We describe fabrication of ZnO-TiO2 nanocomposites with improved photocatalytic activity. The nanocomposite catalysts were synthesized by chemical co-precipitation approach encapsulating wurtzite ZnO nanoparticles (NPs) with anatase TiO2 shell. The TiO2 thickness was controlled by optimizing the weight ratios of ZnO to TiO2 to investigate the effect of TiO2 shell thickness on the photocatalytic properties of ZnO-TiO2 heterojunctions. ZnO NPs could be uniformly coated by TiO2 layers with desirable shell thicknesses. The band edge energy of the prepared nanocomposite catalysts indicated that the thickness of TiO2 layers could decrease the band gaps of the catalysts compared with the pristine ZnO NPs. The photocatalytic property of ZnO-TiO2 nanocomposites was evaluated by measuring photo-degradation of methylene blue (MB) in aqueous media. The all synthesized nanocomposite catalysts showed improved photocatalytic efficiency in comparison with the pristine ZnO NPs relevant to the red shift generated and higher absorption of photons in UV region. The photocatalytic also results revealed that the photo-activity performance of the samples were improved by increasing the shell thickness because of a decline in the measured band-gaps. The kinetic expressions with different orders were also studied and an appropriate model was demonstrated for the photocatalytic degradation process of MB.
