Effect of ligands on crystallography, morphology and photo-catalytic ability of ZnS nanostructures

Article abstract of DOI:10.1016/j.dyepig.2017.03.013

ZnS nanostructures have been synthesized using zinc complexes: Zn(ethyl xanthate)₂] & [Zn(morpholine4-dithiocarbamate)₂] from ligands potassium ethyl xanthate (KEX) and morpholine4-dithiocarbamate (MDTC) by solvothermal route of synthesis. Crystallographic and morphological analyses of synthesized ZnS nanostructures have been done by X-ray diffraction (XRD) and electron microscopy [Transmission Electron Microscope (TEM)], respectively. Diffraction and electron microscope studies reveal the formation of hexagonal structured ZnS nanocrystals of various morphologies (nanosheets & nanorods). UV–vis. absorption studies have been carried for the detailed optical analyses. Photoluminescence (PL) study was carried out to check luminescence of synthesized ZnS nanostructures in blue region of electromagnetic spectrum. It has been reported that the morphology of synthesized nanostructures strongly depends upon the precursor complexes prepared from two different classes of ligands; potassium ethyl xanthate and morpholine4-dithiocarbamate. Photo-catalytic activity potential of the synthesized ZnS nanostructures has been tested in UV light using methylene blue (MB) dye as a test contaminant in aqueous media. About 88.49% and 87.96% of MB dye was photo-degraded by ZnS nanostructures synthesized from Zn(EX)₂ [ where EX stands for ethyl xanthate] and Zn(MDTC)₂, respectively.

Full text of DOI:10.1016/j.dyepig.2017.03.013

Accepted Manuscript
Effect of ligands on crystallography, morphology and photo-catalytic ability of ZnS
nanostructures
Balwinder Kaur, Karamjit Singh, Ashok Kumar Malik
PII:
S0143-7208(16)31475-9
10.1016/j.dyepig.2017.03.013
DYPI 5839
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 23 December 2016
Revised Date: 21 February 2017
Accepted Date: 6 March 2017
Please cite this article as: Kaur B, Singh K, Malik AK, Effect of ligands on crystallography, morphology
and photo-catalytic ability of ZnS nanostructures, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.03.013.
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ACCEPTED MANUSCRIPT

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Effect of Ligands on Crystallography, Morphology and Photo-catalytic
Ability of ZnS Nanostructures
Balwinder Kaur, Karamjit Singha and Ashok Kumar Malik٭
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Department of Chemistry, Punjabi University Patiala-147 002, Punjab (India)
aDepartment of Physics, Punjabi University Patiala-147 002, Punjab (India)
#Corresponding author e-mail: malik_chem2002@yahoo.co.uk
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Abstract
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ZnS nanostructures have been synthesized using zinc complexes: Zn(ethyl xanthate)2] &
[Zn(morpholine4-dithiocarbamate)2] from ligands potassium ethyl xanthate (KEX) and
morpholine4-dithiocarbamate (MDTC) by solvothermal route of synthesis. Crystallographic and
morphological analyses of synthesized ZnS nanostructures have been done by X-ray diffraction
(XRD) and electron microscopy [Transmission Electron Microscope (TEM)], respectively.
Diffraction and electron microscope studies reveal the formation of hexagonal structured ZnS
nanocrystals of various morphologies (nanosheets & nanorods). UV-vis. absorption studies have
been carried for the detailed optical analyses. Photoluminescence (PL) study was carried out to
check luminescence of synthesized ZnS nanostructures in blue region of electromagnetic
spectrum. It has been reported that the morphology of synthesized nanostructures strongly
depends upon the precursor complexes prepared from two different classes of ligands; potassium
ethyl xanthate and morpholine4-dithiocarbamate. Photo-catalytic activity potential of the
synthesized ZnS nanostructures has been tested in UV light using methylene blue (MB) dye as a
test contaminant in aqueous media. About 88.49% and 87.96% of MB dye was photo-degraded
by ZnS nanostructures synthesized from Zn(EX)2 [ where EX stands for ethyl xanthate] and
Zn(MDTC)2, respectively.
