CTAB-assisted ultrasonic synthesis, characterization and photocatalytic properties of WO3

Article abstract of DOI:10.1016/j.materresbull.2014.10.034

WO₃2D nanostructures have been prepared by ultrasound synthesis method assisted with CTAB using different molar ratios. The formation of monoclinic crystal structure of WO₃was confirmed by X-ray powder diffraction (XRD). The characterization of the WO₃samples was complemented by analysis of scanning electron microscopy (SEM), which revealed morphology mainly of rectangular nanoplates with a thickness of around 50 nm and length of 100-500 nm. Infrared spectroscopy (FT-IR) was used to confirm the elimination of the CTAB in the synthesized samples. The specific surface area was determinate by the BET method and by means of diffuse reflectance spectroscopy (DRS) it was determinate the band-gap energy (E_g) of the WO₃samples. The photocatalytic activity of the WO₃oxide was evaluated in the degradation reactions of rhodamine B (rhB) and indigo carmine (IC) under Xenon lamp irradiation. The highest photocatalytic activity was observed in the samples containing low concentration of CTAB with morphology of rectangular nanoplates and with higher surface area value than commercial WO₃. Photodegradation of rhB and IC were followed by means of UV-vis absorption spectra. The mineralization degree of organic dyes by WO₃photocatalyst was determined by total organic carbon analysis (TOC) reaching percentages of mineralization of 92% for rhB and 50% for IC after 96 h of lamp irradiation.

Full text of DOI:10.1016/j.materresbull.2014.10.034

Materials Research Bulletin 61 (2014) 165–172
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
CTAB-assisted ultrasonic synthesis, characterization and
photocatalytic properties of WO3
*
D. Sánchez-Martíneza , C. Gómez-Solísa, Leticia M. Torres-Martíneza
Universidad Autónoma de Nuevo León, Facultad de Ingeniería Civil-Departamento de Ecomateriales y Energía, Cd. Universitaria, C.P. 66451 San Nicolás de los
Garza, NL, Mexico
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 25 June 2014
Received in revised form 25 September 2014
Accepted 8 October 2014
Available online xxx
WO3 2D nanostructures have been prepared by ultrasound synthesis method assisted with CTAB using
different molar ratios. The formation of monoclinic crystal structure of WO3 was confirmed by X-ray
powder diffraction (XRD). The characterization of the WO3 samples was complemented by analysis of
scanning electron microscopy (SEM), which revealed morphology mainly of rectangular nanoplates with
a thickness of around 50 nm and length of 100–500 nm. Infrared spectroscopy (FT-IR) was used to confirm
the elimination of the CTAB in the synthesized samples. The specific surface area was determinate by the
BET method and by means of diffuse reflectance spectroscopy (DRS) it was determinate the band-gap
energy (Eg) of the WO3 samples. The photocatalytic activity of the WO3 oxide was evaluated in the
degradation reactions of rhodamine B (rhB) and indigo carmine (IC) under Xenon lamp irradiation. The
highest photocatalytic activity was observed in the samples containing low concentration of CTAB with
morphology of rectangular nanoplates and with higher surface area value than commercial WO3.
Photodegradation of rhB and IC were followed by means of UV–vis absorption spectra. The mineralization
degree of organic dyes by WO3 photocatalyst was determined by total organic carbon analysis (TOC)
reaching percentages of mineralization of 92% for rhB and 50% for IC after 96 h of lamp irradiation.
ã 2014 Elsevier Ltd. All rights reserved.
Keywords:
A. Oxides
A. Nanostructures
B. Chemical synthesis
D. Catalytic properties
1. Introduction
of scientists and researchers in last decades because it is a more
stable phase [18–20]. Furthermore, through these synthesis
Tungsten oxide (WO3), an important n-type semiconductor, has
received wide attention owing to its promising application for
electrochromic and photochromic devices, secondary batteries
and photocatalysts [1–4]. In this sense, WO3 has been widely
investigated because of its potential application in information
displays [5], energy-saving smart windows [6,7], variable-reflec-
tance marrows [8], and photocatalytic [9–11] reactions.
