Template free architecture of hierarchical nanostructured ZnIn2S4 rose-like flowers for solar hydrogen production

Article abstract of DOI:10.1166/jnn.2017.12718

We have demonstrated the controlled synthesis of hierarchical nanostructured ZnIn₂S₄ using a facile template free hydrothermal/solvothermal method. The effect of solvents on the morphology and microstructure of ZnIn₂S₄ has been studied by using water, methanol and ethylene glycol as a solvents. The hierarchical nanostructure, i.e., rose-like morphology composed of very thin (5-6 nm) nanoplates of length ～1 μm which was obtained in aqueous mediated ZnIn₂S₄. The porous structure (distorted flowers) and agglomerated nanoparticles were obtained using methanol- and ethylene glycol-mediated ZnIn₂S₄. Considering the band gap in the visible region, ZnIn₂S₄ is used as a solar light driven photocatalyst. An ecofriendly photocatalytic process for the conversion of poisonous H₂S into H₂ which is a green unconventional energy source has been demonstrated. The nanostructured ZnIn₂S₄ is employed as a photocatalyst for hydrogen production from H₂S via a solar light-driven eco-friendly approach. The stable photocatalytic activity of hydrogen evolution, i.e., 3964 μmol h^-1 was obtained using 0.5 gm of such hierarchical nanostructured ZnIn₂S₄ under visible light irradiation. The unique hierarchical nanostructured ZnIn₂S₄ ternary semiconductor having hexagonal layer is expected to have potential applications in solar cells, LEDs, charge storage, electrochemical recording, thermoelectricity, other prospective electronic and optical devices.

Full text of DOI:10.1166/jnn.2017.12718

Article
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Nanoscience and Nanotechnology
Vol. 17, 1447–1454, 2017
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Printed in the United States of America
Template Free Architecture of Hierarchical
Nanostructured ZnIn2S4 Rose-Like Flowers for
Solar Hydrogen Production
Bharat B. Kale1ꢀ∗, Ashwini P. Bhirud1, Jin-Ook Baeg2ꢀ∗, and Milind V. Kulkarni1
1Centre for Materials for Electronic Technology, Panchawati, Off Pashan Road, Pune 411008, India
2Division of Green Chemistry and Engineering Research, Korea Research Institute of Chemical Technology,
100 Jang-dong, Yuseong, Daejon, 305-600, Republic of Korea
We have demonstrated the controlled synthesis of hierarchical nanostructured ZnIn2S4 using a
facile template free hydrothermal/solvothermal method. The effect of solvents on the morphology
and microstructure of ZnIn2S4 has been studied by using water, methanol and ethylene glycol
as a solvents. The hierarchical nanostructure, i.e., rose-like morphology composed of very thin
(5–6 nm) nanoplates of length ∼1 ꢀm which was obtained in aqueous mediated ZnIn2S4. The
porous structure (distorted flowers) and agglomerated nanoparticles were obtained using methanol-
and ethylene glycol-mediated ZnIn2S4. Considering the band gap in the visible region, ZnIn2S4 is
used as a solar light driven photocatalyst. An ecofriendly photocatalytic process for the conversion
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of poisonous H2S into H2 which is a green unconventional energy source has been demonstrated.
IP: 46.161.59.116 On: Mon, 15 Jan 2018 10:50:15
The nanostructured ZnIn S is employed as a photocatalyst for hydrogen production from H S via
Copyright: American Scientific Publishers
2
4
2
a solar light-driven eco-friendly approach. The stable photocatalytic activity of hydrogen evolution,
i.e., 3964 ꢀmol h−1 was obtained using 0.5 gm of such hierarchical nanostructured ZnIn2S4 under
visible light irradiation. The unique hierarchical nanostructured ZnIn2S4 ternary semiconductor hav-
ing hexagonal layer is expected to have potential applications in solar cells, LEDs, charge storage,
electrochemical recording, thermoelectricity, other prospective electronic and optical devices.