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Keywords:
Potassium Ethyl Xanthate (KEX)/ Ethyl xanthate (EX); Morpholine4-
dithiocarbamate (MDTC); Zinc Suphide; Nanostructures; Solvothermal; X-ray Diffraction;
Transmission Electron Microscope ; UV-vis. Absorption Spectroscopy; Photoluminescence;
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Photo-catalysis.
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Introduction
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Zinc sulfide (ZnS) is a II-VI binary metal-chalcogenide
semiconductor with a wide band gap (3.647eV) with various morphologies like nanorods,
nanobelts, nanocombs etc [1-6]. ZnS nanomaterials have potential applications in the field of
semiconductors like optoelectronics, photo-catalysis, bio-imaging, sensors etc [7-12].
Dithiocarbamates (DTCs) are the class of anionic ligands, which contain two sulfur donor atoms.
These ligands stabilize the positive charge on metal ions towards the periphery of complex. The
metal bis(morpholine4-dithiocarbamate) & metal bis(ethyl xanthate) complexes have been
known to be a single source precursor for the synthesis of metal sulphide nanoparticles, since
they are easy to prepare, nontoxic and stable in nature[13-18]. Variation in derivatives of
dithiocarbamate and xanthate ligands in metal complexes remarkably effects the crystallography
and morphology of metal-sulphide nanostructures[19].
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In the present research work, solvothermal route of synthesis has been
employed for the synthesis of ZnS nanostructures using single source precursors: Zn(EX)2 &
Zn(MDTC)2. The photo-catalytic activity potential of synthesized ZnS nanostructures have been
checked using MB dye as test contaminant in aqueous solution. To the best of our knowledge,
this is the first attempt to explore the morphology dependent photo-catalytic activity of ZnS
nanostructures synthesized using Zn(EX)2 and Zn(MDTC)2 precursors.
Experimental
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All the procured reagents were used without further purification. The analytical reagent grade
chemicals: morpholine (C4H8ON) (99.50%), zinc acetate Zn(C2H4O2) (99.50%), sodium
hydroxide (NaOH) (98.00%), potassium hydroxide (KOH)(98.00%) and ethanol
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(C2H5OH)(99.90%) were procured from Sisco Research Laboratory, Mumbai (India), S D Fine
Chem Ltd, Mumbai (India), Loba Chemie, Mumbai (India) and Changshu Yangyuan Chemical,
China. The laboratory reagents grade chemicals: carbon disulfide (CS2) (99.00%), methylene
blue dye (C16H18N3SCl) (99.00%) & diethylenetriamine (N3C4H12) (98.00%) were procured from
Loba Chemie, Mumbai (India) & Spectrochem Pvt. Ltd, Mumbai (India), respectively. Diethyl
ether (C2H6O) required for synthesis was procured form Merck Pvt. LTD, Mumbai (India).
Preparation of Potassium Ethyl Xanthate (KEX)
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Potassium hydroxide and ethyl alcohol were refluxed at 70oC for one hour. Then carbon
disulphide was added drop wise to the solution, in an ice bath with continuous shaking followed
by addition of diethyl ether. The resulting potassium ethyl xanthate (KEX) was filtered and
washed with dry ether. The product was purified by dissolving in the minimum volume of hot
acetone followed by filtration and cooling of the filtrate in an ice bath. Precipitation was
observed on addition of 20 ml of dry ether [20-21].
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Preparation of Zn(ethyl xanthate)2
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Zn(EX)2 complex has been prepared by dissolving 25 ml aqueous solution of the zinc acetate (5
mmol) to 25 ml of aqueous solution of KEX (0.01 mol). White precipitates were formed
immediately and the resulting suspension was stirred for about 45 min followed by filtration and
washing with distilled water [22].The schematic route of preparation of ligand KEX and Zn(EX)2
complex is shown in Fig.1.
