Functionalized ZIF-7/Pebax® 2533 mixed matrix membranes for CO2/N2 separation

Membrane-based separation technology has evolved as a competitive approach for CO2 capture from flue gas (mainly N2). To achieve high separation performance, three partially NH2-, OH- and CH3OH- functionalized mixed-linker-ZIF-7 were successfully synthesized, and incorporated into polyether-block-amide (Pebax® 2533) polymer to form mixed-matrix membranes (MMMs). As evidenced by the CO2 adsorption isotherms, introducing functional groups in the ZIF-7 framework was indeed beneficial for CO2 adsorption. All MMMs composed of ZIF-7-NH2, ZIF-7-OH and ZIF-7-CH3OH offered better CO2/N2 separation performance than the parent ZIF-7-Pebax® 2533 membrane, suggesting the positive effect of functionalized ZIF-7 fillers on the gas separation performance. Among the three functionalized ZIF-7 based MMMs, the ZIF-7-OH-Pebax MMMs exhibited the best performance for CO2/N2 separation, which might be ascribed to the highest adsorption selectivity of CO2 over N2 predicted by ideal adsorbed solution theory (IAST) for ZIF-7-OH fillers. The 14% ZIF-7-OH-Pebax MMM showed high CO2 permeability of 273 Barrer and CO2/N2 separation factor of 38, which increased by 60% and 145% as compared with the neat Pebax membrane. The strategy of preparing functionalized MOFs with strong affinity for CO2 provides an effective method to develop MMMs for highly efficient CO2 separation.