Metal–Organic Framework Nanocomposite Thin Films with Interfacial Bindings and Self-Standing Robustness for High Water Flux and Enhanced Ion Selectivity

Abstract

Metal-organic framework (MOF)-based materials are promising candidates for a range of separation applications. However, the fabrication of self-standing MOF-based thin films remains challenging. Herein, a facile solution casting strategy is developed for fabricating UiO-66 nanocomposite thin films (UiO66TFs) with thicknesses down to ∼400 nm. Nanosizing UiO-66 and incorporating sulfonated polysulfone additives render high dispersity and interfacial bindings between MOFs and polymer matrices, so UiO66TFs are more mechanically robust and thermally stable than their pure-polymer counterparts. Enhanced microporosity with sub-nanometer pore sizes of the self-standing membranes enables the direct translation of UiO-66-based sorption and ion-sieving properties, thus increasing water flux and separation performance (Na₂SO₄ rejection of 94-96%) under hydraulic pressure-driven processes and eliminating internal concentration polarization in osmotic pressure-driven processes. Enhanced separation performances are achieved with water/Na₂SO₄ permselectivity of 13.5 L g^-1 and high osmotic water permeability up to 1.41 L m^-2 h^-1 bar^-1, providing 3-fold higher water/Na₂SO₄ permselectivity and 56-fold-higher water flux than polymer membranes for forward osmosis.