Keywords: ZnIn2S4, Hydrothermal, Solvothermal, Rose-Like Flowers, H2 Generation.
1. INTRODUCTION
is a high-fuel-value, high-efficiency, long-term storage
and clean energy.3 However, current hydrogen produc-
tion mainly relies on the reformation of coal and natu-
ral gas,4 which will definitely increase the consumption
of non-renewable energy resources and cause environmen-
tal pollution problems. Thus, establishing a photochemical
system as an alternative energy resource is very important
and is also a fundamental method to solve energy and envi-
ronmental problems.5 Among the various routes for hydro-
gen production, the photodecomposition of water using
semiconductor photocatalysts has attracted much attention
due to economics the cost and environmental issues. Apart
from water, H2S could become an alternative source of
hydrogen as H2S splitting requires less energy compared
with the photocatalytic decomposition of water. Emission
of huge amounts of H2S (10–25%) from oil refineries is a
global threat to the environment. The acidic and gaseous
hydrogen sulphide (H2S) is an environmental pollutant
The nanostructured semiconductors have immense impor-
tance due to their size and dependent properties. These
properties have been wisely utilized in the advance
applications like solar cells, batteries, photocatalysis and
optoelectronic.1 In the context of photocatalyst, nanos-
tructured semiconductors and especially hierarchical nano-
structures are playing key role in the drastic enhancement
in the efficiency due to control on recombination of photo
generated charge carriers. Hence, we focused the use of
such hierarchical nanostructures as a visible light active
photocatalyst for hydrogen production.
Research on new energy systems based on clean,
renewable energy sources has attracted considerable atten-
tion owing to the energy crisis and environmental pol-
lution caused by fossil fuel consumption.2 Hydrogen
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2017.12718
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Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
Kale et al.
because of its toxic, malodorous and corrosive nature.
Every year, millions of tons of H2S is produced around
the world from oil-refinery plants or natural-gas extraction,
which is predicted to increase in the future. Due to such
environmental problems and consequent harmful effects to
the human life decomposition of H2S to a green product
has attracted attention throughout the world.
Currently, the conventional Claus process is the most
popular technique used for H2S decomposition. H2S gener-
ated is used to produce elemental sulphur and water along
with SO2 to some extent.6 This process is not an eco-
nomically viable process as the chemicals used here are
expensive in nature and also it creates further acute envi-
ronmental problems as large amounts of untreated H2S are
released into the atmosphere.6b Therefore, scientific com-
munity all over the world is actively engaged working on
this area of conversion of H2S to H2 under ecofriendly
condition. In this context, photocleavage of H2S to H2 by a
semiconductor-particle photocatalyst has been considered
to convert solar energy into fuel. Hydrogen being a clean
and green fuel, its production of cheap hydrogen has great
significance.
and potential applications. Up till now, various shapes of
ZnIn2S4 nanostructures, such as nano-crystals, nanosheets
and microspheres consisting of flakes have been suc-
cessfully fabricated by a variety of chemical or physical
approaches.14
In our previous report, we described the synthesis of
ZnIn2S4 by triethylamine-assisted hydrothermal method
for hydrogen generation.15 Herein, we delineate the syn-
thesis of hexagonal ZnIn2S4 in different solvent-mediated
conditions via a hydrothermal/solvothermal method. The
effects of solvents on the morphology, crystallinity and
photocatalytic activity of ZnIn2S4 have also been studied.
2. EXPERIMENTAL DETAILS
2.1. Synthesis
A stoichiometric amount of Zn(NO3ꢁ2 · 6H2O, In(NO3ꢁ3 ·
5H2O and double excess thiourea were dissolved in water
or methanol or ethylene glycol for different products. The
mixed solution was then transferred into a Teflon-lined
stainless steel autoclave of 200 ml capacity. The autoclave
was filled with double-distilled watꢀer up to 80% of its vol-
ume and then maintained at 140 C for 72 h. A yellow
precipitate thus obtained was then washed with ethanol and
dried at 70 ꢀC. Herein ZnIn2S4 is synthesized in aqueous-,
methanol- and ethylene glycol-mediated conditions which
are labeled as Z1, Z2 and Z3 respectively.
