Evaluation of accessible and inaccessible microporosities of microporous carbons

Abstract

A fine pore characterization method for less-crystalline porous solids has been applied to activated carbons. In the analysis, the microporosity of the solid was classified into effective micropores and inaccessible pores, depending upon the accessibility of the pore to an N₂ molecule at 77 K. The volume fraction of each pore was determined via a N₂ adsorption isotherm and two types of density measurements. The Debye–Bueche plot of the small-angle X-ray scattering (SAXS) was used to obtain the correlation length characteristic of the sample, followed by estimation of the average transversal length of the pore and the solid part. These dimensions were compared with the structural parameters given by the adsorption method and X-ray diffractometry in order to examine the geometric features of the system. The number and size of inaccessible pores were calculated for a sample with symmetrically shaped pores, considering the volume fraction of effective micropores and inaccessible pores, and specific surface areas due to these pores.