A Review of Iron-Based Catalysts for Persulfate Activation to Remove PFAS in Water: Catalytic Effects of Various Iron Species, Influencing Factors and Reaction Pathways

Numerous studies highlight the potential degradation of per- and polyfluoroalkyl substances (PFAS) through advanced oxidation processes. A recent focus involves an innovative technology utilizing iron-based catalysts activated by persulfate, renowned for its exceptional PFAS removal efficiency. However, existing literature lacks a thorough comparison of various iron species catalyzing persulfate for PFAS oxidation, with limited analysis of key degradation factors. This paper conducts a comprehensive review, analyzing PFAS degradation efficiency, mechanisms, and pathways using persulfate activated by ferrous ions, zero-valent iron/nano zero-valent iron, iron-based multimetallic catalysts, and various supported iron catalysts. The influence of solution pH and Fe²⁺ concentration on the degradation process is also explored. The review reveals promising PFAS removal performance, often exceeding 90%, by iron-based materials activated with persulfate. Catalysts enhance performance through synergistic elements, optimized structural design, and diverse carriers. Acidic environments favor persulfate activation for organic pollutant degradation, while appropriate Fe²⁺ concentrations enhance removal efficiency, with Fe³⁺ regeneration being the rate-determining step. Iron-based catalyst-activated persulfate follows free radical (SO•- 4, ·OH, O₂^−•) and non-free radical pathways (Fe(IV), ¹O₂, direct electron transfer). Perfluorooctanesulfonic acid (PFOS) degradation involves desulfurization, forming the intermediate product perfluorooctanoic acid (PFOA), followed by defluorination. The critical step is removing one CF₂ unit in each round, leading to complete mineralization. The paper proposes future research directions for iron-based activated persulfate in water treatment for PFAS.