In situ analysis of oxygen vacancy modified TiO2-Ov/g-C3N4 S-scheme heterojunction by 2D-PCIS spectroscopy for efficient synergistic photocatalytic degradation of naphthalene in water

The S-scheme heterojunction notably improves the separation and transport of photogenerated carriers due to its distinctive charge transfer mechanism and structural advantages. In this study, TiO₂ was synthesized in situ on g-C₃N₄ using a hydrothermal method, followed by calcination to introduce oxygen vacancies and construct the S-scheme heterojunction photocatalyst (TCN). Experimental results showed that the optimal performance was achieved with a TiO₂-O_v content of 30%, where the TCN-30 catalyst degraded over 82.44% of naphthalene (Nap) within 180 minutes. Electron spin resonance (ESR) analysis confirmed the presence of many oxygen vacancy defects in TCN-30, as well as the generation of reactive oxygen species (ROS) during the experimental process, which played a key role in enhancing Nap degradation. Subsequently, a series of photoelectrochemical tests were conducted to demonstrate the excellent synergistic effect between oxygen vacancies and the strategy of constructing heterojunctions. Additionally, density functional theory (DFT) calculations helped clarify the working mechanism of the TCN S-scheme heterojunction and revealed its structure–activity relationship in photocatalytic applications. This study offers a theoretical foundation and technical guidance for the future design of photocatalysts tailored to specific functional needs.