Recently, investigations of WO3 have been focused on its
application as a photocatalyst because of its relatively narrow
band-gap energy (less than 3.0 eV). Such a situation allows the use
of WO3 as a novel eco-material for energy renewal, energy storage
and environmental cleanup [12]. Because of its ease of preparation,
WO3 has been synthesized via several experimental techniques,
such as thermal decomposition [13], acid precipitation [14], sol–
gel [15], hydrothermal synthesis [16] and electrospinning [17],
among others. The WO3 presents the phenomenon of polymor-
phism, where the monoclinic phase (m-WO3) has drawn attention
methods mentioned previously, m-WO3 is commonly obtained
using different experimental conditions, in some cases very
specific conditions, making it difficult to obtain. In addition,
WO3 exhibits strong absorption in the visible region at wavelength
greater than 480 nm [21], which makes it an attractive candidate
for photocatalytic applications under solar irradiation.
Recently, the use of the ultrasound method for the synthesis of
semiconductor oxides has received wide attention, which has
proved to be an effective technique for generating nanoparticles
with attractive properties in a short period of reaction time. The
enhanced chemical effect of ultrasound is due to acoustic
cavitation phenomena. The major advantage of this method, apart
from its fast quenching rate and operation at ambient condition, is
that it is a simple and energy efficient process [22]. For this reason,
the growing number of publications dealing with ultrasonic
irradiation gives an idea about the great potential of the method
because of its simplicity and efficiency [23].
On the other hand, in order to control the morphology of the
semiconductor oxides, organic additives such as ethylene diamine
tetra-acetic acid (EDTA) [24,25] and polyethylene glycol (PEG)
[26,27] are commonly added into the reaction system to
manipulate the nucleation and growth of the particles. In this
* Corresponding author. Tel.: +52 81 8329 4000x7270/1442 4400x5143; fax: +52
81 8376 0477/1442 4443.
E-mail address: dansanm@gmail.com (D. Sánchez-Martíneza).
http://dx.doi.org/10.1016/j.materresbull.2014.10.034
0025-5408/ã 2014 Elsevier Ltd. All rights reserved.

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D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
sense, cetyltrimethyl ammonium bromide (CTAB) assisted by
ultrasound technique has emerged as an attractive technique to
carry out the synthesis of WO3 nanostructures. For this reason, in
this work the effects of different concentrations of CTAB on the
morphologies and photocatalytic properties of WO3 oxide by
ultrasound synthesis method were investigated in the degradation
reactions of rhodamine B (rhB) and indigo carmine (IC) in aqueous
solution.
6000-K with a luminous flux of 90 500 lux was used as UV and
visible-light radiation source.
The photocatalytic activity of WO3 samples was evaluated in the
degradation reactions of rhodamine B (rhB, CAS 81-88-9) and
indigo carmine (IC, CAS 860-22-0) in aqueous solution. 200 mL of
dye solution containing 200 mg of WO3 powders were put in a
glass beaker and then placed in an ultrasonic bath for 2 min to
eliminate aggregates after that the solution was transferred to the
reactor. By considering the molar extinction coefficient of the dyes,
the initial concentrations were determined to be 5 mg Lꢁ1 for rhB
and 30 mg Lꢁ1 for IC. The solution was kept in the dark for 1 h in
order to ensure that the adsorption–desorption equilibrium of the
dye on the catalyst surface has been reached. After this time, the
light source was turned on. During the reaction, samples were
taken from the reactor at different time intervals, the powders
were separated by centrifugation and then the filtered solution was
analyzed in a UV–vis spectrophotometer following the procedure
established in a previous work [29].
2. Experimental
2.1. Synthesis of WO3 oxide
WO3 oxide was obtained by ultrasound synthesis method
assisted with cetyltrimethyl ammonium bromide (C19H42BrN,
CTAB, Sigma–Adrich) in aqueous solution using different molar
ration of ammonium tungstate hydrate (H42N10O42W12.xH2O,
99% purity, Sigma–Aldrich) and CTAB; 1:01, 1:0.25, and 1:0.5.
The samples were prepared by the following procedure: 1.65 g
(5.39 ꢀ10ꢁ4 mol) of ammonium tungstate hydrate was dissolved
in 100 mL of a nitric acid solution (10% v/v, HNO3) under
continuous stirring in an ultrasonic bath (42 kHz ꢂ 6%, 100 W).
