A Room-Temperature Route to Bismuth Nanotube Arrays

Article abstract of DOI:10.1002/ejic.200300347

A room-temperature aqueous-chemical route has been developed to synthesize a high proportion (above 80%) of bamboo-raft-like bismuth nanotube arrays using bismuth chloride and metallic zinc powder as reagents. The prepared Bi nanotubes have uniform diameters of approximately 3-5 nm and lengths from several hundred nanometers to several micrometers. HRTEM observations show that the axial direction of the prepared nanotubes is along the normal direction of the (012) lattice planes of the rhombohedral bismuth. The possible formation mechanism is discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300347

SHORT COMMUNICATION
A Room-Temperature Route to Bismuth Nanotube Arrays
Baojun Yang,[a,b] Cun Li, Hanmei Hu, Xiaogang Yang, Qiaowei Li, and
[a]
[a]
[a]
[a]
Yitai Qian*[
a]
Keywords: Bismuth / Nanostructures / Nanotubes / Synthesis design
A room-temperature aqueous-chemical route has been de-
crometers. HRTEM observations show that the axial direction
veloped to synthesize a high proportion (above 80%) of bam- of the prepared nanotubes is along the normal direction of
boo-raft-like bismuth nanotube arrays using bismuth chlor-
ide and metallic zinc powder as reagents. The prepared Bi
the (012) lattice planes of the rhombohedral bismuth. The
possible formation mechanism is discussed.
nanotubes have uniform diameters of approximately 3−5 nm ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
and lengths from several hundred nanometers to several mi-
Germany, 2003)
Introduction
rational technique to prepare 1D Bi nanomaterials. Re-
[
14]
cently, Bi nanowires
(with a proportion of about 20%)
The discovery of carbon nanotubes[1] has initiated enor-
mous interest in one-dimensional (1D) nanostructured ma-
terials, such as nanorods, nanowires, nanobelts and nano-
tubes, due to both their interesting physical properties and
the wide range of their potential applications.[ Over the
past several years, various nanotubular materials, including
have been solvothermally synthesized at 160 °C, using bis-
muth nitrate [Bi(NO ) ·5H O] and ethylenediamine as start-
3
3
2
[11a]
ing materials. Bi nanotubes
0%) have been hydrothermally synthesized at 120 °C, using
bismuth nitrate and aqueous hydrazine [N H ·H O] as
(with a proportion of about
3
2]
2
4
2
[11b]
starting materials. Bi nanotube arrays
thermally synthesized at 200 °C, using bismuth oxide
Bi O ) and ethylene glycol as starting materials.
have been solvo-
[
3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
oxides, sulfides, BN, NiCl2, Te, Au, Ni, Pt,
[
11]
and Bi have been successfully synthesized.
(
2
3
Bismuth (Bi) is a semimetal with a quasi-layered structure
formally like that of rhombohedral graphite and black
Herein, we report a novel room-temperature aqueous-
chemical route that has been developed in our synthesis of
a high proportion (above 80%) of bamboo-raft-like bismuth
nanotube arrays through the reduction of bismuth chloride
by metallic zinc powder. The prepared bismuth nanotubes
are arrayed side by side along the axial direction with uni-
form diameters of approximately 3Ϫ5 nm and lengths from
several hundred nanometers to several micrometers. This
method requires no complex apparatus or technique, and
requires no catalyst or template.
[
12]
phosphorus.
The distances between one Bi atom and its
three close neighbors in the same layer and the neighboring
layers are 3.072 and 3.529 A, respectively. Bismuth has un-
˚
usual electronic properties that result from its highly aniso-
tropic Fermi surface, low carrier concentration, small effec-
tive mass and long mean free path of the carriers.[13] These
properties make Bi a good candidate to study quantum-
confinement effects in 1D systems and very promising ma-
terials for thermoelectric applications. However, due to the
relatively low melting point of Bi (273.1 °C), most of the
existing high-temperature approaches, such as laser ab- Results and Discussion
lation, plasma-arc, or CVD (chemical vapor deposition) are
inappropriate to synthesize 1D Bi nanomaterials. Hence, a
low-temperature chemical approach may provide a more
Figure 1 shows a typical XRD pattern of a prepared
sample. All of the sharp peaks can be indexed to a pure
¯
rhombohedral phase [space group: R3m (166)] of crystalline
[
[
a]
b]
˚
Structure Research Laboratory and Department of Chemistry, Bi. The calculated cell constants are a ϭ 4.544 A and c ϭ
University of Science and Technology of China,
Hefei, Anhui 230026, P. R. China.
˚
1.85 A, which are in good agreement with the literature
1
˚
˚
values of a ϭ 4.547A and c ϭ 11.86 A (JC,PDS 44-1246).
This XRD pattern indicates that the reduction of Bi3 to
elemental Bi is complete and pure phase crystalline Bi prod-
ucts can be obtained under current synthetic conditions.
The morphologies and the size of the prepared Bi
samples were characterized by TEM. As shown in Fig-
ure 2A and 2B, a high proportion (above 80%) of the
Fax: (internat.) ϩ 86-551/360-7402
E-mail: ytqian@ustc.edu.cn
ϩ
The School of Chemical Engineering, Hefei University of
Technology,
Hefei, Anhui 230009, P. R. China.
Fax: (internat.) ϩ 86-551/290-2956
E-mail: lhmybigy@mail.ustc.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2003, 3699Ϫ3702
DOI: 10.1002/ejic.200300347
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3699

