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Research Article

Synthesis and Characterization of Nanosize Sb2Se3 from a Single

Source Precursor

Nilkamal Maiti

Assistant Professor, Department of Chemistry; Midnapore College (Autonomous); Midnapore-

721101; West Bengal; India.

Correspondence should be addressed to Nilkamal Maity: nkmaiti@gmail.com

Abstract

One dimensional (ID) rod shaped nano compounds of Sb2Se3 have been achieved from

single source precursor, [(SbL2Cl2)Cl]2(CH3)2CO (where L represent N, N-dimethyl

selenourea) via a simple and mild solvothermal method using nucleophilic solvent, ethanol

without any surfactants or additives at very low temperature (78C). The products have been

characterized by X-ray powder diffraction (XRD) and transmission electron microscopy

(TEM). From this experiment it showed that the Sb2Se3 is composed of single crystalline Sb2S3

nanorods, belong to the orthorhombic phase with cell parameters a = 11.62Å, b = 11.77Å, c =

3.962Å. The probable formation mechanism of rod shaped nano structure of Sb2Se3 has also

been proposed.

Key words: Single precursor, solvothermal, nanorod.

Introduction

One-dimensional (1D), semiconducting and layer structure, antimony triselenide with

orthorhombic phase have been attracted enormous attention due to its high thermoelectric

power and good photo conducting power due to its low band gap energy, which promote to the

possible applications in opto and thermo electric cooling devices1; photo conducting devices2,

solar energy converter3,4.

One-dimensional (1D) nanostructure semiconducting composite materials of group V-

VI elements, having various synthetic techniques have been reported during the last few

decades. Some of the more notable examples are solvothermal method5-8, sonochemical

method9, microwave irridation10,11, single source precursor12 and so on. Among the various

techniques, solvothermal route give the various morphology such as nano wire, nanorod,

Maiti, N.: Synthesis and Characterization of Nanosize Sb2Se3………

52

nanoribon and so on. Again solvothermal route having single source precursor have much

advantages due to the mildness, safety, ease of separation and eco-friendly. Recently Chang

et.al.12, have been demonstrated the solvothermal synthesis of nano wires from single source

precursor Sb(Se2P(oiPr)3. However, this method takes long reaction time and high reaction

temperature. Therefore, it is of great importance to develop a new synthetic method that

enables the facile synthesis of 1D Sb2Se3 nanostructures without the requirement of any

surfactants and additives.

In this study, we have demonstrated the viability of a rapid and eco-friendly

solvothermal route for the synthesis of Sb2Se3 nanorodes having dimension of 100-140 nm in

diameter and 2.5-7.36 µm in length from a single-source precursor, [(SbL2Cl2)Cl]2(CH3)2CO,

in ethanol under very low reaction temperature without any surfactants or additives. The

advantage of this developed method is the relatively low reaction temperature (78C). In

addition, the rod-like Sb2Se3 nanocompounds may furnish new opportunities for fundamental

studies to explain the growth mechanism of newly shaped nanocompounds from single-source

precursors without using any surfactants or additives. In comparison to other methods, this

single-source approach is a more convenient process with respect to the ease of separation of

the product, and it is also environmentally friendly.

Experimental and Instruments

Materials and methods

Materials

All the reagents and solvents are of analytically pure and were purchased from Marck,

India. All the chemicals were used without further purification.

Preparation of single precursor

The precursor, [(SbL2Cl2)Cl]2(CH3)2CO, where L represent N, N-dimethyl selenourea,

have achieved by adapting the reported procedure13. In brief, a three necked round bottom flask

was fitted with N,N-dimethyl selenourea (132 mg; 0.877 mmol) and a magnetic bar. The flask

was degassed for 10 minutes and filled with nitrogen. After that 30 ml of dichloromethane was

added to the round bottom flask to dissolve the N, N-dimethyl selenourea. Dichloromethane

(30 ml) solution of SbCl3 (100 mg, 0.438 mmol) was added drop wise during a period of 30

minutes in to the reaction mixture with vigorous stirring. A yellow precipitate was observed.

