Thermodynamic implications of size, hydrophilicity, and fluorine content on perfluoroalkyl adsorption in NU-1000

Abstract

The molecular mechanisms that drive adsorption are critical for engineering new adsorbents to capture environmental contaminants, such as perfluoroalkyl substances (PFAS). Metal–organic frameworks (MOFs) have been shown to adsorb some classes of PFAS, yet a fundamental understanding of how PFAS identity and water competition affect adsorption capacity is unknown. Here, grand canonical Monte Carlo simulations of perfluoroalkanoic acids (PFAAs) adsorption in the MOF NU-1000 were performed with coadsorbed water and varying carbon chain length sizes to interrogate how PFAS structure affects adsorption capacity. We found that larger PFAAs adsorb favorably into NU-1000 than shorter chain PFAAs due to the formation of pore-filling aggregates that stabilize anionic adsorption to the node. Due to their size and hydrophilicity, shorter chains tend to limit interactions with the adsorbent. These insights offer directions for developing novel materials that promote aggregate formation to capture and retain a wider set of PFAS from aqueous solutions.