Gate Opening, Diffusion, and Adsorption of CO₂ and N₂ Mixtures in ZIF‑8

Diffusion and adsorption of CO₂/N₂ mixtures in the zeolitic imidazolate framework ZIF-8 are investigated by molecular dynamics (MD) and Gibbs ensemble Monte Carlo (GEMC) simulations. Structural changes called “gate opening” could be found for the adsorbed single-component gases and for the mixture. The gate opening appears for the mixture at a total number of guest molecules per cavity between that for the pure CO₂ and that for the pure N₂ but closer to that of N₂ which is lower. Due to the stronger dependence of CO₂ adsorption upon the temperature in comparison with N₂, the adsorption selectivity is predicted to be higher at lower temperatures, which is in accordance with experimental findings.