for phenol (and MO) degradation during the photocatalytic process. This work would offer a simple route to design and fabricate junction structures with high interface quality for photocatalytic applications.

Full text of DOI:10.1039/c8ce00101d

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Volume 18 Number 1 7 January 2016 Pages 1–184
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HIGHLIGHT
Tiddo J. Mooibroek, Antonio Frontera et al.
Towards design strategies for anion–π interactions in crystal engineering
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Synthesis of Bi O -Bi V O heterojunctions with high interface
2
3
4
2
11
quality for enhanced visible light photocatalysis in degradation
of high-concentration phenol and MO dyes
Ting Liu, Yan Ge Mao, Yin Peng*
Oneꢀdimensional Bi
photocatalytic performance were synthesized by high temperature calcination of
Bi(OHC )•2H OꢀBi VO5.5 precursors. The Bi 11 nanosheets uniformly grew on
the Bi porous rods by crystallographicꢀoriented epitaxial growth, which increased
the interface quality and then provided the smallest penetration barrier for
electron–hole pair transfer between Bi ꢀBi 11 interfaces. The photocatalytic
2 3 4 2
O ꢀBi V O11 heterostructures with enhanced visible light
2
O
4
2
2
4 2
V O
2
O
3
2
O
3
4 2
V O
performance of the obtained products was evaluated by degradation of phenol and
methyl orange (MO) with high concentration under visible light irradiation. The
results show that Bi
2 3 4 2
O ꢀBi V O11 heterostructure displays higher photocatalytic
activity than pure phase Bi O and Bi V O , and more encouragingly, 40 mg/L of
2
3
4
2
11
phenol can be completely degraded in 30 min under visible light irradiation using the
Bi ꢀBi 11 (DSꢀ2) heterostructure as photocatalyst. This enhanced photocatalytic
performance is ascribed to the synergistic effect of the suitable band alignment of the
2
O
3
4 2
V O
Bi
2
O
3
and Bi
4
V
2
O11, high interface quality and oneꢀdimensionally ordered
+
nanostructure. Radical scavenger experiments indicate that holes (h ) and superoxide
−
radicals (•O
2
) were the main active species for phenol (and MO) degradation during
the photocatalytic process. This work would offer a simple route to design and

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fabrication of junction structures with high interface quality for photocatalytic
applications.
Introduction
In the past few decades, the rapid development of industry has caused serious
1
–4
environmental pollution. Therefore, development of high efficient, green energy
sources and ecoꢀfriendly methods for environmental remediation is highly in demand.
As is known, the photocatalytic technology is a green and effective way to solve the
problems, which can decompose organic pollutants into small molecules, such as
CO , H O, etc. In order to improve the photocatalytic performance, a great deal of
2
2
effort has been made, such as the formation of semiconductor heterostructures,
coꢀdeposition of noble metals, doping, surface hybridization and incorporation with
other technologies. Among these approaches, the heterojunctionꢀtype photocatalysts
have attracted much attention because of the tuneable band structures and efficient
electronꢀhole separation and transportation, which endows them with suitable
5
ꢀ9
properties superior to their individual components.
However, in practical studies, it has been found that the photocatalytic activity of
the heterojunction is easy to deactivate after several times. This is mainly due to the
low junction interfacial quality. For heterojunction photocatalysts, the interfacial
quality plays a key role in the photocatalytic activity, stability and reusability. An
excellent heterojunction photocatalyst should have junction interfaces with low
interfacial defects and chemically strong bonds across the interface with large contact
areas. Crystallinity and the concentration of defect affect the carrier recombination

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rate, semiconductor transport and material reaction. In general, almost all types of
defects ꢀ grain boundaries, dislocations, eigenvalue defects and substitution of
impurities will promote the scattering and recombination of carriers, and the interface
happens to be the necessary way for carrier transport. So, the high crystallinity and
few nonꢀequilibrium defects will reduce the carrier recombination; The interfacial
charge transfer between the semiconductor interfaces is done in the picosecond, so the
fast transfer rate requires the interface to provide the smallest energy barrier (large
1
0,11
coupling area).
A difference in lattice spacing between two semiconductors likely
causes lattice mismatch, resulting in chemically weak bonds and high penetration
barrier at the junction interface, which is responsible for the instability of the
heterojunction photocatalyst. Therefore, low interfacial defects and chemically strong
bonds across the interface with large contact areas (namely interface with small lattice
12ꢀ20
mismatch) are preferred for eliminating the penetration barrier in the interface.
Over the past decade, fabrication of a high interface quality in heterostructured
16ꢀ27
catalysts has attracted a growing attention worldwide.
According to the reported
results, it is believed that the similar composition (or structure) on both sides of the
interface can provide continuity of the bonding across the heterostructural boundary,
which may facilitate the charge transfer across the interface. Sr
2 4 3
TiO /SrTiO (La, Cr)
heterojunction photocatalyst shows higher photocatalytic activity towards hydrogen
1
6
production than individual SrTiO
morphology studies showed that well defined heterojunctions are formed by matching
the lattice fringes of SrTiO (La,Cr) and Sr TiO (La,Cr); Peng et al. synthesized
3 2 4
(La, Cr) and Sr TiO (La, Cr). Microscopic
3
2
4

