synthesis of wo3 in nanoscale with the usage of sucrose ester

Synthesis of WO
3
in nanoscale with the usage of sucrose ester
microemulsion and CTAB micelle solution
N. Asim
a,
⁎
, S. Radiman
a
, M.A.bin Yarmo
b
a
School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor Darul Ehsan, Malaysia
b
School of Chemical Science and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM),
43600 Bangi, Selangor Darul Ehsan, Malaysia
Received 21 June 2006; accepted 9 October 2006
Available online 30 October 2006
Abstract
WO
3
nanoparticles were successfully prepared using first the low temperature hydrolysis method and second the chemical reaction method in
water-in-oil sucrose ester microemulsion consisting of S1570, 1-butanol, tetradecane and aqueous phase. In this study WO
3
nanoparticles also
were prepared using the CTAB micelle solution. The resultant WO
3
nanoparticles have been investigated with X-ray diffraction (XRD),
transmission electron microscopy (TEM), variable pressure scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis
(EDX) and X-ray photoelectron spectroscopy (XPS). The shape and particles size of the resultant WO
3

nanoparticles from both methods in
sucrose ester microemulsion show similar spherical shape and size range between 10 and 50 nm. The WO
3
nanoparticles prepared with the CTAB
micelle solution show spherical shape with the size range average of 25–50 nm.
© 2006 Elsevier B.V. All rights reserved.
Keywords: WO
3
; Nanoparticles; Sucrose ester microemulsion; X-ray techniques
1. Introduction
Tungsten trioxide is a simple compound in terms of
stoichiometry, but it is complex in terms of structure and phase
transitions. Tungsten oxide is known as a photochromic and
electrochromic material since it changes color upon the absorp-
tion of light and in response to an electrically induced change in
oxidation state.
WO
3
exhibits the electrochemical effect [1] and can be used
for the fabrication of smart windows and displays [2].In
addition WO
3
appears to be one of the best candidates for gas
sensing [3]. It can be operated reversibly and usually has stable
chemical and thermal properties over extended periods of use.
Gas-sensitive resistors based on tungsten oxide are useful for
the measurement of low level s of ozone in air [4,5]. Recently,
WO
3
has drawn more attention because of its high efficiency in

photocatalytic degradation of organic compounds, including a
large fraction of environmental toxins [6].WO
3
is a novel
purificatory ecomaterial suitable for application in energy
renewal, energy stor age and environmental cleanup. In all of
these applications, the morphological characteristics of the
materials like grain size or shape are very important and depend
strongly on the preparation method.
In the last decade, there has been an increasing interest in the
study of nanocrystalline materials owing to the different
physical and chemical properties compa red with convent ional
coarse-grained structures [7–10]. The surface-to-bulk ratio for a
nanocrystalline material is much greater than for a material with
large grains, which yields a large interface between the solid and
a gaseous or liquid medium.
Many different methods have been used for the production of
nanometer particles. Microemulsions that contain surfactant, oil,
water and sometimes co-surfactant have been used widely for the
synthesis of nanomaterials in the last two decades. Sucrose esters
are biodegradable surfactants that can be manufactured in various
hydrophilic–lipophilic properties using different fatty acids
varying in their lipophilic chain length. Sucrose esters exist in a
large variety of HLB values. The physical properties of sucrose
Materials Letters 61 (2007) 2652 – 2657
www.elsevier.com/locate/matlet
⁎
Corresponding author. Tel.: +60 3 89214131; fax: +60 3 89269470.
E-mail address: (N. Asim).
0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.matlet.2006.10.014
esters are somewhat unique. Unlike the alkyl ethoxylates, the
sucrose esters do not significantly change their HLB with in-
creasing temperature. Consequently, increasing the temperature
does not induce a phase inversion in microemulsion systems based
on sucrose esters, as was observed in microemulsions based on
alkyl ethoxylates. Temperature-insensitive sucrose ester-based
microemulsions are described in the literature [11–13].Itwas
found in general that sucrose esters are not able to form micro-
emulsions without co-surfactants [14]. Since the most common
sucrose esters are hydrophilic it was not expected that these
surfactants will form reverse micelles or w/o microemulsions.
However, Garti et al. [15] showed that the addition of a co-solvent/
co-emulsifier, such as short- or medium-chain alcohols, induces
the formation of reverse micelles and the solubilization of
Fig. 1. The VPSEM images of WO
3
nanoparticles prepared in this study.
Fig. 2. The TEM images of WO3 nanoparticles prepared in this study.
2653N. Asim et al. / Materials Letters 61 (2007) 2652–2657
significant amounts of water into the micellar core to form water-
in-oil microemulsions. In this study WO
3
were prepared in
nanosize with different size ranges using sucrose ester and CTAB
surfactants and its chemical and physical properties were
investigated.
2. Materials and methods
2.1. Materials
Nonionic surfactant of food grade sucrose fatty acid ester

