A facile hydrothermal method to BiSbO4 nanoplates with superior photocatalytic performance for benzene and 4-chlorophenol degradations

Article abstract of DOI:10.1039/c1dt10130g

BiSbO₄ nanoplates with a large BET specific area has been prepared successfully via a facile hydrothermal reaction from Sb ₂O₃ and Bi(NO₃)₃. The effects of reaction conditions and the precursors on the final products were investigated. It is proposed that the redox reaction between Sb₂O₃ and Bi(NO₃)₃ plays a pivotal role in the formation of nanocrystalline BiSbO₄. The hydrothermally prepared nanocrystalline BiSbO₄ was characterized by X-ray diffraction (XRD), N ₂-sorption BET surface area, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The DRS result clarifies that BiSbO₄, originally believed to be a visible light responsive photocatalyst, is indeed UV light responsive with a band gap of 3.5 eV. The existence of Bi containing an impurity may be responsible for the visible light response of BiSbO₄ prepared via a conventional solid state reaction. BiSbO₄ nanoplates prepared via the hydrothermal method showed superior photocatalytic performance for the degradation of benzene and 4-chlorophenol (4-CP) as compared to BiSbO₄ prepared via a solid state reaction and Degussa P25. BiSbO_4(Hy) nanoplates can be a promising photocatalyst in the treatment of environmental pollution. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10130g

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PAPER
A facile hydrothermal method to BiSbO4 nanoplates with superior
photocatalytic performance for benzene and 4-chlorophenol degradations†
Qingqing You, Yanghe Fu, Zhengxin Ding, Ling Wu, Xuxu Wang and Zhaohui Li*
Received 22nd January 2011, Accepted 24th March 2011
DOI: 10.1039/c1dt10130g
BiSbO4 nanoplates with a large BET specific area has been prepared successfully via a facile
hydrothermal reaction from Sb2O3 and Bi(NO3)3. The effects of reaction conditions and the precursors
on the final products were investigated. It is proposed that the redox reaction between Sb2O3 and
Bi(NO3)3 plays a pivotal role in the formation of nanocrystalline BiSbO4. The hydrothermally prepared
nanocrystalline BiSbO4 was characterized by X-ray diffraction (XRD), N2-sorption BET surface area,
UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning
electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission
electron microscopy (HRTEM). The DRS result clarifies that BiSbO4, originally believed to be a visible
light responsive photocatalyst, is indeed UV light responsive with a band gap of 3.5 eV. The existence of
Bi containing an impurity may be responsible for the visible light response of BiSbO4 prepared via a
conventional solid state reaction. BiSbO4 nanoplates prepared via the hydrothermal method showed
superior photocatalytic performance for the degradation of benzene and 4-chlorophenol (4-CP) as
compared to BiSbO4 prepared via a solid state reaction and Degussa P25. BiSbO4(Hy) nanoplates can be
a promising photocatalyst in the treatment of environmental pollution.
up of corner-shared SbO6 octahedra, while Bi atoms locate in the
1. Introduction
interlayers and coordinate to eight O atoms to form edge-sharing
Semiconductor photocatalysts have been widely employed in the
distorted BiO8 polyhedra. The open structure with the presence of
treatment of all kinds of organic contaminants, including organic
distorted BiO6 polyhedra contributes to the photocatalytic activity
dyes,1–3 volatile organic compounds3–5 and persistent pollutants.6–8
Photocatalysis has many advantages over other treatment meth-
of BiSbO4. However, the already reported BiSbO4 was prepared
via a solid state reaction. Generally, the product obtained via the
ods. It is environmentally friendly, capable of being performed at
solid state process suffers from shortcomings in that it may contain
room temperature and can treat organic pollutants at extremely
an undesirable phase and is usually inhomogeneous with large
low concentrations9,10 Effective application of photocatalysis in
particle size and low surface area due to the high-temperature
environmental remediation requires that the photocatalysts should
sintering process. To develop a method in the preparation of
be of high photocatalytic efficiency. Therefore during the past
nanocrystalline BiSbO4 with a high surface area is important in
decade, tremendous effort has been devoted to the development
of new photocatalysts.3–8
Recently, we and others have reported a series of antimonate-
view of its application in photocatalysis.