In the context of photocatalysis, researchers are actively
involved in the development of visible light active photo-
catalysts for hydrogen generation from H2O. A number of
oxide semiconductors7 were reported as photocatalysts for
hydrogen production via water splitting. But these oxide
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semiconductors have a wide band gap and they show activ-
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ity under UV light (ꢀ < 389 nm), which is only 5% of
2.2. Characterization Techniques
Copyright: American Scientific Publishers
the solar spectrum falling on the Earth’s surface.8 Many
researchers are reported the visible light-active photocata-
lysts such as CdS, CuS, In2S3, Bi2S3/CdS, but their stabil-
ity and activity were observed to be very poor.9 Hence, it is
necessary to develop stable and active visible light photo-
catalysts capable of utilizing large amounts of energy from
the solar spectrum for various purposes. Binary sulphide
photocatalysts having a narrow band gap with valence
bands at relatively negative potentials compared to the
oxides can act as good photocatalysts under visible light.
But these sulphides easily undergo photocorrosion because
photogenerated holes oxidize the photocatalyst itself. This
problem of photocorrosion can be solved by incorpora-
tion of metal sulphides into the interlayer.10 However, such
stable catalysts showed very poor photocatalytic activ-
ity. Recently, a new class of multi-component sulphides
has also been reported which show high photocatalytic
efficiency.11
As an important II–III2–VI4 semiconductor, ZnIn2S4
has attracted increasing attention due to its considerable
chemical stability, environmental benign and suitable band
gap for visible light response.12 ZnIn2S4 has also been
found with great potential applications in different fields,
such as thermoelectricity, photoconduction, charge stor-
age, photocatalysis, hydrogen production and solar cell.13
Therefore, great effort has been made to prepare novel
ZnIn2S4 nanostructures and investigate their properties
The structural study of the as synthesized products
(Z1–Z3) was performed using X-ray Diffractometer
(XRD-D8, Advance, Bruker-AXS). The morphological
study of the samples was performed using Field Emis-
sion Scanning Electron Microscopy (FESEM) technique
(Hitachi, S-4800) and High-Resolution Transmission Elec-
tron Microscope (HRTEM, JEOL 2010F) with an acceler-
ated voltage of 300 kV. The surface characterization of the
ZnIn2S4 was carried out using X-ray Photoelectron Spec-
troscopy (XPS, ESCA-3000, VG Scientific Ltd., England).
The UV-Visible Diffuse Reflectance Spectra (UV-DRS)
were recorded on a Lambda 950 Perkin Elmer spectropho-
tometer within the wavelength range of 200–800 nm.
2.3. Photocatalytic Study
The photocatalytic reactions were carried out in a cylindri-
cal quartz photochemical reactor. Reactor has arrangement
for circulation of water to maintain the constant tempera-
ture throughout the reaction time. A 300 W Xe lamp light
(LOT ORIEL GRUPPE, EUROPA, LSH302) with 420 nm
cut off filter (≥420 nm). Known quantity of photocatalyst
powder (0.5 gm) was dispersed in 700 ml KOH solution
(0.5 M) and suspension was homogenized by stirring it
using magnetic stirrer. The suspended catalyst was then
transferred into reactor followꢀed by purging with argon.
At a constant temperature (25 C), the suspended catalyst
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Kale et al.
Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
was flushed with argon gas for half an hour and then H2S
was bubbled through the solution at the rate of 1.6 ml/min
for 3 h. All the experiments were carried out under identi-
cal conditions. The excess hydrogen sulphide was trapped
into the trap containing NaOH solution. The suspension
was exposed to visible light for different time intervals.