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1
9
Bi
2
2
O
3
3
ꢀBi
2
2
O
2.33 heterostructures through high temperature calcinations. The obtained
Bi
O
ꢀBi
O
2.33 heterostructures exhibit outstanding photocatalytic performance to
degrade phenol and MO dyes with high concentration in short time under solar/visible
light irradiation. Small interfacial lattice mismatch improves photogenerated carrier
transportation at the junction interfaces; A new crystal facetꢀbased CeO
2
homojunction was synthesized through solutionꢀbased crystallographic oriented
epitaxial growth. This homostructural interface with completely matched lattice
fringes provides convenient and fast channels for the photogenerated carrier
1
8
transportation between two units of homojuntion. Inspired by the above conclusions,
we design and synthesize bismuth oxide (Bi
composition on both sides of the interface.
2 3
O ) heterostructure with the similar
Bi
4
V
2
O
11 has a layered structure that consists of [Bi
2
O
2
] slabs which are interleaved
As a layered Aurivilliusꢀtype compound, Bi 11 can be used as
visible light photocatalyst owing to its peculiar structural and optical properties.
Furthermore, some typical heterojunction systems such as BiVO /Bi
αꢀBi 11 and CdS/Bi 11 have been
synthesized. However, there is no report on the synthesis and photocatalytic
performance of Bi ꢀBi 11 heterostructure with high interfacial quality.
In this work, we synthesized oneꢀdimensional Bi O ꢀBi V O heterostructures
2
ꢀ 28,29
by (VO3.5□0.5) .
4 2
V O
3
0
4
4 2 11
V O ,
4
V
2
O
11/βꢀBi
4
V
2
O
11
,
Bi24
O
31Br10/Bi
4
V
2
O
4 2
V O
31ꢀ34
2
O
3
4 2
V O
2
3
4
2
11
with well matched lattice fringes by high temperature caclining
Bi(OHC )•2H OꢀBi VO5.5 precursors. Phenol and methylene orange (MO) were
used as model compounds to investigate the photocatalytic activities of the
2
O
4
2
2

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Bi
2
O
3
ꢀBi
4
V
2
O
11 heterostructure under visible light irradiation. The results
ꢀBi 11 photocatalyst is highly efficient for degradation
demonstrated that the Bi
2
O
3
4 2
V O
of high concentration phenol and MO dyes, and the DSꢀ2 sample shows an excellent
photocatalytic activity as compared to the recently reported Biꢀbased photocatalysts
1
9,35ꢀ48
under the similar conditions.
attributed to a synergistic effect of the following three factors: (1) suitable band
alignment of the Bi and Bi 11 drives electrons and holes to reach the most
The enhanced photocatalytic performance is
2
O
3
4 2
V O
stable energy configuration and then leads to a spatial charge separation; (2) the
interfaces with well matched lattice fringe provide small penetration barrier for the
2 3 4 2
photogenerated carriers transfer across the Bi O ꢀBi V O11 heterojuntions; and (3)
oneꢀdimensional ordered nanostructure is desirable for facilitating high efficient and
directional transport and separation of electrons and holes. This work provided a
simple route to design and synthesize advanced materials with high interface quality
for photocatalytic applications.
Experimental Section
Sample Preparation
All reagents were analytical grade and used without any further purification in our
experiment.
6
Bi(OHC O )•2H O nanorods were synthesized according to our earlier report.
2
4
2
Bi(OHC
2
O
4
)•2H
2
OꢀBi
2
VO5.5 precursors were then prepared by the hydrothermal
)•2H O nanorods were
O mannitol solution under magnetic stirring. Then,
method. In the typical synthesis, firstly, 0.35 g of Bi(OHC
added to 40 ml of Bi(NO •5H
2
O
4
2
3
)
3
2