In the past decades, hydrothermal–solvothermal method has
been demonstrated to be one of the most effective soft chemical
based photocatalysts and their application in the photocatalytic
methods in the preparations of nanocrystalline metal oxides
degradations of benzene and organic dyes.11–15 Among them, mon-
with large specific surface area. The hydrothermal–solvothermal
oclinic BiSbO4 is found to be an effective visible light responsive
method is facile and flexible in that the reaction conditions such
photocatalyst in the degradation of the organic dye methylene blue
as the reaction precursors, stoichiometry and pH value can be
(MB).15 The structure of BiSbO4 consists of layered sheets made
easily modified, which can lead to final products with different
morphologies and crystal structures. The preparations of mul-
tiplex metal oxide nanocrystallites like CuGeO3,16 ZnGa2O4,17,18
Research Institute of Photocatalysis, Fuzhou University, State Key Lab-
oratory Breeding Base of Photocatalysis, Fuzhou, 350002, P. R. China.
KNbO3,19,20 LiMn2O4,21 BaTe3O7 and Sr2Sb2O7 directly from
the corresponding metal oxides via a hydrothermal method have
also been reported.
22
14
E-mail: zhaohuili1969@yahoo.com; Fax: 86-591-83779105; Tel: 86-591-
83779260
† Electronic supplementary information (ESI) available: The schematics
of the experimental equipments (Fig. S1–S2), XRD patterns of products
prepared from different precursors (Fig. S3–S10), IR spectra of Bi(NO3)3
and a mixture of Sb2O3 and Bi(NO3)3 (Fig. S11), temporal evolution
of HPLC graphs in the presence of BiSbO4(Hy), BiSbO4(SSR) and direct
photolysis (Fig. S12–S14). See DOI: 10.1039/c1dt10130g
Herein, we report the preparation of BiSbO4 nanoplates with a
large specific area from Sb2O3 and Bi(NO3)3 via a hydrothermal
method. The preparation of BiSbO4 directly from Bi3+ and Sb5+
under normal hydrothermal condition is not possible, probably
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due to the low coordination capability of Sb5+ ion and the high
hydrolysis of Bi3+. However it is found that the redox reaction
between Sb2O3 and Bi(NO3)3 plays a pivotal role in the formation
of nanocrystalline BiSbO4(Hy). Our result reveals that BiSbO4,
originally believed to be a visible light responsive photocatalyst, is
indeed UV light responsive with a band gap of 3.5 eV. The existence
of a Bi containing impurity may be responsible for the visible
light response of BiSbO4 prepared via a conventional solid state
reaction. The hydrothermally prepared BiSbO4 shows superior
photocatalytic performance for the degradations of benzene and
4-chlorophenol (4-CP) as compared to P25 and BiSbO4 prepared
from the conventional solid state reaction.
source and a charge neutralizer. All binding energies were referred
to the C 1s peak at 284.6 eV of the surface adventitious carbon.
The total organic carbon concentration (TOC) was conducted in
Shimadzu TOC-V (CPH) total carbon analyzer.
2.3. Photocatalytic activity measurements
Schematics of the experimental equipments for photocatalytic
degradation of benzene and 4-chlorophenol are shown in Fig. S1–
S2.† The photocatalytic oxidation of benzene was conducted in a
tubular quartz microreactor operating in a continuous-flow mode.
The reactor was surrounded by four 4 W UV lamps (wavelength
254 nm). The catalyst loading was 0.3 g (50–70 mesh). Benzene
was diluted with a zero air stream (21% oxygen, 79% nitrogen,
H2O < 5 ppm, total hydrocarbons < 1 ppm). The resulting
gaseous mixture was used to afford a reactant stream. The initial
concentrations of benzene and carbon dioxide in the stream were
220 and 0 ppm, respectively. The flow rate of the reactant mixture
was kept at 20 mL min-1. Simultaneous determination of the
concentrations of benzene and carbon dioxide was performed
with an online gas chromatograph (HP6890) equipped with a
flame ionization detector, a thermal conductivity detector, and
a Porapak R column. The reaction temperature was controlled
at 27 ◦C by an air-cooling system. Benzene was found to be
stable in the catalyst-loaded reactor without illumination, and
no degradation of benzene was observed when it was illuminated
in the absence of BiSbO4(Hy). For comparison, the photocatalytic
activities of commercial TiO2 (Degussa P25) and BiSbO4(SSR) were
also tested under the same reaction conditions and equal catalyst
2. Materials and methods
2.1. Syntheses
All the reagents were analytical-grade and used without further
purification. Nanocrystalline BiSbO4 samples were prepared by
the hydrothermal method using Bi(NO3)3·5H2O and Sb2O3 as
starting materials. In a typical procedure, Sb2O3 powder (0.7288 g,
2.5 mmol) was added to 10 mL of aqueous solution containing
Bi(NO3)3·5H2O (2.4254 g, 5.0 mmol) under stirring. The pH of the
resulting mixture was adjusted by nitric acid solution or sodium
hydrate solution under vigorous stirring. The mixture was loaded
into a 23 mL Teflon-lined autoclave, filled with deionized water up
to 60% of the total volume and sealed tightly. Then the autoclave
was kept at 180 ◦C for 48 h. After cooling to room temperature, the
precipitate was collected, washed with distilled water and absolute
◦
weight as those employed for BiSbO4(Hy)
.
