Amino‐Functionalized ZIF‐7 Nanocrystals: Improved Intrinsic Separation Ability and Interfacial Compatibility in Mixed‐Matrix Membranes for CO2/CH4 Separation

Highly permeable and selective, as well as plasticization‐resistant membranes are desired as promising alternatives for cost‐ and energy‐effective CO2 separation. Here, robust mixed‐matrix membranes based on an amino‐functionalized zeolitic imidazolate framework ZIF‐7 (ZIF‐7‐NH2) and crosslinked poly(ethylene oxide) rubbery polymer are successfully fabricated with filler loadings up to 36 wt%. The ZIF‐7‐NH2 materials synthesized from in situ substitution of 2‐aminobenzimidazole into the ZIF‐7 structure exhibit enlarged aperture size compared with monoligand ZIF‐7. The intrinsic separation ability for CO2/CH4 on ZIF‐7‐NH2 is remarkably enhanced as a result of improved CO2 uptake capacity and diffusion selectivity. The incorporation of ZIF‐7‐NH2 fillers simultaneously makes the neat polymer more permeable and more selective, surpassing the state‐of‐the‐art 2008 Robeson upper bound. The chelating effect between metal (zinc) nodes of fillers and ester groups of a polymer provides good bonding, enhancing the mechanical strength and plasticization resistance of the neat polymer membrane. The developed novel ZIF‐7 structure with amino‐function and the resulting nanocomposite membranes are very attractive for applications like natural‐gas sweetening or biogas purification. Amino‐functionalized zeolitic imidazolate framework‐7 (ZIF‐7‐NH2) nanocrystals fabricated from a mixed‐linker strategy exhibit enlarged aperture size and enhanced CO2 uptake capacity compared to the original ZIF‐7 structure. Incorporation of these fillers into a poly(ethylene oxide)‐based rubbery polymer membrane can significantly improve the gas permeability, selectivity, and plasticization‐resistant properties. The developed novel ZIF structure and the resulting hybrid membranes are very attractive for natural‐gas sweetening or biogas purification.