New\nInsights into Thermal Degradation Products of\nLong-Chain Per- and Polyfluoroalkyl Substances (PFAS) and Their Mineralization\nEnhancement Using Additives

The products of incomplete destruction\n(PIDs) of per- and polyfluoroalkyl\nsubstances (PFAS) represent a substantial ambiguity when employing\nthermal treatments to remediate PFAS-contaminated materials. In this\nstudy, we present new information on PIDs produced in both inert and\noxidative environments from five long-chain PFAS, including three\nnow regulated under the U.S. Safe Drinking Water Act, one cationic\nprecursor compound, and one C10 PFAS. The data did not support the\ngeneration of tetrafluoromethane from any of the studied PFAS, and\ncarbonyl fluoride was found only from potassium perfluorooctanesulfonate\n(K-PFOS) when heated in air in a narrow temperature range. Oxidative\nconditions (air) were observed to facilitate PFAS thermal degradation\nand accelerate the mineralization of K-PFOS. Spectroscopic data suggest\nthat PFAS thermal degradation is initiated by the cleavage of bonds\nthat form perfluoroalkyl radicals, leading to organofluorine PIDs\n(e.g., perfluoroalkenes). In air, perfluoroalkyl radicals react with\noxygen to form oxygen-containing PIDs. The mineralization of PFAS\nwas enhanced by adding solid additives, which were categorized as\nhighly effective (e.g., granular activated carbon (GAC) and certain\nnoble metals), moderately effective, and noneffective. Remarkably,\nsimply by adding GAC, we achieved >90% mineralization of perfluorooctanoic\nacid at 300 °C and ∼1.9 atm within just 60 min without\nusing water or solvents.