Preparation of Zirconium-based Metal-organic Cage Mixed Matrix Membranes and Its Gas Separation Performance

For CO₂/CH₄ separations, two novel metal-organic cages (MOC-1-2OH and MOC-1-OH) were synthesized and co-blended with polyimide (6FDA-DAM) in dimethyl sulfoxide (DMSO) to form transparent casting solution, which were then processed into mixed matrix membranes. The prepared membranes were characterised by X-ray powder diffractometer (X-ray powder diffractometer, XRD), scanning electron microscope (scanning electron microscope, SEM), Raman, nanoindentation and differential scanning calorimeter (DSC), revealing that the prepared membranes were dense and homogeneous, with excellent thermal stability and mechanical properties. In the gas separation performance test, the best membrane performance was achieved at 2.17% (the mass ratio of filler to the whole membrane) loading of MOC-1-2OH, with a CO₂ permeability of 966.38×10⁴ m²/s and a separation selectivity of 21; similarly the best membrane performance was achieved at 2.17% loading of MOC-1-OH, with a CO₂ permeability of 784.25×10⁴ m²/s and a separation selectivity of 20.15. Comparative studies revealed that the separation performance of the membrane with w(MOC-1-2OH)=2.17% is superior to that of the membrane prepared with w(MOC-1-OH)=2.17%, exceeding the Robeson upper bound of CO₂/CH₄ in 2008.