Photocatalytic degradation of methylene blue by ZnGa2O4 thin films

ZnGa2O4 thin films were synthesized using a sol–gel process, characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–vis spectrophotometry measurements. The photocatalytic decomposing properties to methylene blue (MB) dye were studied for the first time. Effects of calcining temperature, grain size and film thickness on the photocatalytic activity were investigated. The film obtained at calcining temperature of 700 °C, consisting of the smallest crystallites, exhibits highest photocatalytic activity. With increasing the film thickness, the photocatalysis rate constant increased first to 0.0195, and then decreased drastically to 0.0089 due to the competition between UV absorption and carriers diffusion. The photocatalytic activity of ZnGa2O4 films maintained more than 90% of the initial value after 6 cycles, compared favorably with the 70% of ZnGa2O4 powder.