A Novel Mixed Reverse Microemulsion Route for the Synthesis of Nanosized Titania Particles

Abstract

The main objective of this work was to prepare nanosized titania (TiO 2) particles by mixed reverse microemul-sion route. In this work titania was prepared by quaternary microemulsion system (water/surfactant/co-surfactant/ oil-phase). Span-80, Aerosol-OT, n-Propanol, Isooctane, and Titanium tetra isopropoxide (TTIP) were used as surfactant, co-surfactant, oil-phase and titania precursor respectively. The effect of water to surfactant ratio (w 0) on the size of titania particles was studied. The X-ray diffraction pattern shows the presence of pure Anatase phase with tetragonal crystal structure. The calculation of particle size using scherrer equation shows that the particle size of titania nanoparticles increases with increasing water to surfactant ratio. The TEM image exhibited spherical morphology and narrow size distribution of the nanosized titania particles. The nanoparticles thus prepared can find applications in i.) For gas sensing. ii.) Photo-electrodes for dye-sensitized solar cells. iii.) In removing the organic chemicals which occur as pollutants in wastewater effluents.

Full text

68 The Open Mineral Processing Journal, 2010, 3, 68-72
1874-8414/10 2010 Bentham Open
Open Access
A Novel Mixed Reverse Microemulsion Route for the Synthesis of
Nanosized Titania Particles
Renu Hada1, Amod Amritphale2, S. S. Amritphale1,* and Savita Dixit3
1Advanced Materials & Processes Research Institute (CSIR), Hoshangabad Road, Bhopal-462026 (M.P), India
2Netaji Subhash Chandra Bose Govt. Medical College, Jabalpur, India
3Department of Chemistry, Maulana Azad National Institute of Technology, Bhopal, India
Abstract: The main objective of this work was to prepare nanosized titania (TiO2) particles by mixed reverse microemul-
sion route. In this work titania was prepared by quaternary microemulsion system (water/surfactant/co-surfactant/
oil-phase). Span-80, Aerosol-OT, n-Propanol, Isooctane, and Titanium tetra isopropoxide (TTIP) were used as surfactant,
co-surfactant, oil-phase and titania precursor respectively. The effect of water to surfactant ratio (w0) on the size of titania
particles was studied. The X-ray diffraction pattern shows the presence of pure Anatase phase with tetragonal crystal
structure. The calculation of particle size using scherrer equation shows that the particle size of titania nanoparticles
increases with increasing water to surfactant ratio. The TEM image exhibited spherical morphology and narrow
size distribution of the nanosized titania particles. The nanoparticles thus prepared can find applications in i.) For
gas sensing. ii.) Photo-electrodes for dye-sensitized solar cells. iii.) In removing the organic chemicals which occur as
pollutants in wastewater effluents.
Keywords: Mixed reverse microemulsion, nanosized, titania, pure anatase phase, spherical shape, narrow size distribution.
INTRODUCTION
Nanosized titania particles have been the subject of a
great deal of research because of their unique physicochemi-
cal properties and applications in the areas of pigments,
catalysts and supports, fine ceramics, cosmetics, gas sensors,
inorganic membranes, environmental purification, and
dielectric materials [1-9].
Much interest has been shown in photochemical reactions
on nanosized titania particles due to their potential applica-
tion in the conversion of solar energy into chemical energy
[10-13] and electric energy [14, 15]. When titania powder is
irradiated with photon energy larger than the band-gap en-
ergy, electrons (e) and holes (h+) are generated in the con-
duction band and the valence band, respectively. These elec-
trons and holes are thought to have the respective abilities to
reduce and oxidize chemical species adsorbed on the sur-
faces of titania particles [16]. The uses and performance for a
given application are, however, strongly influenced by the
crystalline structure, the morphology, and the size of the
particles. It is well known that titania exists in three kinds of
crystal structures namely anatase, rutile and brookite. Ana-
tase and brookite phases are thermodynamically metastable
and can be transformed exothermally and irreversibly to the
rutile phase at higher temperatures. The transition tempera-
tures reported in the literature ranges from 450 to 1200 C.
The transformation temperature depends on the nature
and structure of the precursor and the preparation condi-
tions [17, 18]. Among the three kinds of crystal structures of
*Address correspondence to this author at the Advanced Materials &
Processes Research Institute (CSIR), Hoshangabad Road, Bhopal-462026
(M.P), India; Tel: +91 755 2587244; Fax: +91 755 2587042;
E-mail: ssamritphalerrl@yahoo.co.in
titania, commercially available anatase titania fine particles
are the most effective for photocatalytic degradation of or-
ganic compounds. Therefore, it is very important to develop
methods for the synthesis of nanosized titania particles
in which the particle size and the crystal structure of the
products can be controlled.
Various synthesis methods including the CVD method
[19], colloidal template [20], hydrolysis [21, 22], sol-gel [23-
25], microemulsion (or reverse micelle systems) [17, 18, 26,
27] and hydrothermal synthesis [28, 29], have been used to
prepare nanosized titania particles. The sol-gel method [30]
requires costly organic solvents. The direct hydrolysis of
titanium salts and chemical vapor deposition procedure, in
which TiCl4 vapor is oxidized at very high temperatures
(500 C) can be used to prepare nanosized titania particles
[31-33].
In the last few years reverse micelle method was success-
fully applied to synthesize nanosized titania particles in
reverse micelles or water/oil (W/O) microemulsion systems
using titanium alkoxides as starting materials [18-20].
Reverse micelles are small aggregates (60-800 Å) formed by
surfactant molecules that surround a well defined nanometer-
sized water core [34]. This unique formation of water
droplets in an microemulsion may be considered as a small
reactor used for the synthesis of nanoparticles. The reactants
are confined within such dispersed droplets when water-
soluble precursors are used. It has been shown that this struc-
ture is the most suitable for the preparation of fine inorganic
colloidal particles, since the aggregates have very small size
and are monodispersed. Additionally, the fact that most
metal precursors are water-soluble that enhances the particle
synthesis procedure, which takes place inside the water core
of the reverse micelles. Even though the microemulsions