Stirring was continued for another 2 hr followed by filtration through Whatmann-41 filter

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paper. Wash the precipitate for several times. The precipitation was dissolve in minimum

volume of acetone and kept in a refrigerator for crystallization. Yield was of 80%. M.P.

(decomposition) is 81C. Anal. Calc. for C15H28Cl6N8OSb2Se4: C, 16.11; H, 3.42; N, 10.02%.

Found: C, 16.42; H, 3.49; N, 10.16 %. IR (cm-1): 3291, 3195 (NH), 1620 ( NH2), 1568 (CN).

Preparation of nanorod

The as prepared precursor, 100 mg was taken in a three necked round bottom flask. The

flask was degassed for 10 minutes and filled with nitrogen. After that 50 ml of ethanol was

injected to it. The solvent was then reflux at 78C for 6 hr. During refluxing, colour of the

solvent changing from orange to brown and finally black precipitation was observed in the

flask. The flask was then cooled to room temperature and particles were collected by

centrifugation, wash with ethanol and water for several times and dried in a vacuum at 60 C

for 2 hr. The obtained powders were then used for characterization with XRD, TEM and XPS

spectral analysis.

Characterization techniques

The elemental analysis of the precursor was performed using FISONS EA-1108 CHN

analyzer. The IR spectra were recorded on a Perkin-Elmer Spectrum 2 FT-IR

spectrophotometer with sample prepared by KBr pellets. Transmission electron microscopy

(TEM) images and the selected area electron diffraction (SAED) patterns of antimony selenide

nanorods were recorded using a CM 12 PHILIPS along with EDX analyzer at an accelerating

voltage 200 kV. The TEM samples are prepared by placing a drop of dilute ethanol dispersion

of Sb2Se3 on the surface of a 200-mesh carbon-coated copper grid. Powder X-ray diffraction

(XRD) was recorded using a Rijaku Miniplate 600 diffractometer.

Result and Discussion

The reaction between N, N-dimethyl selenourea [Me2NC(Se)NH2], L with

antimony(III) chloride in dichloromethane at room temperature, produced yellow complex of

composition [(SbL2Cl2)Cl]2(CH3)2CO, adapting the reported procedure13.

Fig. 1 shows the XRD pattern of as-prepared Sb2Se3 at 78C in ethanol. All diffraction

peaks can be well indexed to the corresponding orthorhombic phase of Sb2Se3 having cell

parameters a =11.62Å, b = 11.77Å and c = 3.962Å, which are comparable with the values given

in JCPD file No. 97-001-6680. Sharp peaks and no other peaks related to the impurities like

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Sb2O3 and Se were detected, indicating that the as-prepared nanorods are well crystalline and

purely single phase samples.

Fig. 1. A typical XRD pattern of the as-prepared Sb2Se3 compounds obtained at 78C for 6 hr.

I have also examined the size, structure and morphology of as-prepared Sb2Se3 using

field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy

(TEM). The FE-SEM image (Fig. 2) indicated that the morphology of Sb2Se3 is rod-like

morphology with dimension 2.5 - 7.36 µm in length and 100 - 140 nm in diameter. Fig. 3(a)

represents the TEM image of a single nanorod. Fig. 3(c) represents a high resolution TEM

(HRTEM) image of Sb2Se3 nanorod in which crystal lattice fringes are clearly visible and the

observed lattice spacing of 0.284 nm which indicated that the Sb2Se3 nanorodes are single

crystalline in nature with their growth are unidirectional along the (001) axis. The electron

diffraction pattern [Fig 3(b)] was taken from a selected area of the Sb2Se3 nanorod. The spotty

pattern indicates that the as-prepared samples are single crystalline. The composition of Sb2Se3

is examined by EDX (energy dispersive X-ray spectroscopy) analysis (Fig. 3), which shows

that the atomic ratio of Sb:Se is 1:1.76 (the Cu and C peaks are arise from the copper carbon

grid).

