ABSTRACT
The environmentally benign metal-organic framework (MOF) CUK-1 based on 2,4-pyridine dicarboxylate has been prepared for the first time using Mn(II) as the inorganic node and water as the only solvent. Mn-CUK-1 shows reversible and efficient capture of H2O, SO2, and H2S. Compared to previously studied Co(II) and Mg(II) versions of the same MOF, Mn-CUK-1 also exhibited unique temperature-induced structural flexibility due to organic linker torsion, as detailed by variable-temperature single-crystal X-ray diffraction studies. Owing to this inherent solid-state flexibility, Mn-CUK-1 showed stepwise adsorption for polar gases, which induce structural deformations upon adsorption, while the nonpolar guest adsorbates were reversibly sorbed in a more classical manner. Notably, Mn-CUK-1 demonstrates the highest reported H2S capacity-to-surface area ratio among MOFs that are chemically stable toward this reactive acidic molecule. Moreover, Mn-CUK-1 displays exceptional structural stability in the presence of high relative humidity and corrosive gases and shows soft crystalline behavior triggered by changes in both the adsorption temperature and guest molecule identity.
ABSTRACT
Kinetic CO2 adsorption measurements in the water-stable and permanently microporous Metal-organic framework material, Mg-CUK-1, reveal a 1.8-fold increase in CO2 capture from 4.6 wt% to 8.5 wt% in the presence of 18% relative humidity. Thermodynamic CO2 uptake experiments corroborate this enhancement effect, while grand canonical Monte Carlo simulations also support the phenomenon of a humidity-induced increase in the CO2 sorption capacity in Mg-CUK-1. Molecular simulations were implemented to gain insight into the microscopic adsorption mechanism responsible for the observed CO2 sorption enhancement. These simulations indicate that the cause of increasing CO2 adsorption enthalpy in the presence of H2O is due to favorable intermolecular interactions between the co-adsorbates confined within the micropores of Mg-CUK-1.