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S
Refluxing for
1 hour
KOH
+
CS2
Carbon
Disulphide
O
SK
OH
70o C
Ethanol
Potassium
Hydroxide
Potassium ethyl xanthate
Zn(CH3 COO)2
S
S
S
O
Zn
O
S
Zinc (ethyl xanthate)2
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Fig.1 Schematic synthesis route of KEX & Zn(EX)2
Preparation of Morpholine4- dithiocarbamate [MDTC]
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Morpholine4- dithiocarbamate [MDTC] has been prepared by addition of 0.1 mol morpholine in
150 ml diethyl ether in an ice bath maintained at 0˚-5˚C followed by complete addition of 0.1 mol
carbon disulphide. Then a concentrated solution of 0.1 mol sodium hydroxide was added slowly
to above solution maintained at same temperature. The resulting mixture was stirred for 4h in an
ice bath. A pale yellow solid product was separated with filtration and washed with small amount
of ether. Finally, pure MDTC was obtained by recrystallization from acetone.
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Preparation of Zn(morpholine4- dithiocarbamate)2
Zn(MDTC)2 has been prepared by dissolving 25 ml aqueous solution of 5 mmol zinc acetate to
25 ml of aqueous solution of 0.01 mol MDTC. Solid precipitates were formed immediately and
the mixture was stirred for about 45 min, filtered and rinsed several times with distilled water
[23]. Fig.2 shows the schematic synthesis route of MDTC followed by synthesis of Zn(MDTC)2
complex.
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O
O
00-50 C
CS2
NaOH
Stirring
N
N
H
Sodium
Hydroxide
Carbon
Disulphide
Morpholine
S
S
Na
Morpholine4-
dithiocarbamate
Zn(CH3COO)2
S
S
S
O
N
Zn
N
O
S
Zn(MDTC)2
Fig.2 Schematic synthesis route of MDTC & Zn(MDTC)2
Preparation of ZnS Nanostructures
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ZnS nanostructures were prepared from Zn(EX)2 & Zn(MDTC)2 complexes via solvothermal
route with slight modification of chelating solvent used by Srinivasan et.al [24]. ZnS
nanostructures were prepared by refluxing 0.5g of Zn(EX)2 in 15ml of diethylenetriamine at
199˚C for 2 min. The off white coloured product was centrifuged, filtered and washed with
ethanol. Similar, synthesis protocol was opted for the synthesis of ZnS nanostructures from
Zn(MDTC)2 . Figs. 3 & 4 show schematic route of preparation of ZnS nanostructures.
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O
O
Zn
O
S
S
S
S
S
S
Diethylenetriamine
NH2
NH2
Zn
NH
199oC
S
S
O
Intermediate Complex
Zinc (ethyl xanthate)2
ZnS Nanostructures
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Fig.3 Schematic synthesis route of ZnS nanostructures prepared from Zn(EX)2
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O
N
O
N
NH2
NH2
Diethylenetriamine
199oC
S
S
S
S
S
S
S
S
Zn
NH
Zn
N
O
N
O
Intermediate Complex
Zn(MDTC)2
ZnS Nanostructures
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Fig4. Schematic synthesis route of ZnS nanostructures preparation from Zn(MDTC)2
Characterization
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Powder XRD patterns were recorded for the crystallographic analysis of synthesized
nanostructures. The diffraction patterns were recorded in 2θ range of 20˚ - 80˚ using Rigaku
Miniflex-600 Powder X-ray diffractometer by keeping scan speed and step size of 4˚/min and
0.02˚, respectively. The Energy Dispersive X-ray spectroscopic (EDX) studies were carried by
Oxford INPA energy dispersive spectrophotometer by mounting sample on brass stub for
elemental composition analyses. The transmission electron microscope (TEM) measurements for
morphological analysis were carried by placing a drop of well dispersed ethanolic solution of
nanoparticles on carbon coated copper grid. The samples were dried at room temperature and
analyzed on Hitachi (H-7500) electron microscope at accelerating voltage of 100 kV. The UV-
vis. absorption spectra of synthesized ZnS nanostructures have been recorded in wavelength
range 300nm-500nm, using Labtronics spectrophotometer. The photoluminescence spectra of
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samples were analyzed on RF-5301PC spectrofluorophotometer by dissolving ethanol & taken in
quartz cuvette of 5mm path length. The photo-catalytic activity potential of the synthesized
nanostructures was checked under UV light irradiation using MB dye as a test contaminant in
aqueous media. The stock solution of dye was prepared by dissolving 3mg MB dye in 500 ml of
water. Before illumination, the suspension of ZnS nanostructures (0.01g ZnS in 100ml dye
solution) in dye, was stirred in dark for 60 min to ensure complete adsorption of dye on surface
of ZnS nanostructures. After equilibration of solution, the suspension was illuminated with UV
irradiation for 90 min. During irradiation, the aliquots were collected after regular time intervals
(15 min) to analyze the photo-degradation of MB dye by UV-vis. absorption spectrophotometer
in visible region (400-750 nm) of electromagnetic spectrum.
