Highly efficient aerogel adsorbent for cleaning process water effluents with high concentration of PFAS

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Many industries largely use per- and polyfluoroalkyl substances (PFAS). However, their removal from process effluents has been a major concern due to their spreading and accumulation in soils and water. This work aims to investigate the adsorption of PFAS through silica-based aerogels as an alternative method for removing PFAS at high concentrations in effluents. Two silica-based aerogel adsorbents were synthesized from a combination of silanes, one having hydroxyl and methyl groups in the silica structure and the other having additional amine groups. These were used for the removal of selected PFAS, namely perfluorooctanoic acid (PFOA), heptadecafluorooctanesulfonic acid (PFOS), and perfluorobutane sulfonic acid (PFBS), covering different chain lengths and polar groups. The amine-modified adsorbent showed superior performance for uptake PFAS, since the amine protonation at pH 6 water allows additional electrostatic interactions with the PFAS. This aerogel effectively contributed to the removal of concentrated solutions of the long-chain PFAS. For the short-chain PFAS (PFBS), the amine-containing aerogel performed better in the lowest concentration tested (5 mg L –1 ). The variation of adsorbent loads (1.4–10 g L –1 ) did not significantly impact the removals achieved for the PFOA and PFOS with the amine-modified aerogel (93–99 %). For the PFBS, the removals were around 60 %, achieving a maximum of 75 %. The adsorption kinetics showed a very fast adsorption of the PFAS by aerogel, reaching the equilibrium within the first few minutes of contact. Furthermore, a cumulative adsorption test showed that the amine aerogel did not reach saturation when exposed to 4 cycles of high concentration of PFOS.