b. gorji, m.r. allahgholi ghasri, r. fazaeli, n. niksirat - journal of applied chemical research, 6,...
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Journal of Applied Chemical Research, 6, 3, 22-26 (2012)
Journal of App l ied Chemical Research
www.jacr.k iau.ac. i r
Synthesis and Characterizations of Silica Nanoparticles by a New Sol-Gel Method
B. Gorji1*, M.R. Allahgholi Ghasri2, R. Fazaeli1, N. Niksirat1
1Department of Chemistry, Islamic Azad University, South Tehran Branch, Tehran, Iran2Department of Chemistry, Islamic Azad University, Shahr-e-ray Branch, Tehran, Iran
(Received 14 Dec. 2011; Final version received 23 May. 2012)AbstractSilica nanoparticles were synthesized by chemical methods from tetraethylorthosilicate (TEOS),
polyethylene glycol 5% and hydrochloric acid 0.001 N. The sol-gel process was applied for the preparation of nano silica gel. This method is hydrolysis and condensation reactions of TEOS as
precursor of silica. The optimal synthesis conditions for the preparation of silica nanoparticles were obtained and the produced silica nanoparticles were characterized by x-ray diffraction (XRD), scanning
electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that
the silica nanoparticles were successfully formed. The prepared samples change from amorphous to -crystallite phase. The XRD analysis indicated the amorphous structure of the synthesized silica
nanoparticles while the SEM and TEM images exhibited monodispersedNano sized silica particles
with a size about 34 nm. In this study, the soft process of sol-gel reaction is favourable from a view point of energy conservation. Additionally, the advantages of this technique were the purity of products and ability to control nanometer sized internal structure.Keywords: Silica nanoparticles, Tetraethylorthosilicate, Sol-Gel process, Characterization.
* Corresponding author: Dr. Banafsheh Gorji, Department of Chemistry, Islamic Azad University, South Tehran Branch, Tehran, Iran. Email: banafsheh_gorji@yahoo.com, Tel: +9821- 88830820, Fax:+9821- 88828956.
Introduction
FNanoporous materials have stimulated
increasing interests due to their extensive
applications in the fields of catalysis, drug
delivery, chemical sensors, chromatography,
microreactor and biological images [1-6].
Nano silica has been proven to be a very
promising material due to its low density,
good thermal and mechanical stability, and
chemical inertia [7-9].
The sol-gel methods are the most general
method of synthesis silica nanoparticles.
Appetence in the sol-gel processing of ceramic
and glass materials started in the half of
1800s by Ebelman and Grahams researches
on silica gels [10]. The sol-gel technique is
inexpensive and the silica gels manufactured
are non-poisonous matters [11-16].
Stober supplied monodisperse and nonporous
silica spheres with the hydrolysis of
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B. Gorji et al., J. Appl. Chem. Res., 6, 3, 22-26 (2012) 23
tetraethylorthosilicate (TEOS) in strongly
basic medium. Stober and Fink promoted
chemical reactions which checked up the
growth of spherical silica particles [17]. Bogush
and Zukoski procure monodisperesed silica
particles with controlled hydrolysis of TEOS
in ethanol [18]. Sung Kyoo Park provided
silica nanoparticles from TEOS in ethanol in
order that controlled particle properties using
a semi-batch process [19]. Ryu had prepared
amorphous silica by oxidation of silicon [20].
In the present work, we suggested a novel
method for preparing amorphous silica
nanoparticles through the sol-gel techniques
Experimental
Materials and Methods
Pure nano silica gel was prepared
with hydrolysis and condensation of
tetraethylorthosilicate (TEOS) as precursor
material. The procedure is prepared from
TEOS in the presence of polyethyleneglycol
5% (PEG) and hydrochloric acid (HCl)
0.001 N.5g TEOS was dissolved in 80g PEG
(solution 1). Solid silicagel was produced by
drop-wise addition (~ 1 ml/10 min) of 30 ml
HCl 0.001 N to solution 1 with stirring (250
rpm) at room temperature until a cloudy
solution was formed.Then it was homogenized
by homogenizer device model Art-micra D-8
n 11037 (19000 rpm) for about 30 minutes.
