The role of the porosity and oxygen groups on the adsorption of n-alkanes, benzene, trichloroethylene and 1,2-dichloro ethane on active carbons at zero surface coverage

The adsorption at low concentration (zero surface coverage) of n-alkanes (from n-C-2 to n-C-5) benzene, trichloroethylene (TCE) and 1,2-dichloroethane (DCE) on active carbons has been measured by inverse gas-solid chromatography (IGC). The results offer new unexpected insights on the nature of the adsorption mechanisms of these systems under conditions very close to those found in the real applications for the elimination of atmospheric pollutants. In particular, the adsorbate-adsorbent interactions are governed mainly by dispersive forces even for those adsorbates with strong dipolar moment (TCE and DCE) which are capable of specific interactions. Although the introduction of large amounts of oxygen groups on the surface of the adsorbent increases the specific component of the adsorption, still the dispersive component is clearly dominant. In addition, the introduction of oxygen groups produces a decrease in the adsorption capacity. Nevertheless, it is shown that the presence of pores with appropriate sizes (close to the molecular dimension) has a more important effect on the retention of the adsorbates than chemical surface groups. Therefore, it is more desirable to have active carbons with accessible pores of the appropriate size than oxygen groups to get a good performance in the adsorption of these molecules. (c) 2007 Elsevier Ltd. All rights reserved.