Architecture of rose and hollow marigold-like ZnIn2S4 flowers: Structural, optical and photocatalytic study

Article abstract of DOI:10.1039/c3ra45767b

In the present investigation, a surfactant-assisted hydrothermal route has been employed to design self-assembled rose and hollow marigold-like ZnIn ₂S₄ flowers. In the absence of the surfactant, uniform (～3-5 μm) marigold-like flowers are observed. The self-alignment of the transparent petals (～3-5 nm thick with a length of ～25-100 nm) leads to the formation of hollow marigold-like flowers, for which a plausible growth mechanism has also been proposed. Moreover, DEA assisted ZnIn₂S ₄ demonstrates a rose flower-like via self assembly of hexagonal nanoplates. Structural and optical characterization shows the existence of hexagonal structures with a band gap in the range of ～2.4-2.6 eV. Considering the ideal band gap in the visible region, we have used such unique nanostructured self assemblies of ZnIn₂S₄ as photocatalysts and demonstrated visible light-driven photocatalytic production of clean hydrogen by toxic hydrogen sulphide, which is abundantly available as a waste gas from oil refineries (15-20%). We believe that continuous efforts in this direction may open up new insights into the design of controllable nanostructures and their potential applications in advanced fields.

Full text of DOI:10.1039/c3ra45767b

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Architecture of rose and hollow marigold-like
ZnIn2S4 flowers: structural, optical and
photocatalytic study†
Cite this: RSC Adv., 2014, 4, 12182
*
Nilima S. Chaudhari, Sambhaji S. Warule and Bharat B. Kale
In the present investigation, a surfactant-assisted hydrothermal route has been employed to design self-
assembled rose and hollow marigold-like ZnIn2S4 flowers. In the absence of the surfactant, uniform
(ꢀ3–5 mm) marigold-like flowers are observed. The self-alignment of the transparent petals (ꢀ3–5 nm
thick with a length of ꢀ25–100 nm) leads to the formation of hollow marigold-like flowers, for which a
plausible growth mechanism has also been proposed. Moreover, DEA assisted ZnIn2S4 demonstrates a
rose flower-like via self assembly of hexagonal nanoplates. Structural and optical characterization shows
the existence of hexagonal structures with a band gap in the range of ꢀ2.4–2.6 eV. Considering the
ideal band gap in the visible region, we have used such unique nanostructured self assemblies of ZnIn2S4
as photocatalysts and demonstrated visible light-driven photocatalytic production of clean hydrogen by
toxic hydrogen sulphide, which is abundantly available as a waste gas from oil refineries (15–20%). We
believe that continuous efforts in this direction may open up new insights into the design of controllable
nanostructures and their potential applications in advanced fields.
Received 11th October 2013
Accepted 14th January 2014
DOI: 10.1039/c3ra45767b
www.rsc.org/advances
Recently, a new class of multi-component sulphides has also
been reported to show a high photocatalytic efficiency.8–11 Among
Introduction
these, ZnIn2S4 is a n-type semiconductor with a bandgap of
2.4 eV, which possesses photo- and chemical stablility.12 It
exhibits a layered structure in the AB2X4 (A ¼ Cu, Ag, Zn, Cd, etc.;
B ¼ Al, Ga, In; C ¼ S, Se, Te) family, which has attracted
considerable attention due to its outstanding electrical and
optical properties.13 There are several reports of ZnIn2S4 in the
literature with different morphologies using effective methods/
strategies.13–18 Furthermore, Shen et al. employed nano-
structured ZnIn2S4 for hydrogen evolution, and the photo-
catalytic activity of the ZnIn2S4 was greatly affected by the crystal
plane spacing along the c-axis.17 Considering the importance of
the band and crystal structure of ZnIn2S4, hierarchically hollow
microspheres and faceted growth of nanosheets are usually
relevant to the self-assembly process, and are promising in
photocatalytic hydrogen evolution. Also, the issue of highly toxic
hydrogen sulphide and necessity of producing hydrogen from it
by photocatalysis has been described in our previous report.11,19,20
Hence, the fabrication and designing of different morphologies
of ZnIn2S4 is highly desirable, and their photocatalytic hydrogen
generation from hydrogen sulphide will be signicant.