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Fig.2. FE-SEM image of Sb2Se3 nanorodes

Fig. 3. TEM images of Sb2Se3 at 78C (a) nanorod obtain by solvothermal process after 6 hr.

(b) SAED pattern of the nanorod and (c) HRTEM image of the nanorod.

Fig. 3. EDX pattern the as-prepared Sb2Se3 nanorods obtained at 78C for 6 hr (Cu and O peaks

are arising from the copper carbon grid).

(a) (b) (c)

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The precursor contains intra and inter molecular hydrogen bonds between amine

nitrogens and chlorides13. The hydrogen bonds are promoted for the formation of antimony

selenides. During solvothermal process, hydrogen chlorides are produce in solution as by

products. The formation of Sb2Se3 nanorods may be explained as shown in Scheme 1 and 2.

The decomposition of the single precursor is shown in Scheme 1, in which CH3COCH3 is

omitted for clarity. A lone-pair electron from CH3CH2OH approaches to the electron deficient

carbon center of N, N-dimethyl selenourea (electrophilic site of the ligand) which is promoted

by the release of HCl in solution. The C–Se bond is then cleaved followed by subsequent

formation of an amide bond. Further cleavage of the organic ligand and release of chloride ion

lead to the formation of SbSe2- species in the reaction medium. It has been reported that the

chalcogenides of antimony give rise to a variety of complex building units, including Sb3Se63-

(or SbSe2-), which has been identified as a secondary building unit in Sb2Se3

14. It is assumed

that the SbSe2- ions in the reaction medium combining with each other lead to the formation of

spherical amorphous Sb2Se313 and precipitation of antimony selenide is the driving force for

the reaction (Scheme 1). Under solvothermal process, a small nanocrystallites of Sb2Se3 (nuclei

or seeds) are generated on the surfaces of these amorphous particles, through a heterogeneous

nucleation process. Subsequently, as a result of the solvothermal ripening, the growth occurs

preferentially in an energetically favourable localized region with relatively high

concentrations of amorphous Sb2Se3 through a solid–solution–solid formation mechanism15.

Thus, one small rod-like particle one after another is created and finally rod shaped

nanocompounds [Fig. 2 and 3(a)]. Thus it is assumed that this spontaneous process occurs

continuously until all the amorphous Sb2Se3 particles have been consumed, leaving behind

phase pure nanorod products.

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In solution-phase synthesis, without any surfactants or additives and at very low

reaction temperature, the morphology of the final product is highly dependent on the

anisotropic nature of the [Sb4Se6]n building blocks. Sb2Se3 is a highly anisotropic

semiconductor having a layered structure parallel to the growth direction16,17. The growth

direction is along the [001] (c-axis), which is confirmed by HRTEM observation [Fig. 3(c)].

Conclusions

In summary, we have demonstrated the viability of a rapid and eco-friendly

solvothermal route for the synthesis of Sb2Se3 nanocompounds of orthorhombic phase, from a

single-source precursor, [(SbL2Cl2)Cl]2(CH3)2CO, in ethanol under very low temperature

without any surfactants or additives. Formation of the nanorods requires reaction temperatures

of 78C. The outcome of the results has also shown that the nucleophilic solvent, ethanol, plays

an important role in the formation of the rod-like products. The growth rates of the nanorods

are along the [0 0 1] axis. The present synthetic route is also expected to provide an alternative

method for the ease of preparation of Sb2Se3 nanocompounds with unique morphology. It may

also be effective for the synthesis of other metal selenide 1D nano structures.

Acknowledgements

I am very much thankful to Department of Chemistry, Midnapore College

(Autonomous) for providing me a Laboratory, Chemicals and Instrumental facilities to achieve

this result.

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