Afterwards, it was added to the solution a quantity of CTAB of
accord to the corresponding molar ration under continuous
stirring until the formation of homogeneous solution. Then the
solution was maintained without stirring in the ultrasonic bath
during 5 h. This step produced a yellow precipitate (hereafter
called precursor), which was washed several times with distilled
water to neutralize the pH of the solution and finally dried in air
at 80 ꢃC during 24 h. The precursor was thermally treated at
500 ꢃC from room temperature to the specific temperature with
a heating rate of 10 ꢃC minꢁ1 in order to obtain of the WO3 oxide.
For comparative purposes it was used also the commercial WO3
(99% purity, Fluka) and also the oxide prepared without CTAB.
The dyes mineralization degree was examined by analyzing the
total organic carbon (TOC) content in solutions using a SHIMADZU
TOC-VSCH analyzer. For these experiments were employed 200 mL
of the dye solution (50 mg Lꢁ1 for rhB and 100 mg Lꢁ1 for IC)
containing 200 mg of photocatalyst.
3. Results and discussions
3.1. Structural characterization
The obtained powders of WO3 with the different molar ratios of
ammonium tungstate hydrate and CTAB (1:0.1, 1:0.25, and 1:0.5)
were thermally treated at 500 ꢃC. For comparative purposes, the
oxide also was prepared without CTAB and thermally treated at
same temperature. The materials formed presented a greenish
tinge. The X-ray powder diffraction patterns of the WO3 sample
without CTAB (hereafter identified as W500) and with CTAB
(hereafter identified as W0.1-500, W0.25-500 and W0.5-500) are
shown in Fig. 1. It was noticed for all samples that the materials
crystallized in the monoclinc polymorph of WO3 according the
JCPDS card no. 01-085-0950. All samples presented its main
2.2. WO3 samples characterization
Structural characterization of WO3 samples was carried out by
X-ray powder diffraction analysis using a BRUKER D2 PHASER
diffractometer with CuK
data of the samples was collected in the 2
a
radiation (
l
= 1.5418 Å). X-ray diffraction
diffraction peaks located at 2u = 23.1, 23.6, 24.3, 26.6, 28.6, 33.3,
u
range of 10–70ꢃ with a
34.2, 41.8 and 49.9ꢃ, which are well defined and typical of the
scan rate of 0.02ꢃ and 0.2 sꢁ1. Infrared spectroscopy (NICOLET
380 FT-IR) was used to confirm the elimination of the surfactant
(CTAB). The morphology and particle size analysis of the samples
was investigated by scanning electron microscopy in a FEI Nova
200 NanoSEM.
monoclinic structure.
The band-gap energy (Eg) was determined by means of the UV–
vis diffuse reflectance absorption spectra of the WO3 samples,
which were taken using a UV–vis spectrophotometer PerkinElmer
Lambda 35 equipped with an integrating sphere. The Eg value was
calculated for direct transition from the UV–vis spectrum through
extrapolating a straight line to the slope of the x-axis, using the
following equation: Eg = 1240/lg, where, lg is the wavelength (nm)
of the exciting light and Eg the band gap energy [28]. The BET
surface area of WO3 samples was determined by adsorption–
desorption N2 isotherms using a BELSORP Mini-II surface area and
pore size analyzer. The isotherms were evaluated at ꢁ196 ꢃC after a
degassing of the samples by means of a heat treatment at 150 ꢃC for
24 h.
W0.5-500
W0.25-500
W0.1-500
W500
Commercial
2.3. Photocatalytic experiments
JCPDS No. 01-083-0950
10
20
30
40
degree
50
60
70
The photochemical reactor employed was a homemade device
consisting of a borosilicate glass beaker embedded in a water jacket
to maintain the reaction temperature at 25 ꢂ1 ꢃC. A Xe lamp of
2θ
Fig. 1. X-ray powder diffraction patterns of the WO3 samples assisted with and
without CTAB.

D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
167
nanoplates to ovoid particles mainly with a size of around 100 nm
and irregular shape as it is shown in Fig. 3d. Only the sample W0.5-
500 showed different morphology, which is similar to the tendency
natural of the commercial WO3 to form particles of ovoid shape
(see Fig. 3e).
W0.5-500
W0.25-500
W0.1-500
Therefore, accordingly to these results we can conclude that the
WO3 samples prepared by ultrasound synthesis method assisted
with CTAB presented mainly uniform morphology of rectangular
nanoplates with a thickness of around 50 nm and length of 100–
500 nm; this morphology was favored by low concentration of
CTAB. Whilst with the increase of the CTAB concentration, the
morphology of particles gradually change showing a tendency
natural to form the morphology characteristic of commercial WO3.