ethanol several times and then dried in air at 60 C. The sample
The photocatalytic degradations of 4-CP in liquid phase were
conducted in a quartz tube with 4.6 cm inner diameter and 17 cm
length. Four 4 W UV lamps with a wavelength centered at 254 nm
(Philips, TUV 4W/G4 T5) were used as the illuminating source.
0.15 g photocatalyst was suspended in 150 mL of 4-CP solution
(3.5 ¥ 10-4 M) and stirred overnight to ensure the establishment
of an adsorption–desorption equilibrium. An aliquot of about
3 mL was taken at a certain interval during the experiment and
centrifuged (TDL-5-A) to remove the powder. The filtrate was
analyzed on a liquid chromatography (Waters 2487) equipped with
a Merck C18 column to determine the concentration of 4-CP as
well as the intermediates. The eluant used was a mixture composed
of water, methanol and acetonitrile (40 : 50 : 10 by volume). The
flow rate was 1 mL min-1. The concentration of chloride ion
in the suspension was determined by an ion chromatograph
(881Compact IC pro) equipped with Metrosep A supp 5 250/4.0.
thus obtained was denoted as BiSbO4(Hy)
.
Bulk BiSbO4 (BiSbO4(SSR)) sample was prepared from Bi2O3 and
Sb2O3 via the conventional solid-state reaction according to the
literature.15 Mixed powders were calcined at 600 ◦C for 48 h in an
alumina crucible in air. After that, the powders were ground and
heated at 850 ◦C for 12 h to obtain BiSbO4(SSR)
.
2.2. Characterizations
X-Ray diffraction (XRD) patterns were collected on a Bruker
D8 Advance X-ray diffractometer with Cu-Ka radiation. The
accelerating voltage and the applied current were 40 KV and 40
mA, respectively. Data were recorded at a scanning rate of 0.002◦
2q s-1 in the 2q range of 10◦ to 80◦. It was used to identify the
phase present. UV-visible absorption spectra (UV-vis DRS) of the
powders were obtained for the dry-pressed disk samples using a
UV-visible spectrophotometer (Cary 500 Scan Spectrophotome-
ters, Varian). BaSO4 was used as a reflectance standard in the UV-
visible diffuse reflectance experiment. The transmission electron
microscopy (TEM) and high-resolution transmission electron
microscopy (HRTEM) images were measured by a JEOL model
JEM 2010 EX instrument at an accelerating voltage of 200 kV. The
powder particles were supported on a carbon film coated on a
3-mm-diameter fine-mesh copper grid. A suspension in ethanol
was sonicated, and a drop was dripped on the support film. The
morphology of the sample was characterized by field emission
scanning electron microscopy (SEM) (JSM-6700F). X-Ray pho-
toelectron spectroscopy (XPS) measurements were performed on
a PHI Quantum2000 XPS system with a monochromatic Al Ka
3. Results and discussion
3.1. Syntheses
The preparation of nanocrystalline BiSbO4(Hy) was not as
straightforward as that of nanocrystalline Sr2Sb2O7 we reported
previously.14 Reactions carried out using Bi(NO3)3 and Sb2O5
as precursors under hydrothermal conditions only gave Sb6O13
(01-071-1091) and Bi6O6(OH)3(NO3)3·1.5H2O (00-053-1038) no
matter what the reaction pH was (supporting materials Fig. S3†).
