Growth of Sb2O3 nanotubes via a simple surfactant-assisted solvothermal process

Article abstract of DOI:10.1246/cl.2004.334

Sb₂O₃ nanotubes were successfully prepared via a simple surfactant-assisted solvothermal method. The nanotubes have an orthorhombic structure with outer diameter range from 40 to 150 nm, the wall thickness of 10 to 40 nm and a length of up to several micrometers. The formation of nanotubes followed a rolling-up mechanism.

Full text of DOI:10.1246/cl.2004.334

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Chemistry Letters Vol.33, No.3 (2004)
Growth of Sb O Nanotubes via a Simple Surfactant-assisted Solvothermal Process
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Yunxia Zhang, Guanghai Li, and Lide Zhang
Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031, P. R. China
(Received November 19, 2003; CL-031122)
Sb2O3 nanotubes were successfully prepared via a simple sur-
factant-assisted solvothermal method. The nanotubes have an or-
thorhombic structure with outer diameter range from 40 to
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50 nm, the wall thickness of 10 to 40 nm and a length of up to
several micrometers. The formation of nanotubes followed a roll-
ing-up mechanism.
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Since Iijima discovered carbon nanotubes in 1991, nano-
tubes materials have attracted much attention in both fundamental
and industrial studies owing to their unique structural and physical
characteristics: extraordinary mechanical properties, electrical
properties, unusual adsorption, and advanced catalysis, etc.2
These properties render nanotubes very promising candidates
for the realization of highly functional, effective, and resource-
saving nanodevices, e.g., single electron transistors, sensor capac-
Figure 1. XRD pattern of as-prepared samples. (a) Sb2O3 nanotubes in
the above layer; (b) Sb materials in the below layer.
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itors, or storage and release systems. Nanotubes of different com-
position have been synthesized in an attempt to create tubular
structures with novel and tailored properties. Most inorganic ox-
ide nanotubes have been prepared by using an anodic alumina
template method and sol–gel processing, e.g. titania nanotubes
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by chemical processing, silica nanotubes by an anodic alumina
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template method and vanadium oxide nanotubes by a sol–gel re-
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action following hydrothermal treatment. It is a challenge to find
new synthesis routes to other oxide tubular structures.
Antimony oxide is a very attractive material because of its in-
Figure 2. (a) SEM and (b) TEM images of as-prepared samples.
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teresting applications as catalysts and gas sensors. In addition,
Sb2O3 is very useful as a high-efficiency flame-retardant synergist
be indexed to the hexagonal structure of Sb (JCPDS 85-1324).
And no characteristic peaks of impurities were appeared in both
patterns, which substantiates that the as-prepared products are
very pure. These results also indicate that Sb2O3 products can
be easily separated from Sb.
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in plastics, paints, adhesives, and textile back coatings. Neverthe-
less, there are few reports about the growth of Sb2O3 nanotubes.
Recently, Ye et al. reported the synthesis of Sb2O3 fibrils and tu-
bules by a vapor–solid route.10 In this work, we have synthesized
The SEM image shows that the as-prepared products are very
copious (shown in Figure 2a). Figure 2b is a typical TEM image of
the Sb2O3 nanotubes. It can be seen that the Sb2O3 nanotubes are
basically straight and have outer diameters range from 40 to
of Sb2O3 nanotubes by a surfactant-assisted solvothermal method.
All the reagents were of analytical grade and were used with-
out further purification. A typical preparation procedure of Sb2O3
nanotubes is as follows: 0.04 mol SbCl3, 0.032 mol CTAB (cetyl-
trimethylammonium bromide), 0.028 mol NaBH4, and 40 mL
ethanol were added to a 50-mL flask. And then the mixtures were
stirred in a magnetic stirrer for 30 min before being transferred to
150 nm with the wall thickness of 10 to 40 nm and the length of
up to several micrometers. In addition, the walls of some nano-
tubes do not have the equal thickness. Rem sˇ kar et al. also ob-
served the phenomenon of unequal thickness of the WS nano-
ꢀ
a Teflon-lined autoclave. The autoclave was kept at 150 C for
0 h and then cooled to room temperature on standing. More inter-
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tubes and ascribed them to the strain of the inner molecular
layers of nanotubes.11
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estingly, the samples in the autoclave were automatically separat-
ed into two layers. The above layer was white powder (about
Figure 3a is a TEM image of an individual nanotube and se-
lected area electron diffraction [the inset in Figure 3a] substanti-
ated that the nanotubes we obtained are of single crystals. Figure
3b shows a typical HRTEM image of a single nanotube and the
inset is the magnified image of the rectanglar region. As can be
seen from the high-resolution fringes, the walls of the nanotube
are composed of regularly ordered molecular layers and contain
