Adsorption of polycyclic aromatic hydrocarbons onto graphite

Abstract

Adsorption of aromatic hydrocarbons takes place on the basal plane and edge surface of graphite, but there are surprising differences in the amount of adsorption for graphite samples having predominantly basal plane surface, but prepared by different methods. Thus, compared with oleophilic graphite (graphite flakes prepared by grinding in liquid n-heptane), graphitised carbon black adsorbs only half the amount of pyrene per unit area of basal plane. The adsorption is especially pronounced in “polar” graphites prepared by grinding synthetic graphite in vacuum, which contain a relatively high proportion of “polar” edge sites.

For all the graphite samples the areas occupied by adsorbed polycyclic aromatics are much larger than the areas calculated from the dimensions of molecular models situated in a close-packed monolayer on a model basal plane surface of graphite. It appears therefore that the amount and strength of adsorption of aromatic hydrocarbons is greatly influenced by the method of preparation of graphite adsorbents.