Copper-based Advanced Oxidation Processes for Micropollutant degradation: A review of Reaction mechanisms, Modulation strategies, and Future applications

The growing occurrence of harmful organic micropollutants in aquatic environments presents critical challenges for water reuse and environmental safety. Advanced oxidation processes (AOPs) have emerged as powerful treatment technologies. However, conventional iron (Fe)-based AOPs are constrained by acidic operating conditions, sludge production, and slow redox cycling. In contrast, copper (Cu)-based AOPs offer distinctive advantages with the multivalent redox flexibility, better stability at neutral pH, and faster electron-transfer kinetics. This critical review comprehensively examines Cu-based AOPs from mechanistic, structural, and practical perspectives. We first extend the fundamental differences between Cu- and Fe-based oxidation in terms of aqueous speciation, redox thermodynamics, reaction kinetics, and pH resilience. Then, we summarize the degradation pathways of micropollutants, highlighting emerging evidence for dual radical/non-radical regimes and the complex role of transient species. Furthermore, the review evaluates key operational factors, including oxidant selection, catalyst loading, pH, temperature, anions, and dissolved organic matter on degradation efficiency. Finally, we identify major knowledge gaps and propose future potential studies. This review argues that Cu-based AOPs should be regarded not merely as alternatives to conventional Fenton systems, but as a mechanistically distinct catalytic platform whose rational deployment requires integrated understanding of redox speciation, pathway selectivity, catalyst architecture, and matrix-dependent performance.