The change in the morphology of WO3 oxide by effect of CTAB
can be explained as follow: when ammonium tungstate hydrate
(H42N10O42W12.xH2O) was dissolved in distilled water and nitric
acid (HNO3), it was obtained a yellow solution of tungstate acid
(H2WO4.xH2O). Then, the solution was maintained in ultrasound
bath during a time period causing that the tungstate acid
decomposed to produce WO3 nuclei, containing layers of octahe-
drons [WO6]6ꢁ. The addition of CTAB in the solution provokes the
ionization of CTAB into CTA+ and Brꢁ. In this sense, the CTA+ is
attracted by the four negatively charged oxygen atoms in the
planar surface of [WO6]6ꢁ. Therefore, this causes the formation of
[CTB-WO6]2ꢁ, which orient the planes of the particles to form WO3
nanoplates [31]. For this reason, the CTAB plays a very important
role in the final morphology of the WO3 powders.
W0.5
W0.25
W0.1
CTAB
Commercial
3.3. Band-gap energy and BET surface area analysis
The optical properties of the samples W500, W0.1-500, W0.25-
500, and W0.5-500 were analyzed using UV–vis diffuse reflectance
spectroscopy. Table 1 shows the band-gap energy (Eg) values of the
samples analyzed. The Eg values determined are found in the range
reported in the literature (2.5–2.8 eV [32,33]); similar to Eg value of
commercial WO3, which is 2.62 eV.
The specific surface area of WO3 samples measure by BET
method is also incorporated in Table 1. The surface area values of
samples prepared with and without CTAB were higher than
commercial WO3. With the increase of the CTAB concentration the
specific surface area value decreases. Therefore, the sample with
the highest surface area value was W0.1-500. Fig. 4 shows the
adsorption–desorption isotherm of WO3 samples with and
without CTAB. In general, a type of profile was observed in all
the samples analyzed. The samples (W500, W0.1-500, W0.25-500,
and W0.5-500) exhibited typical behavior of a material, which is
not porous, or macroporous, respectively (i.e., type II isotherms,
according to the classification previously establish for adsorption–
desorption isotherm [34]) as it is observed in Fig. 4a–d.
1200 1100 1000 900
800
700
600
500
400
Wavenumber (cm-1)
Fig. 2. FT-IR spectra of the WO3 samples, precursor materials, CTAB, and
commercial WO3.
Fig. 2 shows the IR spectra for WO3 samples heated at 500 ꢃC,
their precursor materials (W0.1, W0.25, and W0.5), the CTAB and
commercial WO3. The presence of a broad (W—O—W) band,
characteristic of WO3, was observed in synthesized samples to
different molar ratios (W0.1-500, W0.25-500, and W0.5-500) at
approximately 450, 674, 724, and 855 cmꢁ1, and the same time
(W
O) at 950 cmꢁ1. On the other hand, no bands that correspond
to O—H, C—H or C—O were observed when the precursors were
heated at 500 ꢃC, which indicate that the CTAB was decomposed
during this process [30].
¼
3.2. Morphological studies
The morphology and particle size of WO3 samples were
analyzed by SEM. Fig. 3 shows the SEM micrographs of samples
obtained by ultrasound irradiation with and without CTAB at
500 ꢃC. When the oxide was prepared without CTAB (W500) were
observed particles with heterogeneous morphology in shape of
rectangular, square and ovoid nanoplates with a thickness of
around 50 nm and length of 100–500 nm (see Fig. 3a). In the
samples obtained with CTAB using molar ratio of 1:0.1 and heated
at 500 ꢃC (W0.1-500), it was observed more uniform morphology
principally of rectangular nanoplates, with a thickness of around
30 nm and length of 100–200 nm (see Fig. 3b). For the samples
prepared with molar ratio of 1:0.25 (W0.25-500), it was observed
morphology of rectangular nanoplates principally, similar to the
samples W0.1-500 but with a length approximately 500 nm as it is
shown in Fig. 3c. Although some ovoid particles were also observed
to a lesser extent. In the samples with molar ration of 1:0.5 (W0.5-
500) it was observed a change in the morphology from rectangular
Therefore, these experiments reveal the modification of surface
area of WO3 oxide by effect of the addition CTAB. This means that at
low molar ratios of CTAB, the surface area increases of WO3
samples. Whilst with a high concentration of CTAB the WO3
particles tend to agglomerate.
