Transition metal-mediated composite systems for peracetic acid-based AOPs in water treatment: Mechanisms, influencing factors, and application outlook

Peracetic acid-based advanced oxidation processes (PAA-AOPs) have garnered significant interest in water treatment due to the high efficiency, low toxicity, and minimal pH dependence. However, single transition metal catalytic systems often suffer from limited pH adaptability, surface passivation, metal leaching, and a narrow spectrum of reactive oxygen species (ROS) generation. To overcome these bottlenecks, transition metal-mediated composite PAA-AOPs have been developed, which integrated synergistic components such as secondary metals, sulfur modifiers, reductants, chelators, or external energy inputs. This review systematically summarized the current development of these composite systems, with a focus on the construction strategies and underlying mechanisms for enhanced PAA activation. The synergistic effects driving bimetallic redox cycles, electron donation, metal-ligand complexation, and energy-assisted electron transfer were critically examined, alongside the generation pathways of both radical and non-radical ROS. Furthermore, the key factors governing process performance, like solution pH, catalyst and PAA dosages, reductant/chelator concentrations, and water matrix constituents were evaluated. The practical application potential of these systems was assessed in terms of catalyst stability, performance in real water matrices, and ecological toxicity reduction. Finally, this review offered prospects for future research, emphasizing the integration of artificial intelligence and machine learning to accelerate catalyst design and process optimization, advancing the development of intelligent, efficient, and low-carbon water treatment technologies.