Effect of synthesis conditions on the photocatalytic behavior of ZnS-ZnO heterojunctions for the H₂ generation

In the present work, the synthesis and photocatalytic performance for H₂ production of ZnS-ZnO composites at different compositions of cubic sphalerite (ZnS-c), hexagonal wurtzite (ZnS-h) and zincite (ZnO) phases are shown. The synthesis was carried out by the solvothermal method using mono ethylene glycol and thiourea as solvent and sulfur source, respectively, for the partial sulfidation of ZnO at different temperatures (150 °C, 200 °C, and 250 °C). When the temperature is increased in the solvothermal process, the hexagonal phase grows at the expense of the cubic phase. The materials as powders were characterized by X-ray diffraction, scanning and transmission electron microscopy, UV–visible spectroscopy, X-ray photoelectron microscopy, N₂ adsorption-desorption isotherms, and photoelectrochemical techniques. These materials were applied in H₂ production as an alternative source of clean and sustainable energy generation. It was found that the most photoactive material was the one synthesized at 200 °C, this photocatalyst presented an H₂ production rate of 580 µmol h⁻¹ g⁻¹. The enhancement of the photocatalytic activity is due to the optimization of the interfacial properties between ZnS-c/ZnS-h and ZnO as a model system for coupled photocatalysts.