Design Principles for PFAS Adsorption in Three-Dimensional Covalent Organic Frameworks

Recent concerns over the accumulation of per- and polyfluoroalkyl
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 three-dimensional 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 has 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.

近年来，针对全氟和多氟烷基物质（per- and polyfluoroalkyl substances, PFAS）在地表水与地下水源中累积的相关担忧，推动了用于选择性吸附PFAS的新型多孔材料研究。共价有机框架（covalent organic frameworks, COFs）是该应用领域极具潜力的材料家族之一。本研究探讨了三维COFs的化学组成与结构对全氟辛酸（perfluorooctanoic acid, PFOA，一种常见PFAS分子）吸附行为的影响。通过蒙特卡洛（Monte Carlo, MC）模拟，我们发现含氮COFs对PFAS吸附具备较高应用潜力。同时，COF孔道的孔隙率对PFOA吸附存在显著调控作用：高孔隙率结构的PFAS吸附潜力弱于中等孔隙率结构。此外，我们还研究了对COF接枝−CF3与−NH2官能团的改性效果，结果表明两种官能团均可增强PFOA分子与COF之间的相互作用，但会降低有效吸附PFOA所需的孔隙率。对于孔道尺寸足够大的COFs，添加此类官能团可大幅提升PFOA吸附性能，进而实现从水环境中更高效地捕获PFAS。