Pure TiO2 and Cr doped TiO2 (0.1-1.0wt% Cr) nanoparticles were synthesized via sol gel method. This
study focusing on narrowing the TiO2 band gap energies in order to enhance the photocatalytic efficiency
under visible light. The synthesized samples were characterized by X-Ray diffraction method (XRD), field
emmision (FESEM) and also UV-Vis diffuse reflectance spectroscopy (DRS).The photocatalytic activity
under sunlight irradiation was demonstrated by photocatalytic decomposition of methylene blue in water
using UV/Vis spectrophotometer. The XRD analysis of pure TiO2 and doped TiO2 calcined at 500oC
showed a mixture of anatase and rutile phases with decreasing crystallites size from 13.3 nm to 11.6 nm
as the concentration of Cr was increased. The anatase-rutile phase transformation increased from 28.8%
to 57.4%. An indication shows that at 0.75wt% Cr the anatase and rutile phases have equal composition
percentage. This study demonstrated that band gap energy of TiO2 was reduced with Cr doping which
could enhance the photocatalytic efficiency. Sample containing 1.0wt% exhibit the lowest optical band
gap energy at 2.86 eV. The optimum chromium doping concentration was found to be at 0.1 wt% Cr
corresponding to band gap energy of 2.87 eV and degradation rate of 84%.