Manipulating Intrapore Energy Barriers in Graphene Oxide Nanochannels for Targeted Removal of Short-Chain PFAS

Removal of per- and polyfluoroalkyl substances (PFAS) from water has become a research topic of interest in recent times. However, it is very challenging to remove short-chain (<C₈) PFAS from water sources using traditional means, especially in mixtures. Herein, a β-cyclodextrin (βCD)-modified graphene oxide (GO-βCD) membrane is designed with asymmetrically sized nanochannels that exhibit strong affinitive binding interactions with PFAS. PFAS transport is significantly hindered within the GO-βCD lamella due to interactions with the strategically embedded βCD sites and complementary molecular dynamics simulations reveal that short-chain PFAS exhibit ∼20% stronger binding affinity to βCD compared to that of alternative structures of cyclodextrins. The GO-βCD membrane demonstrates remarkable simultaneous retention of over 90% from a mixture of perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), and perfluorooctanoic acid (PFOA) while achieving a permeance of 21.7 ± 2 L m^-2 h^-1 bar^-1 and upconcentrating the feed by ∼300%. The performance of GO-βCD was compared to that of polyamide membranes, which exhibit a significant decline in capacity to retain short-chain PFAS (∼35% for PFBA). In combining permeation experiments and molecular dynamics simulations with the transition state theory model, it was demonstrated that the energy barrier for transport of PFAS is greater within the GO-βCD laminar architecture compared to that of GO-αCD and pristine GO. These modified membranes have strategically embedded sites capable of hindering PFAS transport and provide an approach for removing broad-spectrum PFAS under realistic conditions, over long-term operation (24 h), and at concentrations relevant to surface and ground waters.