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.
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