Materials Sciences and Applications, 2011, 2, 476-480
doi:10.4236/msa.2011.25064 Published Online May 2011 (
Copyright © 2011 SciRes. MSA
Sol-Gel Preparation of Nanoscale TiO2/SiO2
Composite for Eliminating of Con Red Azo Dye
Abdolreza Nilchi, Simin Janitabar-Darzi, Somayeh Rasouli-Garmarodi
Nuclear Science and Technology Research Institute, Tehran, Iran.
Received May 1st, 2010; revised June 21st, 2010; accepted May 11th, 2011.
A new anatase/SiO2 nanocomposite was synthesized by sol-gel method at room temperature using titanium tetrachlo-
ride and tetraethylorthosilicate as raw materials. Characterization of the product was carried out by means of X-ray
diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), Brunauer-Em-
mett-Teller (BET) specific surface areas, Thermogravimetry analysis (TGA), Fourier transform infrared (FT-IR), and
UV-vis absorption spectroscopy. Thermal phase transformation studies of composite were carried out up to 1100˚C
which showed the establishment of anatase TiO2 phase. The presence of some tetrahedral coordination of TiO2 species
in SiO2 matrix was confirmed by UV-Vis study. The produced TiO2/SiO2 nanocomposite has good photocatalytic pro-
perties due to its anatase phase, existence of tetrahedral coordination of TiO2 in the SiO2 matrix and very large surface
area. Furthermore, the synthesized anatase/SiO2 shows significant adsorption ability towards Congo Red (CR) azo dye
in comparison with the pure commercial TiO2 which is known as Degussa, P25.
Keywords: TiO2/SiO2, Nanocomposites, Sol-Gel Preparation, Photocatalyst, Congo Red
1. Introduction
In the area of advanced oxidation technology, titanium
dioxide semiconductor photocatalysis has been widely
studied because of its potential application in air clean-up
and water purification. TiO2 is largely used as photo-
catalyst due to its beneficial characteristics: high photo-
catalytic efficiency, physical and chemical stability, low
cost and low toxicity [1-9].
TiO2/SiO2 composites are very promising in field of
heterogeneous photocatalysis, since they could provide
simultaneously enhanced photocatalytic and thermal pro-
perties compared to pure TiO2 photocatalyst [10-13]. It
has been reported that photocatalytic reactivity of TiO2/
SiO2 nanocomposites is highly dependent on the Ti/Si
ratios [14-17]. The photocatalytic activity and mechani-
cal stability was reported to improve by the addition of
about 50% SiO2 [18].
In the present study, anatase/SiO2 nanocomposite was
synthesized via sol-gel method at room temperature. The
effect of calcination temperature on particles size, BET
surface area and phase transformation of anatase to rutile
TiO2 were investigated. Moreover, characterization of the
coordination sphere of Ti ions incorporated into silica
matrix of the composite was studied. These investiga-
tions could provide vital information for the design of
highly efficient photocatalytic systems in the degradation
of toxic compounds diluted in a liquid phase.
2. Experimental
2.1. Chemicals
The chemicals used in this study were titanium tetrachlo-
ride (TiCl4, 99.9%), Fluka, as a titanium precursor, tetrae-
thylorthosilicate (TEOS, 98%), as silica source, Congo
Red (C32H22N6Na2O6S2), HNO3 (70 wt%, d = 1.42 g·cm1),
NH4OH (25 wt%), and anhydrous ethanol (C2H5OH)
from Merck.
2.2. Preparation of TiO2/SiO2 Composite
Titanium tetrachloride was added to distilled water under
vigorous stirring in an ice water bath. The produced dis-
persion was treated by NH4OH and pH adjusted to 7. The
resulting solid was collected by filtration and washed
with distilled water. The precipitation was dispersed in
200 mL of 0.3 M HNO3. The mixture was refluxed under
vigorous stirring at 70˚C for 16 h as Titania sol was pre-
pared. 25 mL of tetraethylorthosilicate was added drop
Sol-Gel Preparation of Nanoscale TiO2/SiO2 Composite for Eliminating of Con Red Azo Dye
Copyright © 2011 SciRes. MSA
wise to the above sol and stirred at 70˚C. The resulting
powder was filtered and washed with distilled water then
dried at room temperature. The composite produced was
denoted as TSR. In order to study phase transformation
of prepared composite, it is calcined for 1 h at 800˚C and
1100˚C and the obtained samples were denoted as TS800
and TS1100, respectively.
