Effect of the molecular interactions on the separation of nonpolar mixtures using Cu-BTC metal–organic framework

We report an investigation on the adsorption of nonpolar molecules using the copper(II) benzene-1,3,5-tricarboxylate metal–organic framework (Cu-BTC) by means of molecular simulations. This metal–organic framework is formed by small, tetrahedral cages of 5 Å in diameter and by large cages of 11 and 13 Å in diameter. We focus on the effect that the molecular interactions adsorbents–adsorbates and adsorbates–adsorbates exert on the adsorption that takes place inside the tetrahedral cages. The study is carried out for simple gases modeled as spherical pseudoatoms and for their mixtures. These mixtures are composed by molecules of argon – that are accessible to the tetrahedral cages – and by hypothetic molecules with sigma Lennard–Jones parameters that span from 3.6 Å (sigma defined for the molecule of argon) to 4.66 Å (sigma defined for the molecule of carbon tetrafluoride). When the value of sigma is low enough to allow the molecule to enter the tetrahedral cages, we observe that it competes with argon for the adsorption in these cavities. This competition is enhanced for the molecules with the largest values of the sigma Lennard–Jones parameter.

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► We study the effect that sigma LJ parameters exert on the preferential adsorption of several molecules.
► We analyze the preferential adsorption sites of Cu-BTC for the molecule under study.
► The results obtained in this study can be exploited for tailoring existing materials.