Perfluoroalkyl substances (PFASs) are a class of environmental contaminants of emerging concern which encompass multiple functional groups and chain lengths. Such diversity poses a challenge to traditional water remediation adsorbents. Swellable organically modified silica (SOMS) is a highly porous, hydrophobic material which can undergo micromechanical expansion upon adsorption of organic liquids. SOMS was modified by the addition of covalently attached fluoroalkyl groups and quaternary amines to target the adsorption of PFASs. In addition, the expandable pores of SOMS were also used to entrap a quaternary amine polymer (poly-QA-SOMS).  In total, 18 modified SOMS variants were produced. Adsorption isotherms and kinetics were performed for twelve representative PFASs (PFDA, PFNA, PFOA, PFHpA, PFHxA, PFPeA, PFBA, PFOS, PFHxS, PFBS, PFOSA, PFOSaAm) and compared to granular activated carbon (GAC). Adsorption experiments were performed at 0 mM and 50 mM ionic strength. Increasing the ionic strength increased the rate of adsorption while resulting in a variable effect on the affinity dependent on the adsorbent surface chemistry and PFAS chain length. Poly-QA-SOMS was shown to be the most effective adsorbent across the suite as it combined both ionic and hydrophobic interactions to target a broad range of PFASs. Adsorption capacities for poly-QA-SOMS were relatively high: capacity at equilibrium (at equilibrium concentration Ce=200 ppb) were 12.7 mg/g for PFOA and 8.9 mg/g for PFOS (compared to 4.3 mg/g and 5.6 mg/g for GAC). At 50 mM ionic strength, a fluoroalkyl modified SOMS showed capacities (Ce=200 ppb) of 22.6 mg/g for PFOA and 68.0 mg/g for PFOS and PFOA (compared to 2.5 mg/g and 2.3 mg/g for GAC). SOMS and its derivatives show promise for the remediation of PFASs as they outperformed GAC in capacity and effectively targeted a broad range of PFASs.

Evaluation of PFAS-specific organosilica adsorbents using adsorption isotherms and kinetics

2019 Fall National Meeting

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