3.4. Evaluation of photocatalytic activity
The photocatalytic activity of the WO3 samples was evaluated in
the degradation reactions of rhB and IC molecules in water under
Xe lamp of 6000-K irradiation. Fig.
5 shows the temporal
degradation of rhB (5 mg Lꢁ1) with the different synthesized
WO3 samples. After 240 min of Xe lamp irradiation it was observed
that all samples exhibited better results than sample without CTAB
(W500) and commercial WO3. In general, all the samples were able
to bleach the rhB solution in large measure. The best photocatalytic
activity was showed by the sample with the low concentration of

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D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
Fig. 3. SEM analysis of the morphology of the WO3 samples obtained by ultrasound synthesis method assisted with and without CTAB: (a) W500, (b) W0.1-500, (c) W0.25-
500, (d) W 0.5-500, and (e) commercial WO3.
CTAB (W0.1-500), i.e., the sample that presented the highest
surface area value and consequently the mainly morphology of
rectangular nanoplates.
Fig. 6 shows the photocatalytic activity of WO3 with and
without CTAB in the degradation of IC (30 mg Lꢁ1). It is observed
higher activity than with the rhB although the initial IC
concentration was 6 times higher. This is due to their respective
molar extinction coefficients. All the samples presented better
activity than the sample without CTAB and commercial WO3. After
120 min of exposure under Xe lamp the samples with CTAB (i.e.,
W0.1-500, W0.25-500, and W0.5-500) were able to bleach in
almost 100% the IC solution. The WO3 sample that showed the best

D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
169
Table 1
Physical properties of the WO3 samples synthesized under different experimental conditions.
Method
Morphology
Test conditions
Photocatalytic
activity
Reference
Precipitation in ethanol The particles tend to form large agglomerates formed by small particles 35 W Xe
68%
[11]
solution
(100 nm) and of irregular shapes
Ovoid morphology with particles sizes between 20 and 50 nm
lamp.Batch typereactor.1:1
(catalyst:rhB solution)
Microwave-assisted
hydrothermal
Ultrasound assisted
CTAB
88%
[37]
Morphology of rectangular nanoplateswith a thickness of around 50 nm
and length of 100–500 nm
100%
This work
activity was the W0.1-500, i.e., the sample that exhibited a more
uniform morphology of rectangular nanoplates and the smallest
size. In fact it is the sample that presented highest surface area
value. In this sense, it can be observed that increasing the surface
area of the WO3 samples increases the degradation rates of rhB and
IC (see Fig. 7).
On the other hand, for comparison purpose it was selected the
sample that presented the best activity (W0.1-500) and its
photocatalytic activity was compared against TiO2 (P25) in the
degradation of rhB and IC under the same experimental conditions.
Fig. 8 shows the temporal degradation of rhB (a) and IC (b) with
WO3 against TiO2. It was observed that WO3 presented
a
It is well known that surface area play a determinant role in the
photocatalytic properties. In this sense, high surface area values
generate more active sites and high reaction rates of photo-
generated electron–hole pairs on the surface of photocatalyst to
interact with the reaction medium. Such a situation provokes an
increase in the efficiency of photocatalytic processes. In the same
way, other factor that favors the activity of WO3 samples is the
morphology of rectangular nanoplates, which was favored at low
concentration of CTAB. Whilst a high concentration of CTAB the
WO3 particles are agglomerated to obtain a morphology of ovoid
particles principally. Therefore, these experiments reveal that the
factors governing the photocatalytic activity of the WO3 samples in
this work are principally the morphology of rectangular nano-
plates, specific surface area and addition of CTAB in low
concentration.
photocatalytic activity similar to TiO2 for rhB solution after
240 min under Xe lamp irradiation (bleach about of 90%). Whilst
for IC solution, the WO3 synthesized in this work showed an
activity higher than TiO2 after 120 min under Xe lamp irradiation.
These results corroborated the potential of WO3 synthesized by
ultrasound method assisted with CTAB as photocatalyst in the
degradation of organic compounds, even showing better photo-
catalytic activity than TiO2 (P25), in particular for the degradation
of IC.
