Mechanochemical Destruction of PFAS: Critical Effects of Co-Milling Agents

Abstract

This perspective explores the emerging field of mechanochemical degradation of per- and polyfluoroalkyl substances (PFAS) as an innovative, scalable, and sustainable approach. The degradation of PFAS, particularly their robust carbon–fluorine bonds, remains a significant challenge. Mechanochemical methods utilizing co-milling agents can facilitate the destruction of PFAS compounds. Here, we highlight the importance of reported co-milling agents, such as potassium hydroxide (KOH), silica (SiO₂), alumina (Al₂O₃), sodium persulfate (PS), and lanthanum oxide (La₂O₃). Each co-milling agent demonstrates varying degrees of effectiveness in PFAS degradation. Mechanochemical degradation in the presence of KOH alone has strong degradation capabilities (99% after 3 h, 275 rpm) but also produces hazardous byproducts such as potassium fluoride (KF) that present waste management and safety concerns. In contrast, SiO₂ and Al₂O₃ exhibit slower PFAS degradation rates (42.2 and 98% degradation efficiency, 2 h, 350 rpm) and require other additives, but yield product mixtures that have improved sustainability. Studies have shown a near-complete degradation (99.95–100%) of perfluoroalkyl sulfonates (PFSAs), which entail stable Si–F bonds, by using co-milling agents, such as SiO₂, and full degradation of PFOS, PFOA, PFHxS, and PFBS using La₂O₃, through electron donation to the carbon atom, which destabilizes the C–F bond. Mechanistic stages of PFAS degradation, such as mechanical activation, bond cleavage, mineralization, and the role of protonation, electron transfer, and the formation of stable bonds in the degradation process, are emphasized. Further research to refine and optimize mechanochemical processes, with a focus on novel co-milling agents and synergistic approaches, can enhance PFAS remediation and address global environmental concerns.

This review examines mechanochemical PFAS degradation using co-milling agents, highlighting their potential as scalable, low-energy solutions for remediating persistent pollutants and reducing environmental contamination in soils and wastes.