An ultramicroporous metal–organic framework with dual functionalities for high sieving separation of CO2 from CH4 and N2

The removal of carbon dioxide from fuel gases and N2-rich flue gas are critical for chemical energy industry, and reduction of carbon emission. Adsorptive size-sieving based gas separation is highly desired to maximize the separation efficiency but rarely reported. Herein, an ultramicroporous metal–organic framework built from copper(II) and 5-fluoropyrimidin-2-olate, termed as Cu-F-pymo, has been studied for the separation of CO2 from CH4 and N2. Cu-F-pymo can exclusively capture CO2 over CH4 and N2 with significant high IAST selectivity (>107) and a high adsorption capacity of 69.2 cm3 cm−3. Such molecular size-sieving effect is attributed to the small pore size of Cu-F-pymo (∼3.3 Å), which can only allow the diffusion of CO2. The oxygen moieties decorated on the channel surface enforced the binding affinity toward CO2 through electrostatic and hydrogen-bonding interactions as confirmed by molecular simulation studies. The outstanding size-sieving CO2 separation performance was further confirmed by cycling column breakthrough tests, which demonstrated the dynamic CO2 capture capacity of 1078 mmol kg−1 and 941 mmol kg−1 for CO2/CH4 (50:50), CO2/N2(15:85) mixtures, respectively. More importantly, the mild regeneration feature of Cu-F-pymo underlies its potentials for practical carbon capture applications.