TiO2-modified g-C3N4 nanocomposite for photocatalytic degradation of organic dyes in aqueous solution

In the current study, a direct S-scheme titanium dioxide/graphitic carbon nitride (TiO2/g-C3N4) heterojunction structure was fabricated via simultaneous calcination of TiO2 precursors and g-C3N4. Guava leaf extract was utilized as a reductant for TiO2 production through a green synthetic method, and g-C3N4 was prepared by thermal decomposition of melamine. The pristine and nanocomposite photocatalysts were characterized by XRD, FTIR, BET, TGA, HRTEM, UV-vis DRS, and PL to elucidate their physicochemical properties. The photocatalytic activity of synthesized photocatalysts was examined through the degradation of rhodamine B (RhB) and methylene blue (MB) dyes under simulated solar light irradiation. The nanocomposite exhibited commendable photocatalytic performances with 96% degradation efficiency of RhB attained in 120 min and 95% degradation efficiency of MB achieved in 150 min. The enhanced photocatalytic activities were attributable to visible light-harvesting characteristics and the formation of an S-scheme heterojunction system between two catalysts which promotes interfacial charge separation efficiency and longer charge carrier lifespan. After 4 consecutive cycles, the degradation efficiencies of both RhB and MB remained above 85%. According to the trapping experiments, OH• and O2 •- radicals were critical in the degradation of RhB, while h+ and O2 •- radicals were dominant in the degradation of MB. The nanocomposite was also tested for elution of actual water pollutants by combining two dyes, and above 90% degradation efficiencies were achieved for both dyes after 240 min.