Water Effects on Postcombustion CO2 Capture in Mg-MOF-74

Mg-MOF-74, one of the best metal–organic framework (MOF) materials for CO 2 adsorption and separation, has been widely explored in CO 2 capture. In this work, water effects on postcombustion CO 2 capture in Mg-MOF-74 are evaluated by using a combination of Grand Canonical Monte Carlo and density functional theory (DFT) simulations. Our results show that in this MOF the CO 2 adsorption capacity is decreased by the presence of water molecules linked to coordinatively unsaturated metal sites (CUMs). This effect is a consequence of the reduction of binding energy between CO 2 and the water-coordinated Mg-MOF-74 framework. DFT calculations indicate that such binding energy is much lower than that without coordinated water. More importantly, we find that the difference of the binding energy between CO 2 and CUM in a MOF and that between CO 2 and CUM-coordinated water are good descriptors to evaluate water effects on CO 2 capture in MOFs with CUMs. At the same time, these investigations further demonstrate that the CUMs in MOFs play an important role in their performance for CO 2 capture from a practical stream containing water and other impurities.