The amount of hydrogen gas evolved was collected into a
graduated cylinder and measured. The evolved hydrogen
was then analyzed for its purity using a Gas Chromato-
graph (Model Shimadzu GC-14B, MS-5 Å column, TCD,
Ar carrier).
3. RESULTS AND DISCUSSION
3.1. XRD Analysis
Figure 1 depicts the XRD pattern of ZnIn2S4 samples
(a) aqueous (Z1), (b) methanol (Z2), (c) ethylene gly-
col (Z3) mediated conditions, respectively. The XRD
pattern confirms hexagonal crystal structure with lattice
parameter a = 3.85 Å, c = 24.68 Å and is in good agree-
ment with JCPDS data (ICDD-JCPDS card No. 72-0773).
No other impurities such as ZnS, In2S3, oxides or organic
compounds related to reactants were detected, indicating
the phase purity of ZnIn2S4.
Figure 2. Diffuse reflection spectra of ZnIn2S4 prepared in
(a) aqueous-(Z1), (b) methanol-(Z2) and (c) ethylene glycol-(Z3)
mediated conditions.
edge for the organic-mediated samples may be due to the
nanocrystalline nature of ZnIn2S4.16 The steep shape of the
visible edge and the strong absorption in the visible region
reveal that the absorption band of ZnIn2S4 is because of the
transition from the valence band to the conduction band11c
and is not due to the transition from the metal impurity
level to the conduction band, as observed for the metal
ion-doped semiconductors.17
3.2. UV-DRS Study
To investigate the possible influence of the size, shape
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of nano and macro-material on the optical properties,
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we measured the UV-Visible diffuse reflectance spectra
(UV-DRS). Figures 2(a–c) shows diffuse reflectance spec-
tra of aqueous (Z1), methanol (Z2) and ethylene gly-
col (Z3) mediated ZnIn2S4. All the samples show strong
steep absorption edge in the visible region. However, their
absorption edges are located at different wavelengths i.e.,
506 (Z1), 501 (Z2) and 494 nm (Z3), respectively. The
band gap of sample Z1 is 2.45 eV while the shift in the
band gap to 2.47 and 2.51 eV observed for samples Z2
and Z3, respectively. Such blue shift in the absorption
Copyright: American Scientific Publishers
3.3. FESEM Analysis
The morphology and size of the as-synthesized products
were investigated by FESEM technique. Figures 3(a, b)
shows the FESEM images of ZnIn2S4 obtained in aqueous
mediated condition (Z1) indicating formation of uniform
rose-like flowers composed of nanoplates originated from
well-organized plates. The size of the flower was observed
in the range of ∼1 ꢂm and thickness of the petal ∼5–6 nm.
The aspect ratio was observed to be extremely significant
due to lower thickness of the petal. It is found that the sol-
vent used in the synthetic system has significant influence
on the morphology of ZnIn2S4. Figures 3(c, d) shows the
FESEM images of ZnIn2S4 prepared in methanol-mediated
condition (Z2). The sample (Z2) shows the porous struc-
ture with 50–100 nm cavities. However, ethylene gly-
col mediated ZnIn2S4 shows agglomerated nanoparticles
(Figs. 3(e–f)) of size ∼20–30 nm.
3.4. TEM Analysis
The morphology and structure of the samples is confirmed
using TEM as shown in Figure 4. Highly thin and trans-
parent petals along with few curving petals are observed
in case of aqueous mediated ZnIn2S4. The thickness of the
petal might be in the range of 5–6 nm which we could
not measure exactly due to problem for mounting the sam-
ple, vertically (Figs. 4(a, b)). The SAED pattern (Fig. 4(c))
clearly demonstrates single crystalline nature of ZnIn2S4.
Figure 1. XRD patterns of ZnIn2S4 prepared in (a) aqueous-(Z1),
(b) methanol-(Z2) and (c) ethylene glycol-(Z3) mediated conditions.
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Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
Kale et al.
