Solvent-thermal preparation of nanocrystalline tin chalcogenide

Article abstract of DOI:10.1016/S0022-3697(98)00229-7

Nanocrystalline β-SnS₂ has been successfully prepared by the reaction between SnCl₄ and anhydrous Na₂S using a solvent-thermal method at 150 °C, which is similar to the well-known hydrothermal process except that toluene is substituted for water. X-ray diffraction analysis indicates that the product is the β-SnS₂ phase, and no Sn-O vibrations are found in the IR spectra. Transmission electron microscopy shows that the average particle size is about 12 nm.

Full text of DOI:10.1016/S0022-3697(98)00229-7

JPCS 1513
Journal of Physics and Chemistry of Solids 60 (1999) 415–417
Solvent–thermal preparation of nanocrystalline tin chalcogenide
X.F. Qiana, b, X.M. Zhanga, C. Wanga, W.Z. Wanga, Y. Xiea, b, Y.T. Qiana, b,
*
aChemistry Department, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
bStructure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
Received 17 September 1997; accepted 29 May 1998
Abstract
Nanocrystalline b-SnS2 has been successfully prepared by the reaction between SnCl4 and anhydrous Na2S using a solvent–
thermal method at 150ЊC, which is similar to the well-known hydrothermal process except that toluene is substituted for water.
X-ray diffraction analysis indicates that the product is the b-SnS2 phase, and no Sn–O vibrations are found in the IR spectra.
Transmission electron microscopy shows that the average particle size is about 12 nm. ᭧ 1999 Elsevier Science Ltd. All rights
reserved.
Keywords: A. Chalcogenides; B. Chemical synthesis; C. High pressure
1. Introduction
ZnS using the hydrothermal process at 150ЊC. However, tin
chloride has been found to be very susceptible to water, so
nanocrystalline b-SnS2 cannot be synthesized by the hydro-
thermal method.
In this study, we successfully synthesized nanocrystalline
b-SnS2 at 150ЊC via a solvent–thermal process, which is
similar to the well-known hydrothermal process except
that toluene is substituted for water.
Tin chalcogenide (SnS2) has interesting optical and elec-
trical properties [1–3], and has been used widely as a semi-
conductor and a photoconductor [4]. Conventionally, SnS2
is synthesized by direct combination of the elements [5], by
the vapor-phase reaction of the halides with hydrogen
sulfide [6–8], and by a solid-state methathesis reaction,
the reaction of SnI4 and Li2S [9]. All the above procedures
are carried out in sealed tubes and in the temperature range
400–700ЊC.
2. Experimental
Chianlli and Dines [10] synthesized a number of transi-
tion metal dichalocogenides in non-aqueous solution at
room temperature by the reaction between an anhydrous
transition metal chloride and either lithium sulfides or
ammonium hydrogen sulfide. The products had large
surface areas, but were poorly crystalline or were amor-
phous. Schleich and co-workers [11–14] also prepared
amorphous transition metal sulfides by the reaction between
metal halides and organic sulfur compounds such as hexam-
ethyldisilane (HMDST), di-tert-butyldisulfide (DTBDS), di-
tert-butylsulfide (DTBS), and tert-butylmercaptan (TBMC)
at low temperature.
All the manipulations were carried out in a dry-box filled
with nitrogen since the reagents had been found to be very
susceptible to oxidation.
Anhydrous tin tetrachloride (SnCl4) was of analytical
grade (Shanghai Chemistry Co.). Na2S was prepared from
stochiometric amounts of the elements in liquid ammonia
under an inert atmosphere [16]. Toluene was distilled with
˚
sodium to remove water, stored over 3 A molecular sieves,
and degassed with dinitrogen prior to use.
In a typical reaction, stoichiometric amounts of SnCl4 and
anhydrous Na2S were added to a Teflon-lined autoclave of
120 ml capacity. The autoclave was filled with toluene up to
75% of the total volume. At room temperature, there was no
observable reaction of SnCl4 with Na2S. The autoclave was
maintained at 150ЊC in an oven for 6–8 h, then cooled to
room temperature naturally. After being washed several
The hydrothermal process is an effective crystallization
process. Recently, Qian et al. [15] prepared nanocrystalline
* Corresponding author. Fax: ϩ0086-551-3631760; e-mail:
yqian@mail.ach.ustc.edu.cn
0022-3697/99/$ - see front matter ᭧ 1999 Elsevier Science Ltd. All rights reserved.
PII: S0022-3697(98)00229-7

