Ltd., Shanghai 201900, China Received 23 December 2004; received in revised form 31 January 2005; accepted 1 February 2005 Available online 4 March 2005 Abstract Synthesis of WO3/TiO2nan
Trang 1Synthesis of WO 3 /TiO 2 nanocomposites via sol–gel method
Huaming Yanga,∗, Rongrong Shia, Ke Zhanga, Yuehua Hua, Aidong Tangb, Xianwei Lic
aDepartment of Inorganic Materials, School of Resources Processing and Bioengineering, Central South University, Changsha 410083, China
bInstitute of Functional Materials, School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
cInstitute of Resources and Environmental Engineering, Technology Centre, Baoshan Iron and Steel Co Ltd., Shanghai 201900, China
Received 23 December 2004; received in revised form 31 January 2005; accepted 1 February 2005
Available online 4 March 2005
Abstract
Synthesis of WO3/TiO2nanocomposites by a sol–gel method was investigated using differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques Thermal treatment of the precursor at 400◦C in air resulted in the formation
of WO3/TiO2nanocomposites with a particle size of about 60 nm The c-axis parameter of TiO2in the WO3/TiO2nanocomposites, lower than that of pure TiO2, increased with increasing calcination time Doping TiO2with WO3can lower its band gap and shift its optical response to the visible region This nanocomposite should be effective as a visible-light-driven photocatalyst
© 2005 Elsevier B.V All rights reserved
Keywords: WO3 /TiO 2 nanocomposites; Photocatalysis; Sol–gel method; Lattice parameters
1 Introduction
It is well known that nanosized TiO2 powder is one of
the suitable semiconductors for photocatalyst and has been
widely applied in various photocatalytic fields, such as
en-vironmental purification, decomposition of organic
contam-inants and water photosplitting into H2and O2[1–5]
How-ever, its properties, not only the photo-efficiency or activity
but also the photoresponse, are not sufficient[6] The vital
snag of TiO2 semiconductor is that it only absorbs a small
portion of solar spectrum in the ultraviolet (UV) region (band
gap energy of pure TiO2is 3.2 eV) Hence, in order to absorb
maximum solar energy, it is necessary to shift the absorption
threshold towards the visible region The high
recombina-tion ratio of photo-induced hole–electron pairs also reduces
its catalytic efficiency Recently, various modifications have
been performed on nanosized TiO2to extend its optical
ab-sorption edge into the visible light region and to improve its
photocatalytic activity, including surface modification, metal
depositing, transition metal and transition metal oxide
com-plexes[7–13] Coupling TiO2 with WO3, which is a
semi-∗Corresponding author Tel.: +86 731 8830 549; fax: +86 731 8710 804.
E-mail address: hmyang@mail.csu.edu.cn (H Yang).
conductor used as photocatalyst (Eg= 2.8 eV), can achieve
an efficient charge separation It is reported that WO3/TiO2 nanocomposites have higher photocatalytic activity[14,15]
In this paper, synthesis of WO3/TiO2nanocomposites via the sol–gel method was attempted
2 Experimental details
The starting materials were AR-grade Ti(OBu4), am-monium tungstate and anhydrous alcohol Ten millilitres Ti(OBu4) was dissolved in 10 ml anhydrous alcohol, and ul-trasonically dispersed to form a mixture Five millilitres water was slowly dripped into the mixture, which was stirred for 1 h
at room temperature Then different additions of ammonium tungstate solution were dripped into the mixture according to the required amount of WO3in the WO3/TiO2 nanocompos-ites The pH value of the solution was kept to be 10 The so-lution was aged for 12 h at ambient temperature, followed by filtering, washing for several times with deionized water and anhydrous alcohol, drying at 80◦C for 12 h to produce a
pre-cursor Subsequent calcination of the precursor at 400◦C for
different hours in air resulted in the formation of WO3/TiO2
nanocomposites
0925-8388/$ – see front matter © 2005 Elsevier B.V All rights reserved.
