ZnO nanoparticles were synthesized by thermal decomposition of oxalate precursor method. The nanopowders were characterized using Powder X-Ray Diffraction Technique and Scanning Electron Microscopy and sample was found to have hexagonal wurtzite structure of ZnO. Average crystallite size of ZnO was found to be~27 nm. The photocatalytic activity of ZnO was evaluated by using Methyl Orange (MO) as probe molecule. It was inferred from control experiments that presence of both ZnO and UV light is necessary for photodegradation. From photocatalytic experiment it was observed that MO is completely degraded in 80 min when the amount of catalyst is 1 g/L and initial concentration of MO is 0.03 mM. The effect of dye concentration, catalyst loading and solution pH on photodegradation rate was also investigated. It was found that optimal conditions for photodegradation of MO are 1 g/L catalyst at a solution pH 9. Photodegradation of MO was found to follow pseudo-first
