Postsynthetic Modification of Zn/Co-ZIF by 3,5-Diamino-1,2,4-triazole for Improved MOF/Polyimide Interface in CO2–Selective Mixed Matrix Membranes

Amine-functionalized zeolite imidazolate frameworks (ZIF) are known to improve the mixed matrix membranes (MMM) separation performances for CO2/CH4 applications. In this study, 3,5-diamino-1,2,4-triazole, a ligand with −NH2 functionality and uncoordinated −NH group, was used in the postsynthetic modification of dual metal Zn/Co-ZIF for partial substitution of 2-methylimidazole to obtain a biligand Zn/Co-ZIF (Zn/Co-TZ1h) with retained crystallinity, tunable pore size and enhanced CO2 adsorption capacity. A series of mixed matrix membranes were then fabricated at a single concentration (7.5 wt %) of parent Zn/Co-ZIF or Zn/Co-TZ1h in 6FDA-ODA or Matrimid polyimides to compare the effect of modified ZIF to its unmodified analogue on the MMM properties and CO2/CH4 separation performance. Zn/Co-TZ1h MMM showed enhanced mechanical properties and better filler integration into the polymer matrix as a result of better interfacial interactions via hydrogen bonding while retaining the same thermal stability as Zn/Co-ZIF MMM. Moreover, the combination of ZIF gate size control, improved size discrimination, and specific chemical interaction gave the NH2-functionalized Zn/Co-ZIF MMM the possibility to significantly overcome the CO2/CH4 separation performance of the pure polymer. Postsynthetic modification of ZIF by amine-functionalized ligands can be an effective strategy to improve the filler/polymer interface quality resulting in improved MMM separation properties.