Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are emerging contaminants of concern as they persist in natural environments due to their unique chemical structures. This paper critically reviewed the adsorption of PFOA and PFOS, depending on their chemical structure, by different adsorbents as well as soil. Adsorption of PFOS generally surpasses that of PFOA across various adsorbents. Despite having the same number of carbons, PFOS exhibits greater hydrophobicity due to two major structural differences: firstly, it has one extra CF₂ unit and secondly, the sulfonate group in PFOS, being a relatively hard base, readily adsorbs on oxide surfaces, enhancing its adsorption compared to the carboxylate group in PFOA. While comparing activated carbon (AC) adsorption performance, powdered activated carbon (PAC) demonstrates higher adsorption capacity than granular activated carbon (GAC) for PFOS and PFOA. Anion exchange resin (AER) outperforms other adsorbents, with a maximum adsorption capacity for PFOS twice that of PFOA. Carbon nanotubes (CNTs) exhibit two-fold higher adsorption for PFOS compared to PFOA, with single-walled CNTs showing a distinct advantage. Overall, the removal of PFOS and PFOA under similar conditions on different adsorbents is observed to be in the following order: AER > single-walled CNTs > AC. Moreover, AER, single-walled CNTs, and AC exhibited higher adsorption capacities for PFOS than PFOA. In situ remediation studies of PFOA/S-contaminated soil using colloidal activated carbon show a reduction in concentration to below acceptable limits within 12–24 months. The theoretical and experimental studies cited in this review highlight the role of air–water interfacial adsorption in retaining PFOA and PFOS as a function of their charged head groups during their transport in unsaturated porous media.

The effects of four inorganic ions: magnesium chloride (MgCl₂), potassium nitrate (KNO₃), sodium phosphate (Na₂PO₄), sodium bicarbonate (NaHCO₃), and three organic ions: sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic acid (EDTA), and humic acid (HA) on the adsorption behaviour of five per- and polyfluoroalkyl substances (PFAS) with varying chain lengths (C₅–C₁₁) were systematically investigated using granular activated carbon (GAC) and anion exchange resin (AER). Pseudo-second order (PSO) kinetic modelling showed adsorption capacities (qₑ) ranged from 1.11 to 6.89 mg/g and 4.67 to 8.62 mg/g for GAC and AER, respectively, across all experimental conditions and controls. AER consistently maintained high PFAS removal across diverse water matrices, whereas GAC performance was influenced by PFAS molecular structure and background ion composition. Competitive adsorption among PFAS followed a chain length–dependent trend on GAC; however, distinct selectivity patterns were observed for both adsorbents, highlighting material-specific adsorption mechanisms. Slight pH variations from background water are unlikely to destabilize PFAS adsorption, indicating stable performance of adsorption-based treatment under realistic conditions. Notably, this work reveals a previously unreported ion-mediated enhancement in the adsorption of short- and medium-chain PFAS (perfluoropentanoic acid, PFPeA; perfluorononanoic acid, PFNA) on GAC, attributed to cation-bridging and strengthened electrostatic interactions. In contrast, the longest-chain PFAS (perfluoroundecanoic acid, PFUnDA) exhibited a reversed response, with suppressed adsorption in the presence of ions. Moreover, desorption experiments revealed that co-occurring ions can enhance the retention of highly mobile, shorter-chain PFAS (PFPeA) on adsorbents, limiting PFAS remobilization, thereby improving the long-term reliability of adsorption-based water treatment systems. Overall, these findings provide new mechanistic insight into PFAS-adsorbent interactions under realistic water matrix conditions and offer practical guidance for adsorbent selection and treatment optimization especially for shorter-chains that are more problematic. Graphical abstract