Enhanced CO2 Adsorption in Metal-Organic Frameworks via Occupation of Open-Metal Sites by Coordinated Water Molecules

CO2 is one of the most important greenhouse gases and its removal from flue gas and natural gas has become increasingly important. We report an interesting discovery in which the CO2 uptake and its selectivity over N2 and CH4 in the metal-organic framework (MOF) Cu-BTC were significantly increased by the presence of water molecules coordinated to open-metal sites in the framework. This was first predicted by molecular simulations and later validated by experiments. A detailed analysis of simulation data revealed that interaction between the quadrupole moment of CO2 and the electric field created by water molecules is responsible for the enhanced CO2 uptake. These findings could open new possibilities for tuning the adsorption behavior of MOFs for CO2 capture and other applications.