Surfactant-Modified Clay for Adsorption of Mixtures of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Solutions

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative, and ubiquitous contaminants that are harmful to both humans and ecosystem health. To remove PFAS effectively and efficiently from the aqueous environment, a clay-based adsorbent was synthesized via the modification of montmorillonite by a cationic surfactant cetyltrimethylammonium chloride (CTAC). Through the coexposure adsorption tests with organic dyes and PFAS mixtures, the optimal ratio of CTAC to cation exchange capacity (CEC) was identified. The optimal modified clay exhibited drastically improved adsorption performance, achieving 100% removal efficiency of the PFAS mixture consisting of nine short- and long-chain PFAAs, GenX, and three precursors at initial concentrations of the parts per billion (ppb) level. Additionally, the modified clay outperformed other commercial adsorbents with respect to adsorption performance. The adsorption kinetic data of all PFAS, which were well described by the pseudo-second-order model, suggested an expeditious adsorption process and an adsorption behavior dependent on the initial concentration and carbon chain length. Among the three examined adsorption isotherms, the Sips model combining Langmuir and Freundlich models showed the best fitting correlation, indicating that multiple interactions might be involved in the adsorption process. This hypothesis was supported by characterizations showing that the modified clay possessed physicochemical properties favorable for electrostatic interactions and hydrophobic interactions.

Surface Modification of Graphene Oxide for Fast Removal of Per- and Polyfluoroalkyl Substances (PFAS) Mixtures from River Water

“…This allows PFAS to form micelle structures at concentrations lower than its CMC (critical micelle concentration) and enhances the adsorption capacity of PFAS via the process of micelle aggregation. − The results of all screening tests thus yielded GO-CTAC as the best adsorbent, exhibiting almost 100% removal of all target PFAS. This observation can be correlated with previous literature, which shows that the CTAC addition enhanced PFAS removal performance . As detailed below, an extensive investigation was conducted to fully comprehend the adsorption performance and processes involving GO-CTAC.…”

Highly Efficient Cationic Surfactant Functionalized Alginate Hydrogel for Perfluorooctanoic Acid Adsorption: Optimization through Response Surface Methodology and Performance Evaluation for Aqueous Media

“…Moreover, the alginate moiety can be easily functionalized through PFAS-selective species to enhance its affinity toward specific PFAS compounds, improving selectivity and adsorption capacity. 36 Since PFAS can be adsorbed on adsorbents through hydrophobic and electrostatic effects, hydrogen bonding, and π−π bonding, CTAB distinguished by its possession of a quaternary ammonium group along with a lengthy alkyl chain has been chosen for its potential to strengthen the affinity of the adsorbent toward PFAS via hydrophobic and electrostatic interactions. 28,37 Importantly, the protonation state of the quaternary ammonium group remains constant across a broad pH spectrum, thereby ensuring cationic charge across varied pH conditions, which will be useful for removing PFAS anion via electrostatic interaction.…”

Enhanced Adsorption of Mixtures of Per- and Polyfluoroalkyl Substances in Water by Chemically Modified Activated Carbon

“…11,12 In contrast, adsorption has emerged as a well-established and reliable technology for PFAS removal, both as a standalone process for point-of-use applications and as a component of water treatment processes. 13,14 Currently, a variety of commercial and synthetic sorbents have been documented in the literature for PFAS removal, including clays, 15 granular activated carbon (GAC), 16 powdered activated carbon (PAC), 17 resins, 18 and surfacemodified biopolymers. 19 GAC and PAC have exhibited effectiveness in adsorbing long-chain PFAS, but both suffer from certain limitations.…”

“…Currently, a variety of commercial and synthetic sorbents have been documented in the literature for PFAS removal, including clays, granular activated carbon (GAC), powdered activated carbon (PAC), resins, and surface-modified biopolymers . GAC and PAC have exhibited effectiveness in adsorbing long-chain PFAS, but both suffer from certain limitations.…”