An aminopyrimidine-functionalized cage-based metal–organic framework exhibiting highly selective adsorption of C2H2 and CO2 over CH4

Abstract

There has been considerable interest in adsorptive separation of C₂H₂/CH₄ and CO₂/CH₄ gas mixtures due to its industrial significance and scientific challenge. In this work, we have designed and synthesized a bent diisophthalate ligand functionalized with aminopyrimidine groups, and constructed via a solvothermal reaction, a porous copper-based framework. Single-crystal X-ray diffraction studies show that the framework is a three-dimensional network containing three different types of polyhedral nanocages, which are stacked together to form two distinct types of one-dimensional channels along the crystallographic c axis. The compound after activation shows exceptionally high C₂H₂ and CO₂ uptakes of 211 and 120 cm³ (STP) g⁻¹ at 295 K and 1 atm, as well as impressive adsorption selectivities towards C₂H₂ and CO₂ over CH₄. High C₂H₂ and CO₂ uptake capacities as well as significant adsorption selectivities of C₂H₂ and CO₂ over CH₄ imply potential applications in the adsorptive separation and purification of C₂H₂/CH₄ and CO₂/CH₄ gas mixtures, which have been verified by column breakthrough experiments. Several important binding sites for C₂H₂ and CO₂ in ZJNU-54 were revealed by quantum chemical calculations, demonstrating that the organic linkers in ZJNU-54 form unique structures that facilitate the adsorption of C₂H₂, while the amine groups and the Lewis basic pyrimidine-ring nitrogen sites in the organic linker improve the adsorption energies for CO₂, finally leading to the increase of adsorption capacities for these two gas molecules. This work provides an efficient strategy for incorporating specific functional groups into cage-based MOFs for generating new adsorbents for highly selective gas storage and separation.