Study on the effects of solvents and surfactants on hydrogen production of synthesized zinc sulfide/copper sulfide composite photocatalysts

In this study, the hydrothermal method was used to prepare zinc sulfide/copper sulfide (ZnS/CuS) composite photocatalysts in different solvents, including water, 1:1 water/ethanol, and 1:1 water/EDA (ethylenediamine) mixtures, with CuSO4·5H2O, Zn(CH3COO)2·2H2O, and Na2S·9H2O as precursors. The results showed that when a mixture of 0.4 M sodium sulfide and 0.2 M sodium sulfite was used as the sacrificial agent, the composite photocatalyst ZCNS-0.5PE produced the highest hydrogen yield of 6959 μmole/g within 4 hours. This yield could be attributed to the fact that adding an appropriate amount of PVP can reduce the crystal size and increase the specific surface area, thereby increasing the surface reactivity and resulting in better photocatalytic performance. However, adding too much PVP would inhibit light absorption, reducing the hydrogen production efficiency. High-resolution X-ray photoelectron spectroscopy (XPS) systematically verified the coexistence of variable-valence copper species (Cu+/Cu2+) and a high concentration of surface oxygen vacancies, which served as powerful electron-trapping centers to accelerate interfacial carrier separation. In cyclic hydrogen production stability tests, the photocatalyst prepared using the water/ethanol mixture as a solvent showed the smallest decrease in efficiency, at 5.01%. In durability tests, the composite photocatalyst ZCNS-1PE accumulated 10,283 μmoles of hydrogen after 24 hours. These results indicated that the use of ethanol solvent and PVP made the photocatalyst more promising for improving the efficiency of hydrogen production.