In-situ grown NH2-ZIF-8 with optimized polymers compatibility and rigidity for enhanced CO2/CH4 separation performance in mixed matrix membranes

By combining the advantages of polymers and porous nano-fillers, mixed matrix membranes (MMMs) have demonstrated outstanding gas separation performance. However, the ideal matching between polymers and nano-fillers is still a challenge especially under high filler loading conditions. To address this interfacial challenge, an in-situ grown amino-functionalized ZIF-8 (NH 2 -ZIF-8) is embedded in 6FDA-DAM to prepare MMMs. Compared to ZIF-8, NH 2 -ZIF-8 not only can enhance compatibility and interfacial adhesion because of the extensive hydrogen bonding, but also effectively modulates its structural flexibility by increasing the rigidity of Zn–N bonds within the ZIF-8 framework. The enhanced framework rigidity of NH 2 -ZIF-8 successfully improves the CO 2 /CH 4 separation capability of the MMMs. Under a high filler loading of 30 wt%, the CO 2 /CH 4 selectivity of the optimized NH 2 -ZIF-8/6FDA-DAM MMMs reached 35.1 and the permeability reached 1225.9 Barrer, which increased by 25.36 %, and 8.94 % respectively compared to the ZIF-8 MMMs, exceeding the 2008 Robeson upper bound. Molecular simulations further reveal the enhanced diffusion selectivity of NH 2 -ZIF-8 and the strong interactions between surface –NH 2 groups and electron-rich O/F heteroatoms in the 6FDA-DAM polyimide matrix. These simulations quantitatively elucidated the critical role of interfacial structure in determining gas separation performance. The mechanistic insights provided in this study offer valuable theoretical guidance for the development of high-performance membrane materials for CO 2 capture and gas purification applications.