Tellurium nanorods and nanowires prepared by the microwave-polyol method

Article abstract of DOI:10.1246/cl.2004.760

Tellurium nanorods and nanowires have been successfully prepared in liquid phase by the microwave-polyol method without using any seed, or template or surfactant. The reduction of tellurium dioxide by ethylene glycol and formation of Te nanorods and nanow

Full text of DOI:10.1246/cl.2004.760

760
Chemistry Letters Vol.33, No.6 (2004)
Tellurium Nanorods and Nanowires Prepared by the Microwave-Polyol Method
Ying-Jie Zhuꢀ and Xian-Luo Hu
State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics,
Chinese Academy of Sciences, Shanghai 200050, P. R. China
(Received January 7, 2004; CL-040027)
Tellurium nanorods and nanowires have been successfully
ed by centrifugation, washed with absolute ethanol several
times, and dried at 80 ꢁC in vacuum.
prepared in liquid phase by the microwave-polyol method
without using any seed, or template or surfactant. The reduction
of tellurium dioxide by ethylene glycol and formation of Te
nanorods and nanowires were achieved by microwave heating
at 185 ꢁC for 30 min. The as-prepared samples were character-
ized by X-ray powder diffraction and transmission electron
microscope.
X-ray powder diffraction (XRD) patterns were recorded in
2ꢀ range from 20 to 70ꢁ, using a D/max 2550V X-ray diffrac-
ꢀ
tometer with high-intensity Cu Kꢁ radiation (ꢂ ¼ 1:54178 A)
and a graphite monochromator. Transmission electron micro-
scope (TEM) images were taken with JEOL JEM-2010 and
JEM-200CX instruments, using an accelerating voltage of
200 kV.
The properties of nanostructured materials show a strong de-
pendence not only on size but also on shape of building
blocks.1–3 Since the discovery of carbon nanotubes in 1991,4
one-dimensional (1-D) nanostructures, such as nanorods, nano-
wires, and nanotubes, have been intensively studied because of
their potential applications as important components and inter-
connects in nanodevices.5–8
Tellurium is a p-type semiconductor with many useful and
interesting properties, for example, photoconductivity, catalytic
activity toward some reactions, high piezoelectricity, thermo-
electricity, and nonlinear optical responses. In addition, Te
reacts readily with other elements to generate many functional
materials. Recent progress has been made with the preparation
of 1-D nanostructures of Te.9–13
20
30
40
50
60
70
2θ / degree
Microwave heating is promising because of its unique ef-
fects compared with the conventional heating, such as rapid
volumetric heating, higher reaction rates, shortened reaction
time, and energy saving. The microwave-polyol method has
recently been used to prepare nanoparticles of Pt, Ag,14 CdSe,15
Cd1ꢂxZnxSe,16 TiO2,17 CuInSe2, CuInTe2,18 HgS, and PbS.19
However, these nanoparticles prepared were spherical in shape
instead of nanorods or nanowires. In this paper, we demonstrate
that the microwave-polyol method can be used to prepare Te
nanorods and nanowires without using any seed or template or
surfactant. This makes it possible to avoid subsequent compli-
cated workup procedures for the removal of templates, seeds
or surfactants.
Analytical grade of tellurium dioxide and ethylene glycol
(EG) were purchased and used as received without further puri-
fication. The mixture of the reagents was placed in a 100-mL
round-bottomed flask and heated to 185 ꢁC and held at this tem-
perature for 30 min by microwave heating. The microwave oven
used was a focused single-mode microwave synthesis system
(Discover, CEM, USA). The unique, circular single-mode cavity
focuses the microwave on the reactants, ensuring the sample is in
a homogenous highly dense microwave field. Temperature was
accurately controlled by automatic adjusting of microwave pow-
er. The microwave synthesis system was equipped with a water-
cooled condenser outside the microwave cavity and a magnetic
stirring system. White reactant TeO2 was transformed to black
suspension after microwave heating. The products were separat-
Figure 1. XRD pattern of a typical sample (sample 1) prepared
by microwave-heating a mixture of 0.638 g TeO2 and 40 mL EG
at 185 ꢁC for 30 min.
Figure 1 shows XRD pattern of sample 1 prepared by micro-
wave-polyol method. It indicates a single phase of well-crystal-
lized elemental Te with the hexagonal structure. No TeO2 was
detected by XRD. Other samples prepared by changing the
amount of TeO2 have XRD patterns similar to Figure 1. The
yield of Te powder collected after washing and drying was usu-
ally higher than 90%.
The morphologies of samples were investigated with TEM.
Figure 2 shows TEM micrographs and electron diffraction pat-
terns of as-prepared Te samples. Figures 2a and 2b are for sam-
ples 2 and 1, respectively. From Figure 2a, one can see Te nano-
rods with diameters of 30 to 80 nm and with lengths ranging
from several hundreds nanometers to ꢃ1 mm. The aspect ratios
of these nanorods are in the range of ꢃ3 to ꢃ20. The aspect ratio
is defined as the length of the major axis divided by the width of
the minor axis. Nanorods are defined as structures that have
widths of 1–100 nm and aspect ratios greater than 1 but less than
20; and nanowires are analogous structures that have aspect
ratios greater than 20.20 The aspect ratio of Te nanostrucrures
increased by increasing the amount of TeO2 (see Figures 2a
and 2b). Te nanowires (sample 1) with diameters of ꢃ40 to
ꢃ110 nm and lengths up to ꢃ10 mm formed (Figure 2b). Figure
Copyright ꢀ 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.6 (2004)
761
2c shows TEM image of an individual Te nanorod (sample 2)
with a diameter of ꢃ70 nm and a length of ꢃ0:75 mm, its corre-
sponding electron-diffraction pattern is shown in Figure 2d,
which was obtained by orienting the crystal along the [210] di-
rection. It confirms the hexagonal structure of Te nanorods, con-
sistent with the result obtained from XRD. The electron-diffrac-
tion patterns of different individual Te nanorods and nanowires
were essentially the same, indicating that Te nanorods and nano-
wires were single-crystalline in structure and that Te nanorods
and nanowires had preferential growth direction along the
[001] (c axis of the crystal lattice).
achieved by microwave-heating at 185 ꢁC. The yield of Te pow-
der collected after washing and drying was usually higher than
90%. This simple, fast and high-yield method is suitable for
large-scale production of Te nanorods and nanowires. It may
also be extended to synthesize other kinds of 1-D nanostructures.
Financial support from Chinese Academy of Sciences under
the Program for Recruiting Outstanding Overseas Chinese
(Hundred Talents Program) is gratefully acknowledged. We also
thank the Fund for Innovation Research from Shanghai Institute
of Ceramics, Chinese Academy of Sciences and the Fund from
Shanghai Natural Science Foundation.
(a)
(b)
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Published on the web (Advance View) May 29, 2004; DOI 10.1246/cl.2004.760