(hereafter denoted as S1570 with HLB value=15) and
tetradecane (99%) were supplied from Mitsubishi-Kagaku
Foods Corporation and TCI respectively. Hexadecyl trimethyl
ammonium bromide (CTAB) (purity approx. 99%) was
purchased from Sigma. 1-butanol (N 98% GC) and 1-hexanol
were purchased from Fluka.
Tungsten (VI) chloride (99%) and ammonia solution (25%)
were purchased from Aldrich and BDH respectively. Deionized
and double distilled water was used for microemulsion and
solution preparation. All the chemicals and solvents were used
as received without further purifications.
2.2. Determination of phase diagr am for sucrose ester
As describe elsewhere [16] for determination of phase
diagram, alcohol, oil, sucrose ester mixtures were titrated with
water. The behavior of the four-component system is described
in pseudo-ternary phase diagrams in which the weight ratio of
two components was fixed. Usually, the oil:alcohol weight ratio
was held constant at 1:1. The construction of the phase diagram
was conducted in a thermostatic bath (37 ± 1 °C).
The weight ratio of tetradecane (oil phase) and 1-butanol (co-
surfactant) was fixed at 1:1, whereas the surfactant phase
consisted of sucrose ester (S1570). The sugar ester used is a
commercial sucrose monoester of stearic acid (S1570, denoted as
SES, HLB = 15, at least 70% monoester) in a mixture with di- and
polyesters of stearic and palmitic acids. The oil phase consists of a
1:1 weight ratio of tetradecane and l-butanol. The addition of the
co-solvent (l-butanol) to the oil phase turned the oil phase into a
better solvent and allowed significant solubilization of the
surfactant into the oil with the formation of inverse micelles.
Fig. 3. The XRD diffractogram for WO

3
(a) bulk, (b) sample 1, (c) sample 2 and
(d) sample 3, respectively.
Fig. 4. The energy dispersive X-ray (EDX) results for WO
3
nanoparticles.
2654 N. Asim et al. / Materials Letters 61 (2007) 2652–2657
The co-solvent is necessary because of the hydrophilicity of the
sucrose monostearate and hydrophobicity of the oil. Upon
addition of 1-butanol to tetradecane , due to its amphiphilic
character it will redistribute into the interface and must therefore
be considered also as a co-surfactant and not just as a co-oil; i.e., it
has the ability to participate in the self-assembly with the
surfactant. The microemulsion system used is solid at room
temperature, but liquefies and structures into a homogeneous
microemulsion when heated above 37±1 °C [17,18].
2.3. Preparation of WO
3
in nanoscale
The typical microemulsion used in the present study has the
following com position: 30 wt.% of S1570, 50 wt.% of
Fig. 5. Peak-fitted W
4f
,O
1s
and C
1s
signals of WO
3
nanoparticles (a) sample 1, (b) sample 2 and (c) sample 3 respectively.

