Functional Porous Organic Cages as Synthetic Channels for Water Desalination: Molecular Simulation Investigation

Achieving both efficient water transport and complete salt rejection in synthetic water channels continues to pose a significant challenge for reverse osmosis (RO) desalination. In this study, we design a series of functional porous organic cages (POCs) by grafting fluorine (-F), hydroxyl (-OH), amino (-NH₂), and methyl (-CH₃) into the interior of a prototypical CC3 cage to construct CC3-F, CC3-OH, CC3-NH₂, and CC3-CH₃ channels, respectively. Subsequently, molecular dynamics simulations are conducted to explore how different chemical functional groups influence the desalination performance of these CC3-based channels embedded in a lipid bilayer. It is revealed that water transports through the channels in a single-file manner, and all the channels exhibit complete salt rejection. Water fluxes follow the order: CC3-F > CC3-OH > CC3 > CC3-NH₂ > CC3-CH₃, as attributed to the steric hindrance and hydrogen bonding of functional groups that affect water-channel interaction and alter the dynamic configuration of confined water molecules in the channels. Furthermore, wetting-dewetting transition is found to be largely suppressed in the hydrophilic channels. From temperature-dependent water flux, activation energies are estimated to range from 12 to 20 kJ/mol in CC3-based channels, lower than those in polyamide RO membranes. From bottom-up, this simulation study reveals molecular-level mechanisms of the role of functionalization in tuning water transport in one-dimensional subnanometer channels and provides a theoretical basis for designing high-performance synthetic water channels toward next-generation desalination technologies.