Synthesis and characterization of CoS2 nanostructures via hydrothermal method

Article abstract of DOI:10.1080/15533174.2013.862650

CoS₂ nanostructures were synthesized successfully via hydrothermal approach with new precursor. The products were characterized with X-ray diffraction and scanning electron microscopy. The effect of different sulfur sources were investigated on

Full text of DOI:10.1080/15533174.2013.862650

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Synthesis and characterization of CoS2 nanostructures
via hydrothermal method
Masoud Salavati-Niasaria, Mohammad Sabeta & Elaheh Esmaeilia
a Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box.
87317–51167, I. R. Iran.
Accepted author version posted online: 18 Aug 2014.
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To cite this article: Masoud Salavati-Niasari, Mohammad Sabet & Elaheh Esmaeili (2014): Synthesis and characterization
of CoS2 nanostructures via hydrothermal method, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, DOI: 10.1080/15533174.2013.862650
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Synthesis and characterization of CoS2 nanostructures via
hydrothermal method
Masoud Salavati-Niasari*, Mohammad Sabet, Elaheh Esmaeili
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box.
87317–51167, I. R. Iran.
*Corresponding author: Tel.: +98 361 5555 333; Fax: +98 361 555 29 30.
E-mail address: salavati@kashanu.ac.ir.
Abstract
CoS2 nanostructures were synthesized successfully via hydrothermal approach with new
precursor. The products were characterized with X-ray diffraction (XRD) and scanning electron
microscopy (SEM). The effect of different sulfur sources were investigated on product size and
morphology.
KEY WORDS: CoS2, Hydrothermal, Nanostructures.
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1. Introduction
Metal sulfides nanomaterials have been the focus of considerable interest due to their unique
optical and electrical properties and their wide variety of potential applications in nanoscale
devices such as electroluminescence and nonlinear optical devices [1, 2]. As one of the most
complicated metal chalcogenides, cobalt sulfides are of particular interest for their unique
catalytic, electrical, optical and magnetic properties [3]. Cobalt sulfides have also been used in
solar cells for their high solar absorption, which is due to the strong intrinsic absorption coupled
with surface morphology effects [4]. Among these cobalt sulfides, CoS2 with a pyrite structure
has received considerable attention due to their electric and magnetic properties [5].
Nanocrystalline cobalt disulfides have been prepared using the solvent–thermal process by
Qian's group [6, 7] and hydrothermal method [8]. Cobalt sulfides of different stoichiometric
composition such as CoS, CoS2, and Co9S8 have attracted great attention due to their potential
application in catalysis [9] semiconductor [10] magnetic materials [11] lithium-ion batteries [12]
and other fields [13]. Many approaches have been explored to synthesize metal sulfides,
including the high temperature solid phase process [14] the hydrothermal and solvothermal
method [15] arc-discharge method [16] low-temperature procedures [17] chemical vapor
decomposition [18] and so on [19]. In this work CoS2 nanoparticles were synthesized via simple
hydrothermal method from Cobalt complex. Different sulfur sources were used in this work. The
products were characterized via SEM and XRD analysis.
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2. Experimental
2.1. Materials and physical measurements
All the chemical's reagents used in experiments such as Co(NO3)2, ethylenediamine (C2H8N2),
phthalic acid and hydrazine (N2H4.H2O) were of analytical grade and used as received without
further purification. XRD patterns were recorded by a Rigaku D-max C III, X-ray diffractometer
using Ni-filtered Cu Kα radiation. Scanning electron microscopy (SEM) images were obtained
on Philips XL-30ESEM equipped with an energy dispersive X-ray spectroscopy.
2.1. Synthesis of precursor ([Co(Pht)(H2O)]n):
For synthesis of the precursor, ligand-contain and metal-contain solutions were prepared
separately. Ligand contain solution was obtained from addition of 2 mmol Phthalic acid
(C8H6O4) to 30 ml ethanol as solvent. Also metal contain solution was prepared from addition of
2 mmol of cobalt nitrate ([Co(NO3)2]. H2O) to 30 ml distilled water as solvent. Then Co2+
contain solution was slowly added to other solution and stirred 30 minutes at 40 oC temperature.