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3 4 2
Na VO •12H O was added and continued stirring for 30 min. Finally, the mixture was
sealed into a Teflonꢀlined stainless steel autoclave and heated at 160 ºC for 12 h. After
being cooled down to room temperature naturally, the products were collected and
washed several times with deionized water and absolute ethanol, and dried at 60 ºC
for 4 h. The asꢀobtained samples were labelled as Sꢀ1, Sꢀ2, Sꢀ3 and Sꢀ4 when the
molar ratio of Bi(OHC
00:25, respectively.
Bi VO5.5 was obtained in the absence of Bi(OHC
reactive system.
4 2
Bi ꢀBi V O11 heterojunctions were obtained by calcining Sꢀ1, Sꢀ2, Sꢀ3 and Sꢀ4
2 4 2 3 3 2
O )•2H O:Bi(NO ) •5H O is 100:1.5, 100:3, 100:6 and
1
2
2 4 2
O )•2H O rods in the above
2
O
3
precursors at 350 ºC for 3 h in air, and the corresponding calcinedꢀproducts were
labelled as DSꢀ1, DSꢀ2, DSꢀ3 and DSꢀ4, respectively.
4 2 2
Bi V O11 was prepared via caclining Bi VO5.5 at 400 ºC for 3 h.
Bi O rods were obtained by caclining Bi(OHC O )•2H O precursors at 320 ºC for
2
3
2
4
2
4
h in air.
Test of photocatalytic performance
Photocatalytic performance of the obtained Bi
2 3 4 2
O ꢀBi V O11 heterostructures was
tested by degrading toxic phenol and MO dye under visible light irradiation. A 300 W
Xe lamp (CELꢀHXF300F, Beijing China Education Auꢀlight Co., Ltd) with a 400 nm
cut off filter were used as visible light source. All the photocatalytic experiments were
carried out at room temperature by a cooling water circulation. In a typical

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photocatalytic experiment, 100 mg photocatalyst and 100 mL phenol (40 mg/L) or
MO (30 mg/L) solution were mixed together under magnetic stirring and formed
suspension. Prior to illumination, the suspension was stirred for 30 min in the dark in
order to reach an adsorptionꢀdesorption equilibrium between phenol (or MO) and
photocatalyst. At each irradiation time intervals, above suspension (3 mL) was
collected and centrifuged, then supernatant was monitored by UVꢀVis absorption
spectra. Additionally, in order to test the durability, the photocatalyst was reused five
times to degrade phenol.
The experiments of trapping active species were similar to the photocatalytic tests.
Ammonium oxalate (AO), pꢀbenzoquinone (BQ) and tꢀbutanol acted as the
−
scavengers of hole (h+), the superoxide radicals (•O
respectively, followed by the photocatalytic tests.
2
) and hydroxyl radicals (•OH),
Photocatalyst Characterization
Field emission scanning electron microscopy (FEꢀSEM) images were recorded on a
Hitachi Sꢀ4800 microscope. Transmission electron microscopic (TEM) images,
highꢀresolution transmission electron microscopic (HRTEM) images were taken using
an ultraꢀhigh resolution field emission gun transmission electron microscope (FEI
Talos F200X TEM). XꢀRay powder diffraction (XRD) was carried out on a Rigaku
(
Japan) D/max ꢀγA Xꢀray diffractometer with CuꢀKα radiation (λ = 0.154178 nm).
UVꢀvis diffuseꢀreflectance spectrum was recorded with a UVꢀ2450 spectrophotometer
in the wavelength range of 200ꢀ800 nm at room temperature. BaSO was used as the
4

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reflectance standard material. The XꢀRay photoelectron spectroscopy (XPS) was
performed on a PerkinꢀElmer RBD upgraded PHIꢀ5000C ESCA system. The
photoluminescence emission spectrum (PL) was recorded on a FLS920
spectrophotometer equipped with a 150W xenon lamp as the excitation source at room
temperature.
Electrochemical impedance spectroscopy (EIS) measurements
Electrochemical impedance spectroscopy (EIS) measurements were conducted at a
frequency between 0.1 Hz and 100 kHz using a CHI660D instrument. A
2 3 4 2
threeꢀelectrode system was used, in which a Bi O ꢀBi V O11 electrode, a saturated
calomel electrode and a platinum sheet were employed as the working electrode, the
reference electrode and the auxiliary electrode, respectively. The working electrode
was prepared by pasting a slurry mixture of the asꢀprepared Bi
80 wt%), acetylene black (15 wt%) and polytetrafluoroethylene binder (5 wt%) using
ethanol as solvent onto a piece of nickel foam and dried under vacuum at 50 ºC for 6
h. 0.5 M Na SO was used as the detecting electrolyte.
2 3 4 2
O ꢀBi V O11 sample
(
2
4
Results and discussion
Structure and morphology of photocatalysts

