Efficient adsorption of perfluorooctane sulfonate and perfluorobutane sulfonic acid from aqueous solution onto amine-functionalized diatomite granules

Per- and polyfluoroalkyl substances (PFAS), often referred to as 'forever chemicals,' are hazardous, bio-accumulative compounds that pose serious risks to both human health and the environment. PFAS are characterized by the presence of strong carbon–fluorine (C-F) bonds, which render them highly resistant to degradation and environmentally persistent. To address these challenges, (3-aminopropyl) triethoxysilane (APTES)-modified diatomaceous earth granules (APTES-DE) were investigated as a potential alternative adsorbent. FTIR, SEM-EDX, XRD, XPS, and BET analyses were used to characterize the APTES-modified diatomaceous earth granules. The adsorption performance of granules synthesized under varying formulation conditions was evaluated against two commonly detected PFAS compounds in contaminated water, perfluorobutane sulfonic acid (PFBS) and perfluorooctane sulfonate (PFOS). The effectiveness of APTES-modified diatomaceous earth (APTES-DE) is evaluated by investigating the adsorptive removal of model long-chain and short-chain PFAS compounds, PFBS and PFOS, under various experimental conditions. The maximum removal efficiency of PFAS reached 92.43% for PFOS and 89.90% for PFBS. The adsorption isotherms of both PFOS and PFBS on APTES-DE were best described by the Freundlich models, indicating the multilayer adsorption on heterogeneous surfaces. Furthermore, regeneration experiments demonstrated that the adsorbent maintained high reusability over five successive sorption-desorption cycles, with only slight declines in adsorption performance of 4.56% for PFOS and 3.62% for PFBS. Adsorption experiments indicate that electrostatic interactions, hydrophobic interactions and hydrogen bonding were the primary mechanisms driving PFAS removal. The lower adsorption efficiency observed for the short-chain PFAS compound, PFBS, compared to PFOS, suggests a positive correlation between adsorption performance and the length of the C–F chain.