(523a) A Consistent Method to Determine Accessible Volume, Area and Accessible Pore Size Distribution (APSD) of Carbonaceous Materials

Accessible volume and accessible area have been introduced recently and argued by the authors as the fundamental structural parameters in the characterization of porous solids because the use of these parameters yields physically realistic Henry constant, isosteric heat and a proper description of surface excess in supercritical adsorption. Recently Fan et al. [1] have provided a detailed computer simulation study as well as an experimental study to derive a proper geometrical area of a nonporous solid and its surface energy distribution. In this presentation we extend their work and present a new procedure to determine the geometrical area and accessible pore volume of a porous carbonaceous solid, and we justify this with a detailed computer simulation study of a number of structured solids. With these model solids whose atom configurations are known we first determine their ?intrinsic? accessible volume and surface area by the method of Monte Carlo integration as suggested by Herrera et al. [2]. These will be the targets to search for in the inverse determination, which is based solely on the information of a ?simulated? adsorption isotherm which we obtain with a Grand Canonical Monte Carlo simulation. Secondly we construct a kernel (which is a set of local isotherms of some model pores) and postulate that the theoretical adsorption isotherm of the solid is a linear combination of all local isotherms in the kernel, and then match the theoretical isotherm to the ?computer-experiment? adsorption isotherm. This matching will allow us to derive the accessible volume, area and pore size distribution, which are then compared against the targets. The results are very promising, suggesting that this method could be a potential tool to determine structural parameters of a porous solid. Detailed discussion of this new method will be presented at the meeting.