Enhanced photocatalytic degradation of cationic and anionic dyes by Ag-modified g-C3N4 composite: Insights on different mechanisms under visible light

Ag/g-C 3 N 4 was synthesized by thermopolymerization and photo-deposition methods, and the performance of Ag/g-C 3 N 4 was evaluated by degrading cationic dye methylene blue (MB) and anionic dye tartrazine (TZ) under visible light. Results showed that the photocatalytic efficiency of Ag/g-C 3 N 4 for MB and TZ was significantly improved compared with pristine g-C 3 N 4 . 80% of MB was removed in 120 min and TZ could be completely degraded in 90 min by Ag/g-C 3 N 4 . The improvement of photocatalytic efficiency can be ascribed to the better light absorption and lower recombination rate of e − /h + after loading of Ag nanoparticles. The degradation efficiency of Ag/g-C 3 N 4 for MB was improved as pH increased, while the efficiency for TZ was decreased at the same condition. This study also revealed the different photocatalytic mechanisms of MB and TZ. It showed that hole played a dominant role in degrading MB, while the degradation of TZ mainly relied on superoxide radical. Graphic Abstract