Water desalination by regular pores: Insights from molecular dynamics simulations

Reverse osmosis offers an energy-efficient method for alleviating water shortages via seawater desalination. However, traditional polymeric membrane materials face a tradeoff between permeability and selectivity. Regular pores with uniform shapes and sizes, which are present in newly emerging nanomaterials, are expected to achieve high permselectivity. It is important to understand the transport mechanisms of water and hydrated ions in regular pores. Due to the advantages of the molecular perspective, non-equilibrium molecular dynamics (NEMD) simulations have become an indispensable tool for studying mass transport mechanisms. In this review, recent progress in NEMD studies on transport mechanisms of water permeation and ion rejection through regular pores is highlighted. For water permeation, the effects of confined space, pore hydrophilicity, pore charge, and bioinspired pore geometry on water transport are analyzed. In addition, modifications to traditional mass transfer theories are discussed. For ion rejection, the effects of size, charge, hydrophilicity, length, and shape of the pores are considered. The separation mechanisms based on the dehydration barrier, charge effect, and intrapore transport difference are discussed, followed by the discussion of theoretical equations for predicting ion rejection. Finally, an outlook for meaningful directions beyond the current state of the art is outlined.