Cross-Linked Mixed-Matrix Membranes Using Functionalized UiO-66-NH₂into PEG/PPG-PDMS-Based Rubbery Polymer for Efficient CO₂Separation

Mixed-matrix membranes (MMMs) with an ideal polymer-filler interface and high gas separation performance are very challenging to fabricate because of incompatibility between the fillers and the polymer matrix. This work provides a simple technique to prepare a series of cross-linked MMMs (xMMM@n) by covalently attaching UiO-66-NB metal-organic frameworks (MOFs) within the PEG/PPG-PDMS copolymer matrix via ring-opening metathesis polymerization and in situ membrane casting. The norbornene-modified MOF (UiO-66-NB) is successfully copolymerized and dispersed homogeneously into a PEG/PPG-PDMS matrix because of very fast polymer formation and strong covalent interaction between MOFs and the rubbery polymer. A significant improvement in gas permeability is achieved in membranes up to a 5 wt % MOF loading compared to the pristine polymer membrane without affecting selectivity. The CO2/N2 separation performance of xMMM@1, xMMM@3, and xMMM@5 with 1, 3, and 5 wt % MOF loading, respectively, surpassed Robeson's 2008 upper bound. In addition, the best performing membrane, xMMM@3 (PCO2 = 585 Barrer and CO2/N2 ∼53), approaches the 2019 upper bound, indicating that the cross-linked MMMs (xMMM@n) are very promising for CO2 separation from flue gas. The experimental results of our study were evaluated and are supported by theoretical data obtained using the Maxwell model for MMMs. Moreover, the developed MMMs, xMMM@ns, displayed outstanding antiplasticization performance at pressures of up to 25 atm and very stable antiaging performance for up to 11 months with good temperature switching behaviors.