An Ultramicroporous Nickel-Based Metal–Organic Framework for Adsorption Separation of CO2 over N2 or CH4

Metal–organic frameworks hold a great potential for selective CO2 capture to mitigate massive CO2 emission. In this work, we report a nickel-based metal–organic framework, Ni-4PyC, with narrow and uniform ultramicropores of 6.8 Å, exhibiting the CO2 adsorption capacity of 3.11 mmol/g at 298 K and 100 kPa and high CO2/N2 (0.15:0.85) and CO2/CH4 (0.5:0.5) selectivities of 51 and 6, respectively. Meanwhile, its dynamic separation performance is also confirmed by breakthrough experiments of the CO2/N2 and CO2/CH4 mixtures, further demonstrating that Ni-4PyC can selectively capture CO2 from flue gas and remove CO2 from natural gas. Molecular simulation reveals that CO2 molecules are close to the organic ligand of Ni-4PyC (pyridine), leading to CO2 being caught in the middle by two pyridines like a plier via hydrogen bonds. Besides, Ni-4PyC has an excellent recyclability without noticeable loss in CO2 adsorption after five consecutive cycles of static and dynamic adsorption experiments. These combinational merits make Ni-4PyC as an excellent adsorbent for related CO2 capture from flue gas as well as natural gas upgrading.