Critical role of the heterojunction interface of silver decorated ZnO nanocomposite with sulfurized graphitic carbon nitride heterostructure materials for photocatalytic applications

The heterojunctions formed at the interfaces between the metal oxide and graphitic carbon nitride (g-C₃N₄) play a critical role in photocatalytic reactions. Herein, we synthesized a series of heterostructures by the integration of 7% Ag-decorated ZnO nanocomposite (NC) with different contents (3.5–75 wt%) of sulphur-doped graphitic carbon nitride (S-g-C₃N₄). A unique heterostructure formed between Ag/ZnO and S-g-C₃N₄ generates a vast number of heterojunctions and abundant catalytic active sites for photocatalytic degradation. The material characterization was performed by XRD, SEM, TEM, XPS, FTIR, UV-Vis spectroscopy, BET surface area, and transient photocurrent response. The as-synthesized 7% Ag/ZnO NC showed maximum methylene blue (MB) degradation among the series (0–9%) under visible irradiation. Interestingly, the 25% Ag/ZnO/S-g-C₃N₄ heterostructure exhibited a significant increase in photodegradation of MB and 98% dye degraded in only 60 min, which was degraded up to 59% by 7% Ag/ZnO NC. Moreover, the photo-corrosion of ZnO NPs was inhibited by simultaneous doping with Ag and coupling with S-g-C₃N₄, which was verified through cyclic photo-degradation with six consecutive dye degradation tests. The synergistic effects of the Ag/ZnO/S-g-C₃N₄ heterojunction, enhanced photocatalytic activity, and photo-corrosion resistance were demonstrated successfully.