Hydrothermal synthesis, characterization, and magnetic properties of cubic MnSe2/Se nanocomposites material

Article abstract of DOI:10.1016/j.jallcom.2014.08.013

The cubic MnSe₂/Se nanocomposites were produced under hydrothermal condition, by reduction of SeCl₄to Se and Se^2-, and reaction of the reduced selenium with Mn²⁺ion during the next step, in the presence of different surfactants using hydrazine as reductant. The main factors affecting the morphology, the particle size and the phase of the products, such as surfactant, reductant and its amount, reaction temperature and time were studied. The pure Se or a mixture of Se and MnSe₂nanorods were obtained in the presence of different surfactants and small amounts of hydrazine. The cubic MnSe₂/Se nanocomposites were formed at 120 °C for 12 h or longer periods of time, in the presence of polyethylene glycol (PEG) and large amounts of hydrazine. The size of the as-prepared cubes decreases with increasing the reaction time. With increasing temperature of reaction from 120°C to 180°C, the morphology of the products changes from cubes to the mixture of nanorods and nanoparticles.

Full text of DOI:10.1016/j.jallcom.2014.08.013

Journal of Alloys and Compounds 617 (2014) 93–101
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Hydrothermal synthesis, characterization, and magnetic properties
of cubic MnSe2/Se nanocomposites material
Azam Sobhani a, Masoud Salavati-Niasari b,
⇑
a Department of Chemistry, Kosar University of Bojnord, Bojnord, Islamic Republic of Iran
b Institute of Nano Science and Nano Technology, University of Kashan, Kashan P.O. Box 87317-51167, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2014
Received in revised form 27 July 2014
Accepted 1 August 2014
Available online 9 August 2014
The cubic MnSe2/Se nanocomposites were produced under hydrothermal condition, by reduction of SeCl4
to Se and Se2ꢀ, and reaction of the reduced selenium with Mn2+ ion during the next step, in the presence
of different surfactants using hydrazine as reductant. The main factors affecting the morphology, the par-
ticle size and the phase of the products, such as surfactant, reductant and its amount, reaction temper-
ature and time were studied. The pure Se or a mixture of Se and MnSe2 nanorods were obtained in the
presence of different surfactants and small amounts of hydrazine. The cubic MnSe2/Se nanocomposites
were formed at 120 °C for 12 h or longer periods of time, in the presence of polyethylene glycol (PEG)
and large amounts of hydrazine. The size of the as-prepared cubes decreases with increasing the reaction
time. With increasing temperature of reaction from 120 °C to 180 °C, the morphology of the products
changes from cubes to the mixture of nanorods and nanoparticles.
Keywords:
MnSe2
Nanocomposites
Nanorods
Hydrothermal
Surfactant
Hydrazine
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
A number of methods for the synthesis of manganese selenides
have been explored, such as hydrothermal [19–22], solvothermal
Transition metal chalcogenides and dichalcogenides have
drawn considerable attention because of their important optical,
electrical, and transport properties [1–9]. Hence, investigations
on the synthesis and modification of the nanosized MnSe2 have
attracted tremendous attentions [10,11]. The MnSe2 belongs to
the family of transition metal chalcogenides, an important class
of semiconductors with numerous applications including photo-
voltaics and thermoelectrics [12]. The MnSe2 has been shown to
be a promising material for use as a solar absorber and continued
study of this material is recommended [12]. This rarely encoun-
tered solid is structurally similar to iron pyrite, which is a NaCl-like
arrangement of M and X2 groups with the axes of the X2 groups
parallel to the various body diagonals [13,14]. The MnSe2 exhibits
interesting electronic, magnetic and transport properties and have
found several applications in the field of materials science [15–18].
These properties show a considerable increase in the MnSe2/Se
nanocomposites compared to the MnSe2 nanostructures. The aim
of making the composite nanomaterials in this study is to improve
the properties and applications of the MnSe2.
[23], reaction elemental Mn and Se [24], and so on. Recently, the
hydrothermal synthesis has proved to be a useful method to pro-
duce semiconductors [25]. For example MnSe2 nanorods and
microcrystals have been synthesized via the hydrothermal process
[26]. Here, we report a facile hydrothermal method to prepare the
cubic MnSe2/Se nanocomposites at low temperature. This work has
provided a simple and effective method to control the composition,
phase structure, and morphology of the metal selenides in the
aqueous solution, which will be important for inorganic synthesis
methodology and further applications of the selenides.
2. Experimental
2.1. Materials and experiments
All the chemicals used in our experiments were of analytical grade, and pur-
chased from Merck and used as received without further purification. A Teflon-lined
stainless steel autoclave with 150 ml capacity was used for the synthesis. Powder
X-ray diffraction (XRD) patterns were collected from a diffractometer of Philips
Company with X0PertPro monochromatized Cu K
a radiation (k = 1.54 Å). Micro-
scopic 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 res-
olution CCD camera. X-ray energy dispersive spectroscopy (EDS) analysis with
20 kV accelerated voltage was done. The magnetic measurement was carried out
⇑
Corresponding author. Tel.: +98 361 591 2383; fax: +98 361 555 2930.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
in
a vibrating sample magnetometer (VSM) (BHV-55, Riken, Japan) at room
temperature.
http://dx.doi.org/10.1016/j.jallcom.2014.08.013
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