few defects such as stacking faults. The dark lines, 0.625 nm apart,
are the images of the basal (121) planes.
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samples were carefully collected, washed with distilled water
0%) and the below one was black (about 20%). The two layer
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and absolute alcohol for several times, and then dried at 80 C
for 8 h.
The XRD patterns of the as-prepared samples with different
color are shown in Figure 1. Figure. 1a is a XRD pattern of the
white products in the above layer, in which all the peaks can be
indexed to the orthorhombic structure of Sb2O3 (JCPDS 11-
During the solvothermal synthesis, the reaction path is very
sensitive to the applied experimental conditions, e.g., tempera-
ture, pH value, and duration of the solvothermal treatment. Sever-
689). Figure. 1b is a XRD pattern of the black products deposited
in the bottom of the autoclave, in which almost all the peaks can
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.3 (2004)
335
Figure 3. (a) TEM image of a single Sb2O3 nanotube; The inset shows
SAED of the nanotube. (b) A HRTEM image of the nanotube. (c) A partial-
ly magnified image of the rectanglar region in (b).
Figure 4. A typical TEM image of the intermediate for shorter reaction
time, which shows the rolling of the sheet-structures.
al experiments were performed to investigate the effect of temper-
ature and duration on the morphology of the final products. In both
cases, the concentration and amount of the reactants remained un-
changed. As a result, only nanorods were obtained at lower syn-
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thesis temperatures (e.g. at 90 C), or only sheet-like structures
and a small amount of nanotubes were formed for shorter periods
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of solvothermal treatment at 120 C. The optimal growth condi-
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tion for Sb2O3 nanotubes is a period of 30 h at 150 C. This sug-
gests that higher temperature or thermal stress might activate the
layered structures link together into tubules. Beside the influence
of the temperature and reaction time, it was found that the concen-
tration or the amount of CTAB in the system is also a very impor-
tant factor in the formation of the Sb2O3 nanotubes. Only nano-
rods were obtained without addition of CTAB. In the present
experiment, it is obvious that CTAB played a role of the soft tem-
plate in the formation of Sb2O3 nanotubes.
Figure 5. Photoluminescence and excitation spectra of the Sb2O3 nano-
tubes and powders.
In summary, a simple surfactant-assisted solvothermal proc-
ess has been developed to synthesize Sb2O3 nanotubes by using
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SbCl3, NaBH4, and CTAB as raw materials at 150 C. Careful
It is well known that the formation mechanism is a very im-
portant for exploring synthetic methods of the nanotubes. Mallouk
and co-workers did a series of significant works on lamellar struc-
tures, in which lamellar sheets, tabular structures, and rolling phe-
control of the reaction factors is indispensable for morphological
control of the products. It is expected that the surfactant-assisted
solvothermal method of nanotubes growth can be extended to the
synthesis of other oxide nanotubes. The formation mechanism of
Sb2O3 nanotubes follows the rolling-up model.
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nomena were observed.
Li et al. and Chen et al. synthe-
sized WS2 and vanadium oxide nanotubes respectively, and
provided strong evidence for their rolling model of layered struc-
tures. To investigate the growth mechanism, we performed sever-
al experiments through intercepting the intermediates at different
time. Under shorter reaction time, a large amount of plate struc-
tures and a small part of nanotubes were obtained. A more direct
evidence for the rolling mechanism is a half-tube or half-plate
structure, as shown in Figure 4, and these sheets were transformed
to nanotubes after treating again under the same condition of
nanotube formation. The partly rolling sheet structure confirmed
that Sb2O3 nanotube is formed by a rolling process.
Figure 5 shows room-temperature photoluminescence and ex-
citation spectra of the Sb2O3 nanotubes at different excitation
wavelengths together with that of Sb2O3 powders. Obviously,
the PL intensity of nanotubes is very stronger than that of pow-
ders, and the optimal excitation wavelength for Sb2O3 nanotubes
is 470 nm, the PL intensity greatly decreases at other excitation
wavelength (e.g. 455 and 485 nm). The PL intensity of Sb2O3
nanotubes is higher than that of Sb2O3 powders under all the cir-
cumstance, which indicates that the nanotubes might have higher
activity than powders. Since the PL peak shape and position of
Sb2O3 nanotubes and powders are basically identical under the
same excitation wavelength, which indicates that the PL mecha-
nism of Sb2O3 nanotubes might be the same as that of Sb2O3 pow-
ders. We speculated that the PL of Sb2O3 nanotubes might origi-
nate from the oxygen vacancies.
This work was supported by National Major Project of
Fundamental Research: Nanomaterials and Nanostructures (Grant
No. G19990645).
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Published on the web (Advance View) February 17, 2004; DOI 10.1246/cl.2004.334