Unveiling radical and non-radical species in ferrate-based advanced oxidation processes for wastewater treatment: Generation, mechanisms, and identification.

The growing prevalence of emerging pollutants in water matrices underscores the imperative need for advanced oxidation processes (AOPs) capable of generating diverse reactive species to facilitate their effective removal. Ferrate (Fe(VI))-AOPs have garnered significant attention as promising systems that leverage strong oxidative capacity for wastewater remediation. However, elucidating the intrinsic interaction mechanisms underlying Fe(VI)-AOPs and precisely identifying the radical and non-radical species involved remain a formidable challenge. This review systematically bridges these gaps by synthesizing state-of-the-art knowledge on the generation pathways, oxidation behaviors, and identification methods of radical and non-radical species in Fe(VI)-AOPs. We first outline the core physicochemical properties of Fe(VI) and its self-decomposition mechanisms. Building on this, we summarize Fe(VI) activation pathways that yield radical and non-radical reactive species, alongside their pollutant oxidation mechanisms, including reactivity mechanisms, pH and water matrix effects. We then critically assess existing strategies for precise identification and characterization of these reactive species, and highlight key unresolved controversies in current research. Finally, we outline critical challenges and future research directions to advance mechanistic studies and real-world implementation of Fe(VI)-AOPs.