Two NbO-type MOFs based on linear and zigzag diisophthalate ligands: exploring the effect of ligand-originated MOF isomerization on gas adsorption properties

Abstract

NbO-type MOFs constructed from dicopper paddlewheel secondary building units and diisophthalate ligands not only exhibit great promise for the separation of environment and energy-related gas pairs but also more importantly provide an excellent platform for the fundamental investigation of structure–property relationships. In this work, two NbO-type MOFs (ZJNU-91 and ZJNU-92) derived from linear and zigzag-shaped thieno[3,2-b]thiophene-functionalized diisophthalate ligands were solvothermally prepared and structurally characterized. Their gas adsorption properties with respect to C₂H₂, CO₂, and CH₄ were systematically investigated, revealing that they exhibit promising potential for selective adsorptive separation of C₂H₂–CH₄ and CO₂–CH₄ binary gas mixtures which are associated with acetylene production and natural gas upgrading. In particular, compared to its isomer ZJNU-92, ZJNU-91 displays larger C₂H₂ and CO₂ uptake capacities as well as higher C₂H₂/CH₄ and CO₂/CH₄ adsorption selectivities under ambient conditions, despite its lower surface area and pore volume. On the basis of structural analyses, the better performance of ZJNU-91 compared to its isomer ZJNU-92 can be ascribed to its more optimized pore size.