Hydrothermal synthesis of CoSe nanostructures without using surfactant

Article abstract of DOI:10.1016/j.molliq.2016.04.099

CoSe nanostructures are synthesized by hydrothermal route in the presence of reductant, without using surfactant. In this work, we use from SeCl₄ as a new selenium source. By varying the type of metal salt and reductant, reaction time and temperature, the method permits us to synthesize products with different morphologies. SEM and TEM images show the morphology and size of the as-synthesized samples. Chemical composition of the samples is characterized by XRD and EDS. Magnetization measurement shows paramagnetic behavior for CoSe nanostructures.

Full text of DOI:10.1016/j.molliq.2016.04.099

Journal of Molecular Liquids 220 (2016) 334–338
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Hydrothermal synthesis of CoSe nanostructures without using surfactant
b,
Azam Sobhani a, , Masoud Salavati-Niasari
⁎
⁎
a
Department of Chemistry, Kosar University of Bojnord, Bojnord, Islamic Republic of Iran
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box 87317–51167, Islamic Republic of Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
CoSe nanostructures are synthesized by hydrothermal route in the presence of reductant, without using surfac-
tant. In this work, we use from SeCl4 as a new selenium source. By varying the type of metal salt and reductant,
reaction time and temperature, the method permits us to synthesize products with different morphologies. SEM
and TEM images show the morphology and size of the as-synthesized samples. Chemical composition of the sam-
ples is characterized by XRD and EDS. Magnetization measurement shows paramagnetic behavior for CoSe
nanostructures.
Received 13 February 2016
Accepted 24 April 2016
Available online xxxx
Keywords:
CoSe nanostructures
SeCl4
© 2016 Elsevier B.V. All rights reserved.
Hydrothermal
Hydrazine
Magnetic property
1. Introduction
purification. A Teflon-lined stainless steel cylindrical closed chamber
with 150 ml capacity was used for the synthesis. Powder X-ray diffrac-
Extensive attention has been paid to the preparation and character-
ization of metal selenides owing to their interesting properties and
potential applications [1–7]. Cobalt selenide semiconductors have ex-
tensively been studied. According to the phase diagram of the Co\\Se
system [8] there are two homogeneous and stable phases at room tem-
perature, CoSe2 and CoSe, and two other possible compositions: Co3Se4
and Co2Se3. Lots of methods of synthesizing cobalt selenide nanostruc-
tures have been developed, including solvothermal [9,10], hydrother-
mal [11,12], co-electrodeposition [13], chemical bath deposition
technique [14], one-pot reaction between metal salts [15] and so on
[16–19]. In this paper, we report a hydrothermal route for the prepara-
tion of cobalt selenide nanostructures. In this route, SeCl4 is used as a
new selenium source. To the best of our knowledge, studies on the syn-
thesis of cobalt selenide nanostrucrures by using SeCl4 have not been re-
ported to date. In this research, we present the results of our perfect
experiments on the dependence of the morphology, particle size, and
phase of the products on the type of metal salt and reductant, reaction
time and temperature.
tion (XRD) patterns were collected from a diffractometer of Philips
Company with X'PertPro monochromatized Cu Kα radiation (λ =
1.54 Å). Microscopic morphology of products was visualized by a LEO
1455VP scanning electron microscope (SEM). Transmission electron
microscopy (TEM) images were obtained on a JEM-2100 with an accel-
erating voltage of 60–200 kV equipped with a high resolution CCD cam-
era. The energy dispersive spectrometry (EDS) analyses were studied by
a XL30, Philips microscope. The magnetic properties of the samples
were detected at room temperature using a vibrating sample magne-
tometer (VSM, Meghnatis Kavir Kashan Co., Kashan, Iran).
2.2. Synthesis of CoSe nanostructures
In a typical experiment for the synthesis of CoSe nanostructures, cobalt
salt (chloride, acetate, sulfate) were dissolved in 40 ml distilled water.
After stirring the solution for 15 min, SeCl4 was dissolved in 20 ml of dis-
tilled water and added into the solution under strong magnetic stirring at
room temperature. Then reductant (N2H4·H2O, KBH4,·Zn) was added
drop-wise. The solution was added to a Teflon-lined stainless steel auto-
clave and maintained at 180 °C for 12 h. The autoclave was cooled to
room temperature on its own. The precipitates were separated by centri-
fugation, then washed with distilled water and anhydrous ethanol several
times, and dried under vacuum at 60 °C for 4 h. Table 1 lists the reaction
conditions of the synthesized CoSe nanostructures.
2. Experimental
2.1. Materials and experiments
All the chemicals used in our experiments were of analytical grade,
and purchased from Merck and used as received without further
3. Results and discussion
⁎
Corresponding authors.
E-mail addresses: sobhaniazam@gmail.com (A. Sobhani), salavati@kashanu.ac.ir
Fig. 1 shows SEM images of cobalt selenide nanostructures produced
from CoCl2·6H2O and SeCl4 in the presence of hydrazine at 180 °C for
(M. Salavati-Niasari).
http://dx.doi.org/10.1016/j.molliq.2016.04.099
0167-7322/© 2016 Elsevier B.V. All rights reserved.

