Ionic liquid-induced synthesis of selenium nanoparticles

Article abstract of DOI:10.1016/j.materresbull.2010.03.005

A simple wet chemical method has been used to synthesize selenium nanoparticles by the reaction of ionic liquid with sodium selenosulphate, a selenium precursor, in the presence of polyvinyl alcohol stabilizer, in aqueous medium. The method is capable of producing spherical selenium nanoparticles in the size range of 76-150 nm under ambient conditions. This is a first report on the production of nano-selenium assisted by an ionic liquid. The synthesized nanoparticles can be separated easily from the aqueous sol by a high-speed centrifuge machine, and can be re-dispersed in an aqueous medium. The synthesized selenium nanoparticles have been characterized by X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry and transmission electron microscopy techniques.

Full text of DOI:10.1016/j.materresbull.2010.03.005

Materials Research Bulletin 45 (2010) 668–671
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Ionic liquid-induced synthesis of selenium nanoparticles
a
b
b
a,
b
Bhushan Langi , Chetan Shah , Krishankant Singh , Atul Chaskar *, Manmohan Kumar ,
Parma N. Bajaj
b
a
Changu Kana Thakur Research Centre, New Panvel 410 206, India
b
Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
A R T I C L E I N F O
A B S T R A C T
Article history:
A simple wet chemical method has been used to synthesize selenium nanoparticles by the reaction of
ionic liquid with sodium selenosulphate, a selenium precursor, in the presence of polyvinyl alcohol
stabilizer, in aqueous medium. The method is capable of producing spherical selenium nanoparticles in
the size range of 76–150 nm under ambient conditions. This is a first report on the production of nano-
selenium assisted by an ionic liquid. The synthesized nanoparticles can be separated easily from the
aqueous sol by a high-speed centrifuge machine, and can be re-dispersed in an aqueous medium. The
synthesized selenium nanoparticles have been characterized by X-ray diffraction, energy dispersive X-
ray analysis, differential scanning calorimetry and transmission electron microscopy techniques.
ß 2010 Elsevier Ltd. All rights reserved.
Received 13 October 2009
Received in revised form 4 February 2010
Accepted 8 March 2010
Available online 16 March 2010
Keywords:
A. Nanostructure
A. Semiconductor
B. Chemical synthesis
C. Differential scanning calorimetry
C. Electron microscopy
1
. Introduction
Synthesis of nano-structured materials have generated a great
ascorbate, or glycol. Oxidation methods are also reported by some
of the researchers for the formation of nano-selenium [6–9]. These
chemical methods required quite harsh experimental conditions
[10].
deal of interest because of their unique optoelectronic, magnetic
and mechanical properties, which differ largely from that of bulk
materials, as well as their applications in the fields of catalysis,
sensors and other nano-devices [1]. An extensive reported
literature exists on the synthesis and applications of nanoparticles
of both noble metals, such as silver, gold, platinum, etc., and
semiconductors, like CdSe, ZnSe, etc. However, research on nano-
metalloids, like selenium, is scanty. The high reactivity of selenium
towards a large number of chemicals has stimulated researchers
recently, to convert selenium into various important nano-
materials, such as ZnSe, CdSe, etc. [2]. Pure selenium, as well as
selenium containing nano-materials, have excellent photoelec-
trical characteristics, semiconductor properties and high biological
activity [3].
Nano-selenium has been widely used in electrical rectifiers,
photocells, photographic exposure meters, xerography, etc.,
because of its high photoconductivity, and large piezoelectric,
thermoelectric and non-linear responses [4]. Selenium is an
essential micronutrient required for most of the living organisms,
including human beings [5]. Most of the nano-selenium syntheses
have been carried out by reduction of selenium dioxide, selenate,
or selenites, with reducing agents, like hydrazine, sodium
In recent years, advantages of ionic liquids in the syntheses of
inorganic nano-materials have been gradually realized, and these
materials have received more and more attention due to their
unique physical and chemical properties. A good number of
research articles as well as reviews on the use of ionic liquids exist
in the literature [11–15]. Many nano-structured materials have
been successfully synthesized by employing ionic liquids as
precursors [16–18]. For quite a long period of time, ionic liquids
have been used as green solvents in organic syntheses, and have
also found applications in the field of catalysis [19].
Due to the great advantages of ionic liquids, we have also used
these for the synthesis of selenium nanoparticles. In this study, we
report a simple wet chemical method which is capable of
producing selenium nanoparticles by the reaction of sodium
selenosulphate with 3-methylimidazolinium methane sulfonate as
an ionic liquid, under ambient conditions. To the best of our
knowledge, the use of ionic liquid for the formation of selenium
nanoparticles is being reported for the first time.
2. Experimental details
Polyvinyl alcohol (PVA) of molecular weight 40,000, obtained
from s. d. Fine Chemicals, and selenium powder from Aldrich, were
used as received. Synthetic grade methane sulphonic acid and
1-methyl immidazole were procured from CDH and Spectrochem,
*
Corresponding author. Tel.: +91 22 27464193; fax: +91 22 27461569.
E-mail address: achaskar@rediffmail.com (A. Chaskar).
0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2010.03.005

