Constructing Molecular Sieve Channels in Mixed Matrix Membranes for Efficient CO₂ Separation

Metal-organic frameworks (MOFs) with robust and three-dimensional pore structures are promising molecular sieve fillers in mixed-matrix membranes (MMMs) for carbon capture. Herein, high-valency metal-carboxylate-coordinated yttrium-MOF Y-abtc (abtc = 3,3′,5,5′-azobenzene-tetracarboxylate) with strong coordination bonds was incorporated into the Pebax-1657 polymer matrix to explore their CO₂/N₂ separation performance. The optimized N-Y-abtc@Pebax-15% MMMs showed simultaneously improved CO₂ permeability (79%) and CO₂/N₂ selectivity (94%) relative to the pristine Pebax membrane, exceeding the 2008 upper bound and approaching the 2019 upper bound. This was ascribed to the synergistic effect of a suitable window aperture, ultrahigh CO₂ adsorption capacity (64.77 cm³/g), high ideal adsorption solution theory selectivity (IAST) (254) for CO₂/N₂ (50/50, v/v) in nanosized Y-abtc (N-Y-abtc), and the newly created molecular sieve channels in N-Y-abtc@Pebax MMMs. Meanwhile, the rigid framework structure and hydrothermal stability of N-Y-abtc provide good pressure resistance and long-term stability for the N-Y-abtc@Pebax-15% MMMs. The successful property translation from the molecular sieve of N-Y-abtc adsorbents into membranes implied its potential application for flue gas treatment and may also shed light on the design of MOF-based MMMs for other challenging separations.