However, when Sb2O3 was used as the precursor, monoclinic
BiSbO4 (00-048-0469) was obtained successfully. In the reactions
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between Sb2O3 and Bi(NO3)3, the pH value played an important
role in controlling the composition of the final products. As
shown in the XRD patterns of the resultant products through
Bi 4f7/2 and Bi 4f5/2 peaks are observed at 158.8 and 164.1
eV, respectively, matching well with that of Bi3+ (Fig. 2a).24,25
However, the peak at 530.7 eV can be deconvoluted to peaks
assigned to lattice oxygen (O2-) at 530.3 eV, surface adsorbed
oxygen (O-) at 532.3 eV and Sb 3d5/2 at 530.86 eV. The adsorbed
oxygen (O-) is believed to exist as surface hydroxyl groups and its
quantity is proportional to the quantity of generated ∑OH radicals
(Fig. 2b).26–28 The peak corresponding to Sb 3d3/2 is located at ca.
540.2 eV, which is quite similar to that observed for bulk Sb2O5
(540.3 eV).13,23,29,30 In view of the charge balance, Sb should exist
◦
the hydrothermal process at 180 C for 48 h under different pH
values (Fig. 1), for the pH value of 13, the resultant products were
a mixture of Bi (01-085-1329) and Sb6O13 (01-071-1091), probably
due to a redox reaction between Sb2O3 and Bi(NO3)3. When the
pH value was 9, a mixture of Sb2O3 (00-011-0689) and Bi2O3 (00-
027-0053, 01-077-0374) was obtained. This indicates that at this
pH, Sb2O3 is not able to reduce Bi(NO3)3 to form Bi. Instead,
the direct hydrolysis of Bi(NO3)3 to form Bi2O3 occurred at this
pH. The phase of BiSbO4 started to appear when the reaction pH
was lower than 7 and pure BiSbO4 was obtained at pH values in
the region of 1–3. The XRD patterns of BiSbO4 samples prepared
at pH = 1 and 3 show that the peaks are wide, indicating that the
average crystallite size of the BiSbO4(Hy) samples is small.
as Sb5+ in the as-prepared BiSbO4(Hy)
.
The XPS results indicate that the formation of monoclinic
BiSbO4 from Sb2O3 under hydrothermal conditions involves an
oxidation of antimony from the chemical valence of +3 to +5. To
elucidate how this redox reaction occurred, a series of controlled
reactions were carried out. BiCl3, ammonium bismuth citrate
and another bismuth nitrate Bi5O(OH)9(NO3)4 were used as Bi
containing precursors to react with Sb2O3 under hydrothermal
conditions. Only the combinations of Sb2O3 and Bi5O(OH)9(NO3)4
led to the formation of BiSbO4. This result implies that the
-
NO3 ion plays an important role in the oxidation of Sb2O3,
leading to the formation of BiSbO4. Precursor Sb2O3 is also
found to be indispensable for the formation of BiSbO4. All the
reactions carried out between Sb2O5 or Sb(Ac)3 and bismuth
containing precursors like Bi(NO3)3, Bi5O(OH)9(NO3)4, BiCl3
or ammonium bismuth citrate only led to bismuth oxide or
oxychloride (Bi2O3, BiOCl etc.) and antimony oxides Sb6O13,
instead of binary metal oxide BiSbO4. The products obtained
with different combinations of the precursors were summarized
in Table 1 and the corresponding XRD patterns were shown in
supporting materials Fig. S3–S10.†
These observations indicate that it is not possible to obtain
mixed metal oxide BiSbO4 directly from Bi3+ and Sb5+ under
normal hydrothermal conditions, probably due to the low co-
ordination capability of Sb5+ ion and the high hydrolysis of
Bi3+ ion. However, by using Bi(NO3)3 and Sb2O3 as the starting
Fig. 1 XRD patterns of BiSbO4(Hy) samples prepared at 180 ◦C for 48 h
-
with different pH values, ( )Bi; (᭜)Sb O (01-071-1091); (ꢀ) Sb2O3; (↓)
materials, the occurrence of a redox reaction between NO3 and
᭹
6
13
Bi2O3 (00-027-0053); (*) Bi2O3 (01-077-0374).
