Cobalt selenide nanostructures: Hydrothermal synthesis, considering the magnetic property and effect of the different synthesis conditions

Article abstract of DOI:10.1016/j.molliq.2016.03.062

Cobalt selenide (CoSe) nanostructures are produced via hydrothermal route from the reaction of cobalt salt and SeCl₄ as precursors, in the presence of surfactant (CTAB, PVA, SDS) and reductant (N₂H₄.H₂O). It is found that the temperature reaction, type of cobalt salt and surfactant play important roles in controlling the composition, structure, morphology and particle size of products. The experimental techniques of XRD, SEM, TEM, EDX and VSM are used to characterize the products and study their magnetic properties.

Full text of DOI:10.1016/j.molliq.2016.03.062

Journal of Molecular Liquids 219 (2016) 1089–1094
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Cobalt selenide nanostructures: Hydrothermal synthesis, considering the
magnetic property and effect of the different synthesis conditions
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:
Cobalt selenide (CoSe) nanostructures are produced via hydrothermal route from the reaction of cobalt
salt and SeCl4 as precursors, in the presence of surfactant (CTAB, PVA, SDS) and reductant (N2H4.H2O). It
is found that the temperature reaction, type of cobalt salt and surfactant play important roles in control-
ling the composition, structure, morphology and particle size of products. The experimental techniques
of XRD, SEM, TEM, EDX and VSM are used to characterize the products and study their magnetic
properties.
Received 27 January 2016
Received in revised form 15 March 2016
Accepted 23 March 2016
Available online xxxx
Keywords:
© 2016 Elsevier B.V. All rights reserved.
Nanostructures
Cobalt selenide
Hydrothermal
SeCl4
Hydrazine
Magnetic property
1. Introduction
In this paper, we report the synthesis of CoSe nanostructures
by hydrothermal method. This method is simple, convenient and
Transition metal chalcogenides, as important semiconductors
materials, have attracted widely attentions because of their wonderful
physical and chemical properties, quantum size effect, luminescence
and non-linear optical properties [1–7]. Also, much attention has
been focused on lithium intercalation in metal chalcogenides due to
their potential application as rechargeable battery electrodes and
electrochromic displays [8,9]. The properties (including physical and
chemical properties) and applications of materials are usually deter-
mined by their compositions, phase structures and morphologies. The
control of chemical composition, crystal structure, size and shape of
materials allows people to observe the unique properties of
nanocrystals and to tune their chemical and physical properties [10,11].
CoSe as a typical example has been selected for synthesis in this
work. According to the phase diagram of the Co–Se system [12] there
are two homogeneous and stable phases at room temperature, CoSe2
and CoSe, and two other possible compositions: Co3Se4 and Co2Se3.
Traditionally, cobalt selenides were synthesized by using a variety of
methods, such as solvothermal [13,14], hydrothermal [15,16], co-
electrodeposition [17], chemical bath deposition technique [18], one-
pot reaction between metal salts [19], etc. [20–23].
effective controlled synthetic procedure and provided an effective
way to the synthesis of chalcogenide materials. The physical prop-
erties as well as the magnetic properties of the new materials are
reported. This study also describes a comparison of features
observed from the products obtained from various conditions.
Over the past years, great interest has been focused on controlling
the shape, structure and size of nanostructured materials because
of the strong correlation between these parameters and their
physical/chemical properties [24]. SeCl4 was selected in our exper-
iments to provide a highly reactive selenium source in aqueous
solution and has given good results. To the best of our knowledge,
it is the first time that SeCl4 was used as Se source for the synthesis
of cobalt selenides. Following this method, we herein report a
convenient and controllable synthetic method for obtaining a
series of cobalt selenides. By simply adjusting the temperature
reaction, type of surfactant and cobalt salt, we could obtain CoSe
samples with the best size and morphology.
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 purification. A Teflon-lined stainless steel cylindrical closed
⁎
Corresponding authors.
E-mail addresses: sobhaniazam@gmail.com (A. Sobhani), salavati@kashanu.ac.ir
(M. Salavati-Niasari).
http://dx.doi.org/10.1016/j.molliq.2016.03.062
0167-7322/© 2016 Elsevier B.V. All rights reserved.