The fabrication of hierarchical nanostructured materials with
well-dened structures and morphologies has currently been
under growing interest due to the experimental ndings that
the properties of nanostructured materials are size and
morphology dependent.1 For example, hollow nanostructures
have widespread potential applications in drug delivery, catal-
ysis, sensors, lithium ion batteries, ion storage and so on,1–6
because they provide a high specic surface area, favoring a
better dispersion. A variety of methods have been developed to
synthesize hollow structures; however, it remains a challenge to
prepare hollow microspheres, which self-assemble from nano-
crystals, with a well-controlled size and morphology for an
improved photocatalytic performance. In addition, photo-
catalysts with a strong absorption in the visible region can show
a more efficient utilization of solar energy than UV-light active
materials. Also, the development of a visible light active stable
photocatalyst (photocorrosion free) has immense signicance.7
Centre for Materials for Electronics Technology (C-MET), Department of Electronic and
Information Technology, Govt. of India, Panchawati, off Pashan Road, Pune-411 008,
India. E-mail: bbkale@cmet.gov.in; Fax: +91 20 2589 8180; Tel: +91 20 25899273
† Electronic supplementary information (ESI) available: Fig. SI-1 and SI-2: XRD
study of different concentrations of PVP and DEA capping agents, Fig. SI-3:
FESEM images of the samples synthesized using (a and b) 100 and (c and d)
200 ppm PVP as a capping agent. Fig. SI-4: BET surface area and pore width
distribution, and Fig. SI-5: error bars of the hydrogen evolution. See DOI:
10.1039/c3ra45767b
Herein, we have reported nanostructured hollow marigold
and rose ower-like ZnIn2S4 using polyvinyl pyrrolidone (PVP)
and diethyl amine (DEA) as capping agents. The effect of the
concentration of PVP and DEA on the morphology has been
demonstrated. The possible growth mechanism has also been
discussed in detail. Finally, the effect of different morphologies
on the photocatalytic hydrogen generation is investigated.
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presence of 300 ppm PVP (S2) as well as 0.015 mmol DEA (S3) as
a capping agent. The XRD pattern conrms the hexagonal
Experimental
Synthesis
˚
crystal structure with cell parameters a ¼ b ¼ 3.85 A and c ¼
˚
24.68 A. This is in agreement with JCPDS data (ICDD-JCPDS
All the chemicals were analytical grade and used as received
without purication. In a typical synthesis of pristine ZnIn2S4
(S1), Zn(NO3)2$6H2O (5 mmol), In(NO3)3$5H2O (10 mmol) and
double excess of thiourea (40 mmol) were dissolved in 100 ml
distilled water. This solution was then transferred into a 200 ml
Teon lined autoclave. Distilled water was added to maintain an
80% volume of the reactor. The reactor was sealed and kept at
150 ꢁC for 30 h. The autoclave was cooled naturally to room
temperature. The product was washed with distilled water and
ethanol and nally dried at 70 ꢁC. In addition to this, PVP
assisted ZnIn2S4 samples were also synthesized in the presence
of different amounts of PVP as a capping agent. In this case,
100 ppm, 200 ppm and 300 ppm (S2) PVP was added in the same
reaction as described above. Diethyl amine (DEA) assisted
ZnIn2S4 was synthesized using 0.01 and 0.015 mol (S3) DEA as a
capping agent instead of PVP.
card no. 72-0773). The crystallite sizes have been calculated
using the Scherrer formula and are found to be ꢀ65, 70 and 32
nm for sample S1, S2 and S3, respectively. The absence of peaks
due to impurities such as binary sulphides and oxides indicates
the high phase purity of the product. In addition, the XRD
patterns of the samples synthesized with different concentra-
tions of PVP and DEA are given in the ESI (SI-1).†
In order to investigate the inuence of the size and shape on
the optical properties, UV-visible diffuse reectance spectra (DRS)
were recorded. Fig. 2 depicts diffuse reectance spectra of all
samples (S1–S3), which show steep absorption edges in the visible
region, indicating the formation of a single phase compound.
The steep shape of the visible edge, and the strong absorption in
the visible region, also reveal that the absorption band of ZnIn2S4
is because of the transition from the valence band to the
conduction band. The samples without a capping agent (S1) and
with PVP (S2) show an absorption edge at ꢀ515 nm with a cor-
responding band gap of 2.4 eV. Meanwhile, the DEA assisted
ZnIn2S4 sample (S3) shows an absorption edge at ꢀ475 nm
(2.6 eV) which is due to the reduced nanoparticle size.