A Novel Mixed Reverse Microemulsion Route for the Synthesis The Open Mineral Processing Journal, 2010, Volume 3 69
have been considered as being stable systems, it was demon-
strated by Agrell, Li and Park [35, 36] that they are dynamic
systems, wherein the droplets collide continuously with each
other, resulting sometimes in formation of coalesced drops
that tend to break up, since as they lose their thermodynamic
stability. As the particle formation takes place inside the
droplet, the nature of the formed colloidal particles will be
influenced by the droplet structure and its ability to exchange
micellar-containing material [37]. Additionally, the size of
the water droplets will determine the size of the catalyst
nanoparticles. Generally, a low water to surfactant ratio (w0)
is required to form reverse micelles, depending also on the
type of the surfactant, i.e. number and length of hydrophobic
chains. For a given surfactants, w0 will give aggregates of
different size and shape (spherical micelles, rod-like micelles
and others) [38]. The synthesis of the metal nanoparticles
may be carried out in two different manners [39, 40]. The
first manner includes the addition of a reducing agent, such
as hydrazine directly into the microemulsion containing the
metal precursor. The second manner involves the mixing of
two reverse-micelle microemulsion solutions, one containing
the metal precursor and the other one containing the reducing
(or precipitating) agent [41].
In the present work we prepared nanosized titania parti-
cles using the single microemulsion system in which mixed
reverse microemulsion of water, surfactant, and oil phase
was used. Titanium Tetra Isopropoxide(TTIP) diluted by
Isopropyl alcohol(IPA) was directly added to the above mi-
croemulsion system. To study the effect of water to surfac-
tant ratio(w0) on the size titania particles, a mixed reverse
microemulsion solution containing water droplets which was
precipitated by TTIP diluted in IPA. The synthesis involves
hydrolysis of TTIP in a reverse micelle system leading to the
formation of phase pure tetragonal nanosized titania particles
at room temperature.
EXPERIMENTAL WORK
Materials
The materials used for making phase pure tetragonal
nanosized titania particles included i.) Isooctane as oil phase
(AR grade, Merck LTD., assay 99.5%), ii.) distilled water,
iii.) span 80(sorbitan monooleate, LOBA CHEMIE, PVT.
LTD., HLB=4.3; viscosity at 25 0 C = 1,000 cp), iv.) AOT
(Dioctyle sulfosuccinate, AR grade, HiMedia Laboratories
Pvt. Ltd., assay 98.0%), v.) n-propanol as cosurfactant(AR
grade, RANBAXY, assay 99.0%), vi.) IPA(Isopropyl alco-
hol, AR grade, CDH (P)), and vii.) TTIP(Titanium tetraiso-
propoxide, laboratory use, HiMedia Laboratories Pvt. Ltd.).
Synthesis of Phase Pure Tetragonal Nanosized Titania
Particles
The flow chart for the preparation of nanosized titania
powder in mixed reverse microemulsion is given in Fig. (1)
and the detailed discussion of the same is as mentioned
below.
For synthesis of nanosized titania particles, titanium tetra
isopropoxide was used as titanium precursor.
Synthesis of Nanosized Titania Powder in Mixed Reverse
Microemulsion at Water to Surfactant Ratio (wo) 4
First of all a mixed reverse microemulsion was prepared
using 150 ml isooctane , 1.5ml Water, 3.33 gms AOT, 6.5ml
SPAN 80, and 20ml n-propanol and this microemulsion mix-
Fig. (1). Flow-Chart for nanosized titania powder preparation.
Water Span 80 + AOT Isooctane n-Propanol
Mixing
TTIP+IPA
Titania reverse
microemulsion
Washing
Drying
Hydrous Titania
Calcination
Titania

