Covalent organic frameworks (COFs) provide an attractive platform for designed, molecular assembly of membrane materials. Unlike other porous polymers, the structural versatility of COFs results in tunable structure and properties along with a high degree of uniformity. The variation of COF structures and properties provide numerous possibilities for design and modification in regard to pore size, pore geometry, and chemical functionality. In this study, computational simulations were performed to systematically investigate three COFs: TpPa-H, TpPa-Me, and TpPa-SO<sub>3</sub>H. The latter two incorporate methyl and sulfonate substituents, respectively, into the COF pores while maintaining the same topology across the series. A nonequilibrium atomistic molecular dynamics (NEMD) model was developed to simulate the performance of single-and multi-layered COF nanosheets in a pressure-driven membrane separations process. Results indicate that the addition of pendant groups to the COF pores (TpPa-Me and TpPa-SO<sub>3</sub>H) provides enhanced rejection of sodium sulfate in comparison to the TpPa-H COF membrane. In addition, for all COF structures, solute rejection increased as the membrane thickness increased. Overall, this work theoretically demonstrates the tunable selectivity of COF membranes through a bottom-up functionalization approach.

Molecular simulation of functional covalent organic framework membranes

ACS Spring 2022

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