Per- and Polyfluoroalkyl Carboxylic Acids Mixture Adsorption on Surfactant-Modified Granular Activated Carbon: Mechanisms and Competitive Effects

Per- and polyfluoroalkyl substances (PFAS) are a type of emerging contaminant associated with significant health risks, such as carcinogenicity, endocrine disruption, and immunotoxicity. The persistent nature and widespread occurrence of PFAS, particularly perfluoroalkyl carboxylic acids such as perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA), necessitate the development of efficient remediation strategies. In this study, granular activated carbon (GAC) was modified with cetyltrimethylammonium chloride (CTAC) to enhance the adsorption capacity of PFAS. The surface morphology and physicochemical properties of unmodified and modified GAC (MGAC) were characterized using scanning electron microscopy and Brunauer–Emmett–Teller analysis, revealing significant surface and pore structure alterations following CTAC modification. Batch adsorption experiments demonstrated that MGAC exhibited superior adsorption capacities for PFOA (93.18 mg/g) and PFNA (130.94 mg/g) compared with unmodified GAC (90.53 mg/g and 103.71 mg/g, respectively). The observed increase in adsorption capacity is attributable to enhanced electrostatic and hydrophobic interactions facilitated by the quaternary ammonium groups and hydrophobic alkyl chains of CTAC. However, competitive adsorption tests indicated a reduction in PFNA adsorption efficiency, suggesting that PFAS cooccurrence affects adsorption dynamics. Adsorption isotherms were best described by the Langmuir model, indicating monolayer adsorption on homogeneous surfaces. The findings underscore the efficacy of surfactant-modified GAC in enhancing PFAS removal from aqueous environments and provide critical insights into the mechanisms governing PFAS adsorption under single and mixed-species scenarios. This study advances the development of adsorbents for PFAS remediation, addressing the challenges of complex environmental matrices and cooccurring PFAS species.