Sb2O3 may make the formation of BiSbO4 possible. It is proposed
that a Bi–Sb polymeric intermediate complex may form during
the reaction. This assumption is confirmed by comparing the
IR spectra of the starting Bi(NO3)3 and the mixture of Sb2O3
and Bi(NO3)3 (supporting materials Fig. S11†). The peaks at ca.
XPS was carried out on the as-prepared BiSbO4(Hy) to determine
the oxidation state of the elements present. The data were treated
according to Huang et al. and the results were shown in Fig. 2.23
Fig. 2 High-resolution XPS spectra of BiSbO4(Hy): (a) Bi 4f and (b) Sb 3d.
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Table 1 Summary of the products obtained with different combinations of the precursors
Bi source
Sb source
Sb2O3
pH value
Products
BiSbO4
Bi(NO3)3·5H2O
1–3
5–7
9
BiSbO4, other unidentified products
Sb2O3, Bi2O3
13
Bi, Sb6O13
Sb2O5
Sb(Ac)3
1–13
5,7,9
1,3,11,13
1
Sb6O13, Bi6O6(OH)3(NO3)3·1.5H2O
Bi2O3
Bi, Bi2O3
BiSbO4
Bi5O(OH)9(NO3)4
Sb2O3
5
7
9
13
BiSbO4, Bi6O6(OH)3(NO3)3·1.5H2O
Sb2O3, Bi6O6(OH)3(NO3)3·1.5H2O
Sb2O3, Sb2O5·H2O
Sb2O3, Bi2O3
Sb2O5
1–11
13
Sb6O13, Bi6O6(OH)3(NO3)3·1.5H2O
Bi2O3, Sb6O13
BiCl3
Sb2O3
Sb2O5
1–9
1–9
BiOCl, Sb6O13, Sb2O3, Bi
BiOCl, Sb6O13, Bi2O3
Bi6O4(OH)4(ClO4)6(H2O)7
Sb2O3, Bi2O3
Ammonium bismuth citrate
Sb2O3
1
3–7
9
11
13
1
3–9
11
13
Sb2O3, Bi2O3
Sb2O3, Bi2O3, Bi2O2CO3
Sb2O3, Bi2O2CO3
BiO2-x, Sb2O3, Bi2O3
Sb6O13, Bi2O2CO3, Bi2O3, Sb2O4.4(OH)1.2
Sb6O13, Bi2O2CO3
BiO2-x, Sb6O13, Bi2O2CO3, Bi6O7
BiO2-x, Sb6O13
Sb2O5
1471 cm-1 and 1280 cm-1 which correspond to coordinated NO3
-
in Bi(NO3)3 shift.31 A new peak at ca. 1385 cm-1 can be observed
on the FT–IR spectrum of the mixture of Sb2O3 and Bi(NO3)3,
-
which indicates that the coordination mode of NO3 has been
significantly changed and the possible formation of the Bi–Sb
polymeric complex. Although the identity of this Bi–Sb polymeric
intermediate complex can not be determined, it surely plays an
important role in the formation of BiSbO4.
3.2. Characterizations
◦
A typical SEM image of BiSbO4(Hy) prepared at 180 C for 48 h
with pH = 1 was shown in Fig. 3a. It shows that the as-prepared
BiSbO4(Hy) consists of bundle-like aggregates in the range of 0.3–
0.5 mm. These bundle-like aggregates are composed of very thin
nanoplates with irregular shapes as observed in the TEM image
(Fig. 3b). The selected area electron diffraction shows the single
crystal nature of each thin nanoplate (Fig. 3d). The HRTEM image
shows clear lattice fringes and the fringe of d = 0.244 nm matches
that of the (020) plane of BiSbO4(Hy) (Fig. 3c).
Fig. 3 Images of BiSbO4(Hy) (a) SEM; (b) TEM; (c) HRTEM; (d) selected
area electron diffraction.
The N2-sorption isotherm for BiSbO4(Hy) nanoplates is shown
in Fig. 4. It exhibits a stepwise adsorption and desorption, which
belongs to the type-IV isotherm. The BET specific surface area
can be determined to be 18.3 m2 g-1, which is about 5 times higher
than that prepared via the solid state reaction (3 m2 g-1). This
demonstrates that the hydrothermal method is an effective method
for the preparation of nanocrystalline multiplex metal oxides with
high specific surface area. The average pore size for BiSbO4(Hy) is
4.0 nm with a narrow distribution of pore size (Fig. 4 inset).