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h
g
JCPDS NO.42-0135
Bi V O
4
2 11
f
DS-4
e
d
c
DS-3
DS-2
DS-1
Bi
O
b
a
2 3
JCPDS NO.27-0050
10
20
30
40
50
60
70
80
2
-Theta(degree)
Fig. 1 The XRD patterns of pure Bi (b), Bi 11 (g) and heterostructures (cꢀf)
and Standard Card of Bi (a) and Bi
Bi(OHC )•2H OꢀBi VO5.5 heterostructures were synthesized by a hydrothermal
method at 160 ºC for 12 h using Bi(OHC )•2H O rods as precursors. Fig. S1 gives
the XRD patterns of the Bi(OHC O )•2H OꢀBi VO heterostructures, pure Bi VO
2
O
3
4 2
V O
O
2 3
4 2
V O11 (h).
2
O
4
2
2
2
O
4
2
2
4
2
2
5.5
2
5.5
and Bi(OHC
can be indexed to the bismuth oxalate (Bi(OHC
loadedꢀ Bi VO5.5 content increasing, a group of new diffraction peaks (Fig. S1d)
2
O
4
)•2H
2
O. From Fig. S1a, it can be seen that all the diffraction peaks
2
O
4
)•2H O) precursor. With the
2
2
appear in S4 sample, which can be indexed to tetragonal Bi
No. 51ꢀ0032).
2
VO5.5 (Fig. S1g, JCPDS
Calcine Sꢀ1, Sꢀ2 Sꢀ3 and Sꢀ4 precursors at 350 ºC for 3 h in air and obtain the
respective calcinedꢀproducts which were labelled as DSꢀ1, DSꢀ2, DSꢀ3 and DSꢀ4,
respectively. Fig. 1 gives out their XRD patterns. It can be found that two sets of
XRD peaks exist in the DSꢀ4 samples, which are indexed to tetragonal Bi
2 3
O (JCPDS
No. 27ꢀ0050) and orthorhombic Bi V O (JCPDS No. 42ꢀ0135). However, no
4
2
11
2 2 4 2 11
Bi VO5.5 XRD peaks are discovered, implying Bi VO5.5 changing into Bi V O

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during the calcining process. No Bi
DSꢀ3 samples, which are due to the low loadedꢀ Bi
Where is Bi 11 from? In order to answer this question, we calcined pure
Bi VO at 350 and 400 ºC. Fig. S2 show the XRD patterns of the pure Bi VO and
4
V
2
O11 peaks are found in the DSꢀ1, DSꢀ2 and
2
VO5.5 content according to Fig.S1.
4
2
V O
2
5.5
2
5.5
o
its calcined products. It can be found that XRD peak of the calcined product at 400 C
(
Fig. S2d) can be indexed to orthorhombic Bi
implies Bi
some purity can be found besides the Bi
4
V
2
O
11 (JCPDS No. 42ꢀ0135), which
o
2
VO5.5 has transformed completely into Bi
4
V
2
O
11 at 400 C. However,
o
4
V
2
O
11 when calcined temperature is 350 C
(
Fig. S2c). From the SEM images of the precursors with high loadedꢀ Bi VO5.5
2
contents and the relative calcined products, it can be discovered that the diameter of
the porous Bi rods from the calcinations of Bi(OHC )•2H O rods has no
obvious change, which shows that no chemical reaction is occurred between the
Bi during caclining process. According to above analysis, it can be
2
O
3
2
O
4
2
2
2 3
VO5.5 and Bi O
said that the loadedꢀBi VO5.5 in Bi(OHC O )•2H OꢀBi VO precursor is changed
2
2
4
2
2
5.5
into Bi
4
V
2
O
11 in the Bi
2 3 4 2
O ꢀBi V O11 heterojunctions.

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Fig. 2 FEꢀSEM images of the precursors and their respective caclined products, Sꢀ1
(a), DSꢀ1 (b), Sꢀ2 (c), DSꢀ2 (d), Sꢀ3 (e), DSꢀ3 (f), Sꢀ4 (g) and DSꢀ4 (h).
Fig. 2 displayed the SEM images of the Bi O ꢀBi V O heterojunctions and their
2
3
4
2
11
precursors. Bi(OHC
2
O
4
)•2H
2
O is rodlike structure with smooth surface (Fig. S3a).
)•2H O transformed to porous Bi
rods due to gas removal (Fig. S3b). The Bi(OHC )•2H OꢀBi VO5.5 precursors are
also 1D rodꢀlike structures, and few Bi VO5.5 nanoparticles grow dispersedly on the
After calcinations at 320 ºC for 4 h, Bi(OHC
2
O
4
2
2 3
O
2
O
4
2
2
2