B. Langi et al. / Materials Research Bulletin 45 (2010) 668–671
669
respectively. All the other chemicals were of GR grade, and
obtained from local market. Aqueous solutions were prepared,
using deionized water. Sodium selenosulphate, Na
prepared by the method reported earlier [20].
2
SeSO
3
, was
Na
2
SO3ðaqÞ þ SeðsÞ ! Na SeSO3ðaqÞ
2
(1)
2 3
Briefly, a mixture of selenium powder (2 g) and Na SO (20 g),
2
4
ꢂ
32ꢂ
and SeSO anions.
Scheme 1. Tetrahedral structure of SO
in 100 ml water, was refluxed at 70 8C, for about 7 h, and then it
was filtered to remove unreacted selenium, and kept in dark to
prevent photo-oxidation. This Na
2
SeSO
3
solution (ꢀ0.25 M) was
the reaction was complete, and no more formation of selenium
nanoparticles was observed on addition of a fresh aliquot of the
ionic liquid. The completion of the reaction was tested only after
separating the selenium nanoparticles from the reaction mixture.
DSC measurements were carried out, using a Mettler TA 3000
thermal analysis system, model DSC-30. XRD patterns were
recorded with a Phillips X-ray diffractometer, model PW 1710
used as a stock solution for Se precursor. PVA stock solution (1%)
was prepared by dissolving 1.0 g of PVA into 100 ml water.
The ionic liquid was synthesized by taking 1-methylimidazole
(0.01 mol) in a round-bottom flask and cooling it to 0 8C. Then,
methane sulfonic acid (0.01 mol) was added slowly with stirring.
The mixture was stirred for 5 min at room temperature, to get 3-
methylimidazolinium methane sulfonate [19]. The reaction is
given in Eq. (2).
system, using a Cu Ka source (l = 0.15406 nm). Energy dispersive
X-ray analysis (EDAX) of the synthesized selenium nanoparticles
was recorded, using an INCAE350 instrument from Oxford, UK.
TEM characterization was carried out with a JEOL-2000 FX electron
microscope, after loading the sample on a copper grid coated with
carbon film.
(
2)
3. Results and discussion
Synthesis of nano-selenium was carried out by addition of the
ionic liquid (in small aliquotes) to aqueous sodium selenosulphate
In the recent past, ionic liquids have been used, either as
ꢂ4
ꢂ3
ꢂ3
solution (concentration 5 ꢁ 10
to 1.5 ꢁ 10 mol dm ), con-
solvents, or precursors, for the synthesis of nanostructure
materials [21,22]. The synthesized ionic liquid is acidic in nature,
and it is known that sodium selenosulphate gets decomposed in
acidic medium [8,9], forming selenium. Thus, taking advantage of
taining PVA stabilizer (0.025–0.100%), while constantly stirring the
reaction mixture. The amount of the ionic liquid required for the
completion of the reaction was found to be dependent on the initial
concentration of sodium selenosulphate present in the solution.
When a small aliquot of the ionic liquid was added, it got
completely consumed, and the unreacted sodium selenosulphate
was left in the reaction mixture. This addition was repeated until
+
ꢂ
the acidic character of the ionic liquid, ([Hmim] CH
3
SO
3
), its
reaction with sodium selenosulphate was carried out, in the
presence of PVA stabilizer, to produce selenium nanoparticles, as
shown in Eq. (3).
(3)
Fig. 1. DSC thermograms of (a) the synthesized selenium nanoparticles, (b) the synthesized selenium nanoparticles brought to ambient temperature after the first run and (c)
standard commercial sample.

