An 10mL of titanium tetrabutoxide (Ti(OC4H9)4) was
added to 12.5mL of ethanol. Then a mixture of doubly distilled
water (0.5 mL), ethanol (12.5 mL) and HCl (0.25 mL)
was added slowly dropwise into the solution under stirring.
The solution was kept stirring at ambient temperature for hydrolysis
and form sol–gel. The resulting TiO2 sol can be used
after aging for 12 h. Silica gel was immersed into the viscous
Ti-precursor sol for 10 min, then taken out and dried. This
process was repeated three times. The coated silica gel was
washed with doubly distilled water to remove the unimmobilized
TiO2, then dried at 100 ◦C for 1 h and subsequently
calcined in 450 ◦C for 2 h to obtain the immobilized nanometer
TiO2.