(607c) Molecular Interactions in Organic Solvent Nanofiltration of Covalent Organic Framework Membranes

Two-dimensional covalent organic frameworks (COFs) continue to attract intense interest due to their excellent properties, including high chemical and thermal stabilities, large and chemically active surface areas, well-defined pores, and atomic thicknesses. COFs would be ideal materials to form selective layers of membranes with high molecular separation performance and robustness for organic solvent nanofiltration (OSN). However, the reports on COF membranes for OSN applications is still limited. Specially, the molecular level understanding of interactions among solvents, COFs, and solutes has not been reported. Interactions between ions, molecules, and confining solid surfaces is a universally challenging and intriguing question. In this study, the separation performance of COF in OSN were studied experimentally and simulated using reactive force field (ReaxFF) molecular dynamics modeling. Among the COF membranes tested, a carboxylated COF (C-COF) membrane exhibits ultra-fast solvent permeance as high as 4500 L m^-2 h^-1 bar^-1which surpasses the current stage-of-the-art. The ReaxFF results reveal that the ultra-fast permeance of C-COF membrane is due to the well-aligned stacking of C-COF pores resulting from the strong H-bonding of C-COF. The role of solvent environment on C-COF membrane permeance and selectivity was studied, showing that both apparent pore size and solvated solute size can change dramatically in different solvent environments.