B. Yang, C. Li, H. Hu, X. Yang, Q. Li, Y. Qian
SHORT COMMUNICATION
sample dispersed on the TEM copper grids exhibits a nano-
tubular morphology. Small amounts of flake-like Bi were
also observed. Interestingly, except for a small amount of
individual Bi nanotubes (marked by the arrow in Fig-
ure 2A), almost all these bismuth nanotubes are arrayed
like bamboo rafts. Each ‘‘bamboo raft’’ is comprised of sev-
eral parallel straight bismuth nanotubes lying side by side
along the axial direction. It can be seen that these Bi nano-
tubes have uniform diameters of approximately 3Ϫ5 nm
and lengths from several hundred nanometers to several mi-
crometers. Energy-dispersive X-ray spectrum (EDS) analy-
sis (Figure 2D) shows that the prepared sample is pure bis-
muth. This result is consistent with the XRD pattern pre-
sented above, in which no impurity phase is observed.
The prepared samples are highly sensitive to electron
beam irradiation during the TEM examination due to the
relatively low melting point of Bi (273.1 °C), which makes
it much more difficult to get clear HRTEM images. The
TEM image of a prepared sample after several seconds of
Figure 1. Typical XRD pattern of the prepared bismuth samples
Figure 2. Typical TEM images (A-C) and EDS spectrum (D) of the prepared bismuth nanotubes
700 www.eurjic.org
3
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2003, 3699Ϫ3702

