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

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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.