Sustainable redox processes induced by peroxymonosulfate and metal doping on amorphous manganese dioxide for nonradical degradation of water contaminants

Abstract

Manganese oxides have been applied in advanced oxidation processes (AOPs), however, underlying oxidation regimes are still debatable. In this work, we synthesized various crystalline manganese oxides and single or dual metal-doped amorphous MnO₂ (M-AMO, M = Fe, Co, Ni, and Cu) for organic oxidation with peroxymonosulfate (PMS). M-AMO at 1 mol% exhibited much higher activities than crystalline manganese oxides and Cu-AMO displayed the rate constant at 3.5 times as high as that of AMO. Different from conventional radical oxidation, nonradical degradation occurred via two pathways. Cu-doping resulted in relatively higher-crystallized structure, more oxygen vacancies, and a higher ratio of Mn⁴⁺/Mn³⁺ for a faster redox cycle between Mn(Ⅳ)(s) and Mn(Ⅲ)(s) to boost PMS activation and direct/indirect (Cu-AMO–PMS complex-based) phenol oxidation. This study contributes to a new insight to the structure-catalysis relationship in manganese-catalyzed PMS oxidation. The outcomes will direct the rational synthesis of reaction-oriented catalysts for nonradical AOPs and novel remediation technologies.