Fig. 9 shows the UV–vis absorption spectra when rhB and IC are
photodegraded by a WO3 sample used as photocatalyst (W0.1-
500); it is the sample that exhibited the best photocatalytic
properties. Accordingly to the UV–vis absorption spectra it is
assumed the complete degradation of rhB via a direct attack to the
aromatic rings of its molecule [35], which leads to the breaking of
40
80
b)
a)
30
60
20
10
0
40
20
0
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
P/Po
P/Po
60
40
20
0
80
60
40
20
0
c)
d)
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
P/Po
P/Po
Fig. 4. N2 adsorption–desorption isotherms of the WO3 samples prepared by ultrasound synthesis method assisted with and without CTAB: (a) W500, (b) W0.1-500, (c)
W0.25-500, (d) W 0.5-500.

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D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
1
0.8
0.6
0.4
0.2
0
100%
80%
60%
40%
20%
0%
Without photocatalyst
Commercial
W500
W0.1-500
W0.25-500
IC
rhB
W0.5-500
0
1
2
3
4
5
6
7
8
9
10
0
50
100
150
200
250
Surface area (m2.g-1)
Time (minutes)
Fig. 7. Effect of surface area of the WO3 samples against the degradation rates of rhB
after 240 min and IC after 120 min.
Fig. 5. Changes in the rhB concentration (5 mg Lꢁ1) during its photocatalytic
degradation in the presence of WO3 under different experimental conditions; a Xe
lamp was used as source of radiation, pH 6.0. The concentration of rhB was
determined through its maximum absorption band (554 nm).
assisted with CTAB as photocatalyst it is possible to provoke a high
mineralization degree of organic dyes. These results were
associated with the UV–vis absorption spectra previously
explained, where it was observed that it is feasible the complete
degradation of rhB and almost the complete degradation of IC.
Therefore, these results confirm that it is feasible to break the bond
the bonds and thus provokes the degradation of the dye
(see Fig. 9a). In the case of IC, it is assumed almost a complete
degradation via a direct attack to the molecule of IC breaking its
C C bond to yield isatin 5-sulfonic acid as the main aromatic
¼
product [36]. This leads to the breaking of the molecule and thus
causes the degradation of the dye (see Fig. 9b).
a)
1
To determine if it is feasible the mineralization of organic dyes
and discard that only the dyes solution is being bleached for WO3
oxide exposed under Xe lamp irradiation. It was determinate the
mineralization degree by means of total organic carbon (TOC)
content of the photocatalytic test in the degradation reactions of
rhB and IC (see Fig. 10). For these experiments it was used the
W0.25-500 sample as photocatalyst for rhB and the W0.1-
500 sample for IC, which have the lowest and highest surface
area, respectively. After 96 h under lamp irradiation the minerali-
zation degree reaches almost 92% for rhB and 50% for IC, therefore
it is concluded that using WO3 synthesized by ultrasound method
0.8
Without photocatalyst
W0.1-500
0.6
0.4
0.2
0
TiO2 (P25)
0
50
100
150
200
250
1
0.8
0.6
0.4
Time (minutes)
1
0.8
0.6
0.4
0.2
0
b)
Without photocatalyst
W0.1-500
TiO2 (P25)
Without photocatalyst
Commercial
W500
W0.1-500
W0.25-500
0.2
W0.5-500
0
Time (min1u5t0es)
0
50
100
200
250
0
50
100
150
200
250
Fig. 6. Changes in the IC concentration (30 mg Lꢁ1
) during its photocatalytic
Fig. 8. Photocatalytic activity of WO3 against TiO2 (P25) in the degradation of: (a)
rhB (5 mg Lꢁ1) and (b) IC (30 mg Lꢁ1) under same experimental conditions; a Xe
lamp was used as source of radiation, pH 6.0.
degradation in the presence of WO3 under different experimental conditions; a Xe
lamp was used as source of radiation, pH 6.0. The concentration of IC was
determined through its maximum absorption band (610 nm).