A. Sobhani, M. Salavati-Niasari / Journal of Molecular Liquids 220 (2016) 334–338
335
Table 1
The reaction conditions of the products synthesized in this work.
Sample no.
Co:Se ratio
t (h)
T(°C)
Reductant
Surfactant
Se source
Cobalt salt
1
2
3
4
5
6
7
8
9
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
6
180
180
180
220
150
120
180
180
180
180
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
KBH4
–
–
–
–
–
–
–
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoSO4·7H2O
Co(CH3COO)2·4H2O
CoCl2·6H2O
CoCl2·6H2O
12
18
12
12
12
12
12
12
12
–
–
10
Zn
Fig. 2. SEM images of samples prepared from CoCl2·6H2O and SeCl4 in the presence
of hydrazine after 12 h hydrothermal reaction at: (a) 220 °C (sample no. 4) (inset:
low-magnification SEM image of sample no. 4), (b) 150 °C (sample no. 5), (c) 120 °C
(sample no. 6).
Fig. 1. SEM images of samples prepared from CoCl2·6H2O and SeCl4 in the presence
of hydrazine at 180 °C for: (a) 6 h (sample no. 1), (b) 12 h (sample no. 2) (inset:
low-magnification SEM image of sample no. 2), (c) 18 h (sample no. 3).

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the different reaction times (6 h, 12 h and 18 h). According to the Fig. 1a,
sponge-like structures are prepared after 6 h of hydrothermal reaction
(sample no. 1). With increasing of time reaction from 6 h to 12 h (sam-
ple no. 2), flower-like structures are formed, as shown in Fig. 1b.
The longer time of reaction allows ample time for the sponge-like struc-
tures to agglomerate and grow into more regular shapes. The low-
magnification SEM image of sample no. 2 inserted in Fig. 1b, clearly re-
veals the diameter of the flowers is about 5–12 μm. The flower-like
structures are broken down and agglomerated nanospheres with an
irregular manner are observed (Fig. 1c), with increasing time to 18 h
(sample no. 3).
For investigating the effect of reaction temperature on the morphol-
ogy of the products, the reactions carried out in the presence of
hydrazine at four different temperatures, including 120, 150, 180 and
220 °C, and other reaction parameters remained unchanged. Fig. 2a
and b shows SEM images of cobalt selenide nanostructures obtained
at 220 °C and 150 °C, respectively. These images show that products
have sponge-like morphology. SEM image of sample obtained at
180 °C (Fig. 1b) showed formation of flower-like structures. Fig. 2c
shows formation sphere-like nanostructures at 120 °C. It can be
observed that with increasing temperature, regular agglomeration of
nanostructures increases and more regular structures (flowers and
sponges) are formed.
SEM images reveal that morphology of products change with using
from different cobalt salts. In case of sample obtained from sulfate salt
(sample no. 7), the aggregated nanoparticles with nearly even distribu-
tion are obtained, as shown in Fig. 3a. Changing the metal salt to acetate
(samples no. 8), we can see aggregated nanospheres (Fig. 3b). The mor-
phology of as-prepared cobalt selenides changes from nanospheres to
flower-like structures, when use from chloride salt (Fig. 1b). The differ-
ent types of particle size and morphology can be due to the different re-
lease rates of Co2+ and Se2− ions from the cobalt salts and SeCl4,
respectively.
In continuation, the effect of the type of reductant on the morpholo-
gy of the nano-sized cobalt selenides at 180 °C for 12 h was investigated.
Fig. 4 shows that the reductant plays a key role in the morphology and
size, and therefore the properties, of cobalt selenides. In the presence
of hydrazine in sample no. 2, nanoflowers were formed (Fig. 1b). On
changing hydrazine to KBH4 (sample no. 9), nanospheres with even dis-
tribution are formed (Fig. 4a). In the presence of Zn (sample no. 10), the
as-prepared products have two morphologies. From Fig. 4b, it is found
that the samples are mixture of aggregated nanoparticles and nano-
spheres. The strong reductant KBH4 and hydrazine in combination
with stirring rapidly create a large number of nuclei and further growth
of the nuclei is limited. The nuclei are aggregated regularly and flower-
like nanostructures (in case of hydrazine) and nanospheres with even
distribution (in case of KBH4) are formed. Zn is slower in the reduction
rate compared to hydrazine and KBH4. Our group attributes the slower
action of Zn as the reason for the formation of the structures with irreg-
ular morphologies.
Fig. 3. SEM images of samples prepared in the presence of hydrazine at 180 °C for 12 h
Fig. 4. SEM images of samples prepared from CoCl2·6H2O and SeCl4 at 180 °C for 12 h in
from SeCl4 and: (a) CoSO4·7H2O (sample no. 7), (b) Co(CH3COO)2·4H2O (sample no. 8).
the presence of: (a) KBH4 (sample no. 9), (b) Zn (sample no. 10).

