Triple-ligand zeolitic imidazolate frameworks for highly CO₂ selective mixed matrix membranes

Here, we report a new class of highly CO₂ selective ZIF nanoparticles, TAZIF-8, consisting of zinc metals and triple ligands, including 2-methylimidazole (MIm), tributylamine (TBA), and 3-amino-1,2,4-triazole (Atz). The Zn-MIm coordination retains an open porous sodalite topology, while the Zn-TBA analogue contributes to high processability. Lastly, the Zn-Atz coordination enables favorable CO₂ permeation via a combination of enhanced size discrimination and specific chemical interactions. A high loading 6FDA-DAM/TAZIF-8 (40 wt%) mixed matrix membrane consequently exhibits an almost threefold increase in CO₂ permeability and a twofold increase in CO₂ selectivity over other light gases (N₂, CO, or CH₄) compared to high performance 6FDA-DAM membrane. Furthermore, it maintains excellent CO₂ separation performance over 90 days and even after exposure to water vapor. Our multiple hybrid modification technique enables the fine-tuning of the physical structure and textural properties of ZIF for enhanced CO₂ separation performance.