Insights into the transformations of Mn species for peroxymonosulfate activation by tuning the Mn3O4 shapes

Abstract

The transformation among MnII, MnIII and MnIV on the surface of the manganese oxides is a critical factor for peroxymonosulfate (PMS) activation. In this work, three kinds of Mn3O4 with different shapes (plate, cube and octahedra) were prepared to tune the surface Mn valence for ciprofloxacin (CIP) degradation, and the relationship between MnIV and PMS activation was established for the first time. The octahedral Mn3O4 (Mn3O4-O) owns high catalytic activity, MnIV is the primary active site on the surface of Mn3O4 for PMS activation to generate the active radicals, while the surface –OH groups play a key role in the formation of reactive intermediates. The quenching experiments and Electron paramagnetic resonance (EPR) results suggest that the SO4− and OH radicals are the main reactive radicals in the catalytic process. The PMS activation should mainly occur in the transformation from MnIV to MnIII. This work is expected to elucidate the relationship between surface valence in manganese oxides and PMS activation by morphology-tuning.