Assessment of Mesoporosity

At present, it must be recognized that adsorption hysteresis may be generated in a number of different ways. In the context of the assessment of mesoporosity, we have seen that there are two major contributing factors (a) on the adsorption branch, the development of a metastable multilayer and the associated delay in capillary condensation (b) on the desorption branch, the entrapment of condensate through the effect of network-percolation. 

BJH, Dollimore-Heal and BdB methods were compared for assessment of mesoporosity. Owing to the pore shape of the material used, the first two methods lead to an underestimation of pore size, and hence to an overestimation of total mesoporous surface. The last method is more general, and when the appropriate shape factor is used, a reliable estimation of the mesoporous texture is obtained. The S sdB estimator is almost a perfectly linear function of y, and vanishes in the X(IOO) sample. The external surface area, Xext, computed from the t-plot leads to an overestimation of the true mesoporous surface. 

The impact of mesoporosity on microporosity assessment by CO2 adsorption, revisited... 

The experimental data for mesopore assessments are the isotherms at their high relative pressure ranges. With mesoporosity present, the isotherms of activated carbons adopt the Type-IV shape, usually terminating without a plateau, at position S (Figure 4.60). The p/p value of 1.0 provides a limit to amounts that can be adsorbed, in units of mmol g. Conversion to volumes adsorbed (Vp in cm g ) is possible using an estimated molar volume, V , (cm mmol ) of the liquid adsorbate. When different liquids are used. 

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