Confined Fe(III) in carbon nitride shifted peroxymonosulfate activation from radical to high-valent iron pathways for efficient dioxin degradation

Fe-doped carbon matrices have garnered significant attention as peroxymonosulfate (PMS) activators for the removal of refractory organic pollutants. However, the role of Fe dopant in PMS activation remains unclear, especially concerning the relative contributions and reaction pathways of high-valent iron oxidations. In this study, a series of Fe-doped carbon nitride (CN) catalysts with varying iron contents was synthesized and utilized for the catalytic degradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Results showed that Fe doping significantly enhanced PMS activation, with the highest TCDD degradation rate achieved by Fe-CN-3, exhibiting a 4.6-fold improvement. Quenching experiment revealed that increasing Fe content shifted the degradation mechanism from a radical-dominated process (76.1 %) to a FeV=O-driven nonradical pathway (55.8 %); consequently, the Fe-CN-3/PMS system exhibited significant resistance to common environmental interferents. Theoretical calculations further confirmed that the Fe(III)-PMS interaction weakened both the O2-O3 and O3-H bonds, thereby enabling their thermodynamically feasible cleavage and the subsequent generation of FeV=O via a coupled electron-proton transfer pathway, which ultimately enhanced the electrophilic σ-attack on TCDD. These findings highlight the criticality of the metal dopant's local coordination environment in steering persulfate activation pathways, guiding the rational design of catalysts for selective oxidant generation.