A bifunctional ligand-based metal-organic framework with rich aromatic pores and open O donor sites for selective C2H6/C2H4 separation

The separation of C 2 H 6 (ethane) from C 2 H 4 (ethylene) to produce C 2 H 4 with high purity is an important but challenging task in chemical industry due to their similar physical properties including molecular sizes and boiling points. Metal-organic frameworks (MOFs) with modifiable pore surroundings give new avenues for the development of functional materials for the targeted gas selective separation, especially for the design of C 2 H 6 -selective ones with simplified separation process and reduced energy consumption compared with those C 2 H 4 -selective ones. In the present study, a new Co(II)-based MOF featuring the formula of {[Co 2 (μ 2 -OH)(CPT) 2 (HCOO)](DMF) 3 (MeOH)} n ( 1 ) has been successfully prepared by reaction of Co(II) salt with a bifunctional organic ligand 4-(4 H -1,2,4-triazol-4-yl)benzoic acid (HCPT). The microporous pore surroundings of 1 feature high density of aromatic benzene ring and triazole groups coupled with uncoordinated O atoms, which collectively generate stronger interactions with C 2 H 6 molecules than with C 2 H 4 as revealed by the following dispersion corrected DFT calculations. As a result, the activated 1 shows a high C 2 H 6 uptake capacity of 109.1 cm 3 /g with a moderate high C 2 H 6 /C 2 H 4 (50:50) selectivity of 1.92 at 298 K and 1 bar, and such a separation ability was further supported by the breakthrough experiment. To further probe the underlying separation mechanism, the molecular dynamic simulation and DFT calculations were carried out, and the results coincide well with the experimental ones, which point out that the multiple synergistic interactions between C 2 H 6 molecules with the pore surface of 1 account for the high C 2 H 6 uptake capacity and C 2 H 6 /C 2 H 4 selectivity.