Nanocrystalline TiO 2 was synthesized by controlled hydrolysis of titanium tetraisopropoxide. The anatase phase was converted to rutile phase by thermal treatment at 1023 K for 11 h. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared absorption spectrophotometry (FT-IR) and N 2 adsorption (BET) at 77 K. This study compare the photocatalytic activity of the anatase and rutile phases of nanocrystalline TiO 2 for the degradation of acetophenone, nitrobenzene, methylene blue and malachite green present in aqueous solutions. The initial rate of degradation was calculated to compare the photocatalytic activity of anatase and rutile nanocrystalline TiO 2 for the degradation of different substances under ultraviolet light irradiation. The higher photocatalytic activity was obtained in anatase phase TiO 2 for the degradation of all substances as compared with rutile phase. It is concluded that the higher photocatalytic activity in anatase TiO 2 is due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst.

This study investigated the role of the band gap, surface area, and phase composition on the photocatalytic activity of nanocrystalline TiO2. Nanocrystalline TiO2 (8−29 nm) was synthesized by hydrolysis of titanium tetraisopropoxide. The crystalline structure, band gap, and morphology of the nanocrystalline TiO2 were determined by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and N2 adsorption (BET) at 77 K, respectively. It is observed that the band gap of the nanocrystalline TiO2 decreases from 3.29 to 3.01 eV with increasing calcination temperature. The crystallite size of the TiO2 samples prepared also shows an increase with increasing calcination temperature. The photocatalytic degradation of an aqueous solution of nitrobenzene (50 ppm) was studied using nanocrystalline TiO2 samples with varying band-gap values, as well as a P-25 Degussa TiO2 sample for comparison. The initial rate of degradation of nitrobenzene was calculated in each case to evaluate the photocatalytic activity of the catalysts. The enhanced photocatalytic degradation of nitrobenzene was observed by purging air through the solution during photocatalysis.

Mesoporous nanocrystalline TiO2 was prepared by hydrolysis of titanium isopropoxide, and the band gap of the TiO2 was modified with transition metal ions Ag, Co, Cu, Fe, and Ni having different work functions by the wet impregnation method. X-ray diffraction (XRD), X-ray photoelectron spectrophotometer, diffuse reflectance spectrophotometer (DRS), scanning electron microscope (SEM), and BET techniques were used for the characterization of the catalysts. By using the DRS technique, the highest red shift of 11 nm and lowest of 1.5 nm were observed for Ni and Fe ion impregnated catalysts, respectively. The investigations were carried out to demonstrate the effect of ionic radius and work function of metal ions on photocatalytic activity of mesoporous nanocrystalline TiO2 for degradation of acetophenone and nitrobenzene in aqueous medium under ultraviolet light irradiation.