Multimodels computation for adsorption capacity of activated carbon

Abstract

The pore size distribution of activated carbon is conventionally characterized with nitrogen adsorption measurements at 77 K. The adsorption isotherms are commonly analyzed with a nonlocal density functional theory in combination with a mathematical model for the pore size and geometry. While nonlocal density functional theory is significantly more accurate than the Brunauer–Emmett–Teller theory for gas adsorption, its application to materials characterization is mostly based on a mean-field approximation for van der Waals attractions that is only qualitative in comparison with alternative versions of nonlocal density functional theory or molecular simulations. Toward development of a more reliable theoretical procedure, we compare mean-field approximation-nonlocal density functional theory with three recent versions of non-mean-field methods for gas adsorption at conditions corresponding to experiments for porous materials characterization. The potential applicability of different nonlocal density functional theory methods for pore size distribution predictions is evaluated in terms of the theoretical error bound scale analysis. We find that the weight density approximation is the most reliable for predicting the pore size distribution of amorphous porous materials. In addition to accurate isotherm, weight density approximation yields the theoretical error bound scale for pore size distribution prediction nearly 104 times narrower than that corresponding to mean-field approximation. The new theoretical procedure has been used to analyze the pore size distribution of four activated carbon samples and to predict the adsorption capacities of these materials.