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Bi(OHC
loadedꢀBi
Bi(OHC
by a large number of Bi VO
2
O
4
)•2H
VO5.5 content, more and more Bi
)•2H O rods (Fig. 2c, e), finally each Bi(OHC
nanoparticles (Fig. 2g). After calcining
Bi(OHC VO5.5 precursors at 350 ºC for 3 h, the shape of the obtained
4 2
Bi ꢀBi V O11 heterostructures were similar with their precursors (Fig. 2b, d, f h).
2
O nanorod (Fig. 2a). Meanwhile, with the increase of the
VO5.5 nanoparticles grow on the
)•2H O rod is covered
2
2
2
O
4
2
2
O
4
2
2
5.5
2 4 2 2
O )•2H OꢀBi
2
O
3
Fig. S4 displayed the SEM image of Bi
2
VO5.5. It can be found the Bi
2
VO5.5 is
flowerꢀlike structure.
a
V2p
b
Bi4f
Bi O
2
3
158.8
164.1
DS-2
DS-2
516.9eV
524.4eV
Bi
V O
4 2 11
Bi V O
2
11
4
156
158
160
162
164
166
512 514 516 518 520 522 524 526
Binding Energy(eV)
Binding Energy(eV)
Fig. 3 The highꢀresolution XPS spectra of (a) Bi 4f and (b) V 2p.
Surface compositions and chemical states in DSꢀ2, Bi and Bi
were obtained by XPS measurement. The high resolution XPS spectra of Bi, V are
shown in Fig. 3aꢀb. Two peaks of Bi 11 located at 516.9 and 524.4 eV are
2 11
ascribed to V 2P3/2 and V 2P1/2, respectively, which proves V ions in Bi V O
2
O
3
4 2
V O11 samples
2
4
V O
4
5+
4 2
sample are in form of V . (Fig. 3a). Compared with Bi V O11, the peaks of V 2P3/2
and V 2P1/2 also appear in DSꢀ2 sample, but the intensity of peaks is weak. This
result proves that the Bi V O exists in the DSꢀ2 sample. Otherwise, according to the
4
2
11
XPS result of DSꢀ2, the molar ratio of Bi and V in the DSꢀ2 sample is 24.77:1.7

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4 2
(14.57), more than the molar ration of Bi and V in Bi V O11 sample, implying only
few Bi
results. The Bi 4f spectrum is displayed in Fig. 3b. Two peaks of DSꢀ2 located at
64.1 and 158.8 eV are ascribed to Bi 4f5/2 and Bi 4f7/2, respectively, which proves
4 2
V O11 existences in the DSꢀ2, in good accordance with the XRD and SEM
1
3+
Bi ions in DSꢀ2 sample are in form of Bi . More importantly, after the Bi O and
2
3
Bi
higher binding energies compared to Bi
interaction between Bi and Bi 11 in the interface.
4
V
2
O
11 are contact each other, the peaks of Bi 4f in DSꢀ2 sample slightly shift to
2
O
3
sample, indicating the strong chemical
2
O
3
4 2
V O
Fig. 4 TEM (a) and HRTEM (b) images of the DSꢀ2 heterostructure.
TEM technology was used to obtain structural information of the obtained DSꢀ2
sample in detail. The TEM and HRTEM images of DSꢀ2 were shown in Fig. 4. It is
4 2 2 3
clearly noted that the Bi V O11 nanoparticles grow onto the surface of the Bi O
porous rod, which is consistent with the SEM results. Fig. 4b shows the HRTEM
image of DSꢀ2, two types of lattice fringes are visible. The lattice spacing of 0.348 nm
corresponds to (210) planes of Bi
2
O
3
, and 0.317 nm corresponds to (014) plane of
11, respectively. The interfacial crystal lattice matches well between Bi and
11 (see the red ring inset in Fig. 4b), indicating the crystallographicꢀoriented,
11 on the Bi surface, which favours the formation of
Bi
4
4
V
2
2
O
O
2 3
O
Bi
V
epitaxial growth of Bi
V
4 2
O
2 3
O

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chemically strong bonds across the large contact interfaces. It was also found that
there were no obvious defects at the interface.
Photocatalytic activity test
1.0
0.8
0.6
0.4
0.2
0.0
a
3.0
.5
2.0
b
2
Adsorption
Bi O
Visible light irradiation
2
3
1.5
1.0
0.5
DS-1
DS-2
DS-3
DS-4
-30min
0min
10min
20min
Bi V O
4
2
11
30min
Blank
20
0.0
200
-
0
20
40
300
400
500
Time(min)
Wavelength(nm)
1.0
0.8
0.6
0.4
0.2
0.0
c
2
.5
d
Visible light irradiation
2.0
Adsorption
1.5
Bi O
2
3
-
30min
DS-1
DS-2
DS-3
DS-4
0min
1
2
1.0
0min
0min
0.5
30min
0min
50min
Bi V O
4
2
11
4
Blank
0.0
-20
0
20
40
2
00
300
400
500
600
700 800
Time(min)
Wavelength(nm)
Fig. 5 Photocatalytic degradation curves of phenol (40 mg/L) (a) and MO (30 mg/L) (c) using
different photocatalysts; UVꢀvis absorption spectra of phenol (b) and MO (d) using DSꢀ2 as
photocatalyst under visible light irradiation.
The photocatalytic activity of the obtained heterostructures was evaluated by
degrading phenol and MO. Fig. 5a and c display the degradation curves of phenol and
MO in the presence of photocatalysts. It can be found that DSꢀ2 displays the excellent
photocatalytic performance among all the samples. When using DSꢀ2, Bi
2 3
O and
Bi 11 as photocatalysts, the degradation efficiencies of phenol (40 mg/L) are
4
2
V O

