Sing, Kenneth S.W. and Williams, Ruth T.
Empirical precedures for the analysis of physisorption isotherms.
Adsorption Science and Technology, 23(10) pp. 839–853.
Empirical methods, which can be used for the analysis of physisorption isotherms, involve the input of adsorption data on reference adsorbents. In particular, the αS-method can be used for the characterization of a porous material when the corresponding standard isotherm has been determined on a well-defined nonporous solid of similar surface structure. The interpretation of αS-plots is based on established principles underlying the mechanisms of physisorption: monolayer-multilayer adsorption, preferential filling of narrow micropores (ultramicropores), monolayer adsorption followed by the filling of wider micropores (supermicropores) and capillary condensation in mesopores. There are various distinctive features of the αS-plots, which allow these different processes to be identified and the internal and external areas and effective pore volumes to be quantified. The validity of BET-nitrogen areas can be checked and also, by using probe molecules of different size, one can obtain a semi-quantitative evaluation of the micropore size distribution. The comparison plot is a simple way of comparing the shapes of two related isotherms. This approach has been found useful for investigating textural changes such as those accompanying the thermal decomposition of hydroxides or the activation of carbons.
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