Amino-functional ZIF-8 nanocrystals by microemulsion based mixed linker strategy and the enhanced CO2/N2 separation

High permeability and selectivity are desirable for mixed matrix membranes (MMMs) based CO 2 separation. Herein, a microemulsion based mixed linker strategy is proposed to introduce amino groups during the growth of ZIF-8. Compared to post-synthetic modification, this method presents a less reduction in S BET of ZIF-8, which is beneficial for CO 2 adsorption. By controlling the ratio of 2-methylimidazole to 2-aminobenzimidazole, NH 2 -ZIF-8 with various morphologies and sizes were synthesized and serve as the filler to fabricate the MMMs for CO 2 capture. From the scanning electron microscopy (SEM), no obvious agglomerations or defects are observed in ZIF-8/Pebax MMMs, due to the amino groups in ZIF-8 can interact with the amide in Pebax chain, which can improve compatibility between ZIF-8 and Pebax. With the amino groups, NH 2 -ZIF-8 shows higher affinity with CO 2 than that of non-amine-functionalized ZIF-8, leading to an enhancement in the separation performances. When the MMM doped with 6 wt% of NH 2 -ZIF-8(10), the CO 2 permeability reaches up to 163.8 Barrer, which increases by around 53% and 107.6% in contrast with the ZIF-8/Pebax MMM and pure Pebax membrane. Besides, the CO 2 /N 2 selectivity is enhanced by around 10% and 27%, respectively. These results indicate that amine-functional modification by mixed ligands is a useful way to construct MOFs-based MMMs with high performance for CO 2 /N 2 separation.