Molecular simulation of CO2, N2 and CH4 adsorption and separation in ZIF-78 and ZIF-79

In this study, we investigated the adsorption and separation behaviours of CO2, N-2 and CH4 in ZIF-78 and ZIF-79 by means of grand canonical Monte Carlo methods. Our simulations indicate that preferential adsorption sites are mainly located at the regions where guest molecules can maximise interactions with the imidazolate (IM) linkers. The -NO2 and -CH3 functional groups are not the major binding sites that directly bind the guest molecules. Instead, they alter the electronic structure and polarity of the adjacent IM linkers to affect the adsorption behaviours. In addition, we found that the selectivity of CO2 over N-2 or CH4 is found to be dependent on the component fractions of CO2/N-2 and CO2/CH4 mixtures. Specifically, the selectivity of CO2 over N-2 increases with CO2 composition fraction, while the trend for the selectivity of CO2/CH4 was opposite.