S-doping promoting dual redox cycles in the ACM@S-Cu/Fe3O4/PMS system under visible light for chloroquine phosphate degradation

• Novel S-doped ACM@Cu-S/Fe 3 O 4 catalyst synthesized for visible-light-driven PMS activation. • Sulfur doping and Cu/Fe bimetallic synergy significantly enhance chloroquine phosphate degradation. • Dual redox cycles of Cu(I)/Cu(II) and Fe(II)/Fe(III) promoted by S-doping ensure catalytic stability and efficiency. • Proposed degradation pathways for chloroquine phosphate and by-product toxicity assessment provided. The activation of peroxymonosulfate (PMS) in metal-based systems is often limited by the slow redox cycle reactions of metal ions, hindering the efficient degradation of pollutants. These sluggish reactions can be enhanced through ion doping, which not only accelerates the redox cycles but also improves the stability of the reaction. The S-doped Cu/Fe 3 O 4 @ACM photocatalyst was synthesized by dispersing a copper-iron bimetallic oxide doped with sulfur onto a ceramic film. Its performance was evaluated in the degradation of Chloroquine phosphate via photocatalysis and PMS activation. The comprehensive morphological, structure, and optical properties were thoroughly evaluated by SEM, TEM, XRD, BET, PL and DRS, and the degradation mechanism was analyzed using XPS, EIS, ESR, and LC-MS characterization of the catalysts. The resulting ACM@S-Cu/Fe 3 O 4 /PMS/visible light (VL) system achieved 98.7% CQ degradation within 30 min, with an apparent rate constant 2.9 times higher than the undoped counterpart. This enhanced performance is attributed to sulfur doping, which facilitated the dual redox cycles of Cu(II)/Cu(I) and Fe(III)/Fe(II), accelerating PMS activation. Quenching experiments and ESR spectra confirmed the involvement of • OH, SO 4 • − , O 2 • − , 1 O 2 , and h + in the degradation process. Notably, the system also demonstrated efficient removal of CQ in real water matrices and rapid degradation of other emerging pollutants. This research provides a promising strategy for developing highly efficient PMS activation systems for wastewater treatment through strategic heteroatom doping, offering mechanistic insights into the enhanced degradation of emerging pollutants.