A preliminary study on assessing the Brunauer-Emmett-Teller analysis for disordered carbonaceous materials

Abstract

The surface area is an important property of porous materials, commonly evaluated through the Brunauer-Emmett-Teller (BET) analysis applied to nitrogen adsorption isotherms at 77 K. However, the applicability of the BET analysis for disordered carbonaceous materials remains under debate. In this work, the disordered carbonaceous materials (coal, kerogen of shale and artificial samples), were chosen as the objective for their BET evaluation. These samples were considered as collections of independent graphite slit pores; the isotherms of these uniform slit pores (kernels) were calculated with Grand Canonical Monte Carlo (GCMC) simulation. Then, the kernels were integrated by following the pore size distribution (PSD) of these real samples to simulate nitrogen adsorption isotherms at 77 K. The BET analysis was conducted for both these simulated isotherms and the uniform slit pores. The results show that the performance of the BET analysis for the carbon slit pores varies with the pore size. As for the mesoporous materials, we found that the BET area derived from the two consistency criteria is reliable, with a maximum overestimation of 18%. For micropores-containing materials, the two consistency criteria shows no obvious advantage over the standard method when the micropore is smaller than 1.8 nm and the micropore volume is non-negligible; the prediction of the BET area (consistency criteria) can be justified by considering the micropore size and percentage of micropore volume. These findings improve the understanding of the BET area and verify the BET analysis on some relevant disordered carbonaceous materials.