Enhancement of visible-light photocatalytic activity of ZnO/ZnS/g-C₃N₄ by decreasing the bandgap and reducing the crystallite size via facile one-step fabrication

Ternary ZnO/ZnS/g-C₃N₄ (ZZGC) nanocomposites were synthesized via a modified high-pressure solvent-free thermal method and subsequently used as highly efficient visible-light-driven photocatalysts to degrade organic pollutants. ZZGC composites were prepared at different temperatures and characterized by several microscopic and spectroscopic techniques. The best composite (named ZZGC-1, prepared at 400℃) exhibited 98.39% photocatalytic efficiency of methylene blue (MB) dye within 70 min under visible-light illumination. In addition, ZZGC-1 showed 1185% and 222% greater activity compared with similar reactions involving no catalyst and involving the corresponding binary composite (ZnO/ZnS prepared at 400℃), respectively. Under the same experimental conditions, ZZGC-1 demonstrated 89.04% efficiency for the deterioration of Congo red dye. The enhanced photocatalytic activity of ZZGC-1 may be due to its greater specific surface area compared with that of other composite photocatalysts. No substantial loss of activity or structural arrangement of ZZGC-1 was detected after five successive cycles. Overall, ZZGC nanocomposites can be used for practical and quick visible-light-driven photocatalytic wastewater treatment.