A review on advanced oxidation processes homogeneously initiated by copper(II)

Cost-effective oxidation is one of the hot topics in the remediation of environmental pollutants in recent years. Copper species have been recognized as efficient activators or catalysts in initiating some advanced oxidation processes (AOPs) to generate strong oxidants. Since many source water/wastewater contain certain amounts of Cu(II), AOPs homogeneously initiated by Cu(II) would have application potential in many cases of polluted water remediation. Although relevant research is increasing, substantial controversies exist in interpreting the mechanism of Cu(II) as an activator or a catalyst. In this review, we presented a relatively comprehensive summary on this topic, comparing the homogeneous hydrogen peroxide-based and persulfates-based AOPs initiated by Cu(II), with an emphasis on the reaction mechanisms. Approaches in literatures to improve the performance of homogeneously Cu(II)-initiated AOPs are illustrated. Furthermore, critical methodologies for the identification of intrinsic reactive species are discussed, including inhibition tests, electron paramagnetic resonance, typical organic compounds degradation, and spectroscopy methods. Finally, concluding remarks and perspectives are made to guide future research. This review is expected to provide a clear interpretation on the homogeneously Cu(II)-initiated AOPs.