A systematic review on photo-based advanced oxidation processes for per- and polyfluoroalkyl substances removal

Per- and polyfluoroalkyl substances (PFAS) are environmentally persistent and pose toxic risks to ecosystems and human health. Conventional treatment processes are ineffective for the elimination of PFAS due to their highly stable C-F bonds. Photo-based advanced oxidation processes (AOPs) have emerged as an effective method for degrading PFAS in aqueous environments. This review summarizes state-of-the-art photo-based AOPs for PFAS removal and comprehensively compares the mechanisms of photolysis, photochemical, photocatalysis, photoelectrocatalysis, photosonolysis, and pseudo-photocatalysis. The solution pH, anion species, and organic matter significantly influenced the PFAS removal efficacy and degradation pathways in photo-based AOPs, whereas hydroxyl radicals, sulfate radicals, and hydrated electrons are the predominant reactive species responsible for PFAS destruction in photo-based AOP. Notably, short-chain PFAS are the dominant byproducts of the oxidation of long-chain PFAS, and there is a paucity of studies on their removal by photo-based AOPs. This review reveals the fundamental aspects, new perspectives, and challenges of PFAS removal, facilitating future research on the development and scaling up of photo-based oxidation processes.