Enhanced sorption of perfluorooctanoic acid with organically functionalized layered double hydroxide

Abstract

Sorption is recognized as an effective and economical approach for the practical treatment of water contaminated with per- and polyfluoroalkyl substances (PFAS). In this study, we reported the development, characterization, and evaluation of a family of new organically functionalized layered double hydroxide (LDH) adsorbents for PFAS removal with a primary focus on perfluorooctanoic acid (PFOA). The organic functional groups were introduced to the Zn-Al LDH by covalent bonding through a post-grafting process. The organically functionalized LDHs were very efficient for PFOA adsorption, likely due to the synergy of the positively charged structural layers of LDHs that provide strong electrostatic interactions and the modified organic functional groups that provide enhanced hydrophobic interactions to capture PFOA. Specifically, our adsorption kinetics and isotherm studies found that organically functionalized LDHs exhibited faster adsorption kinetics and greater adsorption capacities for PFOA than the unmodified LDH. Furthermore, organically functionalized LDHs showed substantially improved performance for PFOA removal under various water chemistry conditions in comparison to the unmodified LDH, and remained more effective following repeated adsorption-regeneration cycles. The best-performed organically functionalized LDH also exhibited high efficiency for the treatment of a mixture of PFAS with varied fluoroalkyl chain lengths and functionalities. Results of this work suggested that organically functionalized LDHs hold great promises for the treatment of PFAS-contaminated water.