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.