Molten-Salt Flux Mediated Synthesis of ZnO-SnO2 Composites: Effects of Surface Areas and Crystallinities on Photocatalytic Activity

In this study, ZnO-SnO2 composites were synthesized using flux synthesis, a synthetic approach different from previous studies, in which molten ZnCl2 acted both as a reactant and as the flux for the reaction. Their photocatalytic properties were measured for the degradation of the organic dye, methylene blue. It was found that as the temperatures of the synthesis increase, the specific surface areas of the ZnO-SnO2 composites decrease, which would decrease their photocatalytic activities due to decreased adsorption of the dye on the surface of the composites; while their crystallinity increases, which would increase their photocatalytic activities due to the smaller concentration of defects and thus improved mobility of the charge carriers. An interplay of those two factors affects their photocatalytic activities, with the composite with the highest photocatalytic activity degrading approximately 95% of the methylene blue dye within 10 minutes. By changing the temperature of the flux synthesis alone, the crystallinity and surface area of the ZnO-SnO2 composite can be changed, which provides a possible way to obtain ZnO-SnO2 composites with relatively high crystallinity and surface area to maximize their photocatalytic activity.