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

In this work, we report a multi-component MOF [CuCe L(Cl-4-bdc)(0.5)(H2O)(2)center dot(H2O)(6)](n) (L = 1H-pyrazole-3,4,5-tricarboxylic acid, Cl-4-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 Cl-4-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 (N-2). According to the adsorption tests, this MOF exhibits a high adsorption capacity for CH4 (28.41 cm(3)/cm(3)) at 298 K and 1 bar, while the N-2 adsorption capacity is only 3.43 cm(3)/cm(3). The DFT calculations demonstrate that the adjacent Cl-4-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/N-2 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.

Automated summary

In this work, a multi-component MOF with a pillar-layered structure was reported. The MOF exhibited excellent separation ability for methane and nitrogen due to its moderate pore size and unique chloride decorated surface of channels. This study provides a new perspective for capturing methane from coal-mine gas to recover fuel and reduce greenhouse gas emissions.