Solid-solvent processing of ultrathin, highly loaded mixed-matrix membrane for gas separation

Mixed-matrix membranes (MMMs) that combine processable polymer with more permeable and selective filler have potential for molecular separation, but it remains difficult to control their interfacial compatibility and achieve ultrathin selective layers during processing, particularly at high filler loading. We present a solid-solvent processing strategy to fabricate an ultrathin MMM (thickness less than 100 nanometers) with filler loading up to 80 volume %. We used polymer as a solid solvent to dissolve metal salts to form an ultrathin precursor layer, which immobilizes the metal salt and regulates its conversion to a metal-organic framework (MOF) and provides adhesion to the MOF in the matrix. The resultant membrane exhibits fast gas-sieving properties, with hydrogen permeance and/or hydrogen–carbon dioxide selectivity one to two orders of magnitude higher than that of state-of-the-art membranes. Nanoporous crystalline materials, represented by zeolites and metal-organic frameworks (MOFs), naturally contain continuous pore systems that can enable the separation of gases, but it is difficult to process them into robust, large sheets. Chen et al . developed a solid-solvent technique for making thin, highly loaded, and defect-free mixed matrix membranes (see the Perspective by Yang and Zhao). Precursor metal salts are dissolved into a polymer and then converted into a MOF material. The authors demonstrate the separation of hydrogen and carbon dioxide, with high permeance and selectivity. —Marc S. Lavine Solid-solvent processing can form ultrathin highly loaded mixed-matrix membranes with interconnected channels for gas sieving.