Modified Zeolites as Alternative Adsorbents for PFAS Removal: A Comparative Study with Granular Activated Carbon

Per- and polyfluoroalkyl substances (PFASs) are persistent and mobile contaminants of global concern, and, while granular activated carbon (GAC) is widely used for their removal, it is limited by the high regeneration and disposal costs. This study investigates surface-modified clinoptilolite zeolites as low-cost and thermally regenerable alternatives to GAC for PFAS removal from water. Natural clinoptilolite was modified through acid washing, ion exchange with Fe3+ or La3+, grafting with aminosilane (APTES) or hydrophobic silane (DTMS), dual APTES + DTMS grafting, and graphene oxide coating. The adsorption performance was evaluated for perfluorooctanoic acid (PFOA, C8) and perfluorobutanoic acid (PFBA, C4) at 100 µg L−1 in single- and mixed-solute systems, with an additional high-concentration PFOA test (1 mg L−1). PFAS concentrations were quantified by liquid chromatography–tandem mass spectrometry (LC–MS/MS) using a SCIEX 7500 QTRAP system coupled to a Waters ACQUITY UPLC I-Class. Raw zeolite showed limited PFOA removal (4%), whereas dual-functionalized APTES + DTMS zeolites achieved up to 93% removal, comparable to GAC (97%) and superior to single-silane or metal-exchanged variants. At lower concentrations, modified zeolites effectively removed PFOA but showed limited PFBA removal (