Fig. 4: Molecular dynamics simulations of ion transport in AO-PIM-1 membrane.
a, Set-up of non-equilibrium model for ion transport through one AO-PIM-1 membrane. The AO-PIM-1 membrane with thickness of 8.8 nm is sandwiched between two water chambers, with graphene sheet pistons at two ends. Standard atmospheric pressures are applied on both graphene sheets. The ion transport is driven by an electric field. b–e, Coordination number of water molecules as a function of the distance from the centre of ions: K+ (b), Na+ (c), Li+ (d), Mg2+ (e). f, Transport energy barrier profiles of ion transport through the membrane. Light blue colour: interface region at membrane surface. Light yellow colour: membrane region. Short dashed arrows indicate the energy barriers for ion partitioning and ion migration and diffusion in membrane, and dashed lines correspond to the levels of free energy of salts. g, Radial distribution function of ions bound to the hydroxyl groups on the AO groups, as a function of the distance between ions with hydroxyl groups in amidoxime groups. h, Modelled mean squared displacement of cations in AO-PIM-1 membrane as a function of time. Cation self-diffusion coefficients were included. i, Schematic diagram showing the mechanism of ion separation through PIM membranes with interconnected subnanometre channels.
