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

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.