Physical adsorption behavior of molecular solids

Abstract

The physical adsorption of nitrogen at 77°K and 90°K is reported for the molecular solids ammonia, methanol, carbon dioxide, benzene, iodine, and bromine. The adsorption isotherms are similar to those previously observed with ice powder and the entire set of molecular solids appears to constitute a group of nonpolar, low-energy adsorbents. Whereas dispersion interaction calculations cannot be made with sufficient accuracy event to predict variations within the group, the converse is suggested to be true. This is that heats of adsorption found experimentally set a limit of about 1800 cal/mole for the dispersion interaction of nitrogen with substrates in general. The corollary conclusion is that the more common refractory or broken-bond adsorbents, which as a group show higher heats of adsorption, do so because of additional types of interactions. Included in this group would be the metals, their oxides, and the various carbon blacks.