Characterization
The as-synthesized products were characterized by an X-ray
diffractometer (XRD) (D8, Advance, Bruker AXS model) using Cu
˚
Ka (l: 1.5406 A). The surface morphological studies of the as-
Fig. 3a shows the FESEM image of pristine ZnIn2S4 (S1),
indicating the formation of uniform marigold owers origi-
nating from well organized petals. The size of the ower is
observed to be in the range of 3–5 mm with the thickness of the
petal being ꢀ3–5 nm. The observed size of the ZnIn2S4 ower
clearly indicates a high aspect ratio. A more detailed structural
analysis of the present marigold-like ZnIn2S4 ower was carried
out using a TEM. Fig. 3b shows the TEM micrograph of the
petals of the marigold ower. The size of the ZnIn2S4 petal is
found to be ꢀ50–200 nm, which is observed to be thin and
transparent. The selected area electron diffraction (SAED)
synthesized samples were carried out using a eld emission
scanning electron microscope (FESEM, Hitachi S-4800). The
single crystalline nature was conrmed using a high resolution
transmission electron microscope (HRTEM, Technai G2 20
Twin, FEI). The surface characterization of the ZnIn2S4 was
carried out using X-ray Photoelectron Spectroscopy (XPS, ESCA-
3000, VG Scientic Ltd, England). The UV-Visible Diffuse
Reectance Spectra (UV-DRS) were recorded on a Lambda 950
Perkin Elmer spectrophotometer in the wavelength range from
200–800 nm. The Brunauer–Emmett–Teller (BET) equation was
used to calculate the surface area from the adsorption branch.
The pore size distribution was calculated by analyzing the
adsorption branch of the nitrogen sorption isotherm, using the
Barrett–Joyner–Halenda (BJH) method.
Photocatalysis measurements
A cylindrical quartz photochemical thermostatic reactor was
lled with 250 ml 0.25 M aqueous KOH and purged with argon
for 1 h. Hydrogen sulphide (H2S) was bubbled through the
solution for about 1 h with a rate of 2.5 ml minꢂ1 at 298 K.
ZnIn2S4 (0.25 g) was introduced into the reactor and irradiated
with a visible light source (Xe-lamp (Oriel, 300 W)) with constant
stirring. The excess hydrogen sulphide was trapped in the
NaOH solution. The amount of hydrogen evolved was measured
using a graduated gas burette and analyzed using a gas chro-
matograph (Model Shimadzu GC-14B, MS-5A column, TCD, Ar
carrier).
Results and discussion
Fig. 1 X-ray diffraction patterns of the ZnIn2S4 synthesized without
using surfactant (S1) and with 300 ppm PVP (S2) and 0.015 mol
Fig. 1 depicts the XRD patterns of the ZnIn2S4 samples
synthesized in the absence of surfactant (S1) and in the DEA (S3).
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concentration plays an important role in the formation of the
hollow marigold ower structures. In the systematic study, at
lower PVP concentration (100 ppm), premature distorted
owers are observed (Fig. SI-3a and b†). As the concentration of
PVP is increased up to 200 ppm, hollow spheres of size ꢀ4–6 mm
with a ꢀ2.5 mm cavity are obtained (Fig. SI-3c and d†). However,
the puffiness of the ower is observed to be much less, due to
the compactness of the petal. When the concentration of PVP is
further increased up to 300 ppm (S2), interestingly, puffy
owers with hollow cavities are obtained (Fig. 4). The petals of
the ower are fully grown and well separated from each other.
These highly porous owers with a cavity represent the hollow
nature of the nanoparticles. Fig. 4b–d reveal that the hierar-
chical nanostructured hollow marigold owers are assembled
by numerous orderly packed nanosheets (petals). Furthermore,
a nitrogen adsorption isotherm was carried out for surface area
analysis study (Table SI-1 and Fig. SI-4†). BET surface areas of
ꢀ40 and 55 m2 gꢂ1 are found for samples S1 and S2, respec-
tively. The hollow marigold owers (S2) show a higher surface
area due to their cavity, in comparison to the marigold owers
only (S1).
Fig. 2 UV-visible diffuse reflectance spectra of the ZnIn2S4 samples
S1, S2 and S3.
