Construction of the dual S-Scheme g-C₃N₄/ZnTiO₃/BiOI ternary heterojunction photocatalyst for efficient degradation of the organic dyes

This study reports the construction of a g-C₃N₄/ZnTiO₃/BiOI ternary heterojunction photocatalyst for the efficient degradation of organic dyes. The optimized g-C₃N₄/ZnTiO₃/BiOI composite with a mass ratio of 1:1:2 exhibited excellent photocatalytic activity toward Rhodamine B (RhB), achieving nearly complete degradation within 40 min at pH 11, with an apparent rate constant of 0.05114 min⁻¹ . The composite also showed photocatalytic degradation ability toward methylene blue (MB) and methyl orange (MO), as well as satisfactory performance in different real water matrices, demonstrating its broader applicability. Structural and surface analyses confirmed the successful formation of the ternary composite, while BET results indicated that the retained mesoporous structure facilitated reactant diffusion and interfacial mass transfer. UV–vis DRS revealed an extended light absorption range beyond 600 nm, and photoelectrochemical measurements demonstrated reduced charge-transfer resistance and enhanced separation and migration of photogenerated carriers. Radical trapping and EPR analyses identified ¹O₂ and •OH as the dominant reactive species. After five cycles, the RhB degradation efficiency remained above 90%, indicating good stability. Combined with Mott–Schottky measurements, XPS analysis, work-function calculations, Bader charge analysis, and differential charge density results, a ZnTiO₃-mediated dual S-scheme charge-transfer mechanism was proposed. This work provides a feasible strategy for designing efficient ternary heterojunction photocatalysts for dye-contaminated wastewater treatment.