Chemical degradation of PFAS in aquatic environments: technological advances and mechanistic insights

Per- and polyfluoroalkyl substances (PFAS) are extensively used in industrial and consumer products owing to their outstanding surface activity and have emerged as global environmental pollutants, posing serious threats to ecosystems and public health. The unique C-F bond structure imparts PFAS with exceptional chemical stability and environmental persistence, making them highly resistant to removal by conventional water treatment methods. Consequently, the development of efficient degradation technologies has become a critical research focus. This review systematically summarizes recent advances in chemical degradation strategies and the underlying mechanisms of PFAS in aqueous environments. First, chemical oxidation and reduction approaches are discussed. In chemical oxidation, modified Fenton systems, persulfate activation, and ozonation generate reactive oxygen species (ROS) that electrons from PFAS headgroup functional moieties, initiating chain shortening with concomitant defluorination. Chemical reduction methods based on hydrated electrons (eaq−), such as UV/sulfite, UV/iodide, and UV/organic systems, along with vacuum ultraviolet and nanozero-valent iron catalysis based on hydrogen atoms (H•), are introduced. In these systems, perfluorooctanoic acid (PFOA) undergoes degradation via parallel pathways involving hydrogen/fluorine (H/F) exchange and chain shortening. Further elaboration is provided on the reductive degradation mechanisms of other PFAS compounds, such as perfluoro-2-propoxypropanoic acid (GenX), trifluoroacetic acid (TFA), perfluoroalkyl sulfonic acids (PFSA), and fluorotelomer sulfonic acids (FTSA). Second, the principles and recent developments of electrocatalytic and photocatalytic technologies for PFAS degradation are systematically summarized. Electrocatalytic degradation is described as proceeding through direct or indirect anodic oxidation, either independently or synergistically. In photocatalysis, the catalytic principles and modification strategies of TiO2-, In2O3-, and BiOX-based systems are emphasized. Both electrocatalytic and photocatalytic degradation mechanisms typically involve two key steps: the migration or adsorption of PFAS onto electrode or photocatalyst surfaces, followed by electron abstraction from functional groups, leading to chain shortening and defluorination. Progress in thermochemical and sonochemical degradation is also reviewed. Thermochemical approaches offer highly efficient and thorough PFAS degradation across various species, demonstrating promising performance in laboratory and pilot-scale applications. In contrast, sonochemical methods alone are often insufficient, prompting the development of ultrasound-assisted hybrid technologies, such as sonolysis-photocatalysis and sonolysis-electrocatalysis, to increase catalytic efficiency. Additionally, emerging degradation technologies, including plasma and electron beam treatments, have been introduced; although promising, these methods remain in the early stages and require further optimization. After a detailed discussion of various approaches is presented, the key attributes of different technologies, including degradation mechanisms, applicable PFAS types, advantages and limitations, energy consumption, engineering feasibility, and potential application scenarios, are systematically analyzed and compared. From an engineering perspective, thermochemical processes are effective for high-strength PFAS waste but are constrained by demanding operational conditions, equipment requirements, and safety concerns, limiting broader deployment. Electrocatalysis offers high efficiency, yet costly and corrosion-prone electrodes, along with side gas evolution, hinder long-term and large-scale application. Photocatalytic and sonochemical systems feature compact design, easy operation, and good scalability, with strong potential for modular integration and coupling with other technologies to enhance system flexibility. Plasma and electron beam methods remain at a preliminary stage, with their engineering readiness, operational complexity, and cost-effectiveness still requiring further validation. Oxidation and reduction approaches offer high versatility and compatibility for tandem or hybrid deployment, enabling synergistic PFAS mineralization with improved treatment efficiency. Finally, the review outlines persistent challenges—such as incomplete mineralization, low selectivity, and limited validation in real water matrices—and emphasizes that future research should focus on combining or integrating multiple strategies to increase PFAS degradation efficiency and support practical application.