1376
S. Shamaila et al. / Materials Research Bulletin 45 (2010) 1375–1382
of the resulting materials including surface area, particle size and
pore structure by adjusting preparation variables.
equation to the full width at half-maximum (fwhm) of the (1 0 1)
peak of anatase. D = K cos . Where is the half-height width of
the diffraction peak of anatase, K = 0.89 is a coefficient, is the
diffraction angle and is the X-ray wavelength corresponding to
the Cu K irradiation. The morphology was studied using scanning
electron microscopy (SEM) (JEOL, JSM-6360LV) and transmission
electron microscopy (TEM, JEM-2011) with an accelerating voltage
of 200 kV. Nitrogen adsorption and desorption isotherms were
obtained at 77 K with a Micromeritics ASAP 2010 system. All the
samples were degassed at 473 K before the measurement. Fourier
transform infrared (FT-IR) spectra were carried out by employing a
Nicolet 740 FT-IR spectrometer equipped with a TGS detector and a
KBr beam splitter.
l
/
b
u
b
Chlorinated phenols widely used as pesticides, herbicides and
wood preservatives, are among the top priority pollutants and
found in aqueous ecosystems as byproducts of chlorinated water.
Moreover, chlorinated phenols are chemical precursors of the
more toxic polychlorinated dibenzo-p-dioxins [30]. Due to this,
chloro-phenol was employed as an environmentally relevant
model pollutant. The chloro-phenol was degraded in an illuminat-
ed suspension of TiO2 according to the following stoichiometry:
u
l
a
TiO2=h
n
2C6H4OHCl þ 13O2 ꢀ! 2HCl þ 12CO2 þ 4H2O
In this work, we report the preparation of mesoporous-TiO2 by
employing PEG with different molecular weights and acetic acid, as
the structural directing reagent and hydrolytic retardants,
respectively. The procedure involves a post-hydrothermal treat-
ment to improve the quality of the resultant mesoporous-TiO2. The
effects of molecular weight of PEG, hydrothermal treatment and
calcination temperatures are studied in comparison to control the
physical properties of the resulting materials including surface
area, particle size and pore structure (structural characteristics) of
the resultant mesoporous-TiO2. The mechanism of chemical
reactions involved in the synthesis of mesoporous-TiO2 and
degradation of chloro-phenol has also been proposed.
2.4. Measurements of photocatalytic activities
Chloro-phenol was chosen as a model pollutant to evaluate the
photocatalytic activities. The photocatalytic reactions were carried
out at 30 8C using a home-made reactor. A high-pressure Hg lamp
of 300 W having the strongest emission wavelength of 365 nm,
was used as a UV light source (the average light intensity was
about 1230
m
W/cm2). It was mounted 10 cm away from the
reaction solution. During the reaction, a water-cooling system
cooled the water-jacketed photochemical reactor to maintain the
solution at room temperature. The photocatalyst (1.5 g Lꢀ1) was
added into a 100 mL quartz photoreactor containing 50 mL of a
50 mg Lꢀ1 aqueous solution of chloro-phenol. The mixture was
sonicated for 20 min and stirred for 30 min in the dark in order to
reach the adsorption–desorption equilibrium. Under UV irradia-
tion and vigorous stir, each reaction was lasted for 5 h. Preliminary
studies indicated a linear light absorbance verse chloro-phenol
concentration and that the decomposition of chloro-phenol in the
absence of photocatalyst or UV irradiation could be neglected.
To analyze the concentration of chloro-phenol and degradation
products, the suspension was first centrifuged and filtered through
2. Experimental
2.1. Materials
Tetrabutyl titanate (TBT) Ti(OBu)4, PEG with different molecu-
lar weights, absolute ethanol and acetic acid (HAc) were analytical
grade. All the above chemicals were purchased from Shanghai
Sinopharm Chemical Reagent Co., Ltd., China. Deionized and
doubly distilled water was used throughout the experiment.
0.22
mm Millipore membrane filters to remove the catalyst. The
2.2. Catalyst preparation
membrane filters are made of mixed cellulose esters and had no
effect on chloro-phenol concentration. The concentrations of
chloro-phenol were measured with a UV–vis spectrophotometer
(Varian Cary 100) with UV absorbance in the range of 200–400 nm
Mesoporous-TiO2 was prepared using the hydrothermal-
assisted sol–gel method. In a typical synthesis procedure 5.0 g
of TBT was added drop-by-drop to 30 mL of acetic acid aqueous
solution (20%, v/v) under vigorous stirring. The mixed solution was
sealed and stirring was continued for 4 h to obtain solution A. In a
separate beaker, 3.0 g of PEG with the molecular weight of 600
(designated as PEG 600) was dissolved in 20 mL ethanol under
vigorous stirring to obtain solution B. Solution B was then added
drop-by-drop to solution A. The final mixed solution was sealed
and stirred for 24 h at room temperature. The resultant solution
was then transferred into a Teflon sealed container for hydrother-
mal treatment under a constant temperature of 140 8C for 48 h. The
precipitations were then collected and dried overnight in air at
80 8C. The as-prepared sample was then subjected to a thermal
treatment process at 450 8C for 4 h. To examine the effect of
calcination temperature, the as-prepared sample was also calcined
at different temperatures. Furthermore, in order to evaluate the
effect of the molecular weight of PEGs, we replaced the PEG 600 by
2000, 10,000 and 20,000, respectively.
and the UV lmax value of chloro-phenol is 280 nm corresponded to
the maximal adsorption of chloro-phenol. The concentrations of
chloro-phenol were calculated from the height of peak by using
calibration curve. The measurements were repeated for the
catalyst and the experimental error was found to be within ꢁ3%.
Chloro-phenol degradation intermediates were determined by
the HPLC series 1100 (Agilent) equipped with a reverse-phase C18
analytical column (Zorbax SB-C18, USA) of 150 mm ꢂ 2.1 mm and
3.5
mm particle diameter. Column temperature was maintained at
22 8C. The mobile phase used for eluting chloro-phenol from the
HPLC columns consisted of methanol and water (50:50, v/v) at a
flow-rate of 1.0 mL minꢀ1
.
3. Results and discussion
Mesoporous-TiO2 was synthesized by using PEG as template and
acetic acid a weak acid for the formation of smaller and uniform
titanium hydrate. Fine mesoporous-TiO2 particles during the
hydrolysis process were obtained due to the better control of the
hydrolysis process of titanium source, chelating effect of acetic
anions and formation of pH buffer [31,32]. The post-hydrothermal
treatment was performed to increase the crystallinity of mesopor-
ous-TiO2 [33]. Mesoporous-TiO2 materialswerefoundtohavea high
crystallinity with a nanocrystalline anatase structure. The addition
ofPEGwithhighermolecularweightenlargedthemesoporesizeand
widened the mesopore size distribution of the material.
2.3. Characterization
The crystal phase composition and crystallinity of the obtained
mesoporous-TiO2 was determined by X-ray diffraction (XRD) with
Rigaku D/Max 2550 VB/PC apparatus (Cu
Ka radiation,
l
= 0.154056 nm) at room temperature operated at 40 kV and
100 mA. Diffraction patterns were recorded in the angular range of
20–808. The crystallite size was estimated by applying the Scherrer