Pyrolysis of Two\nPerfluoroalkanesulfonates (PFSAs)\nand PFSA-Laden Granular Activated Carbon (GAC): Decomposition Mechanisms\nand the Role of GAC

Thermal treatment of perfluoroalkyl and polyfluoroalkyl\nsubstances\n(PFASs) presents a promising opportunity to halt the PFAS cycle. However,\nhow co-occurring materials such as granular activated carbon (GAC)\ninfluence thermal decomposition products of PFASs, and underlying\nmechanisms remain unclear. We studied the pyrolysis of two potassium\nsalts of perfluoroalkanesulfonates (PFSAs, C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub>K), perfluorobutanesulfonate (PFBS-K), and perfluorooctanesulfonate\n(PFOS-K), with or without GAC. PFBS-K is more stable than PFOS-K for\npure standards, but when it is adsorbed onto GAC, its thermal stabilities\nand decomposition behaviors are similar. Temperatures and heating\nrates can significantly influence the decomposition mechanisms and\nproducts for pure standards, while these effects are less pronounced\nwhen PFSAs are adsorbed onto GAC. We further studied the underlying\ndecomposition mechanisms. Pure standards of C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub>K can decompose directly in their condense phase by\nreactions: F(CF<sub>2</sub>)<sub>n</sub>SO<sub>3</sub>K → F(CF<sub>2</sub>)<sub>n‑2</sub>CFCF<sub>2</sub> + KFSO<sub>3</sub> or F(CF<sub>2</sub>)<sub>n</sub>SO<sub>3</sub>K →\nF(CF<sub>2</sub>)<sub>n</sub><sup>–</sup> + K<sup>+</sup> +\nSO<sub>3</sub>. GAC appears to facilitate breakage of the C–S\nbond to release SO<sub>2</sub> at temperatures as low as 280 °C.\nGAC promotes fluorine mineralization through functional reactive sites.\nSiO<sub>2</sub> is particularly important for the surface-mediated\nmineralization of PFASs into SiF<sub>4</sub>. These findings offer\nvaluable insights into optimizing thermal treatment strategies for\nPFAS-contaminated waste.