In order to examine the hollow cavity and crystalline nature
of the 300 ppm PVP assisted ZnIn2S4 sample, TEM analysis was
carried out. The TEM images in Fig. 5a and b conrm the hollow
structure, which is in good agreement with the SEM results. A
magnied TEM image (Fig. 5b) reveals that hollow micro-
spheres, with hierarchical nanostructures assembled with
nanosheets, were obtained. Signicantly, very thin hexagonal
petals of ZnIn2S4 with length ꢀ1 mm are found around the
cavity. Fig. 5c shows a high resolution image taken from the
edge part, and the magnied HRTEM image (inset Fig. 5c)
˚
depicts the lattice fringes of ꢀ3.29 A associated with the (101)
plane of the hexagonal ZnIn2S4. The corresponding electron
diffraction pattern (Fig. 5d) depicts not only the formation of a
single crystalline ZnIn2S4 nanostructure but also gives some
indication that the blur diffraction ring pattern may be due to a
Fig. 3 (a) FESEM images of the samples synthesized without using a
capping agent (S1) and (b and e) TEM images of the petal of the flower
with selective area electron diffraction in (c), (d) HRTEM image with an
FFT pattern in (e).
pattern taken from the surface of the ZnIn2S4 petal (Fig. 3e),
demonstrates the single crystalline nature of the ZnIn2S4
(Fig. 3c). The lattice fringes in the HRTEM image conrm the
high crystallinity of the petal, as shown in Fig. 3d. The HRTEM
image is taken on the edge of the same petal, and the inter-
˚
planar spacing (d) is observed to be ꢀ3.35 A which is consistent
with the (101) plane of the hexagonal ZnIn2S4. A fast Fourier
transform (FFT) pattern taken from the same area is shown in
Fig. 3f. The FFT result indicates a single crystalline nature with a
well dened hexagonal pattern. This is agreement with the
result shown by the XRD pattern.
FESEM studies of the PVP assisted ZnIn2S4 samples with
different PVP concentrations were also carried out to see the
Fig. 4 FESEM images of the sample synthesized using PVP as a
morphological effect. Surprisingly, the variation in capping agent (S2).
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Fig. 7 (a and b) TEM images of the ZnIn2S4 sample synthesized using
diethyl amine as a capping agent (S3), (c) HR-TEM image of nanosheets
and (d) an electron diffraction pattern.
Fig. 5 (a–c) TEM images of the samples synthesized with 300 ppm
PVP (S2) as a capping agent and (d) the electron diffraction pattern.
slightly low crystallinity. Furthermore, detailed observations
reveal that these electron diffraction spots form a hexagonal
geometry in the SAED pattern, which is due to the hexagonal
ZnIn2S4.
The size, shape and growth kinetics of ZnIn2S4 can be
explained on the basis of the capping agents and their
concentration under hydrothermal conditions, which are given
in the following section.
Fig. 6a and b depict the FESEM images of the sample
synthesized using diethyl amine (DEA) as a capping agent (S3).
This clearly shows the rose ower-like morphology of the
ZnIn2S4 with a size of 0.5–1 mm. The individual ower-like
structures consist of aggregated hexagonal nanosheets (petals)
of thickness ꢀ50 nm. These petals, with a random array, are
Reaction mechanism
The current hydrothermal synthesis of ZnIn2S4 is carried out
using Zn(NO3)2$6H2O, In(NO3)3 and thiourea as precursors,
while PVP and DEA act as the capping agents in water. The Zn2+
and In3+ cations (R1) combine with the capping agents (CA) to
form [Zn (CA)]2+ and [In (CA)]3+ complexes (R2). The formation
and dissociation reactions of complexes are reversible (R2).
Meanwhile, the thiourea (NH2CSNH2) hydrolyzes in the
aqueous solution to yield H2S (R3), which further dissociates to
generate S2ꢂ anions ((R4) and (R5)). The dissociation/hydrolysis
reactions of complexes and NH2CSNH2 accelerate at higher
temperatures.
connected to each other to build
architecture.
a rose ower-like
Fig. 7a and b depict the TEM images of the same sample (S3).
The presence of a hexagonal sheet with sharp edges is clearly
observed. The HR-TEM image shows visible lattice fringes with
˚
an inter-planar distance of ꢀ4.11 A (Fig. 7c), which represents
the (006) plane, indicating the [001] direction, i.e. c-axis oriented
growth of the ZnIn2S4. The electron diffraction (ED) pattern
(Fig. 7d) indicates that the nanosheet had a low crystallinity,
which may be due to smaller crystallites.
Zn(NO3)2 + In(NO3)3 + H2O / Zn2+ + In3+
Zn2+ + In3+ + CA / [Zn(CA)]2+ + [In(CA)]3+
NH2CSNH2 / NH2CN + H2S
(R1)
(R2)
(R3)
(R4)
(R5)
H2S + H2O 4 H3O+ + HSꢂ
HSꢂ + H2O 4 H3O+ + S2ꢂ
The released Zn2+, In3+ and S2ꢂ ions combine to form
ZnIn2S4 nuclei, as expressed by (R6):
Fig. 6 FESEM images of the sample synthesized in the presence of (a)
0.01 and (b) 0.015 mol DEA as a capping agent.