The UV-vis DRS spectrum of BiSbO4(Hy) was shown in Fig. 5a.
By defining the absorption edge, l, as the intercept on the
wavelength axis for a tangent line drawn on absorption spectrum,
This absorption edge corresponding to a band gap energy of
about 3.5 eV, indicates that BiSbO4(Hy) is only responsive to UV
light. This result is different from that reported previously by Lin
et al. which showed that BiSbO4 prepared by a conventional solid
state reaction has a band gap of 2.75 eV. To make this clear,
we also prepared BiSbO4 following the method reported by Lin
et al. (denoted as BiSbO4(SSR)).15 The as-prepared BiSbO4(SSR) also
shows absorption in the visible light region. However, a careful
comparison of the UV-DRS of BiSbO4(SSR) and BiSbO4(Hy) reveals
that the absorption of BiSbO4(SSR) actually can be de-convoluted
to two absorption bands (Fig. 5a). The first absorption is almost
an absorption edge of ca. 354 nm was determined for BiSbO4(Hy)
.
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the XRD pattern of BiSbO4(SSR) (Fig. 5d). The result from the
hydrothermally prepared BiSbO4 clarifies that BiSbO4 is indeed
UV light responsive, in contrast to the previous literature.
3.3. Photocatalytic activity
The photocatalytic degradations of benzene and 4-CP were chosen
as model reactions to study the photocatalytic performance of
BiSbO4(Hy). The photocatalytic activity for benzene degradation
over BiSbO4(Hy) was carried out under 254 nm UV illuminations.
The conversion of benzene over BiSbO4(Hy), BiSbO4(SSR) and P25
and the amount of the produced CO2 as a function of illumination
time are shown in Fig. 6a and 6b respectively. Consistent with
the previous report, P25 was deactivated quickly when the feed
gas does not contain sufficient H2O and only a small amount of
CO2 (ca. 20 ppm) was produced. For BiSbO4(Hy), the conversion
of benzene can be maintained at almost 25% for more than 16 h,
and more than 300 ppm CO2 was produced, corresponding to a
Fig. 4 Nitrogen adsorption–desorption isotherms and the pore size
distribution plot for BiSbO4(Hy). The pore size distribution was estimated
from the desorption branch of the isotherm.
high mineralization ratio of about 83%. However, for BiSbO4(SSR)
,
due to its low BET specific surface area, the conversion ratio
was only 17% and about 180 ppm of CO2 was produced. It is
obvious that a higher conversion and mineralization ratio for
the degradation of benzene can be achieved over BiSbO4(Hy) as
similar to that observed for BiSbO4(Hy), while the second one
extends to the visible light region. Since the HRTEM image
of BiSbO4(SSR) shows lattice fringes of d = 0.324 nm and d =
0.418 nm, which corresponds to (310) and (211) crystallographic
planes of Bi2O3 (Fig. 5c), we tend to think that the second
absorption extending to the visible light region may be induced
by Bi2O3 as an impurity in BiSbO4(SSR). However, due to the small
amount of the impurity, no Bi2O3 impurity phase is observed in
compared to BiSbO4(SSR)
.
BiSbO4(Hy) also showed superior photocatalytic activity for the
degradation of 4-CP. Temporal evolutions of the HPLC graphs
over BiSbO4(Hy), BiSbO4(SSR) and a direct photolysis are shown in
supporting materials Fig. S12, Fig. S13 and Fig. S14 respectively.†
Fig. 5 (a) Diffuse reflectance absorption spectra of BiSbO4(Hy) and BiSbO4(SSR); (b) TEM image of BiSbO4(SSR); (c) HRTEM image of BiSbO4(SSR); (d)
XRD patterns of BiSbO4(Hy) and BiSbO4(SSR)
.
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Fig. 6 (a) The conversion of C6H6 over the BiSbO4(Hy) as a function of reaction time, with P25 and BiSbO4(SSR) as references. (ꢀ), (᭡) and ( ) are the
᭹
conversions of C6H6 over the BiSbO4(Hy), P25 and BiSbO4(SSR), respectively; (b) The amount of produced CO2 over the BiSbO4(Hy) as a function of reaction
time, with P25 and BiSbO4(SSR) as references. (ꢁ), (ꢀ) and ( ) are the amounts of produced CO2 over the BiSbO4(Hy), P25 and BiSbO4(SSR), respectively.