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Results & Discussion
Crystallographic Analyses
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XRD was carried out for phase determination. Figs. 5(a-b) show powder X-ray diffraction
patterns of synthesized ZnS nanostructures prepared from zinc complexes. Comparison of
recorded diffraction patterns with standard JCPDS File No. 05-0492 confirm the formation of
wurtzite structured ZnS nanocrystallites. It can be clearly seen from recorded diffraction patterns
in Fig.5(a) that the peaks situated at 2θ values 27.82˚, 28.71˚, 29.68˚, 38.47˚, 53.22˚, 54.43˚ &
77.32˚ for ZnS prepared from Zn(EX)2 corresponds to [100],[002],[101],[102],[110],[103],[112]
& [203] crystal planes. As, it is clearly seen in Fig.5(b) that a slight shifting in peak positions at
2θ values 27.90˚, 28.80˚, 31.40˚,38.65˚,46.41˚,52.58˚,55.45˚ & 77.25˚ was observed in case of
ZnS prepared from Zn(MDTC)2 as compared to ZnS prepared from Zn(EX)2 with similar crystal
planes [24]. Peak broadening was observed in recorded diffractograms reveal the formation of
ZnS nanocrystallites. The average crystallite size values calculated using Scherer formula from
recorded diffraction pattern of ZnS nanostructures synthesized form Zn(EX)2 and Zn(MDTC)2
precursors are ~14.61 & 26.7 nm, respectively. It was observed that X-ray diffraction intensity
strongly depends upon the type of ligand, ZnS nanostructures prepared from Zn(EX)2 show high
crystalline texture compared to ZnS nanostructures prepared from MDTC. Diffraction peaks
observed at 2θ values: 20.17˚, 20.89˚, 22.64˚, 26.75˚ in Fig. 5(a) and 20.38˚, 21.14˚, 22.71˚,
26.90˚ in Fig. 5(b), indicate the presence of rhombohedral phase. In Fig. 5(a) various peaks
observed at 2θ values 31.36˚, 32.37˚, 34.69˚, 35.54˚& 62.85 indicate the chances of auto
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oxidation of ZnS nanocrystals. Similar, peaks with slight shifting in 2θ values are observed in
Fig. 5(b). Some small diffraction peaks observed at 2θ values: 54.54, 57.73 & 59.93, indicate the
chances of formation of cubic ZnS nanocrystallites along with hexagonal phase. Similar
diffraction peaks with slight shifting in 2θ values are observed in Fig. 5(b). Further, the presence
of ZnO nanocrystals has been confirmed by EDX. Hence, mixed phase (hexagonal & cubic) ZnS
nanostructures are synthesized from Zn(EX)2 and Zn(MDTC)2 precursors.