Especially, hydrothermal/solvothermal reactions are well
known for such pretty morphologies. Hence, the formation
of hexagonal ZnIn2S4 using zinc and indium precursors in
the presence of thiourea has significance with respect to
the creation of three dimensional structures. In the present
case, the reaction of the metal salt solutions and thiourea
conferred crystalline ZnIn2S4 particles under solvother-
mal/hydrothermal conditions is as per reaction (1).
The overall reaction for the formation of ZnIn2S4 is pre-
sented as follows:
ZnꢃNO3ꢁ2 +2InꢃNO3ꢁ2 +8ꢃNH2ꢁ2CS +16H2O
→ ZnIn2S4 +8HNO3 +8CO2 +16NH3 +4H2S (1)
Thiourea is stable in solution state at room tempera-
ture but decomposes slowly at higher temperature as per
reaction (2)
ꢃNH2ꢁ2CS → H2S+NH2CN
(2)
The reaction (1) is taking place through the decompo-
sition of thiourea as per reaction (2). The NH2CN formed
as per reaction (2) react with H2O at high temperature and
forms ammonia and carbon dioxide as per the following
reaction.
Figure 3. FESEM images of ZnIn2S4 prepared in (a, b) aqueous-(Z1),
(c, d) methanol-(Z2) and (e, f) ethylene glycol-(Z3) mediated conditions.
The ‘d’ values obtained from the pattern are in consistent
ꢃNH ꢁ CN → 2H O+NH +CO
(3)
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with XRD results and indexed as (108) plane of hexagonal
2
2
2
3
2
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ZnIn2S4.
During reaction at 150 ꢀC, ammonia concentration
increases along with H2S. The zinc and indium ions reacts
with H2S and form respective ZnIn2S4. The overall reac-
tion (1) is taking place at hydrothermal condition via reac-
tions (2) and (3). The proposed mechanism is based on
our experimental evidences.
Copyright: American Scientific Publishers
3.5. Reaction Mechanism
Formation of such typical three dimensional structures
are dependent on the experimental reaction conditions.
3.6. XPS Analysis
To study the surface nature of as-prepared ZnIn2S4 nano-
structures, the sample was characterized by X-ray pho-
toelectron spectroscopy (XPS). The single S2p peak
(Fig. 5(c)) at 161.8 eV is indicative of sulphur being
present as the sulphur ion. Both the In3d and Zn2p spec-
tra (Figs. 5(b and d), respectively) shows two peaks at
1021.8 eV and 1044.7 eV for the Zn2p3/2 and Zn2p1/2
,
445.2 eV and 452.8 eV for the In3d5/2 and In5d3/2
respectively. As it can be seen from the survey spectrum
(Fig. 5(a)) with peak identification, the oxygen peak at a
binding energy of 532.5 eV is due to the presence of H2O
absorbed on the sample surface and no obvious impuri-
ties, for example, In2O3 (O1S for In2O3: 529.80, 530.30
and 530.50 eV) can be detected. The molar ratio based on
the peak surface area was observed to be 1:2.3:4 (Zn:In:S)
which is very closely matching with the theoretical one.
From the elemental analyses (XPS) results, we can con-
clude that, the composition of ZnIn2S4 nanocrystals is
close to stoichiometric proportion of individual atoms.
Figure 4. TEM images of ZnIn2S4 prepared in (a–c) aqueous-mediated
conditions and (d) SAED pattern.
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Kale et al.
Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
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Copyright: American Scientific Publishers
Figure 5. XPS patterns of as synthesized ZnIn2S4 at 140 ꢀC for 72 h in aqueous medium (Z1) (a) survey spectrum and high-resolution spectra for
(b) In3d, (c) S2p, (d) Zn2p.
3.7. Formation Mechanism
3.8. Photocatalytic Activity
In aqueous medium, the ionization of Zinc nitrate and
indium nitrate is quite high due to high polarity of water.
