Performance and mechanism of peroxymonosulfate heterogeneous activation based on FeII-siderite&dithionite for carbamazepine degradation

Abstract

Sulfate radicals-based advanced oxidation process (SO₄⁻-AOPs) exhibits remarkable efficacy for emerging contaminants (ECs) eradication. In this work, we utilized natural Fe^II-siderite as a catalyst with dithionite (DTN) and peroxymonosulfate (PMS) precursors to engineer the Fe^II-siderite&DTN/PMS system. Carbamazepine (CBZ) elimination efficiency exceeded 90% in 10 min with reactive species of SO₄⁻ and OH, even in the anaerobic condition due to the sufficient oxidation species source from broken peroxy bond. The system generated various radicals (e.g., SO₄⁻, SO₃⁻, OH, and SO₅⁻) through redox cycles involving Fe^II-siderite, DTN, and PMS, with Fe^II/Fe^III interconversion driven by PMS oxidation and DTN reduction. Enhanced electron shuttling and Fe^II/Fe^III interconversion at the phase interface, the rate-limiting step in iron-based AOPs, facilitated PMS activation. CBZ degradation followed four pathways including deacylation, ring-opening oxidation, hydroxylation, decarboxylation, and deketonization, with reactive sites at CBZ-7C and CBZ-8C identified by LC-MS/MS and density functional theory (DFT). Oxygen consumption rate (OCR) toxicity assessments revealed persistent toxicity of intermediates, yet the Fe^II-siderite&DTN/PMS system detoxified them effectively based on T.E.S.T. evaluation. And the system demonstrates potential for ECs remediation, particularly in high salinity waters, due to the significant enhancement of higher Cl⁻ concentrations.