4. Conclusion
In conclusion, an ultrathin mixed matrix composite membrane (MMCM) with NH2-ZIF-8 nanocrystals protruding structure was successfully fabricated. Through engineering the polyimide/MOF interfacial hydrogen or covalent bonds, the thickness of the selective layer can be reduced to 280 or 140 nm. The protruding MOF filler can considerably reduce the transport resistance and promote the CO2 permeation. As a result, the MMCMs exhibit a high CO2 permeance of 778 GPU and a CO2/CH4 selectivity of 34, surpassing most of the reported MOF-based MMMs and polyimide composite membranes towards CO2/CH4 separation. Moreover, due to the robustness of the interfacial interactions between MOFs and the polymer chains in the thin films, the MMCMs show a significantly enhanced plasticization-resistant and aging-resistant performance at a high CO2 partial pressure up to 20 bar and exhibit a long-term stability for nearly one month. Overall, this work demonstrates an efficient and general strategy to fabricate advanced ultrathin mixed matrix composite membranes with both high separation performance and excellent stabilities under high pressure, which hold great potential to address many critical separation issues in chemical industry.