2.3. Characterization
Phase identification of the products was carried out by
X-ray diffraction (XRD) obtained on Philips X-pert dif-
fractometer using Cu Kα line radiation. The crystallite
size of the samples was determined by Scherrer equation
[19]. Thermogravimetry analysis (TGA) was performed
using STA 150 Rhenometric Scientific unit. Measure-
ment was taken with a heating rate of 10˚C/min from 25
to 800˚C in argon atmosphere. For the composition ana-
lysis X-ray fluorescence spectroscopy (XRF) using Ox-
ford ED 2000 was employed. Spectroscopic analysis of
the nanocomposite was performed using a Fourier trans-
form infrared (FT-IR) spectrometer (Perkin-Elmer 843)
and UV-vis spectrophotometer (Shimadzu UV 2100).
The morphology of the products was studied by trans-
mission electron microscopy (TEM, Philips-EM208S
electron). The specific surface area of the samples was
determined through nitrogen adsorption using a surface
area analyzer (CHEMBET3000).
2.4. Photoreactor
Photocatalytic activity of the synthesized nanocompo-
sites and commercial TiO2 were evaluated by the degra-
dation of Congo Red. All of the experiments were con-
ducted in an opened Pyrex vessel of 50 ml capacity and
in identical conditions. A 30 W UV-C lamp was used as
light source. The distance between the UV source and the
vessels containing reaction mixture was fixed at 15 cm.
Air was continuously bubbled into the solution in order
to provide a constant source of dissolved oxygen. 0.025 g
of photocatalyst was placed in a 50 mL aqueous solution
of 5 ppm Congo Red. Prior to irradiation, the suspension
was magnetically stirred in the dark for 30 min. Then the
lamp was switched on to initiate the reaction. During
irradiation, the suspension was sampled at regular inter-
vals and immediately centrifuged to remove catalyst par-
ticles. The photocatalytic degradation was monitored by
measuring the absorbance of the solution samples with
UV-vis spectrophotometer.
3. Results and Discussion
3.1. FT-IR Spectroscopy
FT-IR spectrum of the as-synthesized composite (Figure
1) has three characteristic bands that appeared at around
Figure 1. FT-IR spectrum of the as-synthesized TiO2/SiO2
nanocomposite (TSR).
1100 950, and 650 cm1. The bands at around 650 and
1100 cm1 are representative of TiO2 and SiO2 matrixes
in nanocomposite. The band at around 950 cm1 has been
assigned to the stretching of the Si-O species of Si-O-Ti
or Si-O defect sites which are formed by the inclusion of
Ti4+ ions into the SiO2 matrixes. Thus, the appearance of
the band at around 950 cm1 indicates that the TiO2 spe-
cies are embedded into SiO2 matrixes within TiO2/SiO2
nanocomposite. the broad peak appearing at 3100 - 3600
cm1 is assigned to the fundamental stretching vibration
of hydroxyl groups (free or bonded) which is further
confirmed by the weak band at about 1620 cm1 [20-23].
3.2. X-Ray Diffr ac ti on
Figure 2 shows the XRD patterns for synthesized com-
posite and calcined samples. It reveals that as-synthesi-
zed TiO2/SiO2 nanocomposite (TSR) has crystalline ana-
tase phase in amorphous silica matrix. Both calcined na-
nocomposites TS800 and TS1100 have anatase phase
TiO2 but in TS1100, amorphous silica transforms to crys-
tobalite silica phase. Both the interactions Si-O-Ti and
high dispersion of TiO2 in SiO2 prevent the crystalline
transition to rutile [24,25]. The sizes of the anatase crys-
tallites in the prepared TiO2/SiO2 nanocomposite samples
measured according to the Scherrer equation are 5.0, 7.8,
and 26.7 nm for RSR, TS800, and TS1100, respectively.
Doping of SiO2 into TiO2 could effectively retard the
growth of nanoparticles and thus reduce the particle size.
This observation may have resulted from the formation
of the Ti-O-Si bond and due to the presence of amor-
phous SiO2 around TiO2, which would prevent the
growth of TiO2 particles [26]. The particle size of TSR
and TS800 are close together but at 1100˚C a clear jump
in the particle size is shown due to transformation of
amorphous silica to crystobalite.
3.3. Thermogravimetric Analysis
The inset of Figure 2 shows thermogravimetric curve of
TiO2/SiO2 composite (TSR). After the removal of water
and organic residue up to 150˚C, no appreciable change
Sol-Gel Preparation of Nanoscale TiO2/SiO2 Composite for Eliminating of Con Red Azo Dye
Copyright © 2011 SciRes. MSA
Figure 2. XRD patterns of as prepared nanocomposite (TSR)
and calcined composites (TS800 and TS1100), Inset: ther-
mogravimetric curve of (TSR).
of weight is seen in the curve. This reveals that synthe-
sized nanocomposite is thermally stable and no phase
transformation occurs, up to 800˚C.