After evaporation of solvent, obtained powder was washed with ethanol and distilled water
several times and dried at oven.
2.2. Synthesis of CoS2 nanostructures:
In a typical experimental process, different mole ratio of ([Co(Pht)(H2O)]n and different sulfur
sources were added to 100 ml distilled water. After 40 min stirring the reagent was transferred to
the autoclave. The reaction was carried out at 160 oC for 12 h. Then the autoclave was cooled to
room temperature. Obtained precipitate was centrifuged and washed with ethanol and distilled
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o
water several times for removing the probable by pass products and dried at 60 C for 8 h.
Experimental condition for preparation of CoS2 nanostructures are shown in table. 1.
3. Result and Discussion
X-Ray Diffraction pattern (XRD)
Fig. 1 shows XRD pattern of sample no 1 . as shown in this figure beside the CoS2,
CoSO4 was created when (NH4)2S was selected as sulfur source. So by using this sulfure source
we coudn't form pure CoS2. The use of thioacetamid (TAA) as a sulfure source can not lead to
preparation of CoS2 and the product is composed from CoS and Co3S4 (Fig .2). So this sulfur
source is not proper for creating CoS2 structure, too. By using Co complex and thioglycolic acid
as sulfur source, the product is mainly composed from C2CoO4H2O and Co(OH)2 (Fig. 3). It can
be said that thioglycolic acid couldn’t release its S2- in hydrothermal medium and final product
show any sulfur in its structure. Thiourea releases its sulfur easily and reacts with Co source to
form CoS2 structure (Fig. 4). This product has cubic structure with JCPDS= 41-1471. Estimated
particle size from Deby-Sherrer formula was 28.9 nm that is in agreement with obtained SEM
result. Na2S2O3 is other sulfur source that can release S2- and react with Co source to form CoS2
structure with JCPDS=19-0362 (Fig. 5). The particle size of this product was obtained to 38.5
nm from deby-sherrer formula. Table 2. list information about XRD pattern of samples No. 1-5.
Fig. 6 shows SEM image of as-synthesized Cobalt complex. As shown in this figure, this
complex has composed from large, irregular and inconsistent particles. Fig. 7 shows SEM image
of as-synthesized product from [Co(Pht)(H2O)]n and (NH4)2S. The release of S2- from this sulfur
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source is very fast and hence the product contains very small particles. SEM image of the
product that composed from cobalt source and TAA is shown in Fig. 8. Thioacetamid has two
electron donor groups (NH2, CH3) with different strength. So each group has different role in
releasing S2- from TAA. Therefore the release of S2- from thioacetamide is mediocre and hence
the product is composed from aggregated large particles. Fig. 9 shows SEM image of as-
synthesized product from cobalt complex and thioglycolic acid as sulfur source. Thioglycolic
acid is a sulfur source with a strong electron acceptor that causes the release of sulfur fastly. So
interaction between two sources become fast and finally small sphere and large lump-like
structures are created. SEM image of the product that is composed from the reaction between
cobalt complex and thiourea in hydrothermal medium is shown in Fig. 10. Thiourea has two
electron resonance groups but theirs electron donor ability is less than TSC. So larger spheres in
comparison to the product of TSC have been created. SEM image of the product that is
synthesized with cobalt complex and Na2S2O3 is shown in Fig. 11. The use of this sulfur source
led to formation of flower-like structure that is composed of 100-150 nm fragments. Fig. 12
shows SEM image of as-synthesized product from cobalt sourse and CS2 as sulfure source. CS2
release sulfure slowly and therefore there is more time for reaction of sulfure source with cobalt
source. So the product will be composed from too many small particles that are aggregated
together. TSC has two resonance groups that cause S2- release as soon as possible. So interaction
between these two sources leads to formation of very small sphere-like structures that are
aggregated together (Fig. 13). The effect of cystein on product morphology is nearly to TAA.
Because both of them have an electron acceptor and an electron donor that affected on release of
S2- from sulfur source. So the product is composed from very small particles beside the irregular
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and bulk structure (Fig. 14). Table 3 and 4 give morphology of the products and sulfur structures,
respectively.
