Vacuum-Assisted Confined Growth of MOF@COF Composite Membranes with Enhanced Hydrogen Permselectivity

With ordered and periodic network structures, adjustable pore sizes and high chemical stability, covalent organic frameworks (COFs) have drawn much attention for the fabrication of superior separation membranes. However, it is challenging to prepare COF membranes with a molecular sieving property for gas separation due to their relatively large pore size. In this work, we develop the MOF-in-COF concept for vacuum-assisted synthesis of metal–organic framework (MOF) ZIF-8 inside the pores of TB-COF formed from trihydroxy-benzene-tricarbaldehyde (T) and diamino-biphenyl-disulfonic acid (B), thus constructing a novel ZIF-8@TB-COF membrane. Attributing to the formation of a well-defined one-dimensional (1D) nanoscale transport channel, the ZIF-8@TB-COF membrane displays a high hydrogen permselectivity. At 100 °C and 200 kPa, the mixture separation factors of H₂/CO₂, H₂/CH₄ and H₂/C₃H₈ are 21.9, 63.1 and 134.4, respectively, which are much higher than those of the pristine TB-COF membrane due to the precise size sieving channels brought about by the incorporated MOF. The synthesis of ZIF-67@TB-COF membrane demonstrates the versatility of the synthesis strategy.