Simulated solar-driven photo-assisted anodic oxidation of sulfadiazine by C3N4 modified Ti3+ self-doping TiO2 nanotube arrays

In this study, a C3N4 modified Ti3+ self-doping TiO2 nanotube arrays (C3N4-Ti3+/TiO2-NTA) material was innovatively fabricated using a three-step procedure consisting of anodization, chemical vapor deposition, and in-situ cathodic polarization. Simultaneously introducing C3N4 and Ti3+ significantly enhanced the light absorption property and charge separation efficiency of TiO2-NTA, while also increasing the oxygen evolution overpotential to 2.61 V vs the standard hydrogen electrode. C3N4-Ti3+/TiO2-NTA with excellent optoelectronic properties was first applied as an anode in the simulated solar-driven photo-assisted anodic oxidation (PAO) system. It was found that the PAO system for the degradation of sulfadiazine (SDZ) exhibited 12.1-fold and 1.9-fold higher activity compared to the photocatalytic system and the anodic oxidation system alone, respectively, indicating the optoelectronic synergistic interactions over C3N4-Ti3+/TiO2-NTA. Quenching experiments and electron spin resonance results suggested that main reactive species during the degradation of SDZ by the PAO system were hydroxyl radical and superoxide radical. Additionally, three possible degradation pathways of SDZ by the PAO were proposed based on the identification of intermediate byproducts and theoretical calculation. Furthermore, the biosafety evaluation revealed a significant reduction in the biological toxicity of intermediate byproducts of SDZ. These findings provide new insights into the design and manufacturing of novel anode material for efficient degradation of recalcitrant pollutants in practical applications under solar irradiation.