94
A. Sobhani, M. Salavati-Niasari / Journal of Alloys and Compounds 617 (2014) 93–101
Fig. 1. SEM images of samples prepared at 120 °C for 12 h: (a) in the absent of surfactant (sample No. 1) and in the presence of: (b) PVA (sample No. 2), (c) SDBS (sample No.
3), (d) SDS (sample No. 4), (e) PEG4000 (sample No. 5), (f) PEG600 (sample No. 6), (g) CTAB (sample No. 7).
Table 1
The reaction conditions of samples prepared from MnCl2ꢁ4H2O and SeCl4 in this work.
Sample No.
Surfactant
Time (h)
T (°C)
Reductant agent
Morphology
Size
Product
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
ꢀ
12
12
12
12
12
12
12
12
12
12
12
12
24
48
12
24
24
24
120
120
120
120
120
120
120
90
180
120
120
180
120
120
120
120
120
120
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (2.5 ml)
N2H4ꢁH2O (5 ml)
N2H4ꢁH2O (15 ml)
N2H4ꢁH2O (15 ml)
N2H4ꢁH2O (20 ml)
N2H4ꢁH2O (15 ml)
KBH4
Nanorods
Nanorods
Nanorods
Nanorods
Nanorods
Nanorods
Nanorods
Nanorods
Aggregated nanoparticles
Aggregated microstructures
Microcubes
Nanoparticles + rods
Microcubes
Microcubes
Nanorods
Nanorods + microcubes
Microcubes
Microcubes
Diameter: 150 nmꢀ1
l
m
ꢀ
PVA
Diameter: 100–500 nm
Diameter: 150–950 nm
Diameter: 100–400 nm
Diameter: 250 nmꢀ1.8
Diameter: 200–700 nm
Diameter: 200–600 nm
Diameter: 130–500 nm
Micrometer
MnSe2 + Se
Se
SDBS
SDS
PEG4000
PEG600
CTAB
SDS
SDS
SDBS
PEG4000
PEG4000
PEG4000
PEG6000
PEG6000
PEG600
PEG600
PEG600
Se
lm
MnSe2 + Se
MnSe2 + Se
MnSe2 + Se
ꢀ
ꢀ
Micrometer
ꢀ
5–23
Micrometer
5.5–14
8–10
Diameter: 125–650 nm, length: 1–7
Rods: 0.7–1.2 m, cubes: 7–15
lm
MnSe2 + Se
MnSe + Se
MnSe2 + Se
MnSe2 + Se
Se
lm
lm
lm
N2H4ꢁH2O (5 ml)
N2H4ꢁH2O (8 ml)
N2H4ꢁH2O (15 ml)
l
lm
MnSe2 + Se
MnSe2 + Se
MnSe2 + Se
3–10 lm
1.5–7 lm