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337
Fig. 5. (a) TEM image, (b) HRTEM image and (c) SAED pattern of sample no. 8.
Fig. 6. XRD pattern of sample no. 2.
In order to further elucidate the size and the crystal structure of the
products, TEM image and SAED spectrum were taken. TEM image in
Fig. 5a shows the formation of nanospheres with diameters in the
range 10–30 nm. The HRTEM image in Fig. 5b shows the distance be-
tween the two adjacent planes is measured to be 0.25 nm. The intensity
and ordered diffraction spots, also diffused halo ring in the SAED
spectrum in Fig. 5c indicate that the nanospheres prepared are well
crystallized.
The crystal structure and composition of the as-prepared products
are determined by XRD. Fig 6 shows XRD pattern of sample synthesized
by the reaction between CoCl2·6H2O and SeCl4 in presence of the hydra-
zine, without surfactant at 180 °C for 12 h (sample no. 2). The peaks at
Fig. 7. EDS spectrum of the as-synthesized cobalt selenide.

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A. Sobhani, M. Salavati-Niasari / Journal of Molecular Liquids 220 (2016) 334–338
morphology and magnetic property of samples. It is shown that the
type of metal salt and reductant, reaction time and temperature play
important roles in controlling the composition, structure and morphol-
ogy of products.
Acknowledgments
Authors are grateful to the council of University of Kashan (159271/
899) for providing financial support to undertake this work.
References
[1] M. Esmaeili-Zare, M. Salavati-Niasari, A. Sobhani, Ultrason. Sonochem. 19 (2012)
1079–1086.
[2] M. Salavati-Niasari, M. Esmaeili-Zare, A. Sobhani, Micro Nano Lett. 7 (2012)
831–834.
[3] M. Salavati-Niasari, M. Esmaeili-Zare, A. Sobhani, Micro Nano Lett. 7 (2012)
1300–1304.
Fig. 8. M–H hysteresis at 300 K for sample no. 2.
[4] A. Sobhani, M. Salavati-Niasari, Mater. Res. Bull. 47 (2012) 1905–1911.
[5] A. Sobhani, F. Davar, M. Salavati-Niasari, Appl. Surf. Sci. 257 (2011) 7982–7987.
[6] A. Sobhani, M. Salavati-Niasari, F. Davar, Polyhedron 31 (2012) 210–216.
[7] M. Salavati-Niasari, A. Sobhani, Opt. Mater. 35 (2013) 904–909.
[8] M. Hansen, Constitution of Binary Alloys, Geminuim Publ. Co., New York, 1985
502–503.
2Theta values 51.4, 45.5, 33.9 indicate the formation of hexagonal phase
of CoSe.
EDS measurements provide further information for the evaluation of
the composition and purity of cobalt selenides. In the EDS spectrum in
Fig. 7 the characteristic peaks of Co and Se are observed, which indicate
formation pure cobalt selenide.
The magnetic property of cobalt selenide nanostructures has been
measured. Fig. 8 shows plot of the variation of magnetization with mag-
netic field at 300 K for sample no. 2. The plot shows paramagnetic
behavior. The magnetic properties of nanomaterials are believed to
be highly dependent on the material structure, size and shape of the
grain, crystallinity, magnetization and applied field direction, lattice
spacing, chemical composition, temperature, defect concentration,
atomic order, impurities and so on.
[9] J.H. Zhan, X.G. Yang, S.D. Li, Y. Xie, W.C. Yu, Y. Qian, J. Solid State Chem. 152 (2000)
537–539.
[10] J.-F. Zhao, J.-M. Song, C.-C. Liu, B.-H. Liu, H.-L. Niu, C.-J. Mao, S.-Y. Zhang, Y.-H. Shen,
Z.-P. Zhang, CrystEngComm 13 (2011) 5681–5684.
[11] X. Liu, N. Zhang, R. Yi, G. Qiu, A. Yan, H. Wu, D. Meng, M. Tang, Mater. Sci. Eng. B 140
(2007) 38–43.
[12] W. Zhang, Z. Yang, J. Liu, Z. Hui, W. Yu, Y. Qian, G. Zhou, L. Yang, Mater. Res. Bull. 35
(2000) 2403–2408.
[13] Z. Wang, H. Xu, Z. Zhang, X. Zhou, S. Pang, G. Cui, Chin. J. Chem. 32 (2014) 491–497.
[14] M.L. Gaur, P.P. Hankare, K.M. Garadkar, I.S. Mulla, V.M. Bhuse, New J. Chem. 38
(2014) 255–259.
[15] P.K. Khanna, V.V. Dhapte, Int. J. Green Nanotechnol. 4 (2012) 425–429.
[16] T. Kazuhiro, S. Yoshinori, Bull. Chem. Soc. Jpn. 65 (1992) 329.
[17] X. Song, M. Bochmann, J. Chem. Soc. Dalton Trans. (1997) 2689–2692.
[18] P. Ranmdohr, M. Schmitt, Neues Jb. Mineral. Monat. 6 (1955) 133–142.
[19] C.E.M. Campos, J.C. De Lima, T.A. Grandi, K.D. Machado, P.S. Pizani, Solid State Phys. B
324 (2002) 409–418.
4. Conclusions
In this paper, we develop a novel hydrothermal synthetic route
to CoSe semiconductors and study the growth process, structure,