A dense 3d-4f metal-organic framework with "gas pockets" for highly efficient CH/N separation

In this work, we report a multi-component MOF [CuCe L(Cl 4 -bdc) 0.5 (H 2 O) 2 ·(H 2 O) 6 ] n (L = 1 H -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 (CH 4 ) and nitrogen (N 2 ). According to the adsorption tests, this MOF exhibits a high adsorption capacity for CH 4 (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 CH 4 molecules effectively through multiple interactions between Cl atoms and CH 4 . The high performance of this MOF in CH 4 /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 CH 4 from coal-mine gas to recover fuel and reduce greenhouse gas emissions. A pillar-layered dense 3d-4f MOF shows high IAST selectivity for CH 4 /N 2 owing to the enhancement of the interactions between the MOF and CH 4 by the heteroatoms of the pillars.