Boosting organic pollutant photodegradation through electron-cycling mechanism by engineering visible light driven halogenated doped carbon nitride/ S-TiO₂ photocatalyst

The development of high-performance photocatalysts has become a critical focus in water treatment research, particularly for overcoming intrinsic limitations such as rapid electron–hole recombination and insufficient redox efficiency. In this work, a novel sulfur-doped titanium dioxide and chlorine-doped carbon nitride (S-TiO₂/Cl-CN) heterostructure was synthesized via the solvothermal synthesis method, designed to degrade organic contaminants, including the sulfamethoxazole (SMX) antibiotic. Photocurrent and photoluminescence (PL) spectra analyses exhibited that the S-TiO₂/Cl-CN heterostructure significantly enhanced the optical properties of bulk photocatalysts, attributed to a novel electron-cycling charge transfer mechanism through both Z-scheme and type II mechanisms. Cyclic voltammetry (CV) analysis and reusability tests conducted under both light and dark conditions indicated an increased electron lifecycle facilitated by electron-cycling mechanisms. Optimal conditions achieved complete SMX removal with an impressive rate constant of 7.93 × 10⁻² min⁻¹ under visible light irradiation at pH 5, with a catalyst dosage of 0.56 g/L and an initial concentration of 5 ppm, optimized by response surface methodology. Reactive oxygen species, including ^●O^-₂, ^●OH, ¹O_2, and h^+, were identified as the primary radicals through EPR and quenching tests. The photocatalytic reactivity of S-TiO₂/Cl-CN in a natural water sample, including actual wastewater, was assessed, demonstrating a superb 94 % SMX removal in a river water sample, thereby showing its high potential for pollutant degradation under real environmental conditions. This study offers a novel perspective on the mechanism of non-metal doping in photocatalysts, broadening the photocatalytic efficiency to address emergent environmental issues.