Identifying the Nonradical Mechanism in Mn Oxide-Mediated Peracetic Acid Activation Processes: Reactive Metal Species vs Electron Transfer Process

Abstract

Transition-metal oxide-mediated peroxide activation systems have been demonstrated to initiate selective degradation of pollutants, while the underlying mechanism remains unclear and sometimes controversial. In this study, we systematically explored the reactive species/pathways for pollutant degradation in the Mn oxide octahedron molecular sieve (OMS-2)-triggered peracetic acid (PAA) activation system. By separating PAA activation and pollutant oxidation processes using a sequential activation/oxidation system or galvanic oxidation system, we confirm that the OMS-2/PAA system follows the reactive metal species mechanism, where surface reactive Mn(IV) species, rather than Mn–PAA complexes, are primarily responsible for the nonradical oxidation of bisphenol A. OMS-2 shows varied peroxide-activating activities (i.e., catalase-like and peroxidase-like activities) toward different peroxides (i.e., H₂O₂, PAA, and persulfates), depending on the reactivity of surface reactive Mn(IV) species with those peroxides. In addition, the long-lived surface reactive Mn(IV) species exhibit excellent resistance to fluctuations in solution pH and interference from coexisting anions and natural organic matter. This study offers novel insights into the nonradical mechanism involved in Mn oxide-mediated peroxide activation processes.