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, IO4−) 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(MnO4−, Mn(VII)) in the presence of NTA, which indicates the important role of transient manganese-oxo species. 18O 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: PMSO2 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, I2, 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.