Mechanistic Unveiling of Radical and Nonradical Pathways in Periodate Activation for Water Treatment: Generation Mechanism, Oxidative Behaviors, and Functional Merits

The growing presence of emerging pollutants in water underscores the need for advanced oxidation processes (AOPs) that generate a diverse range of reactive species for their effective removal. Periodate (PI)-based AOPs have emerged as energy-efficient systems capable of generating both radical and nonradical pathways to degrade pollutants. This review systematically elucidates the mechanistic aspects of both radical species and nonradical species in PI-based AOPs, highlighting their generation mechanisms and distinct oxidative behaviors toward organic pollutant degradation. The respective advantages of these two pathways are then systematically compared; the radical species offer rapid and high-efficiency degradation through non-selective oxidation, while nonradical species exhibit greater selectivity, enhanced resistance to matrix interference, and reduced risk of secondary pollution. In addition, the critical factors governing pathway selectivity, such as solution pH, coexisting ions, and dissolved organic matter, are systematically investigated to clarify their impacts on reactive species formation and pollutant degradation specificity. This review not only clarifies the mechanistic basis and comparative advantages of radical and nonradical pathways but also outlines future research directions to advance the rational design of PI-based AOPs for efficient and environmentally resilient water treatment.