Page 15 of 28
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DOI: 10.1039/C8CE00101D
1
00%, 80% and 8% in 30 min under visible light irradiation (Fig. 5a and b),
respectively. And 100%, 65% and 5% of MO (30 mg/L) can be degraded in 50 min
Fig. 5c). Moreover, the absorption peaks of phenol at 208 nm almost disappear in 30
min (Fig. 5b) using DSꢀ2 sample as photocatalyst. This indicates that all the phenol
molecules are completely degraded to small molecular compounds, such as CO and
O. Compared with the reported Biꢀbased photocatalysts for degradation phenol
with the similar photocatalytic condition, DSꢀ2 sample shows excellent photocatalytic
(
2
H
2
1
9,35ꢀ48
activity.
This enhanced photocatalytic activity is ascribed to the formation of
high interface quality in the DSꢀ2 sample, which can be seen from the SEM and
HRTEM images (Fig. 2, 4). From the Fig.5, it also can be found that the obtained
heterostructures all exhibit excellent photocatalytic performance besides DSꢀ4. For
DSꢀ4 sample, dense Bi
4
V
2
O
11 nanoparticles cover the Bi
2
O
3
porous rods, as observed
in Fig. 2h, which decreases the light irradiation on Bi
2
3
O rods and the junction
interfaces. This shielding effect of dense Bi V O nanosheets coating on the Bi O3
4
2
11
2
rods reduces the photocatalytic activity of DSꢀ4 sample.
In addition, the photocalytic activity of Bi ꢀBi
2
O
3
4
V
2
O
11 photocatalysts was also
investigated by degrading RhB and MB solutions under visible light irradiation. Fig.
S5 displays the UVꢀvis absorption spectra of the RhB (20 mg/L) and MB(10 mg/L)
solution in the presence of DSꢀ2 sample. It can be seen that all the absorption peaks of
the RhB and MB gradually decrease with irradiation time increase and almost
disappear in 100 and 80 min, respectively. These results show that the obtained
heterostructure DSꢀ2 degrades selectively phenol and MO, especially phenol.

CrystEngComm
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DOI: 10.1039/C8CE00101D
a
100
80
60
40
20
0
1st
2nd
3rd
4th
5th
b
After five repeated cycles
Before five repeated cycles
10
20
30
40
50
60
70
80
2
-Theta(degree)
Fig. 6 (a) Cycling times of the photocatalytic degradation of phenol (40mg/L) in the presence
of DSꢀ2 under visible light irradiation after five repeated cycles and (b) the XRD pattern of
DSꢀ2 before and after five repeated cycles.
To investigate the stability of photocatalytic performance in the visible light region,
the DSꢀ2 sample was used to degrade phenol in five repeated cycles, and the results
are shown in Fig. 6. The DSꢀ2 photocatalyst retains excellent photocatalytic activity
after 5 repeated cycles (Fig. 6a), implying that the DSꢀ2 photocatalyst possesses
favourable stability. Small amounts of Bi
pattern of DSꢀ2 after the recycling photocatalysis (Fig. 6b, see red arrows). This may
be due to the Bi reaction with the CO from the decomposition of phenol in the
process of photocatalysis. From the SEM image of DSꢀ2 sample after five repeated
2 2 3
O CO are found to be present in the XRD
2
O
3
2

