In Situ Formation of Ultrathin Zr-MOF Mixed-Matrix Membrane for Azeotropic Mixture Separation

Mixed matrix membranes (MMMs) combining the processability of the polymer with the transport properties of fillers have shown great potential for precise molecular separation (e.g., azeotropic mixture separation). Facile fabrication of ultrathin defect-free MMMs with high permeance and selectivity remains a grand challenge. Herein, we report a strategy of in situ formation of ultrathin zirconium-metal-organic framework (Zr-MOF) MMM for pervaporation separation of methanol/dimethyl carbonate (DMC) azeotropic mixture. Specifically, negatively charged ligands were preanchored in a positively charged chitosan (CS) polymer chain through electrostatic interactions to form ligand@polymer precursor, followed by in situ coordination with zirconium-oxo cluster to form Zr-MOF filler in the polymer solution. The as-synthesized Zr-MOF@CS solution was spin-coated on a porous substrate to form the ultrathin and defect-free MMM. The in situ incorporated MOF nanofillers highly enhanced the molecular-sieving and adsorption properties of the CS polymer membrane. The resulting Zr-MOF@CS MMM as thin as ∼130 nm showed excellent methanol/DMC separation performance with a total flux of 284.6 g·m^-2·h^-1 and a separation factor of 331.1 under the methanol concentration in feed of 10 wt %, and particularly total flux of 2250 g·m^-2·h^-1 and >97.5 wt % methanol purity in the permeate for methanol/DMC (70/30, w/w) azeotropic mixtures, transcending the upper bound of state-of-the-art membranes, showing great potential for azeotropic separation. Moreover, this ultrathin MMM fabrication strategy was proven to be valid for various kinds of MOFs and polymers.