<p>Ionic liquids (ILs) have garnered significant attention in CO₂ capture and separation due to their tunable physicochemical properties, enabling precise control over CO₂ affinity. While previous studies emphasize the critical role of anions, particularly fluorinated species, for enhancing CO₂ solubility and selectivity, the influence of cationic structure remains largely unexplored. In this work, we investigate the effect of different cations on CO₂ capture efficiency by impregnating ILs into a robust metal-organic framework (MOF). UiO-66, with its strong Zr–O coordination, provides exceptional structural stability, making it an ideal host for IL incorporation. We selected butyl(triethyl)azanium ([N₂₂₂₄]⁺), 1-butyl-3-methylimidazolium ([BMIM]⁺), and butylpyridinium ([BuPy]⁺) cations, all paired with a common tetrafluoroborate (BF₄⁻) anion, to systematically assess cation effect. The ILs were confined within the octahedral pores of UiO-66, and their gas adsorption performance for CO₂, CH₄, and N₂ was evaluated using the grand canonical Monte Carlo (GCMC) simulations. It is interesting to note that aromatic cation enhances the CO₂ selectivity when compared to the aliphatic cation. This is due to the steric hindrance arisen from the aliphatic cation of IL. This study provides critical insights into cation-dependent CO₂ capture mechanisms, establishing key design criteria for optimizing IL@MOF composites in gas separation technologies.</p> Graphical abstract <p></p>