Breathing Assisted Selective Adsorption of C8 Alkyl Aromatics in Zn-based Metal-Organic Frameworks.

Abstract

The breathing phenomenon in metal-organic frameworks (MOFs) has revealed supramolecular host-guest interactions, which could be beneficial for chemical separation in numerous industrial applications. The cost-effective purification of C 8 alkyl aromatics such as o-xylene, p-xylene, m-xylene, and ethylbenzene still remains challenging owing to their similar molecular structures, boiling points, kinetic diameters, polarities, etc. Herein, we report two Zn-based pillar-bilayered MOFs, denoted as [Zn 2 (aip) 2 (pillar)]; aip = 5-aminoisophthalic acid; pillar: bpy = 4,4 -bipyridine or bpe = 1,2-bis(4-pyridyl)ethane, which exhibit a breathing effect depending on the adsorbed guest molecules. Guest-dependent sorption studies using organic solvents such as N , N -dimethylformamide, methanol,\xa0 benzene, and water vapor displays reversible structural flexibility through breathing effect in both framework compounds. Motivated by these sorption studies, the conducted experiments on C 8-alkyl aromatics resulting in both MOF compounds can access these isomers in the shrunken pores and, thereby expand the pore size by framework breathing. In C 8 binary mixtures, these Zn-MOFs exhibit selective sorption properties based on the different interactions between guest C 8 aromatics interactions and framework structure.