4. Conclusion
CoS2 nanostructures were synthesized via hydrothermal method. The complex precursor
[Co(Pht)(H2O)]n, was served for synthesis of this nanostructures. The effects of different
sulfur sources were studied on product size and morphology and it was found that
different sulfur sources were led to synthesis of different structure of cobalt and just some
sulfur source were led to synthesis of pure CoS2 nanostructures.
Acknowledgements
Authors are grateful to the council of Iran National Science Foundation and University of
Kashan for their unending effort to provide financial support to undertake this work by Grant No
(159271/109).
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Figure caption
Fig. 1. XRD pattern of sample no. 1.
Fig. 2. XRD pattern of sample no. 2.
Fig. 3. XRD pattern of sample no. 3.
Fig. 4. XRD pattern of sample no. 4.
Fig. 5. XRD pattern of sample no. 5.
Fig. 6. SEM image of cobalt complex.
Fig. 7. SEM image of sample no. 1.
Fig. 8. SEM image of sample no. 2.
Fig. 9. SEM image of sample no. 3.
Fig. 10. SEM image of sample no. 4.
Fig. 11. SEM image of sample no. 5.
Fig. 12. SEM image of sample no. 6.
Fig. 13. SEM image of sample no. 7.
Fig. 14. SEM image of sample no. 8.
Table 1. Experimental conditions for preparation of CoS2 nanostructures.
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Table 2. XRD pattern information of samples No. 1-5.
Table 3. Morphology of the samples No. 1-8.
Table 4. The sulfur sources stucture.
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Table 1. Experimental conditions for preparation of CoS2 nanostructures.
Sample No
Sulfur source
(NH4)2S
TAA
Temperature (°C)
Time ( (h)
1
2
3
4
5
6
7
8
160
160
160
160
160
160
160
160
12
12
12
12
12
12
12
12
TGA
Tu
Na2S2O3
CS2
TSC
Cystein
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Table 2. XRD pattern information of samples No. 1-5.
Sample No Sulfur source
Component
JCPDS No Crystal system XRD pattern
CoS2
41-1471
15-0701
Cubic
1
2
3
(NH4)2S
TAA
CoSO4.H2O
Monoclinic
CoS
75-0605
75-1561
Hexagonal
Cubic
Co3S4
C2CoSO4.2H2O
Co(OH)2
14-0741
74-1057
TGA
Hexagonal
Cubic
4
5
Tu
CoS2
CoS2
41-1471
19-0362
Na2S2O3
Cubic
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Table 3. Morphology of the samples No. 1-8.
Sample No
1
Morphology
particles
Figure
7
SEM image
2
3
4
5
6
7
Aggregated particles
Large rod-particles
Sphere
8
9
10
11
12
13
Flower-like
Sphere
Sphere-particles
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8
Aggregated particles
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Table 4. The sulfur sources stucture
Sulfur source
abbreviation
TAA
structure
Thioacetamide
Thioglycolic acid
Thiourea
TGA
Tu
Carbon disulfide
CS2
Thiosemicarbazide
TSC
Cysteine
Cysteine
Ammonium sulfide
Sodium thiosulfate
(NH4)2S
Na2S2O3
(NH4)2S
Na2S2O3
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Fig. 1. XRD pattern of sample no. 1.
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Fig. 2. XRD pattern of sample no. 2.
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Fig. 3. XRD pattern of sample no. 3.
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Fig. 4. XRD pattern of sample no. 4.
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Fig. 5. XRD pattern of sample no. 5.
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Fig. 6. SEM image of cobalt complex.
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Fig. 7. SEM image of sample no. 1.
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Fig. 8. SEM image of sample no. 2.
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Fig. 9. SEM image of sample no. 3.
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Fig. 10. SEM image of sample no. 4.
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Fig. 11. SEM image of sample no. 5.
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Fig. 12. SEM image of sample no. 6.
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Fig. 13. SEM image of sample no. 7.
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Fig. 14. SEM image of sample no. 8.
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