Selective and High Sorption of Perfluorooctanesulfonate and Perfluorooctanoate by Fluorinated Alkyl Chain Modified Montmorillonite

Abstract

A novel fluorinated montmorillonite (F-MT) was synthesized via exchange of cationic fluorinated surfactant to selectively adsorb perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) from water. F-MT displayed fast and high sorption for PFOS and PFOA at concentrations below 10 μg/L, and performed better than the best activated carbon and resin previously reported. The spent F-MT can be completely regenerated by methanol solution and can be reused five times without reduction in sorption capacity. Moreover, the F-MT possessed excellent selectivity for PFOS and PFOA in the presence of other organic pollutants. The coexisting phenol, pyridine, dodecylbenzenesulfonate (SDBS), and phenanthrene (PHE) exhibited no effect on PFOS and PFOA sorption. Due to the nanoscale interlayer structure and chemical nature of F-MT, macromolecular humic acid had little effect on PFOS and PFOA sorption. Also, F-MT adsorbed very little SDBS and PHE. The results of competitive sorption and density functional theory calculations verified that PFOS and PFOA were adsorbed on the C–F chain of F-MT, while PHE and SDBS sorption occurred on the hydrocarbon part of F-MT. The unique hydro-oleophobic C–F chain on the F-MT was responsible for selective sorption of perfluoroalkyl acids (PFAAs), providing a new mechanistic insight for the interactions between PFAAs and fluorinated adsorbents. In addition, F-MT offers promising potential for removal of PFOS and PFOA from contaminated water.

Adsorption for perfluorooctanoic acid with graphitic‐phase carbon nitride and its HPLC fluorescence determination

“…In addition, when considering the hydrophobic property of the C‐F chain in PFOA and the electrostatic repulsion between the adsorbed PFOA, there is a tendency for hemi‐micelle formation on the interface of the g‐C 3 N 4 . The considerable adsorption capacity of PFOA onto g‐C 3 N 4 when compared to previous reports can be attributed to the reasons mentioned above …”

“…It has persisted in the environment due to high‐energy carbonefluorine (C─F) bonds. It should be noted that PFOA possesses unique physical chemical properties such as hydrophilicity and oleophobicity, which make it highly water‐soluble as well as easy to transport in an aqueous system. To date, PFOA has been detected in air, water, soil, sediment and sludge, and animals and human beings, and arises from wide use and relatively inefficient removal from the contaminated environment.…”

“…Adsorption, regarded as a simple, low‐cost, and environmentally friendly separation method, has been selected to remove PFOA with high efficiency. Various materials have been used for PFOA removal, including modified magnetic sorbent, fluorinated alkyl chain modified montmorillonite, alumina, boehmite, powdered activated carbon, multiwalled carbon nanotubes, chitosan‐based molecularly imprinted polymer, etc. However, when it comes to practical application, their complex preparation, modification, and susceptibility to being affected by pH or coexisting ions limited their applicability.…”

Modified clays reduce leaching of per‐ and polyfluoroalkyl substances from AFFF‐contaminated soils

“…Activated carbon and modified palygorskite have shown higher efficiency in immobilizing PFOS than other materials. Besides modified palygorskite, modified smectites used in water treatment and soil remediation targeting PFAS have been reported (Du, 2016; Zhou et al, 2010; Zhou et al, 2013). The modified clays are made by embedding amine‐based hydrocarbon surfactants (e.g., quaternary ammonium surfactants) in the exchange sites of expandable clays such as smectites.…”

“…The predominant approach is through sorbent amendment, relying on the high affinity of the adsorbents for PFAS to keep the contaminants immobilized in the solid phase. The approach has been proven effective in reducing the leachability of hydrophobic organic pollutants such as PCBs, PAHs, and DDT in soils, as well as their bioaccumulation in invertebrates and fish (Deng et al, 2010;Ghosh et al, 2011;Hale et al, 2009;Hansen et al, 2010;McLeod et al, 2007;West et al, 2001;Woodard et al, 2017;Yu et al, 2009).…”