3.4. X-Ray Fluorescence Spectroscopy
The XRF analysis shows that the composite consists of
55% TiO2 and 45% SiO2.
3.5. UV-Vis Spectroscopy
Figure 3 shows the absorption spectra of the prepared
samples dispersed in ethanol. The band gap of the sam-
ples calculated from the straight part of the optical ab-
sorption spectra [27,28]. A clear red shift in the absorp-
tion edges of composites by increasing of calcination
temperature is seen in the Figure 3.
The inset shows that the optical band gap of nano-
composite decreases (from 4.25 to 3.82 eV) by heat
treatment from room temperature to 1100˚C. The shift
can be attributed to the difference in grain size in these
samples. Zribi et al. obtained similar evolution of optical
band gap with the temperature and concluded that the
variation of density and the structural modifications may
be responsible for changes in the shape of the fundamen-
tal absorption edge [29]. According to Figure 3 a peak
corresponding to isolated Ti species which have absorp-
tion maxima at about 225 nm is observed in composite
spectra. The absorption peak at 200 - 260 nm can be at-
tributed to the charge transfer absorption process involv-
ing an electron transfer from O2 to Ti4+ ions of the
highly dispersed tetrahedral coordinated TiO4 unit of
these catalysts. Anpo et al. have reported that titanium
oxides having a tetrahedral coordination can be chemi-
cally supported onto silica matrix and have shown that
such composite materials exhibit significant photocata-
lytic activities [30].
3.6. Transmission Electron Microscopy (TEM)
Figure 4 shows TEM image of TSR composite. It can be
Figure 3. UV-Vis absorption spectra of the nanocomposites
dispersed in ethanol. Inset: changes of optical band gap at
thermal treatment.
Figure 4. TEM image of the as-synthesized TiO2/SiO2 nano-
composite (TSR).
seen from TEM image that the composite sample con-
sists of the nanoparticles with sizes of 5 - 9 nm which is
approximately in conformity to XRD result.
3.7. Specific Surface Area Analysis
The specific surface area of the TiO2/SiO2 composite
(TSR) calculated from BET is 707.59 m2·g1. The specific
surface area of TiO2/SiO2 composite decreases when
calcination temperature increases and reaches 142.38 and
13.72 m2·g1 for TS800 and TS1100, respectively.
3.8. Photocatalytic Activity Measurements
Figure 5 shows changes of the UV-Vis absorption spec-
trum of CR after adsorption of dye on TSR at dark and
during photocatalysis. The inset also shows adsorption
ability and photocatalytic activity of the composites and
pure TiO2 (Degussa P25, BET: 50 m2·g1) for removal of
CR from aqueous solution as a function of time at λ =
Sol-Gel Preparation of Nanoscale TiO2/SiO2 Composite for Eliminating of Con Red Azo Dye
Copyright © 2011 SciRes. MSA
Figure 5. UV-Vis spectrum of CR (5 ppm) using TSR photo-
catalyst. Inset: Degree of decolorization by various photo-
497 nm. The efficiency or degree of photodegradation (X)
is given by: X = (C0 C)/C0, where C0 is the initial con-
centration of dye, and C the concentration of dye at time T.
CR dye is strongly adsorbed on the surface of TSR so
that more than 98% of dye decolorization performed af-
ter 30 min adsorption in dark. Percent of decolorization
due to sorption on the surface of Degussa, TS800 and
TS1100 are obtained to be 16.7%, 22.3% and 3.5%, re-
spectively. These results are in a good conformity to the
BET surface area of the samples.
It reveals that the as-prepared composite is the most
effective sorbent and photocatalyst. The samples calcined
at 800˚C and 1100˚C are weaker photocatalyst than the
commercial P25. Finally, it can be deduced from the re-
sults obtained that the well crystallized mixed crystalline
structure (75% anatase and 25% rutile) of P25 would be
responsible for the photocatalysis superiority in com-
parison with the calcined nanocomposites, although the
sample calcined at 800˚C has larger surface area.
4. Conclusion
TiO2/SiO2 nanocomposite was synthesized via sol-gel
process at room temperature. Formation of the Ti-O-Si
bond and amorphous SiO2 in TiO2/SiO2 could effectively
increase the stability of anatase TiO2, limit the growth of
crystallites, and increase the surface area. Significantly,
such an increase in the surface area and the existence of
tetrahedrally coordinated TiO2, improves the photocata-
lytic activities of the TiO2/SiO2 ceramic.
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