pubs.acs.org/Langmuir © 2010 American Chemical Society
Unusual Adsorption Behavior on Metal-Organic Frameworks David Fairen-Jimenez,† Nigel A. Seaton,‡ and Tina D€uren*,† †
Institute for Materials and Processes, School of Engineering, The University of Edinburgh, Edinburgh, United Kingdom, and ‡University of Surrey, Guildford, United Kingdom Received July 15, 2010. Revised Manuscript Received August 16, 2010
Metal-organic frameworks (MOFs) have shown adsorption behavior that is not observed in other microporous materials such as zeolites or activated carbons. This study used grand canonical Monte Carlo simulation to evaluate a particular form of behavior, which corresponds to the presence of unusual type V adsorption isotherms. Study of a series of MOFs in the IRMOF family, containing chemically similar linkers of different length, showed that the presence of type V adsorption depends on a fine balance between the strength of the fluid-fluid and fluid-solid interactions, which in turn is a strong function of the length of the linker and therefore the pore size. A transition from type V behavior to the more common type I behavior is observed as the temperature increases. The temperature at which this transition occurs increases, and the transition becomes more diffuse, as the length of the linker increases. This type V behavior leads to an interesting possibility in the design of MOF adsorbents for use in gas separation and gas storage applications.
1. Introduction Gas adsorption on microporous materials, activated carbons or zeolites, for example, is usually of IUPAC type I (see Figure 1a). The overlapping adsorption potentials in microporous solids (i.e., solids with pore sizes of
