Amorphous Porous Organic Cage Membranes for Water Desalination

Emerged as a new class of nanoporous materials, porous organic cages (POCs) possess salient features of solvent processability and water stability; thus, they are envisioned as promising membrane materials for water desalination. In this study, we propose a simulation protocol to construct atomic models of amorphous POC membranes and examine their desalination performance. Five membranes (AC1, AC2, AC3, AC16, and AC17) with similar cage structure but different periphery groups are considered. All the five membranes exhibit 100% salt rejection. In contrast to crystalline CC1 membrane, which is impermeable to water, AC1 has a water permeability Pw of 3.6 × 10–8 kg·m/(m2·h·bar). With increasing interconnected pores in AC2, AC3, AC16, and AC17, Pw increases. Due to the existence of hydroxyl groups in CC17 cages, AC17 exhibits the highest Pw of 3.17 × 10–7 kg·m/(m2·h·bar), which is higher than in commercial reverse osmosis membranes. Significantly, Pw is found to enhance in mixed AC3/AC17 and AC16/AC17 membranes with up to one-fold enhancement. The enhanced Pw is attributed to the counterbalance between water sorption and diffusion. This simulation study provides the bottom-up insights into the dynamics and structure of water in amorphous POC membranes, highlights their potential use for water desalination, and suggests a unique strategy to enhance desalination performance by tuning the composition of mixed POC membranes.