Enhanced photocatalytic activity of zinc oxide synthesized by calcination of zinc sulfide precursor

ZnO nanoparticles were synthesized by calcination of ZnS precursor in an air atmosphere, in which ZnS had been firstly synthesized through precipitation with sodium sulfide (Na2S) as the precipitator. Detailed structure and morphology of the samples were characterized by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and transmission electronic microscopy. Optical properties were examined by UV–vis absorption spectroscopy. Photocatalytic activities of the samples were evaluated by degradation of Reactive Blue 14 (KGL). The results indicate that ZnS precursor converted into pure ZnO stepwise via calcination at a temperature range of 400–800 °C, and pure ZnO can be achieved above 700 °C. ZnO obtained by calcination at 700 °C had an average crystalline size around 45 nm and exhibited the highest photocatalytic activity, degrading KGL by almost 97.1% after 60 min under ultraviolet irradiation, which was superior to that of the directly synthesized and commercial ZnO. The inherent correlation between different samples and their photocatalytic activities was discussed. The phase, crystalline size, specific surface area and oxygen vacancy defects of the samples were proposed to affect their photocatalytic activity.