Membrane-based separation technology can contribute to reaching net-zero carbon by 2050 owing to its low energy costs. In this work, we demonstrate highly CO2-selective zeolitic imidazolate frameworks containing triple ligands of 2-methylimidazole (Mim), tributylamine (TBA), and 3-amino-1,2,4-triazole (Atz), referred to as TAZIF-8. The TAZIF-8 nanoparticles are prepared by reacting amine-modulated ZIF particles with different amounts of Atz via post-synthetic modification. The role of the respective metal-ligand coordination is as follows: 1) Zn-Mim retains the porous sodalite structure, 2) Zn-TBA enables the high compatibility of TAZIF-8s with 6FDA-DAM polymer even at a high filler concentration (40 wt%), and 3) Zn-Atz enables CO2-selective permeation via a combination of molecular sieving and specific chemical interactions. The resultant TAZIF-8/6FDA-DAM (40/60 w/w) mixed matrix membrane (MMM) exhibits superior CO2 separation performance to that of most previously reported MMMs.