Exploring the adsorption of short and long chain per- and polyfluoroalkyl substances (PFAS) to different zeolites using environmental samples

Abstract

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants that are gaining attention for their ubiquitous distribution, persistence, and toxicity in the environment and ecosystem. Among the PFAS removal techniques from water, adsorption treatment techniques are considered most promising. In this study for the first time, 9 different zeolites and powdered activated carbon (PAC) were tested for 18 PFAS including C₃–C₁₃ perfluoroalkyl carboxylates acids (PFCAs), C₄, C₆, C₈ perfluoroalkane sulfonates (PFSA), three fluorotelomer sulfonate (FTSAs), and perfluorooctane sulfonamide (FOSA) in batch sorption experiments using ultrapure and real environmental water samples. Adsorption experiments showed that zeolite beta with SAR = 25 (silica alumina ratio, SiO₂/Al₂O₃) (99.5% ∑PFAS uptake) and SAR = 300 (99.2% ∑PFAS uptake), and mordenite with SAR = 240 (87.8% ∑PFAS uptake) were the most promising adsorbent media. Sorption of individual PFAS depended on the perfluoroalkyl chain length, functional group and molecule size. Overall, AgY390 and AgY760 silver (Ag) functionalized zeolites (76.4% and 78.3% ∑PFAS uptake respectively) showed better uptake capacity for PFAS compared to the as-synthetized Y390 and Y760 (68.6% and 68.3% ∑PFAS uptake respectively), and could favor catalytic reactions in PFAS degradation. PFAS sorption to PFAS-fortified real contaminated water samples was as follows: Beta25 (99.4%) < Beta360 (97.5%) < MOR (97.1%) < Y760 (95.5%) < CHA (71.4%) (with respect to PAC 99.9%). X-ray structural data revealed that changes in unit cell parameters arise from channel distortions caused by the encapsulation of PFAS inside the zeolites cages. Thermal analyses corroborate these results and revealed degradation of the perfluoroalkyl chain and expulsion upon heating are accompanied by exothermic reactions registered in the differential thermal analysis (DTA). The features of the zeolites, including the specific surface area, pores size and distribution, SAR, temperature, presence of extraframework cations and polarity significantly affected their PFAS adsorption capacity.