Molecular Oxygen Activation for Organic Pollutants Degradation in Water: Strategies, Mechanisms, and Applications

The existence of continually increasing refractory organic pollutants in water has always been a serious potential threat to human and environmental health due to their toxicity and persistence. Conventional water treatment technologies suffer from inherent limitations, including low degradation efficiency, secondary pollution issues, and high operational costs. Recently, molecular oxygen (O2)-based advanced oxidation processes (O2-AOPs) have attracted increasing attention as sustainable and efficient wastewater treatment technologies, as the abundant and environmentally benign oxidant in nature can be activated into reactive oxygen species (ROS), such as superoxide anions (·O2−), hydroxyl radicals (·OH), and singlet oxygen (1O2), enabling the effective mineralization of refractory organic pollutants. This review presents a comprehensive summary of O2-AOPs for water purification, specifically focusing on photocatalytic, electrocatalytic, thermocatalytic, and mechanocatalytic systems. Furthermore, we conduct a comprehensive analysis of the intrinsic reaction mechanisms associated with both free radical pathways and non-free radical pathways, which include processes involving singlet oxygen and high-valent metal-oxygen intermediates. Finally, we discuss the challenges and prospects associated with the degradation of typical organic pollutants, such as phenolic compounds, pharmaceuticals and personal care products (PPCPs), and organic dyes. Despite significant advancements in O2-AOPs, several core challenges persist, including low efficiency in utilizing dissolved oxygen, insufficient catalyst stability, and unclear mechanisms of interfacial electron transfer. Future research should prioritize the precise regulation of material structures, a thorough analysis of reaction mechanisms, and the tailored development of reactors to facilitate the industrial application of this technology in water treatment. Overall, this review systematically outlines the current progress in technologies for removing organic pollutants using molecular oxygen, offering novel insights for mitigating organic pollution in water.