Computational design of tetrazolate-based metal–organic frameworks for CH4 storage

Abstract

CH₄ is considered as an environmentally benign fuel and there is considerable interest in the development of new materials for CH₄ storage. In this study, 424 tetrazolate-based metal–organic frameworks (MOFs) were computationally designed including 304 structures with the, urr and fcu topological nets and 120 structures with diverse nets. The CH₄ deliverable volumetric capacities of all designed nanoporous materials and the adsorption isotherms of the top 10 hypothetical MOFs with high volumetric deliverable capacity at 298 K were predicted using molecular simulations. From the simulation results, tetrazolate blocks adjacent to pyrene or dibenzene linkers in fcu topological MOFs were found to provide lower density CH₄ storage at delivery pressure (5.8 bar) as well as more efficient CH₄ packing at charge pressure (65 or 35 bar), resulting in an obvious enhancement in CH₄ deliverable volumetric capacity. The predicted CH₄ deliverable capacity of Zr-fcu-MOF-2Py between 65 and 5.8 bar can reach 177 cm³ (STP) cm⁻³, the highest among tetrazolate-based MOFs studied. In comparison with NU-Py-fcu (with carboxylate blocks and pyrene linkers), its deliverable capacity increases 45.1% from 122 to 177 cm³ (STP) cm⁻³ under the same conditions. The enhancement mechanism from microscopic insights provided details on how the incorporation of tetrazolate links into MOFs would affect CH₄ adsorption and delivery. This will lead to a novel way to enhance CH₄ volumetric delivery capacity through finely tuning the chemical environment of MOFs with the incorporation of polar functional groups such as tetrazolate blocks.