Solvothermal preparation of tin phosphide nanorods

Article abstract of DOI:10.1016/S0025-5408(00)00263-4

Tin phosphide nanorods were successfully obtained through a mild and simple solvothermal route. The synthesis was performed through the solvothermal process based on metathesis reaction between SnCl₂ and Na₃P at 120-140 °C. Reaction conditions including solvent, temperature, and the valence state of raw materials thin salts were important factors to the morphology, crystallization, and purity of nanocrystalline Sn₄P₃.

Full text of DOI:10.1016/S0025-5408(00)00263-4

Pergamon
Materials Research Bulletin 35 (2000) 675–680
Solvothermal preparation of tin phosphide nanorods
Yi Xie*, Huilan Su, Bin Li, Yitai Qian
Structure Research Lab and Department of Chemistry, University of Science and Technology of China, Hefei,
Anhui, 230026, People’s Republic of China
(Refereed)
Received 26 May 1999; accepted 12 July 1999
Abstract
Sn4P3 nanorods 20 ϫ 400 nm were successfully synthesized through a solvothermal process
based on a metathesis reaction between SnCl2 and Na3P at 120–140°C, using ethylenediamine as
the solvent and template. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: A. Inorganic compounds; B. Chemical synthesis; C. X-ray diffraction
1. Introduction
One-dimensional structures with nanometer diameters, such as nanorods and nanotubes,
are currently the focus of much research due to their special properties [1]. Compared with
micrometer-diameter whiskers, these fascinating systems are expected to exhibit remarkable
mechanical properties, as well as electrical, optical, and magnetic properties, quite different
from their corresponding bulk materials [2]. These new nanoscale materials have potential
applications in both mesoscopic research and development of nano devices. Previous works
in this field focused on carbon nanorods and nanotubes, which are the by-products of
fullerene research [3]. Carbon nanorods or nanotubes are grown conventionally by arc
discharge at a temperature of about 3000 K [4], thermal deposition of hydrocarbons [5], and
vapor–liquid–solid (VSL) growth [6]. Comparatively little research has been conducted on
other one-dimensional materials. Further, nearly all of the methods previously used to
* Corresponding author. Tel.: ϩ86-551-360-3987; fax: ϩ86-551-363-1760.
E-mail address: yxie@ustc.edu.cn (Y. Xie)
0025-5408/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: PII S0025-5408(00)00263-4

676
Y. Xie et al. / Materials Research Bulletin 35 (2000) 675–680
prepare nanorods or nanotubes need extreme conditions. How to prepare nanoscale materials
under milder conditions is an important goal of materials chemists.
Preparation of metal phosphides is a pressing problem in science and engineering at
present [7]. These materials are technologically important as semiconductors, luminescent
devices, and electronic components. Metal phosphides are made conventionally by direct
combination of elements or by the reaction of highly toxic phosphides with metal or metal
hydride via the metal organic chemical vapor deposition or self-propagation high-tempera-
ture synthesis route. These procedures typically require high reaction temperatures (above
1000°C sometimes) and long annealing periods, to produce the crystalline materials [8–10].
For example, Sn4P3 can be obtained by heating stoichiometrical elements in sealed evacuated
silica tubes at temperatures between 400 and 545°C [11]. Recently, Parkin [12] reported
using a solid-state metathesis (SSM) reaction to prepare metal phosphides and arsenides,
such as FeP and InAs, at high temperatures, but tin phosphide was not included. In this work,
pure Sn4P3 nanorods were successfully synthesized through a solvothermal process based on
a metathesis reaction between SnCl2 and Na3P at 120–140°C. Ethylenediamine was used as
the solvent and the morphology template.
2. Experimental
Preparation included two steps:
1. The formation of Na3P: An appropriate amount of analytically pure yellow phospho-
rus was washed free of water by using absolute ethanol and toluene respectively, and
sodium was free of kerosene by using toluene. Both yellow phosphorus and sodium
were used without further purification. Next they were put into a Teflon-lined
autoclave of 100 ml capacity immediately after toluene was put into the autoclave up
to 75% of the total volume. The autoclave was maintained at 150°C for 5 h, then
cooled to room temperature naturally. A black precipitate of Na3P was obtained.
2. The formation of Sn4P3: The solution of toluene was drawn off carefully, then an
appropriate amount of SnCl2 in ethylenediamine was added into the autoclave. The
autoclave was filled with nonhydrous ethylenediamine up to 75% of the total volume,
maintained at 120–140°C for 12 h, and then cooled to room temperature naturally.
The gray precipitate obtained was collected and washed with benzene, absolute
ethanol, and distilled water several times. The final product was dried in vacuum at
60°C for 2 h.
The samples were characterized by powder X-ray diffraction (XRD) patterns employing
a scanning rate of 0.05° sϪ1 in 2␪ range from 20° to 60°, using a Rigaku D/max ␥A X-ray
diffractometer equipped with a graphite monochromatized Cu K␣ radiation (␭ ϭ 1.54178 Å).
The morphology of the products was determined by transmission electron microscopy
(TEM), on a Hitachi H-800 transmission electron microscope with an accelerating voltage of
200 kV. The purity and composition were studied by the X-ray photoelectron spectra (XPS)
on an ESCALab MKII instrument, with Mg K␣ radiation as the exciting source.