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A. Sobhani, M. Salavati-Niasari / Journal of Molecular Liquids 219 (2016) 1089–1094
Fig. 1. SEM images of samples prepared at 180 °C for 18 h: (a) in the absence of surfactant (sample no. 1) and in the presence of: (b) CTAB (sample no. 2), (c) PVA (sample no. 3) and
(d) SDS (sample no. 4).
chamber with 150 ml capacity was used for the synthesis. Powder
X-ray diffraction (XRD) patterns were collected from a diffractom-
eter 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 accelerating voltage of 60−200 kV
equipped with a high resolution CCD camera. X-ray energy disper-
sive spectroscopy (EDS) analysis with 20 kV accelerated voltage
was done. The magnetic properties of the samples were detected
at room temperature using a vibrating sample magnetometer
(VSM, Meghnatis Kavir Kashan Co., Kashan, Iran).
3. Results and discussion
Fig. 1a–d illustrates SEM images of the products synthesized in
the presence of different surfactants at 180 °C after 18 h of
hydrothermal reaction. Fig. 1a shows the SEM image of the product
obtained in the absent of surfactant (sample no. 1). The formation
of nanoparticles with high agglomeration is seen in this figure.
When the CTAB is used as surfactant (sample no. 2), nanoplates
with a diameter of 70–150 nm are formed (Fig. 1b). Fig. 1c shows
that the nanoplates are also obtained in the presence of PVA
(sample no. 3), but with bigger area. The SEM image in Fig. 1d
shows formation of nanoparticles with spherical morphology in
the presence of SDS (sample no. 4).
The effects of reaction temperature on the morphology and shape
of the as-synthesized products in the presence of CTAB and PVA are
shown in Fig. 2. According to Fig. 2a, aggregated nanoparticles
are formed in the presence of CTAB at 120 °C (sample no. 5). With
increasing of the temperature to 150 °C (sample no. 6), the as-
prepared samples have two morphologies: nanoparticles and
nanoplates (Fig. 2b). The nanoparticles disappear at 180 °C, while
there are still nanoplates as was shown in Fig. 1b. Fig. 1c showed
formation of nanoplates in the presence of PVA at 180 °C. Fig. 2c
shows formation of flower like structures with increasing tempera-
ture to 200 °C in the presence of PVA. As a result, the high tempera-
tures increase regular agglomeration of nanoparticles and
formation of nanoplates or nanoflowers.
2.2. Synthesis of CoSe nanostructures
In a typical experiment for the synthesis of CoSe nanostructures,
CoCl2·6H2O and surfactant were dissolved in 40 ml distilled water.
After stirring the solution for 15 min, SeCl4 was dissolved in 20 ml of
distilled water and added into the solution under strong magnetic stir-
ring at room temperature. Then hydrazine was added drop-wise. The
solution was added to a Teflon-lined stainless steel autoclave and
maintained at 180 °C for 18 h. The autoclave was cooled to room tem-
perature on its own. The precipitates were separated by centrifugation,
then washed with distilled water and anhydrous ethanol several times,
and dried under vacuum at 60 °C for 4 h.