In the present case, the concentration of reactants is also
moderately less thus accelerating the nucleation of ZnIn2S4
which initially forms tinny nanoparticles. These nanopar-
ticles are self-assembled via. two or three dimensional
growth and further tends to form the plates in case of
aqueous mediated sample. These plates self-assembled in
the form of flower (Scheme 1(a)) due to surface tension
occurred on the petal at high temperature and prolonged
time. In case of methanol mediated ZnIn2S4, porous struc-
ture is observed. Since, the polarity of methanol is less as
compared to water, the growth of nanoparticles is slower.
Hence, instead of formation of bigger petals small petals
are formed (Scheme 1(b)). At hydrothermal conditions the
vapor pressure of methanol is much higher as compared
to water and hence the small petals look like a porous
structure. Further, the growth of ZnIn2S4 is restricted in
ethylene glycol medium due to low polarity as compared
to water and methanol. Hence, ∼20–30 nm agglomer-
ated nanoparticles are formed at hydrothermal conditions
(Scheme 1(c)).
A comparison of the photocatalytic activity of ZnIn2S4
prepared in aqueous-, methanol- and ethylene glycol-
mediated samples (Z1–Z3) for hydrogen generation is
given in Table I. A linear plot of evolution rate of hydro-
gen is also shown in Figure 6.
An excellent photocatalytic activity was observed
for the ZnIn2S4 sample prepared in aqueous-mediated
(Z1) sample. The maximum hydrogen production rate
achieved was ∼3964 ꢂmol h−1 over naked rose-like
ZnIn2S4, indicating its stability as an active photocata-
lyst for hydrogen sulphide decomposition under visible-
light irradiation. The rate of hydrogen production for
ZnIn2S4 prepared in methanol-mediated (Z2) and ethy-
lene glycol-mediated (Z3) sample is observed to be around
3472 ꢂmol h−1 and 2859 ꢂmol h−1, respectively.
It is noteworthy that among the all ZnIn2S4 sam-
ples, Z1 shows significant hydrogen evolution rate which
is much higher than the previously reported values.18
The aqueous-mediated ZnIn2S4 shows good photocat-
alytic activity as compared to methanol-(Z2) and ethy-
lene glycol-mediated ZnIn2S4 (Z3). Considering the band
gap of aqueous-mediated (Z1) ZnIn2S4 at around 2.45 eV,
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Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
Kale et al.
Scheme 1. Schematic representation of formation of ZnIn2S4 (a) rose like flower (Z1), (b) Marigold flower (Z2) and (c) distorted plates (Z3).
the slightly higher activity obtained is quite understood.
naked hierarchical nanostructure rose-like ZnIn S con-
2 4
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It is quite well known that morphology of the materials
ferred extremely good photocatalytic activity because of
the layered hexagonal structure. In the hexagonal structure
of ZnIn2S4, the atoms are arranged in layers at six equally
separated levels along the c-axis. Each of the ‘Zn’ ions are
in a tetrahedral environment of four ‘S’ atoms (Zn–S4ꢁ;
‘In’ ions are in two environments, an octahedral environ-
ment of six ‘S’ atoms (In–S6ꢁ and a tetrahedral environ-
ment of four ‘S’ atoms (In–S4ꢁ.20 This layered structure
Cop19yright: American Scientific Publishers
also plays a vital role in photocatalysis. As seen, sam-
ple Z2, being porous in nature, may suppresses the trans-
port of electrons to the surface which may be the reason
for having slightly less activity. In the case of sample Z3,
the agglomerated particles of ZnIn2S4 are formed due to
agglomeration and we observed less photocatalytic activity
as compared to sample Z1 and Z2.
