Consequences of cavity size and chemical environment on the adsorption properties of isoreticular metal-organic frameworks: An inverse gas chromatography study

The role of the structure of three isoreticular metal-organic frameworks (IRMOFs) on their adsorption behavior has been studied in this work, selecting different kinds of volatile organic compounds (VOCs) as adsorbates (alkanes, alkenes, cycloalkanes, aromatics and chlorinated). For this purpose, three samples (IRMOF-1, IRMOF-8 and IRMOF-10) with cubic structure and without functionalities on the organic linkers were synthesized. Adsorption capacities at infinite dilution were derived from the adsorption isotherms, whereas thermodynamic properties have been determined from chromatographic retention volume. The capacity and the strength of adsorption were strongly influenced by the adsorbate size. This effect is especially relevant for n-alkanes adsorption, indicating the key role of the cavity size on this phenomenon, and hence the importance of the IRMOF structural properties. A different behavior has been observed for the polar compounds, where an enhancement on the specificity of the adsorption with the π-electron rich regions was observed. This fact suggests the specific interaction of these molecules with the organic linkers of the IRMOFs.

► Thermodynamic properties of three IRMOFs were studied by inverse gas chromatography.
► The n-alkane adsorption is strongly related to the pore opening of the cavities.
► Higher number of carbon atoms in the organic linker increases the adsorption.
► The active sites for the adsorption of n-alkanes are the same for the three IRMOFs.
► The π-electron rich zones enhance the specificity of the interaction.