᭺
In Fig. S12,† peak a with retention time of 6.5 min is attributed
to the initial 4-CP, while peak b with the retention time at 2.5
is attributed to the intermediate, hydroquinone (HQ). It can be
observed that a total conversion of 4-CP over BiSbO4(Hy) can be
achieved after irradiation for 1.5 h. The peak corresponding to
the intermediate (HQ) appeared right after the irradiations and
its concentration reached a maximum value when irradiated for
1 h. This indicated that the first step of the degradation of 4-
CP over BiSbO4(Hy) is dechlorination, leading to HQ as the main
intermediate. The existence of Cl- in the solution was detected
in the very beginning of the photocatalytic reaction by the ion
chromatograph measurement. The intensity of peak b started to
decrease after 1 h of irradiation and after irradiation for 5 h peak
b totally disappeared, indicating that the intermediate HQ can
be further degraded over BiSbO4(Hy). The TOC of the solution
changed from the original 20.37 mg L-1 to 4.95 mg L-1 after 5 h
irradiations (Fig. 7 inset). Although the dechlorination of 4-CP
can also be completed in 2 h over the irradiated BiSbO4(SSR), the
Fig. 7 Temporal changes of 4-CP concentration as monitored by HPLC
over ( ) BiSbO4(Hy), (ꢀ) BiSbO4(SSR) and (᭡) the direct photolysis. (Inset:
᭹
The TOC changes with the irradiations time in the presence of BiSbO4(Hy)
BiSbO4(SSR) and direct photolysis).
,
main intermediates involved are not the same as that of BiSbO4(Hy)
.
Besides HQ (peak b), a peak with retention time at 1.4 (peak c),
which can be attributed to hyroxyhydroquinone (HHQ), appeared
during the photocatalytic reaction over BiSbO4(SSR) (supporting
materials Fig. S13†). Moreover, the further destruction of these
4. Conclusions
In summary, hydrothermal reaction between Sb2O3 and Bi(NO3)3
is an effective method for the preparation of BiSbO4 with a large
intermediates was much slower in BiSbO4(SSR) than over BiSbO4(Hy)
.
After 5 h of photocatalytic reaction, the solution still maintained
a high TOC level (18.64 mg L-1) (Fig. 7 inset). In the case of
direct photolysis, varied intermediates were formed and they were
resistant to a further UV photolysis (supporting materials Fig.
S14†). Besides this, the TOC of the solution after photolysis for
5 h was almost the same as the original one. Temporal changes of
4-CP concentration and TOC over BiSbO4(Hy), BiSbO4(SSR) and the
direct photolysis are shown in Fig. 7.
The photocatalytic results clearly reveal that the photocatalytic
activity of BiSbO4(Hy) is superior to that of BiSbO4(SSR). The higher
photocatalytic performance observed over BiSbO4(Hy) is ascribed
to its higher specific surface area, which favors its adsorption for
organic pollutants. Our results demonstrate that the hydrothermal
method is a facile and effective method in the preparation of high
efficient BiSbO4 photocatalyst.
-
specific surface area. A redox reaction between NO3 and Sb2O3
has been found to be pivotal in the formation of nanocrystalline
BiSbO4. Our result clarifies that BiSbO4 is indeed UV light
responsive, instead of a visible light photocatalyst as reported
previously. BiSbO4 nanoplates prepared via the hydrothermal
method showed superior photocatalytic performance for the
degradations of benzene and 4-chlorophenol (4-CP) as compared
to BiSbO4(SSR) and P25. BiSbO4 nanoplates can be a promising
photocatalyst in the treatment of environmental pollution.
Acknowledgements
The work was supported by National Natural Science Foundation
of China (20977016), National Basic Research Program of China
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 5774–5780 | 5779
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(973 Program: 2007CB613306) and Program for Changjiang
Scholars and Innovative Research Team in University (PC-
SIRT0818). This work is also supported by fund of Fujian
Provincial Key Laboratory of Nanomaterials (NM10-01). The
NSF of Fujian province for Distinguished Young Investigator
Grant (2009J06004) for Z. Li is also acknowledged.
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