Switching Peroxomonosulfate Activation to a Non-Radical Dominant Pathway by Photo-driven Bi0 Mediator in an S-Scheme Heterojunction

Abstract

Conventional photocatalytic activation peroxomonosulfate (PMS) typically relies on transition metals and radical-dominated pathways, which often exhibit poor activity toward target pollutants. Moreover, the static nature of catalyst structures limits further improvement in interfacial reaction efficiency. In this study, a Bi5O7I/g-C3N5 S-type heterojunction was constructed, which generates non-precious metal Bi0 in-situ under visible light, establishing a highly efficient and dynamic Bi5O7I/g-C3N5-Bi0-PMS synergetic reaction system. This synergistic system achieved 83.6% removal of tetracycline hydrochloride (TC) within only 5 min under visible light irradiation. In-situ Kelvin probe force microscopy (KPFM) and in-situ X-ray photoelectron spectroscopy (ISI-XPS) confirmed that metallic Bi0 serves as an effective electronic mediator, activating PMS via a direct electron transfer (DET) process. This mediation shifts the PMS activation pathway from a traditional radical-dominated mechanism to a non-radical route. It triggers a cascade reaction network dominated by singlet oxygen (1O2). Radical trapping tests and electron paramagnetic resonance (EPR) experiments revealed the dominant contribution of 1O2, validating the efficiency of the non-radical pathway. Concurrently, the significant role of superoxide radical (∙O2-) corroborates the exceptional charge separation capability of the S-type heterojunction. This work achieves efficient TC degradation and potentially offers novel insights for designing next-generation advanced oxidation technologies with high selectivity and strong interference resistance through photo-driven dynamic evolution strategies.