Dual role of percarbonate in permanganate activation for micropollutants abatement: Reactive manganese species generation and stabilization.

Reactive manganese species (RMnS) generated from permanganate (Mn(VII)) activation are prone to disproportionation and secondary pollutant, necessitating greener and more efficient strategies to enhance RMnS utilization and micropollutant degradation. Therefore, we propose a strategy that synergistically combined sodium percarbonate (SPC) with Mn(VII) for the degradation of micropollutants. The results indicate that the Mn(VII)/SPC process effectively enhanced the degradation of p-hydroxybenzoic acid (p-HBA) and 4-chlorophenol (4-CP) by 3.2 and 3.4 folds in rate and 15.5% and 31.8% in efficiency respectively, compared to Mn(VII) alone at pH 7.0. Quenching experiments, probe analysis and mass spectrometry results indicate that Mn(III) and Mn(V) are the primary reactive species in this system. Further studies revealed that SPC plays a dual role in this system. On one hand, hydrogen peroxide (H2O2) released from SPC reduces Mn(VII) to Mn(VI) via a single-electron transfer pathway, which is further converted to Mn(V). Subsequently, Mn(V) reacts with H2O2 to generate Mn(III). On the other hand, HCO3- released from SPC can complex with Mn(III) and Mn(V) to form Mn(III)-HCO3- and Mn(V)-HCO3- complexes, synergistically enhancing the oxidative degradation efficiency of micropollutants. The enhanced degradation efficiency of the Mn(VII)/SPC system within the pH range of 4.0-9.0 can be attributed to the fact that higher pH promotes the deprotonation of p-HBA and 4-CP, thereby rendering them more susceptible to oxidation by Mn(V) and Mn(III). Furthermore, the effects of Cl-, SO42-, Ca2+ and NO3-on the degradation of p-HBA and 4-CP were negligible, while the presence of humic acid (HA) and HCO3- enhanced its degradation, likely due to its complexation with RMnS. This system also demonstrated excellent degradation efficacy in real water bodies. Overall, this study reveals a novel dual-pathway mechanism by which SPC enhances Mn(VII) oxidation, providing a promising strategy for micropollutants degradation.