Gas adsorption study on mesoporous metal-organic framework UMCM-1

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.