Generation of interfacial high-spin manganese intermediates as reactive oxidant during peroxymonosulfate activation mediated by amorphous MnOx supported on polymeric substrate

Abstract

The preparation of transition metal oxides based on traditional hydrothermal and calcination processes for heterogeneous PMS activation in contaminants' abatement has been widely reported. A satisfactory PMS activation efficiency often demands the transition metal oxides with crystallographic structure; however, the preparation processes of crystalline metal oxides require more energy input. Besides, achieving the targeted electron transfer between pollutants and reactive oxygen species (ROS) to overcome the disturbance of the actual water matrix is still challenging. Herein, we immobilized manganese oxides onto polymeric substrates under room temperature by a novel redox method with lower energy consumption. The obtained composite was applied for PMS activation to degrade multiple phenolic pollutants mainly through non-radical pathways. Combining the results of multiple characterizations and 18O isotope-tracer experiments, we proposed that the interfacial high-spin MnIII-peroxy complex was the primary reactive oxidant. Besides, a small portion of MnIII-peroxy complex could further undergo interspecies oxygen-transfer to form MnV-oxo species as the secondary reactive oxidant, resulting in the different manganese reduction products (MnIII/MnIV). The proposed mechanism could explain the average oxidation state of Mn changed after PMS activation. Comparing with the radical-based systems, interfacial reactive manganese intermediates exhibited satisfactory resistance against complex water matrices, such as chloride, bicarbonate, natural organic matter (NOM), and effluent organic matter (EfOM). We believe that this study could inspire novel methods with lower energy consumption to prepare active manganese oxides and provide intriguing mechanistic insights into PMS activation mediated by amorphous manganese oxides.