Synergistic Fe-S co-doped in g‑C₃N₄ promotes chlorine activation for enhanced emerging contaminant degradation and...

UV/chlorine process has emerged as an efficient disinfection technology, while still suffering from the insufficient radical yields and toxic disinfection by-product (DBPs) formation. To address these challenges, a novel heterogeneous photocatalytic chlorine activation system based on Fe-S co-doped g-C₃N₄ (Fe-S-g-C₃N₄) was developed. UV-LED/chlorine/Fe-S-g-C₃N₄ process enhanced the degradation and mineralization of the persistent pharmaceutical carbamazepine (CBZ) by 71.9 % and 55.5 %, respectively, compared with UV-LED/chlorine process. Fe sites served as efficient traps for photoelectrons (e_cb^-), while S incorporation increased surface reactive sites and promoted charge transfer, jointly suppressing photogenerated electron-hole recombination and boosting radical generation. Low-valence sulfur species further accelerated the Fe²⁺/Fe³⁺ redox cycle, promoting the in-situ generation of hydroxyl radicals (HO·) and reactive chlorine species (RCS). These reactive species preferentially targeted electrophilic positions on CBZ via hydroxylation and chlorination, yielding transformation products with lower mutagenicity and reduced acute/chronic toxicity. Within the scope of the six quantified DBPs, UV-LED/chlorine/Fe-S-g-C₃N₄ process achieved a 59.8 % reduction in their total concentration and a 57.5 % decrease in the corresponding integrated toxicity risk relative to UV-LED/chlorine system. UV-LED/chlorine/Fe-S-g-C₃N₄ process exhibited excellent performance in real water matrices and outstanding cycling stability, potentially advancing photocatalytic water purification and disinfection technologies.