Synergistic interfacial electron transfer for enhanced tetracycline degradation via magnetite-activated peroxymonosulfate.

This study systematically investigated tetracycline (TC) degradation and the underlying nonradical activation mechanism in the magnetite/peroxymonosulfate (PMS) system, with particular emphasis on interfacial electron transfer. Under the selected operating conditions, up to 95.6% TC removal was achieved within 60 min. The system also exhibited good reusability and adaptability to different real-water matrices. Combined quenching experiments, electron paramagnetic resonance (EPR) analysis, and reactive species quantification consistently demonstrated that TC removal predominantly proceeds via a non-radical oxidation pathway governed by singlet oxygen (1O2). Electrochemical analyses and theoretical calculations revealed that PMS adsorption induced pronounced interfacial charge redistribution and facilitated electron transfer on the magnetite surface. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron probe microanalysis (EPMA) collectively indicated that the bulk crystalline phase of magnetite remained stable, whereas its surface Fe-O coordination environment underwent restructuring accompanied by Fe(II)/Fe(III) valence-state transitions. Liquid chromatography-mass spectrometry (LC-MS), frontier molecular orbital analysis, and Fukui function calculations further revealed a site-selective TC transformation process. This study reveals the coupling among PMS adsorption-induced interfacial electron transfer, Fe-O coordination restructuring, and 1O2-mediated oxidation on unmodified magnetite, providing mechanistic and environmental-management insights into selective PMS activation by mixed-valent iron minerals.