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

Abstract

In this study, we investigated the adsorption and separation behaviours of CO₂, N₂ 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 N₂ or CH₄ is found to be dependent on the component fractions of CO₂/N₂ and CO₂/CH₄ mixtures. Specifically, the selectivity of CO₂ over N₂ increases with CO₂ composition fraction, while the trend for the selectivity of CO₂/CH₄ was opposite.

Keywords:

• ZIF
• CO₂ separation
• adsorption selectivity

Acknowledgements

We thank Dr Shaji Chempath for the help in modifying MUSIC for non-orthorhombic ZIF lattice. This work was financially supported by the National Science Foundation of China, the innovation project from Ningbo Municipal Government and Zhejiang Natural Science Foundation.