Interfacial Built-In Electric Field-Driven S-Scheme g-C3N4/S-Doped TiO2 Heterojunction for Boosting Photocatalytic NO Abatement.

S-scheme heterojunction engineering has emerged as an effective strategy for enhancing photocatalytic NO removal by facilitating charge separation while maintaining strong redox capability. Herein, an S-scheme heterojunction consisting of S-doped TiO2 nanotubes and g-C3N4 was successfully constructed via an annealing-assisted interfacial engineering strategy. Comprehensive band structure analyses using Mott-Schottky measurements, valence band X-ray photoelectron spectroscopy, and Kelvin probe force microscopy confirmed the formation of an S-scheme heterojunction between S-TiO2 and g-C3N4. The experimental results revealed a favorable band alignment and the establishment of an interfacial built-in electric field between S-TiO2 and g-C3N4, facilitating S-scheme charge transfer across the heterointerface and preserving highly reactive electrons and holes with strong reduction and oxidation capabilities, respectively, thereby promoting the generation of ·O2- and ·OH radicals. As a result, the optimized g-C3N4/S-doped TiO2 nanotube photocatalyst achieved an NO removal efficiency of 74.6%, higher than those of pristine S-TiO2 (43.4%) and g-C3N4 (53.4%), while also suppressing NO2 intermediate formation compared with previously reported TiO2- and g-C3N4-based heterojunctions. This work provides insight into the synergistic role of band alignment, interfacial built-in electric field, and S-scheme charge transfer in boosting photocatalytic NO removal performance.