A zinc-octacarboxylate MOF with an unusual (6, 8)-connected ocu topology for high-capacity adsorptive separation of C8 alkylaromatics

The separation of C8 alkylaromatics (xylenes and ethylbenzene) is an industrially important but challenging process. Compared with the presently used distillation method, adsorptive separation using porous materials has the advantages of low energy consumption and high efficiency. Here, we designed and synthesized a novel metal–organic framework (Zn-ETTOB) with an unusual ocu (6, 8)-connected topology using an octacarboxylic acid organic linker (4,4′,4″,4′″,4″″,4′″″,4″″″,4′″″″-((ethene-1,1,2,2-tetrayltetrakis (benzene-4,1-diyl))tetrakis(azanetriyl))octabenzoic acid, H8ETTOB). The saturated adsorption capacities of ethylbenzene (8.15 mmol/g) at 298 K outperforms all previously reported adsorbents. Simulation calculations revealed the difference in the number of C-H···H van der Waals interaction sites between the framework and adsorbates, as well as the variation in the strength of van der Waals interactions resulted in the selective separation of Zn-ETTOB for C8 alkylaromatics. This work provides inspiration for the discovery of high-performance adsorbents towards separation of C8 alkylaromatic isomers.