Reverse filling approach to mixed matrix covalent organic framework membranes for gas separation

Mixed-matrix membranes that combine the merits of polymer and filler materials offer high potential for molecular separations, but precisely engineering the filler phase structure to give full play to the role of filler materials remains challenging. Herein, we explore a reverse-filling approach to fabricate mixed-matrix membranes with continuous and vertically penetrating covalent organic framework channels for CO2 separation. Covalent organic framework nanosheets as building blocks are pre-assembled into a robust and vertically oriented covalent organic framework scaffold via ice templating method, with the subsequent polyimide filling into the scaffold. The scaffold inherits the intrinsic CO2-philic pore structure of nanosheets, which serves as fast and selective CO2 transport channels in the membrane. The resulting membrane exhibits high CO2 permeability of 972 Barrer and CO2/CH4 selectivity of 58, along with long-term stability and scale-up capability. This approach may stimulate the thinking about how to design advanced mixed-matrix membranes.