The stability of ZnIn2S4 photocatalyst (Z1) was eval-
uated by repeating the experiments under similar condi-
tions using the same photocatalyst. After three recycles,
H2 evolution did not decrease which indicates there is
no corrosion of catalyst during the process. The XRD
of reused photocatalyst Z1 did not show any change in
the phase purity, which implies excellent stability of the
photocatalyst for hydrogen generation. We also performed
photocatalytic experiments using ZnS but we could not
get any hydrogen evolution under solar light. As such
Table I. Photocatalytic activity of different morphological ZnIn2S4 for
H2 evolution.
Photocatalyst
Z1
H2 (ꢂmol h−1
)
Morphologies
3964
Rose-like flowers composed
of nanoplates
Z2
Z3
3472
2859
Distorted flowers
Agglomerated nanoparticles
Figure 6. Plot of Photocatalytic study of ZnIn2S4 synthesized at 140 ꢀC
for 72 h (a) water-mediated (Z1), (b) methanol-mediated (Z2) (c) Ethy-
lene glycol mediated (Z3).
Notes: ∗Catalyst weight:0.5 gm ∗∗(a) Water-mediated ZnIn2S4 (Z1), (b) Methanol-
mediated ZnIn2S4 (Z2), (c) Ethylene glycol mediated ZnIn2S4 (Z3).
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Template Free Architecture of Hierarchical Nanostructured ZnIn2S4 Rose-Like Flowers for Solar Hydrogen Production
is responsible for the good photocatalytic activity over a
naked ZnIn2S4.
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ZnIn2S4 shows a decrease in resistivity after exposure
of light which creates hole/electron pairs and the holes get
trapped in the doubly negatively charged level,21 which
ultimately enhances the number of free electrons and their
transport to the surface. This may be the one of the rea-
son for achieving the good photocatalytic activity over
naked ZnIn2S4. It is also reported that photocatalysts com-
prising a P-block metal ion (In3+ꢁ with d10 configuration
are known to possess photocatalytic activities for water
decomposition.22 In the present case since ZnIn2S4 contains
In3+ ions in the d10 configuration, we strongly feel that this
could be one of the reasons for achieving good photocat-
alytic activity. ZnIn2S4 could also be applied in solar cells
as a buffer. Considering its band gap in the visible region
and stability, hierarchical nanostructured ZnIn2S4 may have
potential applications in optoelectronics.
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4. CONCLUSIONS
We have demonstrated the ecofriendly synthesis of hier-
archical nanostructured hexagonal rose-like ZnIn2S4 by
hydrothermal/solvothermal method. The fascinating rose-
like morphology composed of nanoplates was obtained in
aqueous-mediated ZnIn2S4. The effect of solvents on sur-
face morphologies has been discussed in detail. We have
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also demonstrated ecofriendly hydrogen production using
IP: 46.161.59.116 On: Mon1,31. 5(aJ) aXn. H2u0, 1J.8Y1u,0J:.5G0o:1ng5, and Q. Li, Cryst. Growth Des. 7, 2444
this hierarchical nanostructured ZnIn S from abundant
C2 o4pyright: American Scientific Publishers
(2007); (b) W. Seo, R. Otsuka, H. Okuno, M. Ohta, and K. Koumoto,
H2S. Excellent photocatalytic activity for H2 production
via H2S splitting under visible light irradiation has been
obtained. It is noteworthy that nanostructured ZnIn2S4
shows a significant hydrogen evolution rate in aqueous-
mediated ZnIn2S4 (rose like structure) than methanol- and
ethylene glycol-mediated ZnIn2S4. Being a ternary chalco-
genide semiconductor, ZnIn2S4 with hierarchical nano-
structures with hexagonal layered structure is expected to
exhibit potential applications in solar cells, LEDs, charge
storage, electrochemical recording, thermoelectricity and
other prospective electronic and optical devices.
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Acknowledgments: Dr. Baeg appreciates the Korea
Ministry of Environment for support. Dr. Kale would like
to acknowledge the support of C-MET, DeitY, New Delhi
for support as well as help of nanocrystalline materials
group C-MET, Pune.
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Received: 27 October 2015. Accepted 30 December 2015.
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