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95
2.2. Synthesis of MnSe2/Se nanocomposites
In typical experiment for the synthesis of MnSe2/Se nanocomposites,
a
MnCl2ꢁ4H2O 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 stirring at room temperature. Then hydra-
zine was added drop-wise. The solution was added to the autoclave and maintained
at 120 °C for 12 h. The autoclave was cooled to room temperature on its own, the
gray precipitate was separated by centrifugation and transferred into 10 ml of citric
acid (1 M) solution to remove the by-product Mn(OH)2. Then the products were
washed with distilled water and anhydrous ethanol several times, and dried under
vacuum at 60 °C for 4 h. The growth mechanism and the detailed reactions of
mechanism have been described in Ref. [11].
3. Result and discussion
Fig. 1a–g illustrates SEM images of the products synthesized at
120 °C for 12 h in the presence of 2.5 ml hydrazine and different
surfactants. From figure, it can be observed that the nanorods are
the products obtained in the presence of all surfactants. With
change at the surfactant, morphology of the samples remains
nearly constant and only size and agglomeration of the nanorods
change a little. Fig. 1a shows the SEM image of the product
obtained in the absent of surfactant (sample No. 1). The formation
of the nanorods with a high degree of agglomeration is seen in this
figure. Fig. 1c–g shows that the nanorods with large diameters are
also obtained in the presence of SDBS (sample No. 3), PEG4000
(sample No. 5), PEG600 (sample No. 6) and CTAB (sample No. 7).
When PVA is used as surfactant (sample No. 2), the morphology
of the products is nanorods with a smaller diameter (Fig. 1b).
Fig. 1d shows that the nanorods obtained in the presence of SDS
(sample No. 4) array with smaller and same diameters (see
Table 1).
The crystal structure and composition of the as-prepared prod-
ucts were determined by XRD. The XRD patterns of samples No.
2–7 are depicted in Fig. 2. As shown in Fig. 2a, d–f when PVA,
PEG4000, PEG600 and CTAB are used as surfactant and the amount
of hydrazine is 2.5 ml, the samples are found to be a mixture of Se
and MnSe2 phases. In Fig. 2, the peaks which have been indexed
with star indicate the cubic phase of MnSe2 with JCPDS card No.
73-1525. According to Fig. 2b and c, the products obtained in the
presence of SDBS (sample No. 3) and SDS (sample No. 4) are pure
Se with hexagonal crystal lattice and lattice constants a = b =
0.436 nm and c = 0.495 nm.
In this study, the effect of reaction temperature on the morphol-
ogy of samples in the presence of SDS was investigated. Three tem-
peratures were applied and other conditions were constant. The
SEM image of the product obtained in the presence of SDS at
120 °C showed formation of the nanorods with small and same
diameters (Fig. 1d). Fig. 3a and b shows the SEM images of the
products obtained at two different temperatures including 90 °C
and 180 °C. When the reaction temperature is decreased from
120 °C to 90 °C in sample No. 8 (Fig. 3a), nanorods with larger
diameters are obtained. With increasing temperature to 180 °C in
sample No. 9, aggregated nanoparticles and bulk structures are
formed as shown in Fig. 3b. Also, we investigated the effect of
the reaction temperature in the presence of PEG4000 that will be
explained in continuous.
In other side, effect of the amount of hydrazine on the morphol-
ogy, composition and structure of products in the presence of
SDBS, PEG600 and PEG4000 was investigated. During the reaction
process, the amount of hydrazine is important for the formation of
manganese selenides. According to Fig. 3c, aggregated microstruc-
tures are formed in the presence of SDBS and 5 ml hydrazine. With
change at the surfactant from SDBS to PEG600 or PEG4000 and
increase of the amount of hydrazine added to the reaction mixture,
we obtained purer product with more favored morphology. The
XRD patterns and SEM images of the products synthesized in the
Fig. 2. XRD patterns of samples prepared at 120 °C for 12 h in the presence of: (a)
PVA (sample No. 2), (b) SDBS (sample No. 3), (c) SDS (sample No. 4), (d) PEG4000
(sample No. 5), (e) PEG600 (sample No. 6), (f) CTAB (sample No. 7).
presence of PEG600 and different amounts of hydrazine (2.5, 5, 8
and 15 ml) show that the products obtained in the presence of
15 ml hydrazine are purer with more favored morphology and
smaller particle sizes [11]. The nanorods are obtained in the pres-
ence of 2.5 ml hydrazine. These nanorods have been coated with
nanoparticles. With increasing the amount of hydrazine to 5 ml,
the as-prepared samples have two morphologies: rods and cubes.
The surface of each cube has been coated with thousands of nano-
rods and nanospheres. The microrods disappear when 8 ml hydra-
zine is used, while there are still cubic microcrystals. The cubic
microcrystals exist in the presence of 15 ml hydrazine. The size