D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
171
2
1.6
1.2
0.8
0.4
0
Table 2
Photocatalytic degradation of rhB (5 mg Lꢁ1) using WO3 synthesized by different
methods under irradiation Xenon lamp during 3 h.
a)
0
30
60
90
120
150
180
210
240
Sample
Eg(eV)
BET surface area (m2 gꢁ1
)
Commercial
W500
W0.1-500
W0.25-500
W0.5-500
2.6
2.5
2.6
2.6
2.6
3.3
4.4
8.7
5.9
6.2
prepare other materials using CTAB in order to modify its
morphology and specific surface area, allowing an improvement
on its photocatalytic properties in the degradation reaction of
organic compounds.
200
300
400
500
600
700
800
Wavelength (nm)
Also it is important to mention that in previous studies we have
obtained only morphology of ovoid particles by different methods
of synthesis and reported that the photocatalytic properties were
mainly associated to the material crystallinity [11,37]. In this sense,
a comparative study of WO3 obtained by different synthesis
methods used as photocatalyst in the degradation reaction of rhB
under same conditions is shown in Table 2. It is observed that
morphology depends strongly of the synthesis method and it is an
important factor in the photocatalytic applications. In conclusion,
the WO3 with morphology of rectangular nanoplates presented the
better photocatalytic activity; this material was synthesized by
ultrasound method assisted with CTAB.
Therefore, in this work it is important to stand out that it was
obtained WO3 powders mainly with morphology of rectangular
nanoplates and that the photocatalytic activity was attributed
principally to the morphology, specific surface area, and the
presence of CTAB.
2
b)
1.6
1.2
0.8
0.4
0
0
30
60
90
120
150
180
210
240
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 9. Variation of the UV–vis absorption spectra during the photocatalytic
degradation of: (a) rhB and (b) IC in presence of one of the samples that exhibited
the best activity (W0.1–500).
4. Conclusions
WO3 2D nanostructures with morphology of rectangular
nanoplates were successfully synthesized by ultrasound method
assisted with CTAB. The morphology of the WO3 undergoes a
transition from rectangular nanoplates to ovoid particles by effect
of the increase in the addition of CTAB. The specific surface area of
all the synthesized samples was higher than commercial WO3. The
highest surface area value was obtained for the sample synthesized
with the lowest concentration of CTAB. All the synthesized samples
used as photocatalysts showed better photocatalytic activity than
the commercial WO3 in the degradation reactions of rhB and IC in
aqueous solution under Xe lamp irradiation. The sample that
showed the best photocatalytic activity was obtained with the low
concentration of CTAB (W0.1-500), i.e., the sample that presented
highest surface area value and the morphology mainly of
rectangular nanoplates, even showing better activity than TiO2
(P25) in the degradation of IC and a similar result with the rhB. The
photocatalytic activity of WO3 oxide was attributed to the
morphology of rectangular nanoplates, specific surface area, and
the addition of CTAB. The almost complete mineralization it was
achieved after 96 h under Xe lamp irradiation of the organic dyes,
92% for rhB and 50% for IC. This synthesis method can be feasible to
prepare other materials with the addition of CTAB for modify its
morphology, increasing the specific surface area and improving its
photocatalytic properties in the degradation reaction of organic
compounds.
of organic compounds (rhB and IC) during the photocatalytic
reactions.
Unlike the previous work [11,37], this work involved the
successful preparation of WO3 nanoplates by ultrasound synthesis
method assisted with CTAB. In conclusion it was observed that the
addition of low concentration of CTAB in the synthesis favors the
formation of WO3 with morphology of rectangular nanoplates,
increasing the surface area and consequently exhibiting high
photocatalytic activities in the degradation reactions of rhB and IC.
Therefore, this synthesis method can be an alternative route to
100
80
60
40
rhB
IC
20
0
Acknowledgements
0
20
40
60
80
100
Time (hours)
Authors wish to thank to the Universidad Autónoma de Nuevo
León (UANL) for its invaluable support through the project PAICYT
2011–2012; CONACYT, for supports of Projects FON.INST./75/
Fig. 10. Variation of the TOC during the mineralization of rhB and IC under a Xe
lamp irradiation, pH 6.0.

172
D. Sánchez-Martíneza et al. / Materials Research Bulletin 61 (2014) 165–172
2012 “FOTOSÍNTESIS ARTIFICIAL”, CNPq MÉXICO–BRASIL 2012
Clave 174247; and SEP, for support of Projected PIFI 2011–
2012 Apoyo al CA-UANL-244 and PROMEP/103.5/13/6644 Apoyo
UANL-PTC-744.
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