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Fig.5 X-ray diffraction patteren of ZnS nanostructures prepared from different
complexes;
(a) ZnS prepared from Zn(MDTC)2; (b) ZnS prepared from Zn(EX)2
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Energy Dispersive X-ray (EDX) Spectroscopic Analyses
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Energy Dispersive X-ray spectroscopy is a useful analysis tool to check the presence of
constituent elements in the synthesized material. Fig. 6(a) reveals the formation of ZnS by
presence of Zn & S elements with weight percentage (atomic percentage) of 25.22% (7.25 %) &
16.15% (12.03 %), respectively. Along with Zn & S, presence of other constituent elements C, N
& O have been confirmed and their corresponding weight percentages (atomic percentage) are
27.36 % (42.79%), 22.72% (30.47%) & 8.55% (10.04%), respectively. Similarly, in Fig. 6(b) the
presence of Zn, S, C, N & O elements have been confirmed and checked by their weight
percentage
(atomic
percentage)
18.45%(4.69%),12.03%(6.24%),41.78%(57.84%),16.23%(19.26%)
&
11.52%(11.97%),
respectively. Source of carbon is the double sided adhesive carbon tape, which was used to
mount the nanopowders on the brass stubs for EDX studies. It can be clearly seen from the
recorded spectra that ZnS sample synthesized from Zn(EX)2 shows greater weight percentage
(atomic percentage) of back ground carbon as compare to ZnS synthesized from Zn(MDTC)2,
which may be due to larger separation between non-agglomerated nanoparticles formed in case
of Zn(EX)2 precursor as compare to bigger size/agglomerated nanoparticles formed in case of
Zn(MDTC)2. Similarly, higher weight percentage (atomic percentage) of oxygen in Fig.6(b) as
compare to Fig.6(a) is due to high surface to volume ratio of ZnS nanostructures synthesized
from Zn(EX)2 as compare to nanostructures synthesized from Zn(MDTC)2, as oxidation
probability is enhanced in small sized ZnS nanostructures.
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Fig.6 EDX analyses of ZnS nanostructures prepared from Zn complexes;
(a) ZnS prepared from Zn(MDTC)2; (b) ZnS prepared from Zn(EX)2
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The presence of O & N elements in ZnS nanostructures synthesized from Zn(MDTC)2 &
Zn(EX)2 has been also confirmed by Srinivasan et.al [25]. Hence, the auto-oxidation ZnS and
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presence of diethylenetriamine chelating/coordinating solvent on the nanomaterial surface have
been confirmed.
Morphological Analyses
The recorded TEM micrographs of ZnS nanostructures synthesized via solvothermal method
show that morphology of synthesized nanostructures varies from heterogeneous nanosheets to
mixture of nanosheets & nanorods, which suggest that morphology of nanostructures depend
upon type of ligand in precursors.
100 nm
100 nm
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Fig.7 TEM micrographs of ZnS nanostructures;
(a) ZnS
prepared from Zn(MDTC)2; (b) ZnS prepared from Zn(EX)2
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It can be seen from Figs. 7(a-b), that nanostructures synthesized under reflux conditions at 199oC
are nanosheets of ZnS prepared from Zn(MDTC)2 complex, whereas mixture of nanosheets &
nanorods shaped morphology was observed in ZnS synthesized from Zn(EX)2. The nanosheets
dimensions i.e length and width, of calculated from TEM micrographs recorded for ZnS
prepared from Zn(MDTC)2 are 266 nm & 133 nm length, respectively where as diameter of
nanorods obtained in case of ZnS prepared from Zn(EX)2 is 13.30 nm.
Optical Analyses
UV-vis. absorption spectroscopy is a useful technique to monitor the optical properties of
nanomaterials. UV-vis. absorption spectra of ZnS nanostructures prepared from Zn(MDTC)2 &
Zn(EX)2, are shown in Fig.8. It can be clearly seen from the recorded spectra that the synthesized
nanostructures have broad absorption profiles in UV-visible region of electromagnetic spectrum,
which makes these materials suitable for photo-catalytic applications. Moreover, it has been seen
from the recorded spectra that the ZnS nanostructures synthesized from Zn(MDTC)2 have high
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absorption yield as compared to nanostructures synthesized from Zn(EX)2, which reveals that the
optical properties can be tuned with the type of ligands in precursor complexes.
a
b
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
300
350
400
450
500
Wavelength(nm)
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Fig. 8 UV-vis. absorption spectra of ZnS nanostructures;
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(a) ZnS nanostructures synthesized from Zn(EX)2; (b) ZnS nanostructures
synthesized from Zn(MDTC)2
Photoluminescence spectra
Photoluminescence study provides valuable information on quality and purity of nanomaterials.
