Trace Cu(II)-Mediated Selective Oxidation of Benzothiazole: The Predominance of Sequential Cu(II)-Cu(I)-Cu(III) Valence Transition and Dissolved Oxygen

Trace Cu(II), which inherently existsin soil and somewater/wastewater,can trigger persulfate oxidation of some pollutants, but the oxidationcapability and mechanism are not well understood, especially towardrefractory pollutants. We report in this research that benzothiazole(BTH), a universal refractory pollutant typically originating fromtire leachates and various industrial wastewater, can be facilelyand selectively removed by peroxydisulfate (PDS) with an equimolarBTH/PDS stoichiometry in the presence of environmental-relevant contentsof Cu(II) (below several micromoles). Comprehensive scavenging tests,electronspin resonance analysis, spectroscopy characterization, and electrochemicalanalysis, revealed that PDS first reduces the BTH-coordinated Cu(II)to Cu(I) and then oxidizes Cu(I) to high-valent Cu(III), which accountsfor the BTH degradation. Moreover, once the reaction is initiated,the superoxide radical is probably produced in the presence of dissolvedoxygen, which subsequently dominates the reduction of Cu(II) to Cu(I).This facile oxidation process is also effective in removing a seriesof BTH derivatives (BTHs) that are of environmental concern, thuscan be used for their source control. The results highlight the sequentialCu(II)-Cu(I)-Cu(III) transition during PDS activationand the crucial role of contaminant coordination with Cu(II) in oxidative transformation.