Zn2+ + In3+ + S2ꢂ / ZnIn2S4
(R6)
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Zn2+, In3+ and S2ꢂ ions are released gradually (R2–R5), which a core with smaller nanoparticles and an exterior layer with
controls the nucleation rate of ZnIn2S4 and hence the numbers bigger nanoparticles (Scheme 1a). As the concentration of
of ZnIn2S4 nuclei formed in the initial stage are limited. PVP increases up to 300 ppm, the excess of PVP on the ZnIn2S4
Accordingly, there are still large amounts of unreacted Zn2+, nuclei in the core is diffused at 150 ꢁC to the exterior layer
In3+ and S2ꢂ ions in the reaction solution, in the form of (Fig. 4). At this stage, as per the Ostwald ripening phenom-
[Zn(CA)]2+, [In(CA)]3+ and NH2CSNH2, respectively. Depending enon, there is an aggregation of the primary nuclei, followed
on the concentration of the capping agent and the reaction by an outward mass transfer through the growth of larger
time, these unreacted forms release ions to develop a particular crystallites from those of smaller size, and the migration of
morphology, which is explained in the “growth mechanism” crystallites from the inner core to the outer shell. In this
section.
process the inner core is completely consumed and a hollow
cavity is created due to diffusion. During this process, the
excess PVP present in the core is relinquished at 150 ꢁC, to
release the pressure created by the PVP. Hence, some of the
mass of the ZnIn2S4 diffuses from the core. Due to this
reason, a hole or cavity is created on the ower. This
phenomenon creates the hollowness in the ower-like
assembly which is clearly seen in the FESEM and TEM images
(Fig. 4 and 5a and b). The ower-like assembly shows a porous
structure due to the steric effect of the PVP molecules. Hence,
we nd there are many voids in the interior of the spherical
aggregates.23
In an extension of this work, we also used diethyl amine
(DEA) as a capping agent. At lower concentrations of DEA
(0.01 mol), three dimensional growth is observed and hence,
aggregated spherical nanoparticles align and show premature
nanoplates. As the boiling point of DEA is higher than water, the
overall vapour pressure is less than water alone. Hence, growth
is restricted to form a random ower-like structure. As the
concentration of DEA increases up to 0.015 mol, two dimen-
sional growth of the nanoparticles is accelerated. Hence, at
prolonged reaction time, due to the Ostwald ripening
phenomenon a hexagonal plate-like structure is conferred. At
equilibrium conditions, these hexagonal plates are self orga-
nized and the assembly of rose ower-like structure is
conferred. Interestingly, at higher concentrations of DEA due to
the lower vapor pressure, there is no strain created on the plate,
and hence the curving ability is suppressed.18 Therefore, instead
of the marigold structure, the rose ower-like structure is
obtained.
Growth mechanism
In our previous report,19 we discussed a detailed mechanism for
the formation of marigold owers and nanosheets of ZnIn2S4.
Here in this report, we obtained hollow marigold owers of
ZnIn2S4, which has hitherto not been attempted, and hence our
focus is more on this unique morphology. It is reported21–23 that
PVP is a well known surfactant for obtaining hollow nano-
structured materials. On the basis of the above results, we
propose that the synergistic effect of PVP is the prime factor for
the formation of the hollow marigold ZnIn2S4 owers. In the
absence of PVP compact marigold owers are obtained, which
indicates that PVP plays a key role in the formation of the
hollow structure. A possible growth mechanism is proposed in
Scheme 1.
Initially, Zn–PVP and In–PVP complexes are formed
through coordinative bonding with the carbonyl oxygen of the
PVP. At elevated temperatures, thiourea starts to release H2S
as a sulphur source. This H2S slowly reacts with Zn2+ and In3+
ions by replacing the PVP ligand, and forms ZnIn2S4 nuclei.
