Calcium Metal Mechanochemically Defluorinates PFAS to Environmentally Benign CaF2

Fluoropolymers and other per- and polyfluoroalkyl substances (PFAS) are among the most persistent anthropogenic materials. Although bulk fluoropolymers such as polytetrafluoroethylene (PTFE) are often regarded as chemically inert, weathering and abrasion generate long-lived fluorinated microplastics, while molecular PFAS accumulate in the environment as mobile contaminants. Existing destruction strategies can cleave C-F bonds, but typically require incineration or aggressive reagents and frequently generate water-soluble fluoride products that remain environmentally problematic. Here we show that calcium metal enables solvent-free mechanochemical defluorination of PTFE and perfluorooctanoic acid (PFOA) at ambient starting temperature without external heating, while irreversibly sequestering fluorine as calcium fluoride, a nontoxic, insoluble, and environmentally benign solid. Quantitative solid-state 19F NMR, with detection limits explicitly assessed, shows no resolvable PTFE after 30 min of milling with Ca and Mg (<1.0% residual PTFE); Sr gives near-complete conversion (<10% residual PTFE), whereas Ba gives only partial (∼64% residual PTFE) conversion after 30 min of milling. TEM and SEM-EDX reveal CaF2-rich nanocrystalline domains intimately mixed with an oxygen-containing disordered carbonaceous material. By coupling efficient defluorination with fluoride sequestration, this work establishes a mechanochemical strategy for mineralization of persistent fluorinated materials without generating soluble alkali-metal fluoride waste as a secondary environmental hazard, while defining the analytical and process-safety constraints relevant to further development.