Facilitating redox cycles of copper species by peroxydisulfate in the copper-catalyzed Fenton-like system for enhanced oxidation of organic contaminants

Reducing and chelating agents have been extensively employed to strengthen the oxidizing capability of Cu(II)/H₂O₂ process. However, the risk of secondary pollution and the strong scavenging effect for reactive species severely limit their application in wastewater treatment. Herein, a new strategy was proposed for enhanced oxidation of organic contaminants in Cu(II)/H₂O₂ process by adding oxidizing agents (e.g., peroxydisulfate (PDS)). With naproxen (NPX) as the target contaminant, the introduction of PDS improved the degradation efficiency of NPX in Cu(II)/H₂O₂ process across the pH range of 7.0 to 10.5, and enhanced the utilization efficiency of oxidants (over 7-fold). More importantly, the deprotonated H₂O₂ (HO₂^-) acted as a reductant (not an oxidant) playing a crucial role in the reduction of Cu(II) to Cu(I) in PDS/Cu(II)/H₂O₂ process. PDS took precedence over H₂O₂ for reacting with the formed Cu(I) to generate multiple reactive species including ^•OH, SO₄^•− and Cu(III). PDS/Cu(II)/H₂O₂ process also demonstrated well interference resistance to common natural inorganic ions (e.g., NO₃⁻, HCO₃⁻) and humic acid. Furthermore, two possible conversion pathways were proposed based on the detected seven degradation intermediates, and no significant change in toxicity was observed. In summary, this study described a novel strategy to enhance the oxidizing capacity of Cu(II)/H₂O₂ process utilizing oxidants rather than reducing and chelating agents, revealing a new perspective into synergistic role of dual oxidants in the metal valence cycle.