Download Synthesis and characterization of nanostructured

Materials Letters 64 (2010) 1555–1558
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Materials Letters
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis and characterization of nanostructured powders of Bi2O3, BiOCl and Bi
F.I. López-Salinas a,b, G.A. Martínez-Castañón c,⁎, J.R. Martínez-Mendoza d, Facundo Ruiz d
a
Departamento Físico-Matemáticas, UASLP, Álvaro Obregón No. 64, Col. Centro, San Luis Potosí, S. L. P., Mexico
Centro de Investigación en Materiales Avanzados, Av. Miguel de Cervantes No. 120, Complejo Industrial Chihuahua, Chihuahua, Mexico
c
Maestría en Ciencias Odontológicas, Facultad de Estomatología, UASLP, Av. Manuel Nava No. 2, Zona Universitaria, San Luis Potosí, S. L. P., Mexico
d
Facultad de Ciencias, UASLP, Álvaro Obregón No. 64, Col. Centro, San Luis Potosí, S. L. P., Mexico
b
a r t i c l e
i n f o
Article history:
Received 18 March 2010
Accepted 20 April 2010
Available online 29 April 2010
Keywords:
Chemical synthesis
Bismuth
Bismuth oxychloride
Bismuth oxide
Nanopowders
a b s t r a c t
In the last years, synthesis and characterization of bismuth compounds have received a great attention due to
their potential applications. In this work, nanostructured powders of Bi2O3, BiOCl and Bi were prepared by a
simple aqueous precipitation method using elemental bismuth as starting material and varying some
experimental conditions. The samples obtained were characterized using X-ray diffraction (XRD) and
transmission electronic microscopy (TEM); fluorescence, infrared and UV–vis absorption spectroscopies
were also used. The obtained powders present a particle size under 100 nm, irregular morphology and
agglomeration. A quantum confinement effect can be observed in the optical properties of the samples
prepared in this work making them an interesting option for industrial applications.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
In the last years, synthesis and characterization of bismuth compounds have received a great attention due to their potential
applications. Bismuth oxide (Bi2O3) can be used as an additive in
paints and cataphoresis, it is also used as a substitute of lead oxide in
glasses [1], in oxide-ion conductors, piezo-optic materials, solar cells,
gas sensors, and ceramic glass manufacturing [2]. Despite the
importance of bismuth oxide, there are just few works devoted to
its synthesis and characterization by chemical methods [3–6].
Bismuth oxychloride (BiOCl) has been used as pigment in cosmetics
during the last 50 years due to its excellent brightness and whiteness.
BiOCl has industrial applications as catalyst in the oxidative
breakdown of n-butane [7]. The interest in the synthesis of elemental
bismuth arises from its optical properties which make it an interesting
model to study some physical phenomena [8–10]. In this work, due to
the few papers devoted to the preparation of bismuth compounds,
nanostructured powders of Bi2O3, BiOCl and Bi were prepared by a
simple aqueous precipitation method using elemental bismuth as
starting material and varying some experimental conditions; this
preparation method is not new but simpler than previously reported
methods.
2.1. Synthesis
⁎ Corresponding author. Tel./fax: +52 444 826 23 61.
E-mail address: [email protected] (G.A. Martínez-Castañón).
0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.matlet.2010.04.039
2.1.1. Bi2O3
100 mL of a 1.0 mM solution of Bi3+ was prepared by dissolving
209 mg of elemental bismuth with 1 mL of HNO3 and 99 mL of
deionized water. This solution was placed in a reactor vessel and
under magnetic stirring the pH value was raised to 11 using 1.0 M
NaOH solution. A white powder was thus obtained; this powder was
filtered, washed two times with deionized water and two times with
acetone. The powders were dried at room temperature and then
annealed at 400 °C during 30 min; the last product was a yellow
powder.
2.1.2. BiOCl
209 mg of elemental bismuth was dissolved with 1 mL of aqua
regia (HCl:HNO3, 3:1), and 99 mL of deionized water. This solution
was placed in a reactor vessel and under magnetic stirring the pH
value was raised to 9 using NH4OH. A white powder was thus
obtained; this powder was filtered, washed two times with deionized
water and two times with acetone. The powders were dried at room
temperature for its characterization.
2.1.3. Bi
100 mL of a 1.0 mM solution of Bi3+ was prepared by dissolving
209 mg of elemental bismuth with 1 mL of HNO3 and 99 mL of
deionized water. This solution was placed in a reactor vessel and,
under magnetic stirring 0.0502 g of NaBH4, previously dissolved in
10 mL of deionized water, was added. A black powder was thus
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obtained; this powder was filtered, washed two times with deionized
water and two times with acetone. The powders were dried at room
temperature for its characterization.
