Uncertainty in pore volumes derived from alpha(S)-analyses and from the theory for volume filling of micropores

摘要

The evaluation of apparent pore volumes for low- and high-pressure adsorption applications is a difficult process. In this communication we compare the as-plot method of porosity analysis with that proposed within the Theory for Volume Filling of Micropores. For both methods we present an uncertainty analysis of the adsorption data for two commercially available porous activated carbon samples, a cloth as FM1-250 and a powder as Picazine. For the first time, we demonstrate the application of the theory for uncertainty propagation to both methods of analysis. Since both methods rely on graphical means of data evaluation via linear least squares analyses to identify apparent primary micropore volumes, the inclusion of uncertainty in the abscissa and ordinate data guides the correct identification of the linear ranges by restricting the inclusion of points that may cause deviation from pre-defined, high levels of Pearson regression coefficients. The nitrogen adsorption isotherm for FM1-250 is a classical Type I suggesting the presence of micropores only, whereas Picazine gives a Type IV isotherm with an enhanced amount adsorbed in the low relative pressure range suggesting the presence of both micropores and mesopores. Both methods of analysis render statistically equivalent apparent total micropore volumes for the FM1-250 sample; however, statistically significant differences exist for apparent primary micropore volumes. For the Picazine sample, we also applied a two-term Dubinin-Astakhov analysis to generate statistically equivalent primary micropore volumes, but no agreement existed for the apparent total micropore analyses. For the low-pressure adsorption isotherm analysis of pore volumes, we suggest that the us-plot is less sensitive to the presence of mesopores than the TVFM method. (c) 2006 Elsevier B.V. All rights reserved.