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

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

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.

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

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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