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DOI: 10.1039/C8CE00101D
cycles (Fig. S6) , it can be found that some Bi
of Bi ꢀBi
2 2 3
O CO nanosheets grow on the surface
2
O
3
4 2 11
V O .
Light absorption and energy band structures
a
b
Bi O
2
3
DS-1
Bi O (2.26eV)
2
3
DS-2
Bi V O (2.38eV)
4 2 11
DS-3
DS-4
Bi V O
4
2
11
200
300
400
500
600
700
800
1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
Wavelength(nm)
h
ν
(
eV
)
Fig. 7 (a) UVꢀvis diffuse reflectance spectra of Bi O , Bi V O and Bi O ꢀBi V O
2
3
4
2
11
2
3
4
2
11
2
/n
samples, (b) the plots of (αhν) vs. hν of Bi
1).
11 heterojunctions (Fig. 7a) were measured
2
O
3
, Bi
4
V
2 2 3 4 2
O11. (Bi O : n = 4; Bi V O11: n
=
2 3 4 2
The optical properties of Bi O ꢀBi V O
by UVꢀvis diffuse reflectance spectra (DRS), and their optical band gaps (Fig. 7b) can
be determined by the following equation:
n/2
αhν = A(hν − Eg)
in which α, h, ν, A and Eg are the absorption coefficient, Planck constant, light
frequency, a constant and band gap, respectively. Also, n is equal to 4 for the indirect
band gap and 1 for the direct band gap .Here n = 4 for Bi
2
O
3
and n = 1 for
49,32
2/n
Bi V O
. Fig. 7b shows the plots of (αhν) versus hν for Bi O and Bi V O .
4
2
11
2
3
4
2
11
The band gap (ꢁEg) was estimated by extrapolating the straight line to the abscissa
axis; therefore, ꢁEg (Bi ) and ꢁEg (Bi 11) were estimated to be 2.26 eV and
.38 eV, respectively.
2
O
3
4 2
V O
2

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DOI: 10.1039/C8CE00101D
1.0
0.8
0.6
0.4
0.2
0.0
1.0
Adsorption
Adsorption
Visible light irradiation
Visible light irradiation
a
0.8
0.6
0.4
0.2
0.0
b
DS-2
DS-2
AO(0.01mol/L)
TBA(0.01mol/L)
BQ(0.001mol/L)
AO (0.01mol/L)
TBA (0.01mol/L)
BQ (0.001mol/L)
-
30
-20
-10
0
10
20
30
-20
0
20
40
60
Time(min)
Time(min)
Fig. 8. Active species trapping experiments during the photocatalytic degradation to phenol
40 mg/L) (a) and MO (30 mg/L) (b) under visible light irradiation using DSꢀ2 as
(
photocatalyst.
Trapping experiments were performed to detect the active species generated in the
photodegradation process. Tertꢀbutyl alcohol (TBA), ammonium oxalate (AO) and
1,4ꢀbenzoquinone (BQ) were used as scavengers to trap hydroxyl radicals (•OH),
+
−
2
holes (h ) and superoxide radicals (•O ). It can be observed from Fig. 8 that the
photocatalytic degradation of phenol and MO molecules is remarkably inhibited with
the addition of AO and BQ. However, the addition of TBA does not cause significant
deactivation of DSꢀ2 photocatalyst, illustrating that •OH had little contribution to
−
2
+
phenol and MO photodegradation. These results demonstrate that •O and h are the
main active species in the photocatalytic process under visible light irradiation.

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DOI: 10.1039/C8CE00101D
6
000
b
a
Bi2O3
DS-2
5000
Bi V O
4
2
11
4000
Bi O
2
3
DS-2
3000
Bi V O
4
2
11
2000
1000
0
500
1000
1500
2000
400
500
600
700
800
'
Wavelength(nm)
Z (Ohm)
Fig. 9 (a) Photoluminescence (PL) spectra at room temperature and (b) EIS Nyquist plots of
the prepared photocatalyst samples. (λex = 320 nm)
Photoluminescence (PL) spectra provide a valid means to survey the separation
efficiency of the electron–hole pairs. The room temperature PL emission spectra of
2 3 2 3 4 2 4 2
the pure Bi O , Bi O ꢀBi V O11 heterostructures and Bi V O11 are shown in Fig. 9a. It
was found that the PL emission intensity of the DSꢀ2 sample is the lowest among the
three samples, which implies that the formation of junctions could effectively
suppress the recombination of photogenerated carriers, and then improve
photocatalytic performance. The typical EIS spectra of pure Bi
2 3 2 3 4 2 11
O , Bi O ꢀBi V O
heterostructures and pure Bi 11 are shown in Fig 9b. As is wellꢀknown, the arc
4
2
V O
radius in the impedance spectrum can reflect the reaction rate on the photocatalyst
surface, and the smaller arc radius implies a more efficient separation of
photogenerated electronꢀhole pairs and a higher efficiency of charge transfer. The arc
radii of the prepared DSꢀ2 sample is smaller than that of pure Bi
2 3 4 2 11
O and Bi V O ,
suggesting that Bi ꢀBi 11 heterostructure could facilitate the separation and
2
O
3
4 2
V O
migration of photogenerated electronꢀhole pairs in comparison with pure Bi O and
2
3
Bi
4
V
2
O
11
.
Therefore, the EIS measurements demonstrate Bi
2
O
3
ꢀBi
4
V O
2 11

