Affinity between Metal–Organic Frameworks and Polyimides in Asymmetric Mixed Matrix Membranes for Gas Separations

A series of flat-sheet asymmetric mixed matrix membranes (MMMs) have been fabricated with MOF-5, Cu3(BTC)2, and MIL-53(Al) as fillers and PI polymer as a matrix through the dry–wet phase inversion method. After the surface modification by coating a PAA solution (15% wt) on the top of the obtained membrane, a thin defect-free selective skin in the MMM is obtained. The permeance of various gases such as H2, He, CH4, N2, and CO2 and their gas pair selectivity have been investigated, respectively. The results show that Cu3(BTC)2/PI MMM possesses the best gas separation performance with H2 permeance of 0.44 GPU and H2/CH4 selectivity of 100. In addition, the mechanism of MOF fillers in MMMs has been further revealed by the interaction analysis between MOF fillers and PI chains.