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Can. J. Chem. Vol. 83, 2005
splitting. However, there is a demand for a highly efficient
photocatalyst for the photoproduction of hydrogen. In the
development of efficient photocatalyst materials, it is essen-
tial to control the band structure of the photocatalyst.
The approach for the design of the photocatalyst is classi-
fied in three ways. Approach (a) is the doping of foreign
transition elements into active, existing photocatalysts (3–6).
Especially, Ni- and Cu-doped ZnS photocatalysts show ac-
tivity for H2 evolution under visible-light irradiation even
without a Pt catalyst. Many researchers have reported the
doping methods for CdS, ZnS, VS, VS4, and WO3 (7–12).
Approach (b) is to find materials that have a stable valence
band in a more negative position than the valence band of
conventional metal-oxide photocatalysts. The nitrides
(Ta3N5), oxynitrides (TaON, LaTiO2N), and oxysulfides
(Sm2Ti2S2O5) (13–18) have been reported as active
photocatalysts. Approach (c) involves a control of the energy
structure by making solid solutions between semiconductor
photocatalysts with wide and narrow band gaps. The
photophysical properties and photovoltaic efficiencies of
Nb2O5-Bi2O3, Ga2O3-In2O3, SrNb2O7, Sr2Ta2O7, SnO2-TiO2,
ZnS-CdS, CdS-CdSe, and (AgIn)xZn2(1–x)S2 (19–23) have
been studied extensively. Several nanocrystalline photo-
catalysts have been reviewed by Beydoun et al. (24), where
he described the effect of nanoparticles on photocatalytic ac-
tivity. Recently, CdS-TiO2 nanocomposite film (25) has been
used for the photodecomposition of H2S. The stable and
suitable metal-oxide support is lacking in this work. In the
past, the research for the photodecomposition of H2S was fo-
cused on sulfide semiconductor photocatalysts, which are
unstable because of photocorrosion of the catalyst. So, there
is a need to find a stable, economical, and efficient new
metal-oxide photocatalyst for hydrogen production.
Characterization
Powder X-ray diffractograms were recorded with a Model
Rigaku-D/MaX-2200V X-ray diffractometer with Cu Kα ra-
diation and an Ni filter. The surface morphology and particle
size were determined using a field emission scanning elec-
tron microscope (FESEM Model JEOL-JSM6700F). Spec-
troscopic study of the catalyst was carried out using a
UV–vis (Model SHIMADZU UV-2450 diffuse reflectance
mode) spectrophotometer and a Fourier Transform Infrared
Spectrophotometer (Model, JASCO 610-FTIR). Specific
surface area measurements were performed using a BET
Surface Area Analyzer (Model BET-MICROMERITICS
ASAP-2400).
Photodecomposition of H2S
The photocatalyst was introduced as a suspension into a
cylindrical pyrex photochemical reactor with a water-cooled
quartz immersion well and a thermostated water-jacket. A
high-pressure mercury lamp (Hanovia) source of intensity
450 W with pyrex cut-off filter was used. At a constant tem-
perature of 25 1 °C, the vigorously stirred suspension was
purged with argon for 1 h, and then hydrogen sulfide (H2S)
was bubbled through the solution for about 1 h.
Each experiment was carried out using 1 g of catalyst in
500 mL of distilled water with an H2S flow of 10 mL/min.
The excess hydrogen sulfide was trapped in an NaOH solu-
tion. The amount of evolved hydrogen was measured using a
graduated gas burette and gas chromatograph (Model
Shimadzu GC-14B, MS-5A column, TCD, Ar carrier).
Results and discussion
In view of this, we have investigated a novel photo-
catalyst, ZnBiVO4, for the photodecomposition of H2S for
the first time. We investigated the synthesis of this catalyst
by both the solid-state and the solution route. The tentative
structural and morphological study was carried out using
XRD and FESEM. The nanosize ZnBiVO4 was obtained us-
ing the solution route. The influence of the preparation
method on the activity of the photocatalyst was demon-
strated. This paper describes the novelty in the synthesis of
this new product, its characterization, and its photocatalytic
activity.
Synthesis by the solid-state method: ZnBiVO4 (s-s)
ZnBiVO4 has been synthesized for the first time using the
solid-state route. According to the thermodynamics and the
phase diagrams of the individual components (i.e., ZnO,
Bi2O3, and V2O3), the reaction temperature was expected to
be 1000 °C. Since the phase diagram of the V2O3 compo-
nent system was not available in the literature, assumptions
were made with the help of the V2O5 data. The solid solu-
tion was homogenized for 15 h in an alumina crucible at
650 °C, and the compound formed from the reactant compo-
nents at 670 °C on calcination. The product obtained was
crushed, homogenized in mortar, and finally recalcined at
725 °C for 12 h to obtain ZnBiVO4 with good crystallinity.
The composition of the final product was verified using
XRD and EDS analysis. The presence of the VO4 group was
confirmed by IR spectroscopy. No weight loss or gain after
reaction suggested that the stoichiometry of the product was
retained.
Experimental section
Materials
To prepare ZnBiVO4 by the solid-state reaction, a
stoichiometric (1:0.5:0.5) mixture of ZnO, Bi2O3, and V2O3
was thoroughly ground in a mortar, and this homogeneous
reaction mixture was then calcined at 670 °C for 24 h in
static air and recalcined at 725 °C for 12 h. To prepare
ZnBiVO4 by the solution route, a stoichiometric amount of
Zn(NO3)2·5H2O, Bi(NO3)3·6H2O, and ammonium metavan-
adate (NH4VO3) was dissolved in water and heated slowly at
70 °C until evaporation. The powder obtained was calcined
at 180 °C for 12 h. The resulting product was washed sev-
eral times with water and ethanol and then dried at 120 °C
for 5 h.
Synthesis by the solution route: ZnBiVO4 (sol)
Zinc nitrate, bismuth nitrate, and ammonium metavana-
date were taken in stoichiometric quantities in aqueous me-
dium and evaporated slowly at 70 °C until dryness. The
dried powder was crushed, homogenized, and calcined at
180 °C for 12 h. Ammonium vanadate is soluble in water
and forms H3VO4 as per the following reaction:
[1]
H2O + NH4VO3 → NH3 + H3VO4
© 2005 NRC Canada