Novel Fluorinated Metal-Organic Frameworks for CO2 Adsorption and Separation

Metal-organic frameworks (MOFs) are a class of porous materials constituted by the ordered connection of metal clusters and organic linkers.[1] MOFs have been widely studied for many gas separation processes, including post-combustion CO2 capture.[2] Among them, a class of MOFs of particular interest are those featuring phase-change adsorption behavior usually evidenced by steep increase in the adsorbed amount of gas in a narrow pressure region with a peculiar S-shaped adsorption isotherm.[3] We recently reported on a comprehensive study of the CO2 adsorption mechanism of a perfluorinated CeIV-MOF, namely F4_MIL-140A(Ce) based on tetrafluoroterephthalic acid and featuring a sigmoidal shape CO2 isotherm at low relative pressure depending on temperature. We disclosed the complex adsorption mechanism by using several coupled techniques, such as in-situ synchrotron high resolution diffraction, FT-IR, Solid state MAS NMR, DFT calculations and calorimetric techniques.[4] The work has been recently expanded through the solvent-free synthesis of other fluorinated MOFs based on Al and perfluorinated aryl and alkyl linkers (i.e. tetrafluoroterephthalic acid and tetrafluorosuccinic acid) and having the MIL-53 type structure. [5] The former exhibits an interesting phase from narrow pore to large pores purely induced by temperature changes. The same behavior has been observed by increasing the pressure range for the CO2 adsorption. Synthetic procedures, spectroscopic characterization and gas adsorption behavior will be discussed.