A dense 3d–4f metal–organic framework with “gas pockets” for highly efficient CH4/N2 separation

Abstract

In this work, we report a multi-component MOF [CuCe L(Cl₄-bdc)_0.5(H₂O)₂·(H₂O)₆]_n (L = 1H-pyrazole-3,4,5-tricarboxylic acid, Cl₄-bdc = 2,3,5,6-tetrachloroterephthalate) with a pillar-layered structure. In the structure, the polydentate ligand (L) linked Cu^II and Ce^III atoms constitute 3d–4f layers that serve as the pedestal base and the chlorinated Cl₄-bdc ligands acting as bolsters are installed between the layers through Ce^III. The moderate pore size and the unique chloride decorated surface of channels endow this MOF with excellent separation ability for methane (CH₄) and nitrogen (N₂). According to the adsorption tests, this MOF exhibits a high adsorption capacity for CH₄ (28.41 cm³/cm³) at 298 K and 1 bar, while the N₂ adsorption capacity is only 3.43 cm³/cm³. The DFT calculations demonstrate that the adjacent Cl₄-bdc in the network can act as “gas pockets” or nano traps to immobilize the CH₄ molecules effectively through multiple interactions between Cl atoms and CH₄. The high performance of this MOF in CH₄/N₂ separation has been verified by the outstanding IAST selectivity of 13.32 and breakthrough experiments. This work provides a new perspective for capturing CH₄ from coal-mine gas to recover fuel and reduce greenhouse gas emissions.