Y. Xie et al. / Materials Research Bulletin 35 (2000) 675–680
677
Fig. 1. XRD pattern of the as-prepared Sn4P3 nanorods.
3. Results and discussion
All peaks in the XRD pattern (Fig. 1) were indexed to the hexagonal cell of Sn4P3 with
a ϭ 3.98, c ϭ 35.34 Å, in good agreement with JCPDS No. 20-1294. The TEM image (Fig.
2) indicated that the diameter of the nanorods was about 20 nm and the length was up to 400
nm. XPS results (Fig. 3) showed the mole ratio to be Sn:P ϭ 1.44:1, which is close to the
ratio in the form Sn4P3. From the XPS results, one can see that there was a little oxygen, due
to absorption oxygen on the surface of nanocrystalline Sn4P3. In fact, the absorption of
oxygen is very common to powder samples with high special surface area that have been
exposed to atmosphere.
It is well known that the solvents affect grain morphology [13]. In our experiments,
different solvents were tested and the results revealed that the kind of solvents used was the
most influential factor on the quality of the Sn4P3 nanorods. Ethylenediamine was chosen due
to its N-chelation and structure. It possibly binds to Sn(II), to produce a complex. The
dissolution of SnCl2 in ethylenediamine and formation of a complex increased the surface
area of SnCl2 and caused the reaction to occur in the solid–liquid system. The solvent
Fig. 2. TEM image of the as-prepared Sn4P3 nanorods.

678
Y. Xie et al. / Materials Research Bulletin 35 (2000) 675–680
Fig. 3. XPS analyses of as-prepared Sn4P3 nanorods. (a) Survey; (b) Sn region; (c) P region.
ethylenediamine enhanced the reactivity of SnCl2 and promoted the reaction between SnCl2
and Na3P, without high temperature, unlike in solid-state metathesis. Thus, this pathway
differs greatly from the solid-state reaction. Ethylenediamine probably served as a template,

