High valent manganese-oxo species activation of peroxymonosulfate by different phases manganese oxides nanoplates for catalytic water decontamination

Advanced oxidation processes involving high-valent metal-oxo species have garnered increasing attention for their effective pollutant degradation in water. However, less is known about the mechanism of the species in the manganese oxides (MnOx) system. Therefore, it is crucial to design MnOx catalysts to systematically clarify the high-valent metal-oxo species reaction mechanism. In this study, MnOx nanoplates including Mn3O4, Mn5O8, and Mn2O3 were synthesized via a facile thermal treatment of a Mn(OH)2 precursor to activate peroxymonosulfate (PMS) for mechanism studies. The Mn3O4 catalyst exhibited superior catalytic performance and reusability owing to its unique spinel structure and rapid electron transfer properties. The first-order rate constant for Mn3O4 is 0.64 min- 1, which is 3.7 and 1.5 times higher than those of Mn5O8 and Mn2O3, respectively. Scavenging experiments, electron paramagnetic resonance, and electrochemical analysis revealed that free radicals played a negligible role, while the formation of high-valent Mn-oxo species was promoted, facilitated by the Mn3O4-PMS* complex. These high-valent Mn-oxo species were highly reactive towards various pollutants. Moreover, the degradation intermediates of bisphenol A (BPA) in the Mn3O4/PMS system were identified, further elucidating the interactions between high-valent Mn-oxo species and BPA. Additionally, the Mn3O4 catalyst exhibited excellent catalytic performance under practical conditions and maintained superior stability over six cycles. This work provides crucial insights into the role of transition metal oxides in activating PMS for the catalytic degradation of emerging pollutants.