An ultramicropore Co-MOF constructed from mixed N/O-bifunctional organic ligand for highly efficient C2H6/C2H4 separation

A novel ultramicroporous Co-MOF has been constructed using a mixed N/O-bifunctional ligand strategy. • It exhibits preferential C 2 H 6 adsorption over C 2 H 4 at 298 K, with a C 2 H 6 uptake of 3.9 mmol/g at 1 bar. • The IAST selectivity for a C 2 H 6 /C 2 H 4 (10/90) mixture reaches 2.0 at 1 bar, and the separation potential is 1.1 mmol/g. • GCMC simulations and DFT calculations reveal that multiple C–H···O and C–H···π interactions contribute to a higher binding energy for C 2 H 6 (−12.22 kcal/mol) than for C 2 H 4 . The separation of ethane (C 2 H 6 ) from ethylene (C 2 H 4 ) is a crucial but energy-intensive process in the petrochemical industry. Developing adsorbents that preferentially capture C 2 H 6 over C 2 H 4 (inverse selectivity) enables one-step production of high-purity C₂H₄. Herein, we report a novel ultramicroporous cobalt-based metal–organic framework, 1 , constructed from a mixed N/O-bifunctional ligand strategy using 4-(4-carboxyphenyl)-1,2,4-triazole (HCPT) and isonicotinic acid (HINA). Single-crystal X-ray diffraction reveals that 1 features one-dimensional rhombic channels with pore dimensions of 4.48–5.81 Å, fully coordinated Co(II) centers, and pore surfaces decorated with aromatic rings and uncoordinated O atoms. The activated framework ( 1a ) exhibits a Brunauer–Emmett–Teller surface area of 517 m²/g and shows preferential C 2 H 6 adsorption over C 2 H 4 at 298 K, with C 2 H 6 uptake of 3.9 mmol/g at 1 bar. Ideal adsorbed solution theory selectivity for a C 2 H 6 /C 2 H 4 (10/90) mixture reaches 1.81 at 298 K and 1 bar, and the separation potential is 1.1 mmol/g. Grand canonical Monte Carlo simulations and density functional theory calculations reveal that C 2 H 6 forms multiple C–H···O and C–H···π interactions with the framework, resulting in a higher binding energy (−12.22 kcal/mol) than C 2 H 4 (−10.61 kcal/mol). This work demonstrates that the mixed N/O-donor ligand strategy is effective for designing inverse-selective MOFs for energy-efficient ethylene purification. A novel ultramicroporous Co-MOF was constructed using a mixed N/O-bifunctional ligand strategy (HCPT and HINA). The activated framework features one-dimensional rhombic channels (4.48–5.81 Å), fully coordinated Co(II) centers, and pore surfaces decorated with aromatic rings and uncoordinated O atoms. It exhibits preferential C₂H₆ adsorption over C₂H₄ at 298 K, with a C₂H₆ uptake of 3.9 mmol/g at 1 bar. The IAST selectivity for a C 2 H 6 /C 2 H 4 (10/90) mixture reaches 2.0 at 1 bar, and the separation potential is 1.1 mmol/g. Grand canonical Monte Carlo simulations and density functional theory calculations reveal that C 2 H 6 forms multiple C–H···O and C–H···π interactions with the framework, resulting in a higher binding energy (−12.22 kcal/mol) than C 2 H 4 (−10.61 kcal/mol). This work demonstrates that the mixed N/O-donor ligand strategy is effective for designing inverse-selective MOFs for one-step ethylene purification. Download: Download high-res image (319KB) Download: Download full-size image