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As a result of the encouraging properties of hierarchical
nanostructures, research has recently been focused on the
fabrication of controlled size and shaped hierarchically
assembled nanostructures. Many researchers have studied
various morphologies, such as nanotubes, nanoparticles,20
nanowires,21,22 nanorod bundles and dandelion-like nano-
structures,23 and urchin-like nanospheres24 using various
methods of synthesis. However, the use of nanostructured Bi2S3
as a photocatalyst for the generation of hydrogen from the
splitting of H2S under visible light has not been studied in
detail. More signicantly, the effect of Bi2S3 nanostructures on
its photocatalytic activity in sunlight has not been thoroughly
investigated. In view of this, we synthesized Bi2S3 nano-
structures (nanorods/hierarchical nanostructures) and studied
their photocatalytic activity.
2.3. Photo-responsive properties
The experimental setup for the measurements of the photo-
responsive properties of the Bi2S3 nanostructures in given in the
ESI.† A photo-responsive device was built using the as-synthe-
sized Bi2S3 hierarchical microstructures following the device
conguration shown in Fig. SI 1.† The ITO substrate with an
area of 1 Â 2 cm2 was etched by dilute HF in an area of
dimensions 0.2 Â 1 cm2 and the ITO lm was then divided in
two parts, which acted as duel electrodes (see Fig. SI 1†). A
white-light LED lamp (8 mW mÀ2) was used as the illumination
source and a bias voltage (typically 20 mV) was applied on the
ITO electrode.
2.4. Photocatalytic study for H2S splitting
Herein, the photo-cleavage of waste H2S to H2 under normal
sunlight using a Bi2S3 semiconductor photocatalyst is reported.
The effect of Bi2S3nanostructures, such as nanorods and hier-
archical nanostructures on the production of hydrogen and its
mechanism of action has been investigated. The evolution of
hydrogen via water splitting was also investigated using these
nanostructures. The structural and optical study of these
nanostructures have also been reported.
The cylindrical quartz photochemical thermostatic reactor was
lled with 700 mL of 0.5 M aqueous KOH and purged with Ar for
1 h. H2S was bubbled through the solution at a rate of 2.5 mL
minÀ1 at 298 K. H2S was continuously fed into the system
during the photo-reduction. Bi2S3 was introduced into the
reactor and irradiated with normal solar light with constant
stirring. The excess H2S was trapped in the NaOH solution. The
amount of hydrogen evolved was measured using a graduated
gas burette. The experimental setup for measuring hydrogen
production from H2S under sunlight is shown in ESI II.†
2. Experimental
2.1. Material synthesis
2.5. Photocatalytic study of splitting of H2O
All the reactants and solvents were of analytical-reagent grade
and purchased from a reputable rm. The Bi2S3 nanostructures
were prepared by dissolving 2 mmol of Bi(NO)3$5H2O and 8
mmol of thiourea (TU) in 80 mL of aqueous solvent [1 : 3 water–
ethylene glycol (EG)]. Aer stirring for 1 h, the solution was
transferred into a 100 mL Teon-lined stainless-steel autoclave.
To evaluate the photocatalytic activity for the generation of
hydrogen from the splitting of water, a xenon lamp (l $ 430 nm)
was used as the source of visible light. The photocatalyst was
suspended in a quartz photochemical reactor with a water-
cooled quartz immersion well and a water jacket with a ther-
mostat. A high-pressure xenon lamp source (300 W) with a
cutoff lter was used. The reactor containing the catalyst with
the sacricial agents Na2S and Na2SO3 was vigorously stirred at
a constant temperature and purged with Ar for 30 min. Each
experiment was carried out using 0.5 g of catalyst in 100 mL of
solution. The amount of hydrogen evolved was determined by
gas chromatography (Nucon Model 5765, India).
ꢀ
The system was then sealed and placed in an oven at 150 C.
Aer reaction, the system was naturally cooled to room
temperature and the black precipitate obtained was ltered and
washed several times with water and ethanol. The product was
dried at 80 ꢀC and used for further characterization. Sample S1
was synthesized in water with a reaction time of 24 h. Samples
S2 and S3 were synthesized in water–EG (1 : 3) with reaction
times of 24 and 30 h, respectively.
3. Results and discussion
2.2. Characterization
Fig. 1 shows the XRD pattern of the Bi2S3 samples synthesized
The structural investigation was carried out using an X-ray in: water medium, 24 h (S1); water–EG (1 : 3), 24 h (S2); and
diffractometer (Model-D8, Advance and Bruker AXS). The water–EG (1 : 3), 30 h (S3). All the diffraction peaks match the
morphology was observed by FESEM (JEOL, IIT Roorkee and standard JCPDS data (no. 060333). All the planes were indexed,
Hitachi S-4800). The morphology and crystal size were also indicating a pure orthorhombic phase of Bi2S3, and they were all
conrmed by transmission electron microscopy (FEI-Technai). equally crystalline.
The optical study was performed using a UV-visible spectrom-
The optical properties of the samples were investigated by
eter (Model-Lambda-950, PerkinElmer). The photo- UV-visible diffused reectance spectrometry (DRS). Fig. 2 shows
luminescence of the synthesized material was recorded on a the UV-DRS spectrum of Bi2S3 synthesized by the solvothermal
Horiba Fluorolog 3 spectrouorometer. The single-point BET method using different solvents. The direct band gap of the S1,
surface area was measured using a Quantachrome instrument. S2 and S3 samples of Bi2S3 was observed to be at 1.42, 1.48 and
The variation in current was measured using an electrometer 1.45 eV, respectively which is higher than the bulk sample (1.3
workstation (Keithley Electrometer, 6517B) with light eV).11–13 The blue shi in the band gap energy was observed as a
illumination.
result of the nanocrystalline nature of the samples.
49296 | RSC Adv., 2014, 4, 49295–49302
This journal is © The Royal Society of Chemistry 2014
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