Evaluation of the distribution function of adsorption site energies based on the Fermi-Dirac's law in a monolayer

A model is proposed for physical adsorption of gases on homogeneous solid surfaces on the basis of the Fermi-Dirac's distribution function. The carbon fibers before and after anodic surface treatment are employed in this study conducted by the technique of inverse gas chromatography(IGC) at finite dilution. This distribution function leads to the probability of a given state of site energy and then the potential of the molecules (or the adsorption energy level), determining their tendency to move at a gas sold interface. When evaluating the distribution function with the amount adsorbed, we propose, for the starting adsorption value, a method using values measured by IGC at infinite dilution, instead of Hobson's or Adamson's method, It is found that the adsorption energy level measured with n-hexane and ethyl acetate on carbon fibers is increased by the anodic surface treatment. In particular, the results given by ethyl acetate, which is able to display the polar force on the carbon fibers treated, showed a significant increase when compared to nonpolar probes (n-hexane). This is probably due to the effect of surface chemical polar groups on adsorption energetics. (C) 1998 Academic Press.