2.2. Characterization
Characterization was made using X-ray diffraction (XRD) in a GBCDifftech MMA model, with Cu Kα irradiation at λ = 1.54 Å, transmission electronic microscopy (TEM) analysis was performed on a JEOL
JEM-1230 at an accelerating voltage of 100 kV, differential scanning
calorimetry (DSC) and thermogravimetric analysis (TGA) were made
in a DSC system (TA instruments Q600 model) at 20 °C/min; UV–vis
and fluorescence analysis were made using Oceanoptics systems,
S2000 and SF2000 respectively. IR spectra were collected in a Nicolet
AVATAR 360 FT-IR ESP equipment.
3. Results and discussion
3.1. Bismuth oxide (Bi2O3)
Four polymorphic forms of Bi2O3 are known: α, β, γ and δ. Fig. 1a
shows the diffraction pattern of the Bi2O3 obtained; it can be indexed
as β-Bi2O3 (JCPDS 18-0244) [11]. Using Rietveld analysis (MAUD
software) [12] we calculated a crystal size of 46.1 nm. The particles
present irregular morphology and strong agglomeration (Fig. 1b)
probably due to the absence of a stabilizing agent, the particle size
according to TEM observations is about 50 nm.
Bismuth oxide can be used in microelectronics, sensors and optical
coatings due to its photoconductivity and photoluminescence [13]. In
this work, optical properties of Bi2O3 were analyzed; Fig. 1c shows the
absorption spectra of the bismuth oxide synthesized, using this
spectrum and the Brus equation [14] we calculated the band gap in
2.3 eV (the reported value is 2.5 eV). Due to the crystal size calculated
we expected a higher band gap value (a quantum confinement effect),
instead we obtained a lower value; this result could be due to a
surface polarization effect which leads to a red shift of the absorption
band edge [15]. The fluorescence signal of this material is weak
(Fig. 1d) maybe due to its strong agglomeration [16].
3.2. Bismuth oxychloride
Fig. 2a shows the diffraction pattern of the BiOCl obtained; it
can be indexed as BiOCl (JCPDS 82-0485). Using Rietveld analysis
(MAUD software) we calculated a crystal size of 14.3 nm. The
morphology of the particles is irregular and presents strong
agglomeration (Fig. 2b) probably due to the absence of a stabilizing
agent, the particle size of this sample cannot be calculated using this
technique. In order to be applied in cosmetics, BiOCl must absorb
ultraviolet radiation; our material presents an absorption band at
400 nm (Fig. 2c) then this material can be used in cosmetics giving an
ultraviolet protection.
3.3. Bismuth (Bi)
Bismuth is an important material due to its potential applications
as thermoelectric or green lubricant [17]. Fig. 3a shows a TEM
image of the bismuth particles obtained in this work; we can see that
Fig. 1. a) Diffraction pattern; b) TEM image; c) UV–vis absorption spectrum and d) emission spectra of bismuth oxide nanopowders.
F.I. López-Salinas et al. / Materials Letters 64 (2010) 1555–1558
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particles present an irregular morphology and a particle size of about
100 nm.
Diffraction peaks (Fig. 3b) can be indexed as elemental bismuth
(JCPDS 85-1329) [18,19]. Rietveld analysis gives us a crystal size of
63 nm, this crystal size is different of that observed in TEM probably
due to the strong agglomeration showed by the particles.
Infrared absorption in nanostructured bismuth increases at
about 990–1100 cm− 1. This absorption is considered as a result
from indirect intersubband transition. In bulk bismuth, carrier
pockets are located at both the L- and the T-points. Near the Fermi
level, the L-point has both valence and conduction bands, which are
separated by an energy gap of 36 meV at room temperature.
Decreasing size of particles, both the L- and T-point valence bands
move down in energy, but the L-point valence bands move down at a
faster rate than the T-point valence bands. This is why bismuth
nanoparticles have a strong absorption peak in the mid-infrared
[10,20,21]. Fig. 3c shows the infrared spectra of nanostructured
bismuth, it presents a signal at 964 cm− 1, which is a consequence of
Fig. 3. a) TEM image; b) diffraction pattern; and c) infrared absorption spectrum of
bismuth nanopowders.
quantum confinement. The rest of the signals can be assigned to
vibrations of water molecules and nitrates from the precursors used in
the synthesis method [22].
4. Conclusions
Fig. 2. a) Diffraction pattern; b) TEM image; and c) UV–vis absorption spectrum of
bismuth oxychloride nanopowders.
Different bismuth compounds were obtained in the form of
nanostructured powders using a simple aqueous precipitation
method (which is suitable for industrial uses due to its simplicity
and because we can obtain powders in the scale of grams) using
elemental bismuth as a precursor agent and varying some experimental conditions. The obtained materials present a particle size
under 100 nm, irregular morphology and agglomeration. A quantum
confinement effect can be observed in the optical properties of the
samples prepared in this work making them an interesting option for
industrial applications.
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F.I. López-Salinas et al. / Materials Letters 64 (2010) 1555–1558
Acknowledgements
This work was partially supported by Fondo de Apoyo a la
Investigación (FAI) of Universidad Autónoma de San Luis Potosí
(UASLP), Programa de Mejoramiento del Profesorado (PROMEP) and
Consejo Nacional de Ciencia y Tecnología (CONACYT).
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