Gate Opening, Diffusion, and Adsorption of CO2and N2Mixtures in ZIF-8

Diffusion and adsorption of CO2/N2mixtures 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 CO2and that for the pure N2but closer to that of N2which is lower. Due to the stronger dependence of CO2adsorption 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.