416
X.F. Qian et al. / Journal of Physics and Chemistry of Solids 60 (1999) 415–417
Fig. 1. XRD pattern of b-SnS2 formed in toluene.
times with absolute ethanol to removal NaCl, a yellow
powder was collected. The final product was dried at 80ЊC
in a vacuum drier for 4 h.
the half-width of the diffraction peaks using the Debye–
Schererr formula.
Fig. 2 shows a TEM micrograph of the b-SnS2 particles,
which shows the particles to consist of uniform, spherical
crystallites. One can see that the morphology is homoge-
neous and the average size is about 12 nm, which is consis-
tent with that deduced from the XRD pattern.
The solvent–thermal reaction process can be described as
follows. It may be a liquid–solid reaction, as SnCl4 is sol-
uble in toluene.
The X-ray power diffraction (XRD) pattern was recorded
using a Japan Rigaku Damax gA X-ray diffractometer with
ꢀ
Cu Ka radiation (l ˆ 1:54178 A). Transmission electron
microscopy (TEM) images were obtained with use of a
Hitachi H-800 transmission electron microscope. The IR
spectra were obtained using a Shimadzu IR-440 spectro-
meter at room temperature.
SnCl4 ϩ 2Na2S ! SnS2 ϩ 4NaCl
3. Results and discussion
The reaction of SnCl4 with Na2S involves no redox chem-
istry; the oxidative states of the metal atoms in the reactants
do not differ from those of the corresponding metal atoms in
the products.
A typical XRD pattern for the sample is shown in Fig. 1.
All the peaks could be indexed as the hexagonal b-SnS2
phase with cell constants a ˆ 3:65 A, c ˆ 5:90 A, which
is consistent with the literature [17]. The crystal size of
the sample was about 12 nm, which was calculated from
ꢀ
ꢀ
In the preparation of nanocrystalline b-SnS2 through the
solvent–thermal procedure, several factors such as tempera-
ture, reaction time and solvent were considered. Toluene
was chosen due to its appropriate boiling point. Further-
more, toluene is a weakly polar organic solvent that should
prevent the immediate reaction of Na2S with SnCl4 at room
temperature, which is beneficial in controlling the reaction
and in forming crystalline tin sulfide. In the solvent–thermal
process, the optimum conditions for preparing b-SnS2 were
150ЊC for 6–8 h. If the temperature was lower than 100ЊC or
the time was shorter than 4 h, the yield of b-SnS2 was lower
and the as-prepared b-SnS2 was of low quality. In the reac-
tion process, we used specially treated toluene in the rigor-
ous absence of oxygen and water, which may prevent the
oxidation of SnCl4 and Na2S. The IR spectra of the final
product also indicated that there were no tin oxides, because
no Sn–O vibrations was detected in the range 500–
720 cmϪ1 [18]. The NaCl byproduct could be removed by
washing with absolute ethanol.
We also used tetrahydrofuran (THF) as the solvent. As we
slowly added Na2S to the THF solution of SnCl4 at room
temperature in a dry-box, a reaction immediately occurred,
yielding a yellow solid. XRD indicated that the product was
Fig. 2. TEM image of b-SnS2 formed in toluene.

X.F. Qian et al. / Journal of Physics and Chemistry of Solids 60 (1999) 415–417
417
[2] B. Palosz, W. Palosz, S. Gierlotka, Bull. Mineral. 109 (1986)
amorphous. Even if the product were treated under similar
conditions to those of the toluene–thermal process, the SnS2
was still poorly crystalline. The reason is that THF is a polar
solvent, so SnCl4 and Na2S can dissolve in it and can react
with each other to form an amorphous product immediately,
which is not beneficial in forming cystalline SnS2.
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4. Conclusion
In this paper, we have described the preparation of b-SnS2
through the reaction of SnCl4 with Na2S via a solvent–ther-
mal process at 150ЊC, which is similar to the well-known
hydrothermal process except that toluene is substituted for
water. The process is simple and easy to control. XRD indi-
cates that the final product is b-SnS2, and no Sn–O vibra-
tions are found in the IR spectra. TEM images show that the
average particle size is about 12 nm. The byproduct can
easily be removed using absolute ethanol.
[7] S.K. Arora, D.H. Patel, M.K. Agarwal, J. Crystal Growth 131
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Acknowledgements
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(1988) 2804.
[15] Y.T. Qian, Y. Su, Q.W. Chen, Z.Y. Chen, Mater. Res. Bull. 30
(5) (1995) 601.
This work was supported by the Chinese National Foun-
dation of Natural Science Research and Climbing Program
Research–National Foundation Project.
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References
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