Surface and Porosity of Adsorbents

The validity of adsorption methods of measuring specific surface areas of solids (and, in particular, of adsorbents) is limited by the characteristics of the porosity. Methods based on the concept of multilayer adsorption, like the BET method and de Boer's t-method, are applicable only to non-porous or coarsely porous (including mesoporous) adsorbents.
There is no general method of calculating the surface area of microporous adsorbents from adsorption data. For the "crack" model of the micropores in carbon adsorbents we can calculate the size and the geometrical area of the micropores from the parameters of the adsorption equation given by the theory of the volume filling of micropores, using a standard vapour (benzene). Almost identical results are obtained by using the adsorption of water vapour, which forms continuous monolayers in the micropores because of the dominant role of the hydrogen bond in adsorption. The geometric surface of micropores in carbon adsorbents is not a measure of the adsorption capacity of the sample, which is determined by dispersion forces, but it is relevant in kinetics and catalysis.
The presence of micropores in non-porous or coarsely porous adsorbents makes the measurement of surface area by the BET or the de Boer method physically meaningless. In this case we can use the t/F method of Dubinin and Kadlets, which gives a measure of the volume of micropores and of the specific surface of mesopores. Kistler and Kiselev's capillary condensation method gives similar values for the specific area of the mesopores. 23 references.