70 The Open Mineral Processing Journal, 2010, Volume 3 Hada et al.
ture was stirred vigorously using a magnetic stirrer at 1500
rpm at room temperature to obtain transparent solution re-
vealing the formation of micron size water droplets homoge-
nously dispersed in continuous oil phase. Further a fresh
solution of titanium tetra isopropoxide was prepared by tak-
ing 5 ml of titanium tetra isopropoxide and diluting it with 5
ml of isopropyl alcohol and the solution thus prepared was
stored in caped measuring cylinder to avoid its hydrolysis
and the solution was then taken in a burette and was added
drop wise at the rate of 0.2 ml/min to the mixed reverse
microemulsion system using a magnetic stirrer at 1500 rpm at
room temperature till the precipitate of the titanium hydroxide
was appeared. Similar experiments were performed for
obtaining nanosized titania powder in mixed reverse micro-
emulsion at water to surfactant ratio (wo) 6 and 10.
Then the precipitate of the titanium hydroxide so
obtained was filtered using whatmann 42 filter paper, and
was washed repeatedly with 15 ml water deionised water in
each washing cycle and followed by washing with 15 ml
ethanol in each washing cycle, in order to remove the
organic residues and surfactant. The washed material was
then dried in an air oven at 800C for 10 h. The dried material
was powdered with mortar and pestle and was then calcined
at 5000C for 3 h in muffle furnace.
CHARACTERIZATION STUDIES
i) Investigation of Phase Formed in the Calcined Material
using XRD
The X-ray diffraction spectrum of the calcined powder
was recorded using Phillips make X-ray diffraction spec-
trometer (model Bruker D8) using Cu K, radiation operated
at 40 kV and 40 mA current at a scan rate of 0.008 2/s. The
phases present were identified by comparison of intensity
and d values of the possible phases in the synthesized pow-
der with standard values given in JCPDS files [42].
ii) TEM Studies
The morphology of the nano-size materials was studied
using Transmission Electron Microscope (TEM). TEM
images were recorded using JEOL 3010 operating at 300
KeV. the samples were sonicated in water/acetone for 30
min followed by ambient drying and mounted on carbon
coated copper grids.
RESULTS & DISCUSSION
i) X-Ray Diffraction Study
The XRD patterns of the calcined sample of nanosized
titania powder prepared using 4, 6 and 10 water to surfactant
ratio are given in Fig. (2). The presence of peaks of anatase
titania at ‘d’ values 3.49, 1.88, 2.35 have been observed in
all the three XRD patterns. The average crystalline sizes of
nanosized titania has been calculated by applying Scherrer’s
equation (d = k  /  cos) to the anatase (1 0 1) diffraction
peak and is given in Table 1 and found that the particle size
(nm) increases with the increase of water to surfactant ratio
i.e. 4, 6 and 10. The observed increase in size of nanosized
titania particles with increase in water to surfactant ratio
can be attributed to the increased hydrolysis of titanium
tetra isopropoxide precursor solution and thus facilitating
the availability of increased numbers of nucleai of tiatinium
species [41].
Fig. (2). XRD patterns of nanosized titania particles obtained from mixed reverse microemulsions at various water contents.

A Novel Mixed Reverse Microemulsion Route for the Synthesis The Open Mineral Processing Journal, 2010, Volume 3 71
ii) TEM Study
The typical TEM image of the calcined sample of
nanosized titania powder prepared using water to surfactant
ratio 4 is given in Fig. (3). The TEM image shows: a) the
particle size obtained in the range of 20 to 25 nm. b) spheri-
cal shape and c) narrow size dispersability of the nanosized
titania particle.
Fig. (3). TEM microphotographs of calcined sample prepared at
water to surfactant ratio (w0 = 4).
CONCLUSION
The following conclusions can be drawn from the results
described in the present paper.
1. A novel process involving mixed reverse microemulsion
route has been developed for preparing nanosized titania
particles.
2. The novelty of the process lies in the fact that conven-
tionally either catoionic or anionic or non ionic surfac-
tants are used for the synthesis of nanoparticles of titania.
Whereas in the present developed novel process prepara-
tion of nanosized titania particles has been carried out
using a unique blend system consisting of SPAN -80 and
AOT.
3. The X-ray diffraction pattern confirms the presence of
pure Anatase phase with tetragonal crystal structure.
4. Studies performed on the effect of water to surfactant
ratio shows that the particle size of nanosized titania
powder increases with the increase of water to surfactant
ratio.
5. The TEM image exhibits that titania particles spherical in
shape, particle size varies from 20 to 25 nm and have
narrow size dispersibility.
ACKNOWLEDGEMENT
The authors are grateful to the Director, A.M.P.R.I.,
Bhopal, India for encouragement of the present research
work and kind permission to publish this paper.
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Table 1. Physical Properties of Titania Nanoparticles Prepared by Mixed Reverse Microemulsion Method
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Received: January 28, 2010 Revised: May 31, 2010 Accepted: June 04, 2010
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