Y. Xie et al. / Materials Research Bulletin 35 (2000) 675–680
679
just as it does in the formation of molecular sieves. It controlled the nucleation of Sn4P3
grains, made the Sn4P3 grains grow in one direction, and finally resulted in the Sn4P3
nanorods. This is somewhat like the nanorod growth mechanism of VLS [6]. When other
solvents with no N-chelation, such as benzene and tetrahydrofunan, were used, instead of
ethylenediamine, no Sn4P3 nanorods were obtained, the metathesis reaction was incomplete,
and there were large amounts of unreacted SnCl2 in the products. These results clearly
demonstrate that the particular structure and property of ethylenediamine play an important
role in the formation of Sn4P3 nanorods.
The preparation of Sn4P3 nanorods through the solvothermal process was found to be
dependent on several other factors, including temperature, reaction time, and the valence state of
tin salts. In the first solvothermal step, the optimum condition for the formation Na3P was 150°C
for 5 h. As an aromatic solvent was essential to preparing sodium phosphide in liquid phase [14],
toluene was chosen because of its appropriate boiling point. It was observed that at least 20–30%
excess yellow phosphorus in toluene was essential to ensure the complete conversion of Na to
Na3P. Some excess phosphorus could be involved in the subsequent reaction with SnCl2. Excess
phosphorus was dissolved in toluene and removed with the draw of toluene.
The optimum condition for synthesizing pure phase of Sn4P3 was 120–140°C for 12 h. As
the temperature was lower than 100°C and the time was less than 8 h, the yield of the Sn4P3
was lower. A higher temperature than 140°C or longer time than 12 h, however, had no
significant effect on the formation and quality of the products. The byproduct of NaCl, a small
amount of excess P, or possibly unreacted Na3P, could be removed by washing with benzene,
absolute ethanol, and water. Experiments showed that the kind of tin salts was also a critical
factor for the purity of products. When tin tetrachloride was used, the product was a mixture
of Sn4P3, SnP, and a small amount of unknown materials; whereas, when tin dichloride was
used, pure phase of Sn4P3 was obtained. The whole reaction can be expressed as follows:
ethylenediamine
12SnCl2ϩ8Na3P ϩ P
¡ 3Sn4P3 ϩ 24NaCl
4. Conclusions
In summary, Sn4P3 nanorods were successfully obtained through a mild and simple
solvothermal route. Reaction conditions including solvent, temperature, and the valence state
of raw materials tin salts are important factors to the morphology, crystallization, and purity
of nanocrystalline Sn4P3. Based on the results of the present study, we will synthesize other
kinds of metal phosphide nanorods through this route, to determine its scope.
Acknowledgment
Financial support from the Chinese National Foundation of Natural Science Research
through the National Outstanding Youth Fund and the Huo Yingdong Foundation for Youth
Teachers is gratefully acknowledged.

680
Y. Xie et al. / Materials Research Bulletin 35 (2000) 675–680
References
[1] A.M. Rao, E. Richter, S. Bandow, B. Chase, P.C. Eklund, K.A. Willams, S. Fang, K.R. Subbaswamy,
M. Menon, A. Thess, R.E. Smalley, G. Dresselhaus, M.S. Dresselhaus, Science 275 (1997) 187.
[2] A.P. Alivisatos, Science 271 (1996) 933.
[3] S. Iijima, Nature 354 (1991) 56.
[4] D.T. Colbert, J. Zhang, S.M. McClure, P. Nikolaev, Z. Chen, J.H. Hafner, D.W. Owens, P.G. Kotula,
C.B. Carter, J.H. Weaver, A.G. Rinzler, R.E. Smalley, Science 266 (1994) 1218.
[5] V. Ivanov, J.B. Nagy, P. Lambin, A. Lucas, X.B. Zhang, X.F. Zhang, D. Bernaerts, G.V. Tendeloo,
S. Amelinckx, J.V. Landuyt, Chem Phys Lett 223 (1994) 329.
[6] T.J. Trentler, K.M. Hickman, S.C. Doel, A.M. Viano, P.C. Gibbons, W.E. Buhro, Science 270 (1995)
1791.
[7] V.B. Chernogorenko, S.V. Muchnik, K.A. Lynchak, Z.A. Klimak, Mater Res Bull 16 (1981) 1.
[8] J.C. Bailer, H.J. Emelius, R. Nyholm, A.F. Trotman-Dickenson (Eds.), Comprehensive Inorganic Chem-
istry, Vol. 2, Pergamon Press, Oxford, 1973.
[9] J.R. Van Warzer, Phosphorus and Its Compounds, Vol. 1, Interscience, New York, 1958.
[10] P.R. Bonneau, P.F. Jarris, R.B. Kaner, Nature 349 (1991) 510.
[11] O. Olofsson, Acta Chem Scand 21 (1967) 1659.
[12] I.P. Parkin, Chem Soc Rev (1996) 199.
[13] R.J. Davey, S.N. Black, L.A. Bromley, D. Cottier, B. Dobbs, J.E. Rout, Nature 353 (1991) 549.
[14] D.J. Peterson, T.T. Logan, Inorg Nucl Chem 28 (1966) 53.