Bismuth Nanotube Arrays
SHORT COMMUNICATION
intensive electron beam irradiation is shown in Figure 2C.
The specific formation mechanism of the Bi nanotubes is
It can be seen that the morphologies of the bismuth nano- not yet clear and warrants further investigation. Concern-
tubes have become blurry, some individual Bi nanotubes ing the formation mechanisms for nanotubes, several
have melted (marked by the arrow in Figure 2C) and trans- models have been suggested. For instance, curving followed
formed into polycrystalline nanowires. A similar phenom- by seaming of molecular layers (CSML) has been proposed
enon was also reported previously.[
11a,15]
However, some to be responsible for the tube-formation process of materi-
[
16]
distinguishable HRTEM images have been obtained in our als with layered structure. Direct growth through concen-
experiments. A representative HRTEM image of one sec- tration depletion at the surfaces of cylindrical seeds has
tion of a ‘‘bamboo raft’’ is shown in Figure 3. It can be been suggested to explain the formation process of Te nano-
seen that there are four Bi nanotubes which are lying side tubes containing chain-like building blocks,
by side in the image. The discriminable lattice fringes, which nanobelt-twist-join-growth has been suggested for the for-
[
7a]
and helical
[
7b]
[11a]
are perpendicular to the axial direction of the nanotubes, mation of Te nanotubes.
Li and co-workers
have de-
illustrate that the prepared Bi nanotubes are single crystals scribed that the formation of metallic Bi nanotubes may be
˚
in the area shown. The fringe spacing is about 3.2 A, which associated with the quasi-layered structure of metallic Bi.
is close to the interplanar spacing of the (012) lattice planes Similarly, the observation of tubular and flake-like struc-
of the rhombohedral bismuth. This means that the axial tures of Bi strongly induce us to speculate that the forma-
direction of the prepared nanotubes is along the normal tion of Bi nanotubes under our experimental conditions is
direction of the (012) lattice planes of the rhombohedral closer to the CSML model, though further investigation
bismuth.
about a reliable model for the structure and growth of nan-
otubes is necessary. As regards the formation of the ‘‘bam-
boo raft’’, we hypothesize that it might be due to the well-
known surface effects of nanostructured materials. The
small diameters and the high aspect ratios cause the surface
of the newly formed bismuth nanotubes to have large num-
bers of surface atoms, a lack of atomic coordination and
high surface energy. These may lead to a strong tendency
of the newly formed bismuth nanotubes to get close to each
other and then arrange side by side along the 1D direction
(the axial direction), thus forming the bamboo-raft-like
nanostructure. The observations that almost all of these
Figure 3. HRTEM image of a ‘‘bamboo raft’’ comprised of four nanotubes exhibit a bamboo-raft-like nanostructure, and
parallel nanotubes
only a small amount of tubes exist as individual nanotubes,
may indirectly confirm the hypothesis described above.
The overall reaction in our system can be simply formu- However, the intermediate process of the formation of the
lated as shown in Equation (1):
bamboo-raft-like Bi nanostructure is not yet clear.
The proper reducing agent is crucial for the formation of
bismuth nanotubes. Further investigation shows that simi-
lar bamboo-raft-like bismuth nanotubes can also be ob-
tained in alkaline solution at room temperature, using tin
chloride dihydrate (SnCl ·2H O) as reducing agent (see
2
BiCl
3
ϩ 3Zn Ǟ 2Bi ϩ 3ZnCl
2
(1)
The reaction above includes two following steps formu-
lated as Equations (2) and (3):
2
2
Supporting Information). But we failed to get Bi nanotubes
(2) at room temperature by using sodium borohydride or aque-
BiCl
3 2
ϩ H O Ǟ BiOCl ϩ 2HCl
ous hydrazine as reducing agent. The specific reasons for
these observations are unknown.
2
BiOCl ϩ 3Zn ϩ 4HCl Ǟ 2Bi ϩ 2H O ϩ 3ZnCl
2 2
(3)
First, BiCl hydrolyzes in water to form BiOCl, a white
3
precipitate [Equation (2)], which is then reduced by metallic
zinc powder to form metallic Bi. The reduction reaction
[
Equation (3)] is comprised of two half reactions [Equa-
Conclusion
tions (4) and (5)]:
ϩ
Ϫ
Ϫ
BiOCl ϩ 2H ϩ 3e Ǟ Bi ϩ H
2
O ϩ Cl (E°ϭ 0.170 V)
(4)
(5)
In summary, we have described a room-temperature
aqueous-chemical route to obtain a high proportion (above
Zn2 ϩ 2e Ǟ Zn (E°ϭ -0.7626 V)
ϩ
Ϫ
80%) of bamboo-raft-like bismuth nanotubes, which are
According to the standard of the formal potential of half comprised of several parallel straight bismuth nanotubes ly-
reactions (4) and (5), it can be seen that there is a strong ing side by side along the axial direction. HRTEM obser-
tendency for reduction reaction (3) to the formation of met- vations show that the axial direction of the prepared nano-
allic Bi. According to the added quantity of BiCl , the yield tubes is along the normal direction of the (012) lattice
3
of metallic Bi is above 90% by weight.
planes of the rhombohedral bismuth. The present study
Eur. J. Inorg. Chem. 2003, 3699Ϫ3702
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B. Yang, C. Li, H. Hu, X. Yang, Q. Li, Y. Qian
SHORT COMMUNICATION
[
[
1]
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may be advantageous over most of the previously reported
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atus or techniques, and the possibility of production on a
large scale. In addition, as a tubular sacrificing template,
the prepared Bi nanotubes might also be potentially con-
verted into 1D nanostructures of many technologically im-
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Financial support from the National Natural Science Funds and
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Received June 6, 2003
3702
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