Design Principles for PFAS Adsorption in Covalent Organic Frameworks

Recent concerns over the accumulation of per- and poly-fluoroalkyl substances (PFAS) in surface and groundwater sources have stimulated research into novel porous materials for selective PFAS adsorption. Covalent organic frameworks (COFs) represent one of the promising families of materials for this application. Here, we investigated the effects of the chemistry and structure of COFs on the adsorption of perfluorooctanoic acid (PFOA), a commonly seen PFAS molecule. Through Monte Carlo (MC) simulations, we found that nitrogen-based COFs tend to show high potential for PFAS adsorption. We also see that the porosity of the COF pores have a significant effect on PFOA adsorption, with higher porosity structures exhibiting lower potential for PFAS adsorption than those with moderate porosity. We additionally investigated the effects of COF functionalization with -CF3 and -NH2 functional groups, showing that both functional groups strengthen interactions between the PFOA molecule and COF, but may decrease the porosity needed for effective adsorption of PFOA. For COFs with large enough pores, the addition of these functional groups can greatly improve the adsorption of PFOA, and could allow for the improved capture of PFAS from aqueous environments.