Modulation of ion transport through nanopores in water desalination: a molecular dynamics study

Abstract

ABSTRACT A good understanding of ion transport mechanisms through nanopores is an important issue for the development of advanced water desalination technologies. We use the molecular dynamics simulation method to systematically investigate the translation dynamics of ions through nanopores in the water desalination process by designing four kinds of nano-membranes based on carbon nanomaterials. Results indicate that circular-shaped pore exhibits better water permeability, nevertheless, the slit pore has a lower resistance due to the larger pore area; nanochannel membranes increase the residence time of ions. Fluorination induces more ordered ionic hydration structures, and enhances Na + -Cl- ion pair association. -OH groups replace partial ionic hydration water molecules and facilitate ions transport into membranes. The -NH3 +, -COO- groups can strongly adsorb the oppositely charged ions, and substantially slow down ion dynamics. Functionalisation within nanochannel interior can further enhance interfacial friction and transport resistance, even causing pore blocking by charged groups. The fluorinated nanochannel membrane demonstrates complete rejection of ions with a water permeability coefficient of 1.88 × 104 L·m−2·h−1·bar−1, breaking the permeability-selectivity trade-off. This study indicates that ion transport in nanopores could be finely modulated to obtain enhanced performance in water desalination.