Preparation of high-performance and pressure-resistant mixed matrix membranes for CO2/H2 separation by modifying COF surfaces with the groups or segments of the polymer matrix

In this work, we proposed a simple method to prepare high-performance and pressure-resistant mixed matrix membranes (MMMs) for CO2/H2 separation. The groups or segments of poly-(vinylamine) (PVAm) were used to modify covalent organic frameworks (COFs), and COFs with similar frameworks but different surfaces were obtained. Then, modified COFs were mixed with PVAm matrix and used to coat the modified-polysulfone (mPSf) to prepare MMMs for CO2/H2 separation. Modified COFs and the PVAm matrix were highly compatible because COF surfaces possessed the same groups or segments as PVAm. Meanwhile, in the coating solution, COF surfaces were found to induce penetration of PVAm molecules into COF pores, narrowing the pore size of the COFs and providing an amino environment for CO2 preferential absorption and transport. The penetration degree was affected by the hydrogen bond between COF surfaces and the PVAm molecules. In addition, the incorporated COFs effectively restricted the mobility of the PVAm matrix, increasing the pressure resistance for MMMs under high pressure. In the gas permeation test, the optimal MMMs could achieve a CO2 permeance of 957 GPU and a CO2/H2 selectivity of 17.1 at 2.0 MPa because of the high compatibility and size of the channels (0.94 nm).