Tylosin mitigation by PMS activated via electron-rich Fe/N co-doped biochars: coupled radical and non-radical pathways

Abstract

Activating peroxymonosulfate (PMS) and enhancing its catalytic reactivity remain key challenges in advanced oxidation processes, particularly for the degradation of recalcitrant organic compounds. In this study, Fe/N co-doped biochars (NPBC) with Fe⁰/ferric oxide components and electron-rich N configurations in the carbon framework were synthesized to activate PMS for tylosin (TYL) degradation. A high TYL degradation efficiency of 99.9% was achieved even at a low PMS concentration (15 mg/L). The activation of PMS by NPBC involves Fe⁰ oxidation and Fe²⁺/Fe³⁺ redox cycling, as well as electron transfer from N components to PMS. Both non-radical pathways (primarily ¹O₂ and electron transfer) and radical species (mainly ^•OH and O₂^•−) contributed to TYL degradation, with the former playing a relatively more important role. Three potential TYL degradation pathways were proposed, differing primarily in the sequence of amino sugar detachment and lactone ring opening. Pathways I and II began with sugar loss followed by ring opening, whereas Pathway III started with ring opening prior to sugar detachment. Ecological toxicity assessment indicated a reduction in overall toxicity when TYL was degraded to products typically found at environmental levels. Molecular docking analyses suggested that the transformation products exhibited reduced antibacterial activity and a lower potential for promoting antibiotic-resistant bacteria. This work presents a novel strategy for PMS activation using Fe/N-doped electron-rich biochar composites. This method facilitates efficient electron transfer and promotes a synergistic reaction mechanism involving both non-radical and radical pathways, enabling effective degradation of representative antibiotics in wastewater.