(303h) Molecular Design of Zirconium Metal-Organic Frameworks for CO2 Separation

Current investigations on metal-organic frameworks (MOFs) for CO₂ capture have developed considerably large amount of promising candidates, and have suggested several design guidelines for such applications. However, systematical evaluation of certain combination of metal cluster and organic linker remain elusive. In this work, a series of MOFs are molecularly designed from bottom up for CO₂/N₂ and CO₂/CH₄ separations. Specifically, containing zirconium (Zr) clusters and N-rich tetrazolate linkers, 120 hypothetical MOFs are computationally constructed using reversed topological approach based on 40 topological nets. The simulation results match well with experimental data. And the Zr-MOFs not only outperform over their carboxylate counterparts in term of CO₂/N₂ and CO₂/CH₄ separation, but also offer higher CO₂ capacity than many existing MOFs and representative adsorbents, attributed to the rich nitrogen donors from tetrazolate linkers. Among the 120 candidates, the MOF with eft topology (MOF-eft-P) possesses the highest CO₂ uptake and selectivity for CO₂/N₂ and CO₂/CH₄ mixtures, with performance comparable to the best MOFs experimentally reported. The breakthrough simulation also suggests its excellent separation power for both gas mixtures. Furthermore, the structural properties are characterized and correlated with adsorption and separation performance parameters. In order to reach the highest separation performances, moderate void fraction and high isosteric heat of adsorption are desirable. This study not only elucidates the design strategy for new MOFs, but also reveals the molecular insight into CO₂ separation in Zr-MOFs.