A fractal approach to adsorption on heterogeneous solids surfaces. 2. Thermodynamic analysis of experimental adsorption data

The isotherm equations developed in part I of this publication have been fu rther generalized to account for the effects of multilayer adsorption. This was done employing the fractal BET isotherm developed by Fripiat et al. Th eir BET equation takes into account the geometric effects of fractality on the formation of second and subsequent layers, but ignores the energetic ef fects of fractality on adsorption in the first layer, closest to the surfac e. To correct this, their expression was integrated with the generalized ad sorption energy distribution developed in part I (Rudzinski, W.; Lee, S.-L. ; Panczyk, T.; Yan, C.-C. S. J. Phys. Chem. B 2001, 105, 10847). Using the generalized fractal BET equation obtained in this way, we are able to corre late the experimental data from the lowest pressures investigated up to the surface loadings approaching coverage by two layers. Two adsorption system s have been subjected to this analysis. One was nitrogen adsorbed on a comm ercially available silica, and the second nitrogen adsorbed by a commercial ly available activated carbon. As a result of these fittings, there have be en obtained the parameters characterizing both the geometric and energetic heterogeneities of these two gas/solid systems.