Nitrilotriacetic acid-assisted Mn(II) activated periodate for rapid and long-lasting degradation of carbamazepine: The importance of Mn(IV)-oxo species.

Periodate-based (PI, IO) oxidation processes for pollutant elimination have gained increased attention in recent years. This study shows that nitrilotriacetic acid (NTA) can assist trace Mn(II) in activating PI for fast and long-lasting degradation of carbamazepine (CBZ) (100% degradation in 2 min). PI can oxidize Mn(II) to permanganate(MnO, Mn(VII)) in the presence of NTA, which indicates the important role of transient manganese-oxo species. O isotope labeling experiments using methyl phenyl sulfoxide (PMSO) as a probe further confirmed the formation of manganese-oxo species. The chemical stoichiometric relationship (PI consumption: PMSO generation) and theoretical calculation suggested that Mn(IV)-oxo-NTA species were the main reactive species. The NTA-chelated manganese facilitated direct oxygen transfer from PI to Mn(II)-NTA and prevented hydrolysis and agglomeration of transient manganese-oxo species. PI was transformed completely to stable and nontoxic iodate but not lower-valent toxic iodine species (i.e., HOI, I, and I). The degradation pathways and mechanisms of CBZ were investigated using mass spectrometry and density functional theory (DFT) calculation. This study provided a steady and highly efficient choice for the quick degradation of organic micropollutants and broadened the perspective on the evolution mechanism of manganese intermediates in the Mn(II)/NTA/PI system.