Tailoring the pore size and shape of the one-dimensional channels in iron-based MOFs for enhancing the methane storage capacity

Abstract

Herein, iron-based metal–organic frameworks (MOFs), i.e. VNU-21 and VNU-22, and a new MOF termed Fe-NDC Fe₃O(NDC)₂SO₄(HCO₂)(H₂O)₂ (NDC²⁻ = 2,6-naphthalene dicarboxylate), possessing one-dimensional (1D) channels of different sizes and shapes in structures, were synthesized, and their methane storage capacities were measured. As a result of the structural design using mixed linkers for controlling the length and width of the rectangular 1D channels during the isoreticularly structural expanse, VNU-21, with the long-narrow 1D channels of 7.0 × 12.4 Ų, exhibited the high total volumetric CH₄ uptake of 182 cm³ cm⁻³ at 65 bar and 25 °C, which outperformed VNU-22, Fe-NDC and traditional MOFs with large 1D channels (DUT-4 and DUT-5). Remarkably, the CH₄ uptake of VNU-21 was comparable to those of the benchmark materials (e.g. MOF-5, MOF-177, MOF-205, MOF-210 and MOF-905-NO₂) for methane storage at 65 bar despite the significantly lower surface area of this compound. We believe that this design strategy will inspire the synthesis of new porous frameworks such as the reticularly expanded structures of VNU-21, which have been characterized by both high surface area and a strong CH₄-framework interaction for enhancing the methane storage capacity.