Adsorption on Activated Carbon: One Underlying Mechanism?

This paper deals with the differences and similarities that are observed for isotherms of different adsorbates on activated carbon. In stead of the commonly used classification of isotherms in six “basic shapes”, a more general approach is suggested. Each isotherm can be subdivided in different, distinct, parts, each of which is the result of a different adsorption mechanism. The relative importance of these parts, even the fact if they exist or not, depends on a number of parameters. The most important are the pore size distribution (PSD) and active surface groups of the adsorbent, the strength of the adsorbate–adsorbent interactions and the temperature at which the isotherm is measured. As all these parameters are either constant (e.g. PSD) or can be estimated (e.g. interaction energies) it is possible to calculate a complete isotherm for one adsorbate on the basis of that of another one. But in order to achieve this, one must fully comprehend the meaning of each and every part of the isotherm: isotherm equations must reflect the physical processes involved rather than just fit the (complete) isotherm.

Keywords: adsorption; activated carbon; mathematical modelling