doi:10.1016/j.jallcom.2005.02.002
Trang 2Differential thermal analysis (DTA) of the precursor was
carried out using an SDT2960 thermal analyzer at a
heat-ing rate of 10◦/min The structure of the sample was
ex-amined using a D/max-␥A diffractometer (Cu K␣ radiation,
λ = 0.154056 nm) The morphology of the nanocomposites
was observed using a JEM-200CX transmission electron
mi-croscope (TEM) The UV–vis absorption spectra of the
sam-ples were recorded on a Shimadzu UV-3101PC
spectropho-tometer
3 Results and discussion
The precursor was subjected to DTA analysis The purpose
was to determine the temperatures of possible decomposition
and phase changes of the precursor during the thermal
treat-ment.Fig 1shows the typical DTA curves for the as-prepared
precursor The exothermic peak round 280◦C is associated
with the decomposition of residual OH groups and the
con-densation of nonbonded oxygen An exothermic peak at about
430◦C was clearly observed, which possibly can be attributed
to the crystallization alteration of the anatase TiO2phase But
there still exists a little difference in exothermic peak around
430◦C for the nanoparticle precursor with different amount
of WO3
Fig 2 shows the X-ray diffraction (XRD) patterns of
10 wt% and 20 wt% WO3/TiO2 nanocomposites after
cal-cination at 400◦C for 12 h As can be seen, all the peaks can
be assigned to anatase TiO2and no crystalline WO3was
de-tected Ma et al.[14]also reported the same result in their
Fig 1 DTA curves of the precursor with different amount of WO 3 (a)
10 wt%, (b) 20 wt% and (c) 40 wt%.
Fig 2 XRD patterns of the WO 3 /TiO 2 nanocomposites with different
amounts of WO (a) 10 wt% and (b) 20 wt%, respectively.
Fig 3 XRD patterns of 40 wt% WO 3 /TiO 2 nanocomposites after calcined
at 400 ◦C for different hours (a) 4 h, (b) 8 h and (c) 12 h, respectively.
studies, they thought that amorphous tungsten oxide phase covered the TiO2surface
Fig 3 shows the XRD patterns of 40 wt% WO3/TiO2 nanocomposites after calcination at 400◦C for (a) 4 h, (b) 8 h
and (c) 12 h, respectively As shown inFig 3, the WO3/TiO2 nanocomposites prepared by the sol–gel method was ob-served to have the anatase structure and tungsten oxide, show-ing the presence of a sharp peak at 25.3◦of 2θ which is the
major peak for the anatase TiO2 Due to the increase in the calcination time, the intensities of the peaks associated with
WO3increased to some extent.Fig 4shows a TEM micro-graph of the 40 wt% WO3/TiO2nanocomposites after heat treatment at 400◦C for 12 h The particle size of the
nanocom-posites observed in the TEM image was about 60 nm in diam-eter, while monodispersive particles with uniform size were present
WO3/TiO2nanocomposites after calcination were calculated using the formula:
1
d2 = h2+ k2
a2 + l2
where d is the interplane spacing, h, k and l are all Miller’s
indices The values were listed inTable 1 The lattice param-eters of pure anatase TiO2 obtained by the sol–gel method
are a = b = 3.7523 ˚ A, c = 10.0664 ˚A It is clear that the lattice
parameters increase along the a- and b-axes while the c-axis
parameter decreases as tungsten oxide was doped Longer
Fig 4 TEM image of the 40 wt% WO /TiO nanocomposites.
Trang 3Table 1
The lattice parameters of TiO 2 in WO 3 /TiO 2 nanocompositesa
Samples Calcination time (h) a (=b) ( ˚A) c ( ˚A)
a Calcination temperature was 400 ◦C.
Fig 5 UV–vis absorption spectra of the sample.
calcination time resulted in an increase in c-axis parameter
of the 40 wt% WO3/TiO2nanocomposites The decrease in
the lattice parameters of the WO3/TiO2nanocomposites in
comparison to pure TiO2may be attributed to the decrease
in the cation size in the octahedral site The W6+ ions have
a lower ionic radius (41 pm) than Ti4+(53 pm) in the
octa-hedral site of TiO2 This result also indicates that a doping
effect exists in the WO3/TiO2composite nanocrystallites
Fig 5shows the absorption spectrum of the WO3/TiO2
nanocomposites The spectrum shows that the onset of
ab-sorption appears at about 475 nm The onset of the optical
absorption of WO3/TiO2particles relative to the bulk anatase
TiO2(λE= 387 nm) implies a red shift The band gap energy
of the nanocomposites can be determined to be 2.67 eV from
the transformed Kubelka–Munk function, while the band gap
energy of pure TiO2is about 3.2 eV, accordingly, this
absorp-tion feature suggests that the WO3/TiO2 photocatalyst can
possibly be activated by the visible light, which can absorb
the maximum solar energy
4 Conclusions
In summary, WO3/TiO2nanocomposites have been suc-cessfully prepared by a sol–gel method The intensities of the XRD peaks associated with TiO2 increased gradually with increasing calcination time Addition of WO3resulted in a
decrease in the c-axis parameter of the TiO2, which also in-creased with increasing calcination time This nanocomposite
is promising for high-performance visible-light-driven pho-tocatalysts A detailed study on the photocatalytic activity of the nanocomposite is in progress
Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (Nos 50304014, 50474046)
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