6
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B. Langi et al. / Materials Research Bulletin 45 (2010) 668–671
Fig. 2. XRD pattern of (a) the synthesized selenium nanoparticles without heating, and (b) after annealing at 90 8C for 150 min.
The method has advantage over the reported mineral
acid-induced formation of selenium nanoparticles [8,9], which
requires harsh chemical, even though mineral acids are used
frequently in laboratory. The sodium selenosulphate has tetra-
hedral structure, analogues to sulphate anion, as shown in Scheme
1
. The mechanism may be similar to that reported earlier [8,9], in
which proton from a mineral acid, such as hydrochloric acid, reacts
with sodium selenosulphate. In the present study, proton is
released from the ionic liquid, and reacts with sodium selenosul-
phate, to produce elemental selenium, as shown in Eq. (3).
DSC thermogram of the selenium nanoparticles, synthesized by
the reaction of aqueous 1.5 ꢁ 10ꢂ3 mol dm sodium selenosul-
phate with the ionic liquid, in the presence of 0.05% PVA, recorded
up to 250 8C, is shown in Fig. 1a. It shows an exothermic transition
at 87 8C, in addition to endothermic melting peak at higher
temperature. The repeat DSC thermogram of the same selenium
sample, recorded after bringing it to ambient temperature, did not
show any exothermic peak at the mentioned temperature (Fig. 1b).
This clearly indicates that selenium nanoparticles loose their nano-
crystalline nature in the first run itself, and the exothermic
transition is assigned to the increase in crystallinity of the
nanoparticles. DSC thermogram of the standard selenium powder
sample also did not show any such exothermic peak (Fig. 1c). All
the three DSC thermograms showed the melting peak at 217 8C.
Typical XRD patterns of the synthesized selenium nanoparti-
cles, without any heat treatment, and after annealing at 90 8C (just
above the crystallization temperature) for about 150 min, are
ꢂ3
displayed in Fig. 2. The peaks above 2u value of 408 were not
Fig. 3. EDAX pattern of the selenium nanoparticles synthesized by the reaction of
Fig. 4. (a) TEM image of the selenium nanoparticles synthesized by the reaction of
ꢂ3
ꢂ3
ꢂ3
ꢂ3
1
0
.5 ꢁ 10 mol dm sodium selenosulphate with the ionic liquid in the presence of
1.5 ꢁ 10 mol dm sodium selenosulphate with the ionic liquid in the presence of
.05% PVA.
0.05% PVA and (b) the size distribution of the selenium nanoparticles.

B. Langi et al. / Materials Research Bulletin 45 (2010) 668–671
671
resolved properly in the XRD pattern of the unannealed sample
Fig. 2a), due to its nano-crystalline nature. However, its crystal-
selenium nanoparticles, with size of 76–150 nm, could be
obtained. The selenium nanoparticles may serve as a template,
to generate other important nano-materials for their potential
applications.
(
linity increases on annealing, as shown in Fig. 2b. XRD pattern of
the synthesized selenium nanoparticles, after annealing at 90 8C,
matches very well with that of the standard selenium powder,
confirming the formation of selenium particles. This observation is
in corroboration with the DSC results obtained with the
synthesized sample. All the diffraction peaks are indexed,
assuming a triagonal phase, with calculated lattice constants,
Acknowledgements
The authors are thankful to Dr. S.T. Gadade, Principal, C.K.
Thakur College, New Panvel, for providing laboratory facility, and
Dr. L. Varshney, for DSC experiment. The authors also wish to thank
Dr. T. Mukherjee and Dr. S.K. Sarkar, B.A.R.C., for their constant
encouragement during the course of the study.
˚
˚
a = 4.363 A and c = 4.952 A, which are in agreement with the
˚
˚
literature values of a = 4.360 A and c = 4.956 A (JCPDS FILE No., 06-
62) [6]. Chemical composition was determined, using EDAX
3
technique, and as shown in Fig. 3, it also confirms that the
nanoparticles are of pure selenium, and do not contain any other
elemental impurity.
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