Introducing a self-consistent test and the corresponding modification in the Barrett, Joyner and Halenda method for pore-size determination

Abstract

A standard method to obtain the mesopore size distribution of adsorbents is the Barrett, Joyner and Halenda (BJH) analysis of the N2 adsorption?desorption isotherm at 77 K. The availability, over the last two decades, of well-defined model adsorbents in the mesopore range, together with other forms of isotherm analysis with the help of the Density Functional Theory (DFT) has shown that the BJH method tended to underestimate the pore-width when they are smaller than 10 nm. Regarding this fact, we have reported an improved BJH method, where we have remarked that the reconstruction of the adsorption?desorption isotherm from the BJH results leads to some inconsistency. We therefore proposed a simple means to cancel the mentioned discrepancy and inconsistency. This correction can be made by simply adding a corrective term to the standard BJH equation, which value is selected to meet a self-consistent criterion, i.e. the reconstructed isotherm should fit the original one. In the first article, the method was applied for some ordered mesoporous materials (OMM) synthesized in our laboratory, showing only the results without major details. In this work, we validate the test for other samples, in other pore size ranges, introducing some remarks in theoretical aspects and in the importance of obtaining and taking into account the micropore volume. Finally, a detailed procedure to apply the proposal method using only the experimental data of the analysis is presented.