(615d) Novel Macrocycle-Based Sorbents for Effective Removal of per- and Poly-Fluorinated Alkyl Substances (PFAS) from Water.

Per- and poly-fluorinated alkyl substances (PFAS), commonly referred to as “forever chemicals”, exhibit high thermodynamic stability due to their strong C-F bonds. PFAS have been widely utilized in industry and consumer products for a variety of applications including as firefighting foams and in various manufacturing environments, which has led to their release into the environment. Unfortunately, PFAS molecules also exhibit high persistence in the environment, have shown to bioaccumulate in humans, and have shown high toxicity towards humans and animals. Throughout the United States, PFAS contamination in drinking water has been a recurring issue, with concentrations exceeding 70 ng/L, necessitating implementation of treatment technologies. Filtration using sorbents has proved to be an effective technique for organic contaminant removal due to scalability and energy efficiency. Nevertheless, traditional sorbents such as granular activated carbon (GAC) exhibit low affinity for PFAS and are plagued with fouling and regeneration challenges. Macrocycle-based sorbents offer a promising solution owing to their ability to form unique host-guest complexes. These macrocyclic materials can be functionalized to modulate underlying interactions, including dispersion, hydrogen bonding, and sterics, thereby resulting in selective uptake of target molecules. The integration of macrocyclic molecules in porous polymer networks to develop cross-linked macrocyclic polymers presents promise as an effective strategy to remove PFAS from water. In this work, we explored macrocycles of different classes across various functionalization patterns to investigate PFAS-macrocycle interactions. Subsequently, we examined combinations of macrocycles and cross-linkers to evaluate building blocks for macrocycle based polymeric sorbents. To achieve this, we utilized a multiscale computational modelling approach. Density functional theory (DFT) was employed to examine various adsorption motifs and subtle differences in adsorbate binding while, atomistic molecular dynamics (MD) provided molecular level insight into the role of electrostatic and hydrophobic interactions on the adsorption of PFAS molecules on cross-linked macrocyclic polymers. Our simulation results indicate differences in DFT-computed binding energies for PFAS adsorption across different macrocycles which can provide basis for identifying equilibrium selectivities for competitive adsorption in macrocycles. Molecular simulations also reveal distinct patterns in adsorption of short-chain PFAS and long-chain PFAS on cross-linked macrocyclic polymers which can be attributed to differences in size of hydrophobic tails leading to further implications on relative hydrophobic, steric, and electrostatic interactions. Overall, this study enhances our understanding of important interactions related to PFAS adsorption and aids in developing sorbent materials that can effectively remove PFAS from water.