From charge separation to hole confinement: A strategy for maximizing oxidative power in an n-n S-scheme using TiO2–Bi2S3 as a model photocatalyst

Abstract

A novel strategy is developed to maximize the photocatalytic oxidative power of a composite by transitioning from conventional charge-separation models to a targeted hole-confinement mechanism using an n-n TiO2/Bi2S3 S-scheme heterojunction. It is demonstrated how high-potential oxidative species (ROS) are selectively sequestered through engineering of the internal electric field and interfacial band bending. The S-scheme pathway is explicitly confirmed by advanced operando analysis validation using in situ Kelvin probe force microscopy and irradiated X-ray photoelectron spectroscopy, revealing that high-potential holes accumulate in TiO2. Furthermore, the excited-state lifetime of photocarriers is shown by femtosecond transient absorption spectroscopy to nearly double for the TBS-10 heterojunction (898 ps) compared to TiO2 (449 ps). This significant extension indicates that charge carrier recombination is effectively suppressed. The optimized TBS-10 exhibits excellent photocatalytic degradation performance, achieving 100% formaldehyde removal efficiency, an apparent quantum yield of 0.077%, and a clean air delivery rate of 20.13 L min−1. The in-situ DRIFTS reveals a photocatalytic oxidation pathway proceeding through dioxymethylene and formate intermediate toward near-complete mineralization to CO2 and H2O. This work offers a mechanistically guided framework for advancing S-scheme architectures toward high-performance environmental remediation.