A mesoporous metal-organic framework (MOF) material, UMCM-1, has been synthesized and characterized using N2 adsorption, powder X-ray diffraction, scanning electron microscopy, and Fourier transform infrared techniques. A detailed experimental study has been made of the adsorption of pure methane, hydrogen, carbon dioxide, oxygen, and nitrogen at various temperatures (298-338 K) and pressures (up to 25 bar). Multitemperature isotherms were modeled using the Dubinin-Astakhov equation to obtain useful thermodynamic properties including adsorption potential characteristic curves and isosteric heats of adsorption. Results are compared with mesoporous carbons and silicas. Large-pore materials are shown to exhibit relatively high heats of adsorption for CO2 when open metal sites are present. This phenomenon is not observed for methane, which indicates the importance of the CO 2 quadrupole in influencing binding strength. Adsorption results for N2 and O2 show that selectivities in MOFs can be manipulated by the presence or absence of open metal sites. UMCM-1 and MOF-177 show a slight preference for O2 over N2. However, open metal site MOFs such as Cu-BTC show the opposite adsorption preference, which is similar to zeolite selectivities. This experimental study reveals interesting adsorption information about a novel mesoporous MOF within the context of other MOFs and traditional mesoporous adsorbents. These results can be used to advance the development of structure-property relationships for metal-organic frameworks.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films