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heterostructure can significantly promote the separation of photogenerated
electronꢀhole pairs and suppress the recombination of photogenerated electronꢀhole
pairs in the DSꢀ2 samples, thus improving the photocatalytic activities.
Bi O (1.33 eV)
2
3
Bi V O (2.15 eV)
4
2
11
DS-2 (1.62 eV)
-1
0
1
2
3
4
5
6
7
8
Binding Energy(eV)
Fig. 10 VBꢀXPS spectra of Bi and Bi
2
O
3
4
V O .
2 11
To determine the relative positions of conduction band (CB) and VB edges, the
total densities of states of VB for Bi O and Bi V O were measured, as shown in
2
3
4
2
11
Fig. 10. The VB edges of Bi
Compared to Bi and Bi
Bi ) to 1.62 eV due to the formation of junctions. According to the VB edges,
combining with band gap of Bi (2.26 eV) and Bi 11 (2.38 eV), the CB edge
potential of Bi O and Bi V O is ꢀ0.93eV and ꢀ0.23 eV, respectively, calculated
2
O
3
4 2
and Bi V O11 are 1.33eV and 2.15eV, respectively.
2
O
3
4 2
V O11, the VB maximum of DSꢀ2 is upꢀshifted from 1.33
(
2 3
O
2
O
3
4 2
V O
2
3
4
2
11
from the equation of ECB = EVB − Eg.

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DOI: 10.1039/C8CE00101D
2 3 4 2
Fig. 11 Schematic of (a) the energy bands of Bi O and Bi V O11, and (b) the
2 3 4 2
formation of Bi O ꢀBi V O11 heterostructures and the possible charge separation.
Based on the results of the trapping experiments and the VBꢀXPS data, we readily
illustrate the schematic diagram for the photocatalytic reaction mechanism and charge
transfer of the Bi O ꢀBi V O heterostructures under visible light irradiation, as
2
3
4
2
11
shown in Fig. 11. Bi
2
3 4 2
O and Bi V O11 are in contact to form a typeꢀII heterostructure,
according to their CB and VB positions.The difference in CB and VB positions
between Bi O and Bi V O allows the photogenerated electrons and holes to facilely
2
3
4
2
11
move in opposite directions, resulting in their efficient separation before
recombination under visible light irradiation. The formation of a high quality interface
between Bi
2
O
3
ꢀBi
4
V
2
O11 is an important factor to accelerate electron and hole transfer
across the interface. Moreover, 1D Bi
2
O
3
ꢀBi 11 nanostructures also offer a direct
4 2
V O
pathway for charge transport owing to the high surface to volume ratio.
From Fig. 11, it can be seen that the CB potential (−0.23 eV) of Bi
4 2
V O11 is
0
−
50
negative compared to E (O
2
/•O
2
)(−0.046 eV vs. NHE), O
2
adsorbed on the surface
−
of Bi
4
V
2
O
11 can be reduced to •O
2
4 2 11
by the electrons left in the CB of Bi V O
2 3
through one electron reducing reaction. According to the VB potential of Bi O (1.33

CrystEngComm
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DOI: 10.1039/C8CE00101D
eV), hydroxyl groups or water molecules adsorbed on the surface of Bi
2
O
3
cannot be
+
−
directly oxidized to •OH radicals (2.7 eV vs. NHE). Therefore, the h and •O
2
radicals are the main active species and react directly with phenol in the solution for
efficient degradation.
Conclusions
In summary, oneꢀdimensional (1D) Bi
2 3 4 2
O ꢀBi V O11 heterostructured photocatalysts
with high interface quality have been synthesized by calcining
Bi(OHC
2
O
4
)•2H
2
OꢀBi
2
VO5.5 precursors in air at 350 °C for 3 h. Bi
4
V
2
O
11
11
11
nanoparticles grow on the Bi O3 nanorods. The obtained Bi O ꢀBi V O
2
2
3
4
2
heterojunctions exhibit higher photocatalytic activity than pure Bi
2
O
3
and Bi
4
V
2
O
for the degradation of phenol and MO with high concentration under visible light
irradiation. This enhanced photocatalytic activity is due to the formation of high
quality interface between Bi
2 3 4 2
O and Bi V O11. Moreover, 1D ordered nanostructures
are favorable for highly efficient and directional transport and separation of electrons
+
−
and holes. The h and •O
2
radicals are the main active species for photocatalytic
ꢀBi 11. This work provides a facile and
degradation of phenol and MO over Bi
2
O
3
4 2
V O
versatile strategy to fabricate heterojunction with high quality interface for potential
photocatalytic and optoelectronic applications on a large scale.
Acknowledgements
This work is supported by the National Natural Science Foundation of China (21101006),
the natural science foundation of the colleges and universities in Anhui province

Page 23 of 28
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DOI: 10.1039/C8CE00101D
(
KJ2017A309) and the fund of state key laboratory of physical chemistry of solid
surfaces, Xiamen University (201510).
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DOI: 10.1039/C8CE00101D