2655N. Asim et al. / Materials Letters 61 (2007) 2652–2657
tetradecane/1-butanol and 20 wt.% of aqueous solution.
Aqueous solutions containing of 4 wt.% and 14 wt.% of
tungsten (VI) chloride and ammonia solution respectively. Two
methods have been used for the synthesis of WO
3
in nanoscale
with the use of sucrose ester microemulsion.
In the first method, a w/o microemulsion with the
composition: 30 wt.% of S1570, 50 wt.% of tetradecane/1-
butanol and 20 wt.% of aqueous solution containing of 4 wt.%
tungsten (VI) chloride, was stirred vigorously for 2 h at about
45 °C. Then this solution was kept in 60 °C for 4 days and were
washed several times with deionized water and absolute ethanol
in order to remove the surfactant, residual reactants and
byproducts. All the precipitates were place in the furnace at
500 °C for 2 h (hereafter denoted as sample 1).
In the second method, two types of w/o microemulsion with
the composition: 30 wt.% of S1570, 50 wt.% of tetradecane/1-
butanol and 20 wt.% of aqueous solution (containing of 4 wt.%
and 14 wt.% of tungsten (VI) chloride and ammonia solution
respectively) have been prepared.
After stirring and getting homogeny solutions, the micro-
emulsion containing ammonia solution was added to the other
microemulsion containing tungsten (VI) chloride. The mixed
microemulsion was stirred for 3 h at about 45 °C. Then the
mixed microemulsion was kept at room temperature for 3 days
in order to precipitate. After washing several times with
deionized water and absolute ethanol in order to remove the
surfactant, residual reactants and byproducts, the precipitate

was kept in the furnace at 500 °C for 2 h (hereafter denoted as
sample 2). The CTAB micelle solution used in the present study
has a composition of 30 wt.% CTAB, 54 wt.% 1-hexanol and
16 wt.% of aqueous solution. This chosen composition was
found to belong to the reverse micelles region [19]. For WO
3
nanoparticles pre paratio n, two micelle solutions with the
composition mentioned above with aqueous solutions contain-
ing of 3.1 wt.% and 12.5 wt.% of tungsten (VI ) chloride and
ammonia solution respective ly were prepared. After stirring and
getting clear solutions, the micelle solution containing ammonia
solution was added to the other micelle solution containing
tungsten (VI) chloride. The mixed micelle solution was stirred
for 4 h at about 50 °C. Then the mixed micelle solution was kept
at room temperature for 3 days in order to precipitate. After
washing several times with deioni zed water and absolute
ethanol in order to remove the surfactant, residual reactants and
byproducts, the precipitate was kept in the furnace at 500 °C for
2 h (hereafter denoted as sample 3).
2.4. Characterization of WO
3
nanoparticles
The study of the morphology and composition of the cal-
cinated WO
3
nanoparticles were done by variable pressure
scanning electron microscope (VPSEM), (model Leo 1450,
accelerating vo ltage at 30 kV) equipped with energy dispersive
X-ray analysis (EDX) and transmission electron microscopy
(TEM) (mod el Phillips, CM12) operated at 100 kV. The X-ray

diffraction (XRD) measurements were performed by a Bruker
D8 advance X-ray diffractometer with running step =0.02° in
the range of 20–65° 2-Theta, using a monochromatized Cu K α
radiation ( λ = 0.154 nm).
The XPS analyses were performed using a XSAM-HS
KRATOS X-ray photoelectron spectroscop y. X-ray source type
MgK was used with 10 mA current and 12 kV voltage to run
XPS analys is for samples at 10
− 9
Torr pressure.
The pass energy was set at 160 eV for the survey spectra and
at 40 eV for the high resolution spectra of all elements of interest.
Data processing was performed using the Kratos software after
Shirley baseline subtraction and using Schofield sensitivity
factors corrected for instrumentation transmission function.
3. Results and discussion
The mor phologie s a nd s ize of the prepa red n anopar ticles wer e studied
by variable pressure scanning electron microscope (VPSEM) and
transmission electron micro scopy (TEM). They give comparable informa-
tion for morphology and s ize investigations. The VPSEM a nd TEM images
are depicte d in Figs. 1 and 2 respectively and show that the WO
3
nanoparticles prepared via sucrose ester microemulsion for both methods
have spherical shape and approximately the same size range between 10
and50nm.WO
3
nanoparticle s prepared via CTAB microemulsion also
have a spherical shape but with bigger size range between 25 and 50 nm.
The XRD patterns in Fig. 3 shows that the WO
3

