Engineered silver-chitosan@magnetite nanoparticles (Ag-CS@Fe₃O₄ NPs) for the degradation of polyfluoroalkyl...

Polyfluoroalkyl substances (PFAS) have resulted in increasing attention globally due to their frequent discharge into the environment leading to acute and chronic diseases in living organisms. In this study, silver-chitosan@magnetite nanoparticles (Ag-CS@Fe₃O₄ NPs) were synthesized and employed in the degradation of polyfluorooctanoic acid (PFOA) and polyfluorooctane sulfonic acid (PFOS). Characterizations of Ag-CS@Fe₃O₄ by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), Ultra-high Resolution Field Emission Scanning Electron Microscopy (UHR FESEM) and Energy Dispersive X-ray (EDX) clearly verified the successful intercalation of Ag and CS biopolymer into Fe₃O₄ NPs. According to N₂ adsorption-desorption Brunauer-Emmett-Teller (BET), the improved chemical functionality and the accessibility of active binding sites in Ag-CS@Fe₃O₄ accounted for its enhanced catalytic degradation performance. The Ag-CS@Fe₃O₄ achieved efficient catalytic degradation of PFOA and PFOS in 24 h at 10.0 wt% Ag loading, initial PFAS concentration of 0.01 mg L^-1 and initial pH 3. Furthermore, the catalytic degradation tended to follow the pseudo-first-order kinetic model as proven by regression analysis revealing the presence of equally spaced data points around the horizontal axis. The degradation mechanism was proposed based on the shorter chain molecules formed through decarboxylation/desulfonation-hydroxylation-elimination-hydrolysis (DHEH) pathway as evidenced by their mass-to-charge (m/z) ratios from Quadrupole Time-of-Flight Liquid Chromatography-Mass Spectrometry (QTOF-LCMS). Despite the mass loss of 39.8% and 32.5% of Ag-CS@Fe₃O₄ during the degradations of PFOA and PFOS, respectively, the reusability of the catalyst throughout the five cycles without any deactivation enabled it to be a potential candidate for the degradation of PFAS in aquatic environments.