Characterization of pore structure of carbon molecular sieves using DFT analysis of Ar and H2 adsorption data

A combination of hydrogen and argon adsorption isotherms at cryogenic temperatures (77 and 87 K) were used to analyze microporosity of a series of carbon molecular sieves (CMS). The pore size distribution (PSD) for a carbon sample was calculated by fitting the non local density functional theory (NLDFT) model isotherms to a set of experimental data consisting of both Ar and H2 adsorption isotherms. Thus, the calculated PSD is consistent with both isotherms. The range of pore size analysis in this method is extended to smaller pore sizes compared to the standard nitrogen or argon adsorption analysis. In addition, it is shown that the data of the two isotherms are partially complementary so that if the low pressure part of the Ar isotherm is truncated, the calculated PSD remains almost unchanged. The results of the analysis of a series of CMSs show that the presented approach is very sensitive to actual carbon pore structure and allows differentiating between seemingly similar samples. It makes the method a useful tool for a detailed characterization of CMSs.