Observation of binding of carbon dioxide to nitro-decorated metal-organic frameworks

Abstract

Metal-organic frameworks (MOFs) functionalised with amine, amide and hydroxyl groups show great promise for CO2binding due to their ability to form hydrogen bonds to CO2. Herein we report the adsorption and selectivity of CO2in four iso-reticular MOFs adopting the NbO topology. Functionalisation of the parent MOF, MFM-102, with -NO2, -NH2and alkyl groups leads to an enhancement of CO2adsorption of up to 36% for the NO2-decorated MOF and with raised selectivity. MFM-102-NO2shows the highest adsorption capacity for CO2(184 cm3g-1at 273 K and 1.0 bar) within this series, comparable to the best-behaving iso-reticular MOFs. At 298 K and 1.0 bar, MFM-102-NO2shows a CO2/CH4selectivity of 5.0.In situinelastic neutron scattering and synchrotron FT-IR micro-spectroscopy were employed to elucidate the host-guest interaction dynamics within CO2-loaded MFM-102-NO2. Neutron powder diffraction enabled the direct observation of the preferred binding domains in MFM-102-NO2, and, to the best of our knowledge, we report the first example of CO2binding to a -NO2group in a porous MOF. Synergistic effects between the -NO2group and the open metal sites lead to optimal binding of CO2molecules within MFM-102-NO2viahydrogen bonding to C-H groups.