790
Chemistry Letters 2000
Synthesis and Formation Mechanism of Bi(Se,S) Nanowires
via a Solvothermal Template Process
Huilan Su, Yi Xie,* Peng Gao, Hong Lu, Yujie Xiong, and Yitai Qian
Structure Research Laboratory and Laboratory of Nanochemistry and Nanomaterials, University of Science and Technology of China,
Hefei, Anhui 230026, P. R. China
(Received April 24, 2000; CL-000301)
Hexagonal Bi(Se,S) nanowires (20 nm × 1.5 µm) were pre-
pared for the first time via a mild solvothermal template reac-
tion of BiCl3 with triphenylphosphine sulfide (TPPS) and ele-
mental Se in ethylenediamine (en) at 120 °C for 20 h. In this
process, the sulfur source TPPS as a template, the solvent ethyl-
enediamine, and reaction temperature were critical factors of
forming hexagonal Bi(Se,S) nanowires.
Bi(Se,S) with the cell constants a = 4.190 Å, c = 23.21 Å. The
broadening of these diffraction peaks indicates that the sample
is nanosized. The (104) diffraction peak is unusually narrow
and strong, indicating a preferential growth along the c axis in
the crystal. There is a small peak marked with an asterisk,
which can be indexed as (102) diffraction peak of hexagonal
elemental Bi, indicating that probably there is trace elemental
Bi in the sample. Transmission electron microscopy (TEM)
images12 (Figure 2a) reveal that the powders are some
nanowires (20 nm × 1.5 µm) adhering small particles which
may be elemental Bi. IR spectroscopy was carried out to exam-
ine the purity of the product, and indicated the absence of both
ethylenediamine and TPPS. Elemental analysis showed a ratio
of Bi : Se : S as 1.05 : 0.48 : 0.52, indicating that the composi-
tion of the nanowires is close to the formula Bi2SeS.
To demonstrate the influence of different sulfur sources
and reaction temperatures on the final products, and to investi-
gate the formation mechanism of Bi(Se,S) nanowires, a series
of relevant experiments were carried out in ethylenediamine
through similar solvothermal processes. The main experimental
conditions and results are summarized in the following equa-
tions.
One-dimensional (1-D) nanostructures as building blocks
for many novel functional materials are currently the focus of
considerable interests.1–4 The fabrication of desirable nanocrys-
tallites is an ultimate challenge of modern material researches.
The study of reaction mechanisms will help us to understand
the chemical control of nanocrystallite nucleation and growth
process at the atomic level. The general principle in construct-
ing nanocomposites involves the intimate mixing of nanocrys-
tals with processing matrices, which include polymers, glasses,
or ceramics.5,6
Chalcogenides of group 15 have important applications.
For example, bismuth chalcogenides are important semiconduc-
tor materials in temperature-control devices.7,8 We are mainly
interested in the S–Bi–Se system, which is seldom found in the
mixed chalcogenide nanocomposites. Given that binary sul-
fides and selenides commonly have similar crystalline modifi-
cation, Bi–S and Bi–Se have similar properties, so it will not be
difficult to achieve the coexistence of Bi–S and Bi–Se in the
same system S–Bi–Se. In previous researches, we noticed that
ethylenediamine was an active solvent, which always played
important roles in some solvothermal processes.9–11 In addi-
tion, it was critical to select suitable reactants in the chemical
synthesis of desirable materials. In this letter, with ethylenedi-
amine as the solvent, BiCl3, triphenylphosphine sulfide
(TPPS),12 and elemental Se as the reactants, a mild solvother-
mal technique was developed to prepare Bi(Se,S) nanowires.
This process is described as follows.
It is obvious that ethylenediamine was an interesting sol-
vent, and selecting suitable reactants was also very important.
Ethylenediamine had reducing power, could reduce Bi3+ to Bi.
The XRD pattern and TEM image of produced elemental Bi are
shown in Figure 1(b) and Figure 2(b), respectively.
Ethylenediamine could dissolve by-product triphenylphosphine
(TPP) and unreacted elemental Se, which are not present in the
final products. In addition, ethylenediamine could dissolve ele-
mental sulfur and probably formed a stable complex, so the
reaction (3) could not produce bismuth sulfides.
The reaction temperature also played a critical role in both
affecting reaction activity of the system and further controlling
the formation and growth of crystallites. Lower temperature
than 120 °C could not initiate the reactions. At 120 °C for 20 h,
hexagonal Bi(Se,S) nanowires were obtained. At higher temper-
ature, the formation and the growth of crystallites were rapid,
there was not enough predominance for epitaxial growth of
BiCl3 (99.95%, 5 mmol), excessive elemental Se (99.99%,
3 mmol), and TPPS (3 mmol) were put into an autoclave filled
with ethylenediamine up to 90% of the volume (50 mL). The
autoclave was kept at 120 °C for 20 h, then cooled to room tem-
perature naturally. A dark gray precipitate was collected and
washed with ethylenediamine, absolute ethanol and distilled
water, respectively, then dried in a vacuum at 50 °C for 2 h.
Figure 1a shows the X-ray diffraction (XRD) pattern12 of
Bi(Se,S) nanowires. The peaks can be indexed as hexagonal
Copyright © 2000 The Chemical Society of Japan
Su, Huilan