The semiconductor nanostructures have distinctive electronic and optical behavior. The room
temperature PL spectra of ZnS nanostructures prepared from Zn(EX)2 & Zn(MDTC)2 were
recorded in the wavelength range 380 - 580 nm by exciting at 325 nm. It is clear from the
recorded spectra (Fig. 9) that PL emission band is highly symmetric & broadened with multiple
peaks indicating the involvement of different luminescence centers in radiative processes. The
ZnS nanostructures prepared from Zn(EX)2 & Zn(MDTC)2 show strong and symmetric emission
peaks situated at 410 nm and 432 nm which correspond to interstitial sulphur (IS) lattice defect
and interstitial zinc (IZn) lattice defect. A weak shoulder at 469 nm is assigned to dangling sulfur
bonds at interface of ZnS grains [26-29]. The higher luminescence quantum yield of ZnS
nanostructures synthesized from Zn(MDTC)2 is due to higher concentration of recombination
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sites available for photo-generated electron-hole pairs as compared to ZnS nanostructures
synthesized from Zn(EX)2.
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a
b
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100
50
380
400
420
440
460
480
500
520
540
560
580
Wavelenght(nm)
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Fig. 9 Photoluminscence spectra of ZnS nanostructures;
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(a) ZnS nanostructures synthesized from Zn(MDTC)2; (b) ZnS nanostructures
synthesized from Zn(EX)2
Photo-catalytic Degradation of Dye Solution
The photo-catalytic degradation of MB dye in aqueous media by synthesized ZnS nanostructures
was carried out under UV irradiation. When a UV photon interacts with ZnS nanostructures
-
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dispersed in MB dye contaminated aqueous solution, electrons(e ) from valence band jumps to
+
conduction band, leaving behind positive charged hole (h ) in valence band. Fig.10 shows the
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schematic mechanism of various processes involved in photo-catalytic as well as
photoluminescence of ZnS nanostructures. Actually, there are two major possibilities either
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+
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photo-generated e and h can recombine through radiative emission process or these can be
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trapped in defect states followed by recombination or else transferred to the nanostructures
surface, where these may counter with species adsorbed on or close to the surface of the particles. The
valence band holes react with the chemisorbed H2O molecules to form reactive species such as OH•
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radicals, whereas conduction band electrons interact with dissolved O2 to form OH• radicals, which
subsequently react with dye molecules to cause their complete degradation. Photo-catalytic efficiency of
ZnS nanostructures mainly depends upon amount of OH• radicals generated. Therefore, any factor that
supports the generation of OH• radicals will enhance the rate of photo-catalytic degradation of MB dye.
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Fig.10 Schematic presentation of various processes involved in photo-catalytic and
photoluminescence of ZnS nanostructures
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The mechanism of the photo-catalytic reaction can by described as follows:
+
-
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ZnS + hν
ZnS٭ ( h + e
)
The oxidation of water by holes [H2O ↔ H+ + OH-]
.
+
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h + H2O
OH
.
-
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O2 + e
O2
The transient formation of hydroperoxide redicals:
.
.
-
-
2H2O+ e + O2
2OH + 2OH
Tantative degradation reaction between reactive intermediate & dye molecules
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.
-
-
+
2
OH + C16H18N3SCl
CO2 +H2O+SO4 +NH4 Cl
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The structure of MB dye is shown in Fig.11. The conversion of MB dye into simpler molecules
-
2
+1
like CO2, SO4
,
NH4 etc occurs after hetereocyclic & homocyclic ring cleavages as shown
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in Fig. 12. After ring cleavages of MB dye, the complete minerlization of MB dye is done via
.
.
various reactive intermediates like OH & O2 to easily removable and nontoxic gases and ions.
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The schematic photo-catalytic degradation pathways of MB dye by reactive free radicals has
been described in Fig. 12 [30-32].