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Fig. 3 shows the effect of the reaction temperature on the
morphology of the products in the presence of CTAB and acetate
salt. With increasing of the temperature, regular aggregated
structures are formed. With change at the cobalt salt from chloride
to acetate, the morphology of the as-prepared products is changed
from nanoplates (Fig. 1b) to aggregated nanoparticles (Fig. 3a).
We consider that this phenomenon results from the different
interactions between anions and Co2+ cations. The different anions
have different coordinations with metal cations, which might favor
the preferential crystal growth [25].
In order to further elucidate the size and the crystal structure of
the products, TEM image was taken. For preparation of the
TEM image, the powder was dispersed in high-purity ethanol via
ultrasonic equipment for 10 min. Fig. 4a shows the formation of
nanoplates in the presence of PVA at 180 °C for 18 h (sample
no. 3) and confirms SEM results (Fig. 1c). The HRTEM image of
sample no. 3 in Fig. 4b shows the nanoplates are highly crystalline
and distance between the two adjacent planes is measured to be
0.15 nm. The intensity and highly ordered diffraction spots,
also diffused halo ring in the SAED spectrum in Fig. 4c indicate
that the nanoplates prepared in the presence of PVA are well
crystallized.
The crystal structure and composition of the as-prepared
products were determined by XRD. Figs. 5 and 6 show XRD patterns
of samples synthesized by the reaction between cobalt salt and
SeCl4 in presence of the different surfactants. In XRD pattern of
sample obtained in the presence of SDS at 180 °C for 18 h (sample
no. 4, Fig. 5a), the peaks at 2Theta values 51.4, 45.5, 33.9 indicate
the formation of hexagonal phase of CoSe. The type of product
changes from hexagonal CoSe to mixture of hexagonal Se and
orthorhombic CoSeO3, when use from PVA at 180 °C for 18 h
(sample no. 3, Fig. 5b), indicating that these reaction temperature
and time are not quite enough for reduction of SeCl4 and formation
of pure CoSe in the reaction system. In the presence of PVA, with
increasing the reaction time and temperature to 36 h and 200 °C,
respectively (sample no. 7), the samples are found to be the pure
hexagonal CoSe, as shown in Fig. 5c.
In the presence of CTAB and cobalt chloride salt, after hydro-
thermal reaction at 120 °C for 18 h (sample no. 5), impure CoSe is
formed, as shown in Fig. 6a. XRD patterns in Fig. 6b and c show
the formation of the pure CoSe in the presence of CTAB and cobalt
acetate salt. No remarkable diffractions of other phases such as
Se, CoSeO3 or their other compounds can be found in this figure.
With increasing the reaction time and temperature, intensity and
width of the peaks, crystallinity, are unchanged. The XRD results
show that at high reaction temperatures and times the purer prod-
ucts will produce.
Plot of magnetization versus applied field (M–H) at 300 K for
samples no. 4 and 7 are shown in Fig. 7. The plots show paramag-
netic behavior in both samples. Paramagnetism is a form of magne-
tism whereby the paramagnetic material is only attracted when in
Fig. 2. SEM images of samples prepared in the presence of: (a, b) CTAB at 120 °C
(sample no. 5) and 150 °C (sample no. 6), respectively and (c) PVA at 200 °C (sample no. 7).
Table 1
The reaction conditions of the products synthesized in this work.
Sample
Ratio of Co:Se
Time (h)
Temperature (°C)
Reductant
Surfactant
Selenium source
Cobalt salt
Effect
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
18
18
18
18
18
18
36
18
24
180
180
180
180
120
150
200
180
200
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
N2H4·H2O
−
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
SeCl4
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
CoCl2·6H2O
Co(CH3COO)2·4H2O
Co(CH3COO)2·4H2O
Surfactant
CTAB
PVA
SDS
CTAB
CTAB
PVA
CTAB
CTAB
Temperature
Temperature

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Fig. 3. SEM images of samples prepared from Co(CH3COO)2·4H2O in the presence of CTAB at (a) 180 °C (sample no. 8) and (b) 200 °C (sample no. 9).
Fig. 4. (a) TEM image, (b) HRTEM image and (c) SAED pattern of sample no. 3.
the presence of an externally applied magnetic field. Paramagnetic
materials have a relative magnetic permeability greater or equal to
unity (i.e., a positive magnetic susceptibility) and hence are
attracted to magnetic fields. The magnetic moment induced by
the applied field is linear in the field strength; it is also rather
weak. Paramagnetic materials have a small, positive susceptibility
to magnetic fields. These materials are slightly attracted by a mag-
netic field and the material does not retain the magnetic properties
when the external field is removed. Paramagnetic properties are
due to the presence of some unpaired electrons, and from the re-
alignment of the electron paths caused by the external magnetic
field. 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, lat-
tice spacing, chemical composition, temperature, defect concentra-
tion, atomic order, impurities and so on.
employs nontoxic materials and solvent. This method provides an
effective way to the synthesis of other metal selenides.
Acknowledgment
Authors are grateful to the council of Iran National Science Founda-
tion (91053846) and University of Kashan for supporting this work by
Grant No (159271/979).
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Fig. 8. EDS spectrum of the as-synthesized cobalt selenide.
Fig. 6. XRD patterns of samples prepared in the presence of CTAB: (a) at 120 °C for 18 h
(sample no. 5), (b) at 180 °C for 18 h (sample no. 8), (c) at 200 °C for 24 h (sample no. 9).
Fig. 7. M–H hysteresis at 300 K for: (a) sample no. 4, (b) sample no. 7.