Oriented UiO-67 Metal-Organic Framework Membrane with Fast and Selective Lithium-Ion Transport

Metal-organic frameworks (MOFs) membranes with high pore density and tunable pore size down to the subnanoscale exhibit great potential in ion separation when appropriately designed and prepared. By a washing-assisted secondary growing method, a well intergrown UiO-67 membrane with preferential growth along the [022] direction was synthesized on a polyvinylpyrrolidone (PVP)-modified AAO substrate. Because of the oriented growth of UiO-67 nanocrystals, highly interconnected ion-transporting channels are created throughout the UiO-67/AAO membrane capable of achieving an ultrahigh Li⁺ permeance of 27.01 mol m^-2  h^-1 as well as very decent Li⁺ /Mg²⁺ selectivity of up to 159.4. Molecular dynamics simulations reveal that the high selectivity is associated with the large disparity of the transport energy barrier between Li⁺ and Mg²⁺ , which is caused by different extents of ion dehydration in unique bimodal and oriented membrane channels.