N
CH3
CH3
S
N
N
Cl
CH3
CH3
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Fig. 11 Methylene Blue
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N
CH3
CH3
S
N
N
Cl
CH3
CH3
NH2
CH3
CH3
S
N
N
O
CH3
CH3
NH2
COH
N
SO3H
CH3
OH
OH
NH2
CH3
H
N
OH
SO3H
N
CH3
CH3
OH
SO3H
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Fig. 12 Degradation Pathways of MB dye
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The residual dye concentration as the function of UV irradiation time was analyzed by UV-vis.
absorption spectrophotometer. The decoloration of dye could be calculated using following
formula:
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C(%)= [(Ao-A)/Ao] x 100,
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where C is the decoloration degree, A0 and A are the absorption of dye solution before and after
photo-catalysis, respectively. Figs. 13 (a-b) show the absorption spectra of MB dye for different
durations of UV irradiation in the presence of ZnS nano photo-catalysts prepared from Zn(EX)2
& Zn(MDTC)2. Fig. 14 shows the degradation of MB dye vs. time in the presence of synthesized
nano photo-catalysts. It can be clearly seen from the degradation profiles (Fig.14) that the
presence of ligand in precursor complexes acts as an efficient photo-catalytic activity modifier.
The photo-catalytic efficiency basically depends upon the generation of photo-excited carriers
followed by their surface transfer dominance over the radiative recombination. ZnS
nanostructures synthesized from Zn(EX)2 show higher photo-catalytic activity than ZnS
nanostructures synthesized from Zn(MDTC)2, due to high surface to volume ratio & low
luminescence quantum yield of nanorods caused by huge no. of surface states as compare to
volume defects. MB dye after 90 min of UV irradiation was degraded upto 88.49% & 87.96%
by ZnS nanostructures prepared from Zn(EX)2 and Zn(MDTC)2, respectively. Pristine dye
solution was also irradiated for 90 min. in UV reactor to check the photo-bleaching of MB dye,
but no photo-bleaching of MB dye was observed. Hence, the synthesized nanostructures are
efficient photo-catalysts to degrade the MB dye.
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Fig.13 Visible absorption spectra of MB dye for different durations of UV radiation
exposure ; (a) Degradation of dye by ZnS nano-photocatalyst synthesized from
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Fig. 14 Photo degradation of MB dye vs. time in the presence of ZnS nano-photocatalysts
synthesized from different complexes; (a) ZnS nanostructures prepared from Zn
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Conclusions
Highly crystalline ZnS nanostructures have been successfully prepared from single
source precursors Zn(EX)2 & Zn(MDTC)2 by efficient solvothermal route. Electron
microscopic studies reveal that nanostructure morphology is strongly precursor dependent.
Nanosheet like morphologies have been formed in case of Zn(MDTC)2 precursor, whereas
formation of mixture of nanosheets and nanorods have been observed in case of Zn(EX)2
precursor. Similar to morphological analyses, spectroscopic studies infer that electronic structure
and surface states of the synthesized ZnS nanostructures can be easily perturbed with alteration
in precursor material. Both type of morphologies of ZnS nanostructures show symmetrical &
broadened photoluminescence spectra in visible region of electromagnetic spectrum. ZnS
nanostructures synthesized from Zn(EX)2 proven to be better photocatalyst as compare to ZnS
nanostructures synthesized from Zn(MDTC)2 due to high surface to volume ratio & low
luminescence quantum yield of nanorods caused by huge no. of surface states as compare to
volume defects. Synthesized nanostructures seem to be efficient heterogeneous nano photo-
catalysts for the degradation of aqueous pollutants.
Acknowledgment
One of the authors, Balwinder Kaur is thankful to University Grants Commission (UGC), New
Delhi, India for providing financial support under scheme of Maulana Azad National
Fellowships (MANF). The authors are grateful to Sophisticated Instruments Centre, Punjabi
University, Patiala for providing necessary facilities. The authors are also thankful to SAIF,
Panjab University, Chandigarh for TEM analyses. The authors are highly thankful to SAI lab
Thaper University, Patiala for EDX analyses.
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Highlights
A facile solvothermal route to prepare ZnS nanostructures of various
morphologies ( nanosheets to nanorods).
Simple and efficient way to control morphologies of ZnS
nanostructures.
Morphology dependent photo-catalytic activity.