was in the form of
orthorhombic lattice for all of the nanoparticles. More evaluation of the
composition and purity of prepared WO
3
nanoparticles has been done
by energy dispersive X-ray analysis (EDX) and X-ray photoelectron
spectroscopy (XPS). The calculated stoichiometry for the prepared
nanoparticles taken from the atomic ratio data of EDX measurements
(Fig. 4)isWO
3
within the limits of the experimental error.
The wide scan of XPS spectrum within the B.E. range of 0–1100 eV
and the narrow scan have been done for the WO
3
samples. Fig. 5 shows
peak analysis of W
4f 7/2
,W
4f 5/2
,O
1s
and C
1s
signals for WO
3
samples.
Both of the XPS and EDX patterns reveal the existence of W, O and
C in the nanoparticles. The existence of C impurity in nanoparticles is
believed to originate from environmental contamination and also the
residual surfactants absorbed on the nanoparticles.

The C
1s
peak in the XPS results (Fig. 5) is from carbon contamination
that is very usual and in fact, it is often used to calibrate peak position and
in this case we assumed it comes from the residual surfactant and the
environment. The photoelectron peak of the W
4f
region in all of WO
3
samples shows a well-resolved double peak due to the 4f
7/2
and 4f
5/2
components (spin orbit splitting) and reveals the W
+6
state and oxide
form of tungsten in compound according to XPS handbook [20].TheO
1s
band was deconvoluted in 3 components, the first one from right assumed
is terminal oxygen (_O) and the second one is linkage oxygen (–O–)
and these peaks were associated to the O
2−
state, and the third one is
Table 1
Binding energy (eV) for relative peak of WO
3
samples (corrected using
C
1s
= 285 eV as a reference)

Sample Particle size
(nm), shape
O
1s
(1)
O
1s
(2)
O
1s
(3)
W
4f
(1)
W
4f
(2)
W
4f
(3)
W
4f
(4)
WO
3
(bulk) 40–120,
different shapes
530.3 532.1 533.5 35.7 37.8
WO
3

(sample 1) 10–50,
spherical
530.6 532.2 533.6 36.0 38.0
WO
3
(sample 2) 10–50,
spherical
530.5 532.3 533.8 35.9 38.1 37.3 39.7
WO
3
(sample 3) 25–50,
spherical
530.7 532.4 533.6 36.1 38.2
2656 N. Asim et al. / Materials Letters 61 (2007) 2652–2657
assumed to come from different sources, probably coming from rooted
OH groups or from humidity in ambience (Table 1) [20]. The binding
energies show the blue shift for nanomaterials prepared in this study
compared with the bulk one and the more study on XPS blue shift induced
in WO
3
nanoparticles are still in progress.
4. Conclusion
Sucrose ester microemulsion and CTAB micelle solution
systems in the reverse mic elle region have been used as
template for the synthesis of WO
3
nanoparticles. The resultant
nanoparticles have been investigated with XRD, VPSEM, EDX
TEM and XPS methods and the results have shown and
revealed the successful synthesis of WO

3
nanoparticles. It
seems that no obvious difference exists between WO
3
nanoparticles obtained from using the one sucrose ester
microemulsion with heat aging process and using of the mixing
two sucrose ester microemulsions process. In both methods
using sucrose ester microemulsion as a template the shapes are
spherical with the orthorhombic lattice and particles sizes are
approximately between 10 and 50 nm.
WO
3
nanoparticles prepared via the CTAB micelle solution
have spherical shape with bigger size range between 25–50 nm
and orthorhombic lattice. More work to optimize the reaction
conditions like precursors concentration and temperature for all
mentioned methods for preparing smaller size range with very
narrow size distribution is still in progress. Final ly this study
shows that t he sucrose ester (biodegradable surfactants)
microemulsion are suitable for synthesizing WO
3
nanoparticles.
Acknowledgements
The author would like to thank the following UKM staff
namely: Mr. Zaki, Mr. Zailan, Ms. Normala and Mr. Syed for
helpingwiththeuseofVPSEM,XRD,TEMandXPS
respectively.
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