Picolinic Acid-Mediated Catalysis of Mn(II) for Peracetic Acid Oxidation Processes: Formation of High-Valent Mn Species

Metal-based advanced oxidation processes (AOPs) withperaceticacid (PAA) have been extensively studied to degrade micropollutants(MPs) in wastewater. Mn(II) is a commonly used homogeneous metal catalystfor oxidant activation, but it performs poorly with PAA. This studyidentifies that the biodegradable chelating ligand picolinic acid(PICA) can significantly mediate Mn(II) activation of PAA for acceleratedMP degradation. Results show that, while Mn(II) alone has minimalreactivity toward PAA, the presence of PICA accelerates PAA loss byMn(II). The PAA-Mn(II)-PICA system removes various MPs (methyleneblue, bisphenol A, naproxen, sulfamethoxazole, carbamazepine, andtrimethoprim) rapidly at neutral pH, achieving >60% removal within10 min in clean and wastewater matrices. Coexistent H2O2 and acetic acid in PAA play a negligible role in rapid MPdegradation. In-depth evaluation with scavengers and probe compounds(tert-butyl alcohol, methanol, methyl phenyl sulfoxide,and methyl phenyl sulfone) suggested that high-valent Mn species (Mn(V))is a likely main reactive species leading to rapid MP degradation,whereas soluble Mn(III)-PICA and radicals (CH3C(O)O-center dot and CH3C(O)OO center dot) are minorreactive species. This study broadens the mechanistic understandingof metal-based AOPs using PAA in combination with chelating agentsand indicates the PAA-Mn(II)-PICA system as a novel AOP for wastewatertreatment. Peracetic acid-Mn(II) in combinationwith picolinic acidgenerates high-valent Mn species (Mn(V)) that contributes to rapiddegradation of micropollutants with minimal influence from water matrices.