A Novel Low-Dose Mn(VII)/PMS System for Efficient Contaminant Removal with Enhanced Mn(VII) Utilization: Unveiling Mn(VI)-Mediated Mn(VII) Regeneration

Balancing degradation efficiency with environmental sustainability remains a critical challenge for permanganate (Mn(VII))-based oxidation processes in environmental remediation. In this study, we report a novel system initiated by low-dose Mn(VII) dosage (2 μM) in combination with peroxymonosulfate (PMS), enabling efficient removal of emerging contaminants exemplified by bisphenol A (BPA), especially under alkaline conditions (e.g., pH 10). Notably, distinct from conventional radical or nonradical activation mechanisms, we identified a previously unrecognized Mn(VII) regeneration process in the Mn(VII)/PMS system, as supported by a series of complementary evidence from radical quenching experiments, stopped-flow spectroscopy, DFT calculations, and kinetic modeling. The in situ generated Mn(VI) from the reaction of Mn(VII) and BPA was demonstrated to act as the key intermediate, which was subsequently reoxidized by PMS via a multihydrogen-bonded complex back to Mn(VII). This Mn(VI)/Mn(VII) interconversion, reported here for the first time, not only effectively enhanced contaminant degradation but also significantly improved Mn(VII) utilization efficiency. These findings broaden the mechanistic understanding of Mn(VII)-based systems beyond traditional free radical- and Mn(III)/Mn(V)-driven pathways and open new insights for developing efficient and environmentally benign water treatment technologies.