Physicochemical Understanding of the Impact of Pore Environment and Species of Adsorbates on Adsorption Behaviour

Abstract

For a better design of adsorbents, it is important to know the intermolecular interaction among adsorbates and host material, leading to improved guest selectivity and uptake capacity. In this study, we demonstrate the influence of the interaction among adsorbates and substrate, controlled by the pore environment and species of adsorbates, on the adsorption behaviour. We report the unique CO₂ adsorption behaviour of MOF-205 due to distinct pore geometry. The precise analysis through gas-adsorption crystallography with molecular simulation shows that capillary condensation of CO₂ in MOF-205 occurs preferentially in the large dodecahedral pore rather than the small tetrahedral pore, because the interaction of CO₂ with MOF-205 framework is weaker than that among CO₂ molecules, while Ar and N₂ are sequentially filled into two different pores of MOF-205 according to their size. Comparison of the materials with different pore environments reveals that the relative strength of the adsorbate-adsorbate and adsorbate-substrate interaction gives rise to different shapes of isotherms.