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Chemistry Letters Vol.38, No.5 (2009)
Room-temperature Preparation of BaMoO Nano-octahedra by Microemulsion Method
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Yan Mi, Zaiyin Huang, Zeguang Zhou, Feilong Hu, and Qiufeng Meng
College of Chemistry & Ecological Engineering, Guangxi University for Nationalities, Nanning 530006, P. R. China
(Received November 4, 2008; CL-081039; E-mail: huangzaiyin@gxun.edu.cn)
Uniform barium molybdate nano-octahedra with a mean
edge length of 50 nm have been prepared in Triton X-100 water-
in-oil (w/o) microemulsions at room temperature. BaMoO4
nano-octahedra present tetragonal single crystals. The size of
these nano-octahedra can be tuned conveniently by changing
the reagent concentrations and the molar ratio of water and
Triton X-100.
Growth of nanoscale inorganic crystals with uniform shape
and size is of fundamental interest and technological importance
owing to their unique size- and shape-dependent properties and
as potential building blocks for advanced electronic and opto-
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electronic devies. Great efforts have been devoted to the inves-
tigation of effective and efficient methods to obtain fine-tune the
shape and size of inorganic crystals in the past few years, such as
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Figure 1. XRD patterns and inset shows EDX spectra for
BaMoO4 nano-octahedra.
solution methods, often assisted by surface surfactant materials,
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tuning pH values, electrochemical deposition, and chemical
vapor deposition.4
These methods often concentrate on the investigation of tai-
loring the shape of metals and/or oxides. Scheelite-type alkaline
earth molybdates have received much attention in last years
owing to their interesting optical and structural properties.
Barium molybdate (BaMoO4) is one of the most important alka-
the above two microemulsions were mixed slowly and stirred
for 5 min. The resulting solution was aged without stirring for
2 days at room temperature. The aged solution was put in a tube
and centrifuged at 10000 revolutions/min for 10 min. The trans-
parent solution in the upper part of the tube was removed, fol-
lowed by addition of acetone and ethanol (volume ratio 1:1),
and ultrasonic rinsing for 20 min. This procedure was repeated
three times to remove the remaining organics. Pure deionized
water and ethanol were subsequently used to rinse these products
three times, respectively. Finally, white powder products were
obtained after drying in vacuum at room temperature for 12 h.
X-ray diffraction shown in Figure 1 indicates that nano-
octahedrons present tetragonal structure free of deleterious
phases. BaMoO4 signs elements O, Al, Mo, and Ba are observed
in the energy dispersive X-ray (EDX) spectrometry (see inset
Figure 1). Among which Al came from the sample stage, so
the sample was composed of O, Mo, and Ba.
Figure 2a shows field emission scanning electron micros-
copy (FESEM) micrograph of BaMoO4 nano-octahedrons. High
yield of uniform polyhedral crystals with nanometer-size is al-
most the exclusive products in our synthetic result. The particle
size distribution is demonstrated in Figure 2b, acquired by meas-
uring at least 200 particles, which shows a narrow size distribu-
tion. A Gaussian fitting curve indicates that the maximal proba-
bility for crystallite edge length is about 50 nm. Transmission
electron microscopy (TEM) micrograph (Figure 2c) clearly
shows that those particles are all of octahedral morphology.
The corresponding high-resolution transmission electron mi-
croscopy (HRTEM) image (Figure 2d) of the selected area
marked in Figure 2c shows crystalline character with a lattice
spacing of 0.277 nm, which can be indexed to the (200) plane
of tetragonal BaMoO4. The single-crystal structure of the single
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line earth molybdates, which have potential luminescent and
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scintillator properties. However, tuning the shape and size of
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BaMoO4 is lacking investigation. Recently, Cavalcante et al.
reported the obtention micro-octahedrons with average particle
size in the range from 0.7 to 3.1 mm of BaMoO4 by domestic
microwave-hydrothermal method. Since nanodevices or nano-
machines are built of nanoscale blocks, the preparation of
BaMoO4 in nanometer-size is of both theoretical and practical
importance and is still a challenge.
As is well known, the method of water-in-oil microemulsion
for the preparation of nanoscale inorganic crystals is a very fac-
ile and efficient route. Well-dispersed water pools in w/o micro-
emulsions have been shown to be an ideal microreactor, where
ultrafine, uniform, and monodisperse nanoscale inorganic crys-
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tals can form. Herein, we describe a simple solution-phase route
to produce uniform BaMoO4 nano-octahedra with average par-
ticle size of 50 nm by a quaternary reverse microemulsion solu-
tions of Triton X-100/n-octanol/cyclohexane/water system at
room temperature.
In a typical preparation, the quaternary microemulsion was
prepared by dissolving Triton X-100 (3.0 g) in 10 mL of cyclo-
hexane and 2.0 mL of n-octanol. Each solution was stirred for
30 min and then a certain volume of 0.05 M aqueous BaCl2
and 0.05 M Na2MoO4 solution was added, respectively. The
molar ratio of water to Triton X-100 (!) in each solution was
maintained at 10. Another 30 min of stirring was undertaken,
resulting in two transparent microemulsions. Equal volumes of
Copyright ꢀ 2009 The Chemical Society of Japan