Construction of π back donation active site in metal-organic framework for dense packing of C2H2 and efficient C2H2/CO2 separation

The separation of C2H2/CO2 is very important but still a great challenge in industry because of their very similar molecular sizes and physical properties. Considering that CuI site can form both π complex interactions and π back donation interactions with C2H2, herein, we achieved high C2H2 packing density and efficient C2H2/CO2 separation by anchoring CuI ions with synergistic dual-pyrazol sites of MOF-303. The adsorption experiments show that the resulting CuI@MOF-303 could quickly adsorb C2H2 in the low-pressure region, and the C2H2 packing density is up to 477.9 g/L at 1 bar and 298 K, which is higher than any reported adsorbents. The density functional theory calculations show that π back donation of CuI site in CuI@MOF-303 can strengthen the interaction between CuI@MOF-303 and C2H2 by providing electrons from d orbitals of CuI site to the unoccupied antibonding π* orbital of C2H2 molecule. In addition, the C2H2/CO2 selectivity of CuI@MOF-303 at 1 bar is 25.9, which is 6.0 times of the original MOF-303. Breakthrough experiments show that CuI@MOF-303 has good separation performance for C2H2/CO2 gas mixtures, featuring both high C2H2 uptake and high separation factor of 10.6. Satisfyingly, fuel-grade C2H2 (purity ＞ 98.2 %, 82.83 cm3/cm3) can be obtained after desorption. Moreover, CuI@MOF-303 also has good C2H2 adsorption cycle stability and C2H2/CO2 separation regeneration ability, which indicates that it has great potential in industrial C2H2 purification.