Synergetic degradation of PFOS by HALT conditions enhanced by Fe-based amorphous alloys

Global concern over per- and polyfluoroalkyl substances (PFASs), especially perfluorooctane sulfonate (PFOS), disposal prompts the search for effective degradation methods. Subcritical water hydrothermal treatment shows promise but suffers from unclear degradation pathways, hindering engineering application design due to unknown intermediate products. This study introduces Fe-based amorphous alloy to enhance the subcritical water hydrothermal degradation of PFOS, achieving a degradation rate of approximately 85 % under optimized conditions of 325 °C and 1 M sodium bicarbonate (NaHCO₃), compared to 56 % without the alloy. Analysis of liquid and gas-phase products, along with identification of potential intermediate products, led to proposing a reaction pathway for Fe-based amorphous alloy-enhanced subcritical water hydrothermal PFOS degradation. Additionally, the distribution of fluorine in PFOS was determined by fluorine-19 nuclear magnetic resonance (¹⁹F NMR), and the energy changes of key degradation steps were calculated based on DFT, which provided concrete evidence for the degradation process and verified the mechanism of subcritical hydrothermal degradation of PFOS enhanced by Fe-based amorphous alloys. Most importantly, the Fe-based amorphous alloy demonstrated effectiveness upon repeated use after water washing. These results endorse its potential as a PFOS degradation catalyst.