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Fig. 3. SEM images of samples prepared in the presence of: (a) SDS and 2.5 ml hydrazine at 90 °C for 12 h (sample No. 8), (b) SDS and 2.5 ml hydrazine at 180 °C for 12 h
(sample No. 9), (c) SDBS and 5 ml hydrazine at 120 °C for 12 h (sample No. 10).
Fig. 4. SEM images of samples prepared in the presence of PEG4000 and: (a, b) 15 ml hydrazine at 120 °C for 12 h (sample No. 11), (c, d) 15 ml hydrazine at 180 °C for 12 h
(sample No. 12), (e, f) 20 ml hydrazine at 120 °C for 24 h (sample No. 13).
of the as-prepared cubes decreases with increasing the amount of
the hydrazine [11].
cles. The sequential second process is aggregation of the nanopar-
ticles to form the cubic structures. For the formation of the MnSe2
nanoparticles, nucleation takes place immediately after mixing the
precursors. The nucleation rate for the samples can reach a high
value in a short time when amount of hydrazine is large. Therefore,
the nanoparticles are aggregated and cubic structures are formed.
The SEM images of the as-prepared samples in the presence of
hydrazine and PEG 4000 (samples No. 11–13) have been shown
in Fig. 4. Fig. 4a, b, e and f shows that microcubes are products
Scheme 1 shows a schematic diagram of the formation process
of the cubic MnSe2/Se nanocomposites. We have proposed a
growth mechanism of these structures, in which the individual
nanoparticles become unstable and aggregate into three-dimen-
sional cubes. It has been suggested that the formation of the nano-
particles undergoes two dynamic processes [27,28]. The first
process is nucleation, and the nuclei grow to form the nanoparti-

