Desalination performance investigation of TpPa-1 COF and MIL-47(V) MOF bilayer membranes using molecular dynamics simulation

The efficiency of reverse osmosis (RO) desalination heavily depends on the advancement of innovative membrane materials. In this study, we utilized molecular dynamics simulations to assess the desalination performance of pure and hybrid bilayers made from two-dimensional (2D) TpPa-1 COF and MIL-47 (V) MOF materials. Our findings show that a pure TpPa-1 COF bilayer exhibits a water permeability (348 L/cm2/day/MPa) that is over four orders of magnitude higher than commercially-used seawater RO membranes, while still maintaining an 88 % ion rejection rate. On the other hand, the MIL-47(V) MOF bilayer demonstrates an impressive 97 % ion rejection rate with significantly higher water permeability (160 L/cm2/day/MPa) compared to existing membrane materials such as cellulose acetate, polysulfone aromatic polyamides, MoS2, graphene, HAB-derived MOF, and carbon nanotubes. As a result, MIL-47(V) stands out as a promising nanoporous material for advanced RO water desalination with both high water permeability and exceptional rejection efficiency. However, when the COF and MOF materials are combined in a hybrid bilayer configuration, the water permeability becomes lower than bilayers of the same material due to pore misalignment. Our findings indicate that the pore-sieving effect is the primary governing factor for the rejection in the bilayer membrane. The electrostatic interactions and hydrogen bonding formation between water molecules and the oxygen atoms in the bilayers play vital roles in regulating water transport and ion passage across the examined bilayers.