Thermodynamics of Adsorption of a Series of Related Organic Molecules on Graphite and a Carbon Black: Part 1—Heat of Adsorption

Abstract

The isosteric heat of adsorption for a structurally related series of organic adsorbates has been determined at varying degrees of surface coverage on a graphite and a well-characterized carbon black using a gas-chromatographic technique. The method of calculation of the amount adsorbed eliminates “zero adsorption errors”. The data on the graphite show first a very steep fall, and then a slightly rising value for the heat of adsorption as coverage increases. The data on the Spheron are similar, but the initial fall is not so sharp and is followed by a horizontal portion. The initial region could be due to oxygen chemisorbed at the surface. The data are seen to indicate the absence of pores great enough for cooperative adsorption to occur. The value of the difference between the isosteric heats of adsorption and the heats of condensation is 10–15 kJ mol–1.