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97
obtained at 120 °C, in the presence of 15 ml hydrazine for 12 h
(sample No. 11) and also 20 ml hydrazine for 24 h (sample No.
13). These cubes have been coated with nanorods and their edge
180 °C, the peaks of MnSe2 disappear and the characteristic peaks
of cubic MnSe appear after 12 h. However an amount of hexagonal
Se still exists in the product, as shown in Fig. 5b. The high reaction
temperatures lead to a preference for the formation of a thermody-
namically stable phase. The obtained MnSe2 will transform into
MnSe, which is the thermodynamic stable phase when the temper-
ature or time is increased [10,11]. However, with increasing time of
reaction from 12 h to 24 h at 120 °C, MnSe2 is our unique product.
Therefore, 24 h is not long enough for the formation of MnSe, also
higher temperature from 120 °C is need for this target. From Fig. 5,
it can be observed that with increasing the temperature (from
120 °C to 180 °C) or time (from 12 h to 24 h), the crystallinity of
the nanocomposites is increased.
In continuation, the effect of reductant type on the morphology,
crystal structure and composition of products in the presence of
PEG6000 was investigated. The SEM images and XRD patterns of
samples prepared at 120 °C, in the presence of 15 ml hydrazine
(sample No. 14) and KBH4 (sample No. 15) are depicted in Fig. 6.
The SEM images of the sample No. 14 are shown in Fig. 6a. It can
be observed that cubic MnSe2/Se nanocomposites that have been
coated by thousands of nanoparticles and nanorods are product
obtained in the presence of PEG6000 and 15 ml hydrazine. The
sizes are 5–23 lm and 5.5–14 lm in samples No. 11 and 13,
respectively. In our experiments, the microcubes are not obtained
by increasing the temperature of the reaction. From Fig. 4c and d, it
is found that the product obtained at 180 °C (sample No. 12) is
mixture of rod-like structures and agglomerated nanoparticles.
Based on the classical crystal growth theory, nucleation stage
and growth process are involved in the preparation of crystals
[29–31]. Increasing of the reaction temperature always results in
an increase of the rate of reaction; therefore at relatively high tem-
peratures the reaction can be completed within a short time and
more nuclei formed before the growth process, which causes the
formation of nanoparticles and nanorods. The higher rate of reac-
tion at 180 °C does not allow ample time for the particles to
agglomerate and grow into more regular cubic shapes.
Fig. 5 shows XRD patterns of MnSe2/Se and MnSe/Se nanocom-
posites synthesized at different temperatures, in presence of
PEG4000 and different amounts of hydrazine. As shown in Fig. 5a
and c, in the presence of large amounts of hydrazine (15 or
20 ml) when temperature is 120 °C, the samples are found to be
MnSe2/Se nanocomposites. With increasing the temperature to
cubes have edge size in the range of 8–10 lm. The presence of
Fig. 5. XRD patterns of samples prepared in the presence of PEG4000 and: (a) 15 ml hydrazine at 120 °C for 12 h (sample No. 11), (b) 15 ml hydrazine at 180 °C for 12 h
(sample No. 12), (c) 20 ml hydrazine at 120 °C for 24 h (sample No. 13).

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A. Sobhani, M. Salavati-Niasari / Journal of Alloys and Compounds 617 (2014) 93–101
Fig. 6. SEM images and XRD patterns of samples prepared in the presence of PEG6000 and: (a, b) 15 ml hydrazine at 120 °C for 48 h (sample No. 14), (c, d) KBH4 at 120 °C for
12 h (sample No. 15).
Fig. 7. TEM images of MnSe2/Se nanocomposites: (a–c) sample No. 11, (d) sample No. 13, (e) sample No. 18.

