The t-plot approach. The basic principle of the t-method is to compare the nitrogen adsorption isotherm obtained for a given porous solid with a particular reduced form of a standard isotherm (the so-called universal t-curve) corresponding to a non-porous solid of the same. The nitrogen volume, va adsorbed at a relative pressure p/po on a given sample is plotted as a function of the thickness, t, of the adsorbed layer, as given by the "universal t-curve" for the same relative pressure. But the reference t-curve depends on the intensity of adsorbent-adsorbate interactions as illustrated by the CBET constant value. The t-plot approach should then be amended to take into account the adsorbent-adsorbate interaction. Various reference t-curves should be used depending on the CBET value. Through the so amended va -t-plot, valuable information can be obtained about the porous structure of the adsorbent. Several interesting pieces of information can be derived from the so amended t-plot, in particular, the total surface area St which is comparable to BET surface area SBET as well as the external and internal surface areas of the particle Sw and Sµ. Moreover, the shape of these plots combined with the shapes of the nitrogen adsorption isotherms is also very informative. Several examples are given in section 6.3.4.6. Overall, an in-depth analysis of the isotherms and the corresponding t-plots may provide an interesting insight into the texture and the nano character (if any) of the sample. Of course, in a few cases, some ambiguities could remain that can be solved by a qualitative electron microscopy picture.