The obtained solution was stirred (250 rpm)
for 4 days. After this period, pH was measured
(~ 7.8). Finally, 10 ml HCl 0.1 N was added at
once to pH about 2.
The solution was heated to 80 C for forming
a viscous gel. The prepared samples were
subjected to heat-treatment temperature for 3
hours ranging 200 up to 1000 C.The X-ray
diffraction (XRD) patterns of the prepared
samples were recorded with Philips model
PW1800 and the XRD full text were obtained
with X Pert-Philips X-ray diffractometer
with monochromatisedCuK radiation of
wavelength 1.5406 A at 55 kV and 40 mA.
The surface morphology and nanostructure
of the prepared samples was evaluated using
scanning electron microscopy (SEM) (Philips
XL30) and transmission electron microscopy
(TEM) (Philips CM 200).
Results and discussion
The effects of mole ratio of TEOS to water,
amount PEG, concentration and speed of
HCladding and reaction temperature on in
situ nano silica formation were investigated.
These optimal parameters are presented in
experimental section.A typical sol-gel reaction
is hydrolysis and condensation of TEOS
as a precursor of silica. Both reactions are
concurrent and reversible depending on the
reaction conditions such as pH, temperature
and so on. The overall sol-gel reaction can be
written as follows:
Si(OC2H5)4 + 4H2O Si(OH)4 + 4C2H5OH
Si(OH)4 SiO2 + 2H2O
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B. Gorji et al., J. Appl. Chem. Res., 6, 3, 22-26 (2012)24
Figure 2. SEM photogragh of synthesized silica nanoparticles.
The characterization of the prepared silica
nanoparticles was carried out by XRD,
XRD full text, SEM and TEM.XRD analysis
indicates that a high percentage of particles are
amorphous but a few of them are crystalline.
The major phase is SiO2 quarts and the minor
phase is SiO2 cristobalite. Figure 1 shows the
full-text XRD of silica nanoparticles. Using
related data and Scherer equation, we can
predict average size of silica particles. The
Scherer equation is as follow:
D =0.9 / B cos
where is wave length of x-ray (A), B is
FWHM (radian) and is position (radian).
From the results it can be found out that the
size of particles are between 8-80 nm.
Figure 1. Full text XRD spectra of synthesized silica nanoparticles.
It is evident from Figure 2 that Nanosized
silica particles with an average particle
diameter about 34 nm and spherical structures
were formed.
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B. Gorji et al., J. Appl. Chem. Res., 6, 3, 22-26 (2012) 25
Figure3 showsTEM photographs of the
synthesized nano silica gel. It indicates that
diameters of the particles are approximately
several nanometers. It shows these particles
and also the narrow size distribution of these
particles.
Figure 3. TEM images of obtained silica nanoparticles.
Conclusions
In this study, a simple method for the
preparation of nanoporous silica based on the
sol-gel process was investigated. Morphous
silica nanoparticles with regular spherical
structure were obtained successfully using
TEOS as a precursor. The inner diameter of
nanopore size is about 34 nm. It was found
the following synthesis parameter must be
taken into consideration in synthesis of silica
nanoparticles using TEOS. In order to achieve
the best conditions for performing silica
nanoparticles, the optimal parameters should
be considered. This will enhance the use of
silica in many applications in many fields such
as catalysis.
Acknowledgements
This research has been completedthrough
research plan Synthesis of nano-stationary
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B. Gorji et al., J. Appl. Chem. Res., 6, 3, 22-26 (2012)26
phase based on silica and study of its
physicochemical properties in removal of some
pollutants under supports and supervision
of Islamic Azad University, South Tehran
Branch.The authors acknowledge the supports
of Islamic Azad University, South Tehran
Branch and Sharif Industrial University
for the SEM and TEM measurements and
KansaranBinalood co. for XRD measurements.
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