A. Sobhani, M. Salavati-Niasari / Journal of Alloys and Compounds 617 (2014) 93–101
99
Fig. 8. EDS patterns of samples prepared in the presence of: (a) SDBS (sample No. 10), (b) PEG4000 (sample No. 11), (c) PEG6000 (sample No. 14).
nanoparticles and nanorods on the surface of cubes can increase
the specific surface area of the sample and is in favor of some
potential applications such as chemical supports. In Fig. 6b, the
peaks have been indexed with red1 color and . indicate the cubic
phase of MnSe2 (JCPDS card No. 73-1525) and the hexagonal phase
of Se (JCPDS card No. 42-1425), respectively. Thus the cubic MnSe2/
Se nanocomposites that have been coated by nanorods are formed at
120 °C for 12 h or longer periods of time, in the presence of PEG
(PEG600, PEG4000 and PEG6000) and large amounts of hydrazine.
The SEM image of the as-prepared sample in the presence of
PEG6000 and KBH4 (sample No. 15) has been shown in Fig. 6c. In this
figure, nanorods with diameters of 125–650 nm and lengths of 1–
action of hydrazine as the reason for the cubic MnSe2/Se nanocom-
posites obtain. The slower rate of reduction allows ample time for
the particles to agglomerate and grow into more regular shapes.
Fig. 6d indicates a pure Se phase with JCPDS card No. 06-0362 is
formed in the presence of KBH4.
The TEM images were taken for further elucidate the size and
morphology of the nanocomposites and are shown in Fig. 7. The
images show the formation of nanorods and nanoparticles on the
surface of the cubes in samples No. 11, 13 and 18. The TEM images
of the as-prepared sample in the presence of PEG4000 and 15 ml
hydrazine at 120 °C (sample No. 11) show that nanorods and nano-
particles formed on the surface of cubes have uniform sizes
(Fig. 7a–c). The nanoparticles with the diameters of 7–70 nm and
the nanorods with the diameters of 7–50 nm and lengths of
70–700 nm can be observed in this figure. However the nanorods
and nanoparticles still exist on the surface of cubes when the
amount of hydrazine and time are increased (sample No. 13), as
7 lm can be observed. Hydrazine is relatively slower in the reduc-
tion rate compared to hydroborates. Our group attributes the slower
1
For interpretation of color in Fig. 6, the reader is referred to the web version of
this article.

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The MnS2, MnSe2 and MnTe2 show antiferromagnetic ordering
[32]. Hastings et al. performed magnetic susceptibility measure-
ments down to 76 K and neutron diffraction experiments at 4.2 K
[33]. The susceptibility measurement gives
leff = 5.93 lB for
MnSe2, corresponding to a S = 5/2 spin state. The Curie-Weiss tem-
perature is hp = 483 K. The MnSe2 magnetic structure as given by
Hastings et al. can not exist in the immediate vicinity of a sec-
ond-order transition to the paramagnetic state [33]. Dimmock sug-
gested a sinusoidally modulated structure close to TN [34]. From
neutron-diffraction measurements, Plumier and Sougi have shown
the existence of a first-order transition at Tt = 48.5 K from the pre-
viously reported structure to two independent sinusoidally modu-
lated magnetic structures of comparable amplitudes and
propagation vectors along [35]. Plot of magnetization versus
applied field (M–H) at 300 K for samples No. 11 and 14 are shown
in Fig. 9. The plots show antiferromagnetic behavior in both sam-
ples. 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.
4. Conclusion
In the present work, we design a controlled synthetic method in
aqueous solution, which can conveniently produce high-quality
MnSe2/Se nanocomposites at low temperature (120 °C). The MnCl2-
ꢁ4H2O, SeCl4 and hydrazine are used as reactants in this hydrother-
mal method. The effects of preparation parameters such as: kind of
surfactant, kind of reductant and its amount, reaction time and
temperature on morphology, particle size, phase and purity of
the products are investigated. The high yield, simple reaction appa-
ratus, and low reaction temperature give this novel method a good
in future applications.
Fig. 9. M–H hysteresis at 300 K for: (a) sample No. 11 and (b) sample No. 14.
shown in Fig. 7d. From Fig. 7e, the nanorods with the diameters of
20–150 nm and the lengths between 300 nm and 1.2 m are
l
observed on the surface of cubes, in the as-prepared sample in
the presence of PEG600 and 15 ml hydrazine (sample No. 18).
The EDS technique was employed to investigate the chemical
composition and purity of as-synthesized products. The EDS pat-
terns in Fig. 8 confirm the presence of Mn and Se in samples No.
10, 11 and 14. So, the samples can be called MnSe2/Se
nanocomposites.
Acknowledgments
Authors are grateful to the council of University of Kashan for
providing financial support to undertake this work by Grant No
(159271/166).
Scheme 1. Schematic diagram of the formation process of cubic MnSe2/Se nanocomposites.

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