Here, the ZnIn2S4 nuclei are capped with PVP at the surface,
and hence restricted growth of the ower-like morphology is
observed. In this case, the precursors are capped with PVP
and the nanoparticles then aggregate into bigger particles to
decrease their surface energy. At supersaturation conditions,
the crystallites on/near the outermost surface of the aggre-
gates will continue to grow at a slow rate.24 This continuous
growth of aggregates confers a spherical self assembly, having
XPS study
The surface characterization of the hollow marigold ower-like
ZnIn2S4 was performed using X-ray photoelectron spectroscopy
(XPS). The binding energies obtained were corrected for spec-
imen charging by referencing carbon 1s to 284.6 eV. Fig. 8a
depicts the survey spectra while Fig. 8b–d show the core lines
xed at 1022 eV (Zn2p 3/2), 445 eV (In3d5/2) and 162 eV (S2p3/2)
respectively. This implies the existence of chemical states In3+
,
S2ꢂ and Zn2+. The molar ratio based on the peak surface area
was observed to be 1 : 2.3 : 4 (Zn : In : S) which is very closely
matched to the theoretical one. No other peaks pertaining to
any trace impurities were observed.
Photocatalytic activity
The photocatalytic activity of all the ZnIn2S4 (S1–S3) samples for
hydrogen generation via the photodecomposition of H2S was
Scheme 1 Schematic illustration of the possible growth mechanism of
ZnIn2S4 hollow flowers.
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Acknowledgements
The authors would like to thank the Department of Electronics
and Information Technology (DeitY), New Delhi, for the nan-
cial support. We also thank the Executive Director, C-MET, Pune
for providing laboratory facilities.
Notes and references
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Fig. 8 XPS patterns of the as-synthesized ZnIn2S4 at 150 ꢁC for 30 h
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measured in 0.25 M KOH solution. Table SI-2† depicts the
comparison of the amount of hydrogen generated by the pho-
tocatalysts under identical conditions. As ZnIn2S4 is a well
known visible light active photocatalyst, it shows activity for
hydrogen generation via H2S spitting under solar light. Here, we
compared the activity of the ZnIn2S4 samples with respect to
their morphologies. The sample synthesized in the absence of a
capping agent (S1) which has a solid marigold ower-like
morphology shows the lowest activity (8022 mmol hꢂ1 gꢂ1). In
the case of the PVP-assisted ZnIn2S4 sample (S2), porous mari-
gold owers with a hollow cavity are obtained. This could
increase the overall surface area of the ower, which is
responsible for obtaining a higher photocatalytic activity (8682
mmol hꢂ1 gꢂ1) as compared to the solid ower (without a cavity).
Finally, the sample synthesized using DEA assistance (S3)
demonstrates the highest photocatalytic activity (8818 mmol hꢂ1
gꢂ1). The error bar of the hydrogen evolution rate for these
samples is mentioned in ESI Fig. SI-5.† A detailed discussion
about the mechanism and effect of morphology on the activity is
included in the ESI SI-E.†
18 N. S. Chaudhari, A. P. Bhirud, R. S. Sonawane, L. K. Nikam,
S. S. Warule, V. H. Rane and B. B. Kale, Green Chem., 2011,
13, 2500–2506.
Conclusions
In a nutshell, the effect of capping agents and their concen- 19 A. P. Bhirud, N. S. Chaudhari, L. K. Nikam, R. S. Sonawane,
tration on the morphology of ZnIn2S4 was observed. A solid
marigold ower-like structure is observed without any capping
K. R. Patil, J. O. Baeg and B. B. Kale, Int. J. Hydrogen Energy,
2011, 36, 11628.
agent, whereas higher concentration of PVP creates a hollow 20 F. Qin, G. Li, H. Xiao, Z. Lu, H. Sun and R. Chen, Dalton
marigold ower-like structure. However, DEA assisted ZnIn2S4 Trans., 2012, 41, 11263.
shows self assembly of hexagonal plates i.e. a rose ower-like 21 A. M. Cao, J. S. Hu, H. P. Liang and L. J. Wan, Angew. Chem.,
morphology. Furthermore, the photocatalytic activity for Int. Ed., 2005, 44, 4391.
hydrogen generation under visible light irradiation using H2S 22 X. L. Cheng, J. S. Jiang, M. Hu, G. Y. Mao, Z. W. Liu, Y. Zeng
splitting has been demonstrated for these ZnIn2S4 morphol- and Q. H. Zhang, CrystEngComm, 2012, 14, 3056.
ogies. The rose-like ZnIn2S4 nanoowers showed relatively high 23 B. Liu and H. C. Zing, Small, 2005, 1, 566.
photocatalytic activity in comparison with the hollow marigold- 24 D. Beydoun, R. Amal, G. Low and S. McEvoy, J. Nanopart.
like ZnIn2S4 nanoowers.
Res., 1999, 1, 439.
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