Improving the ion sieving performance of MOF polycrystalline membranes based on interface modification†

Abstract

Metal–organic framework (MOF) membranes exhibit promising potential for high-precision molecule and ion sieving due to their uniform and tunable pore structures. Nevertheless, it remains a challenge to address interfacial compatibility to obtain a high-performance MOF membrane. This is because there is a weak interfacial interaction between the MOF and the substrate, which leads to non-selective areas. This work presents an interface-coating method to facilitate dense nucleation and rapid growth of MOF crystals on the substrate towards reinforcing interaction and eliminating defects. Polydopamine (PDA) and β-cyclodextrin (β-CD) were co-assembled on polyvinylidene fluoride (PVDF) substrates to modify the surface chemistry and enhance interfacial compatibility, thereby facilitating the dense growth of ZIF-8. The ZIF-8/PVDF membranes demonstrated an excellent K⁺ permeance of 0.33 mol m⁻² h⁻¹ and a K⁺/Mg²⁺ selectivity of 30.16. The simulation results indicate that the channel of Mg²⁺ through ZIF-8 must overcome a greater transport energy barrier than that of K⁺, resulting in a higher selectivity of K⁺/Mg²⁺.