Selective and rapid degradation of organic contaminants by Mn(V) generated in the Mn(II)-nitrilotriacetic acid/periodate process

The rapid generation of Mn(V) as the dominant reactive species for the selective and efficient degradation of trace organic contaminants (TrOCs) remains still challenging. In this work, aqueous Mn(II) complexed with nitrilotriacetic acid (Mn(II)-NTA complex) was employed for the first time to activate periodate (PI) (Mn(II)-NTA/PI process) to degrade TrOCs. Experiments showed that TrOCs could be degraded in the Mn(II)-NTA/PI process within 30 s. Mn(V), existing as Mn(V)-NTA complex, was identified as the active oxidant in this process by using methyl phenyl sulfoxide as a probe, scavenging experiments, and mass spectrometry analysis. Three-dimensional UV–vis spectra indicated that Mn(III)-NTA complex was firstly generated through oxidation of Mn(II)-NTA complex by PI and then oxidized to Mn(V)-NTA complex via two-electron transfer. The generation of Mn(V)-NTA complex was dependent on NTA concentration, PI concentration, and solution pH, whereas the reactivity of Mn(V)-NTA complex toward TrOCs strongly relied on the functional groups of TrOCs. A high PI utilization efficiency could be achieved in this process. Moreover, due to the catalyst-like role of Mn(II)-NTA complex in activating PI, Mn(V)-NTA complex could be continuously generated and thus the sustainable and efficient degradation of TrOCs occurred in this process even when the concentration of Mn(II)-NTA complex was low. This work advances the understanding of Mn(V) generation from Mn(II) commonly present in aquatic environments.