Importance of the αs-plot method in the characterization of nanoporous materials

Abstract

In this work, an exhaustive study of the calculation of micropore and mesopore volumes with αs-plot method as proposed by Professor Sing is carried out. The method is critically compared with other similar methods such as the Dubinin-Radushkevich, t-plot and those based on density functional theory (DFT). For comparison purposes, several nanoporous materials with different chemical properties were selected. The analysis was segregated into three categories: (i) microporous materials, in which the analyzed samples are activated carbons (ACs) with different pore-size distributions, a single-walled carbon nanotube (SWNT) and a zeolite (MS5A); (ii) mesoporous materials, including ordered mesoporous carbons (CMK-3) and ordered mesoporous siliceous materials (MCM-41 and SBA-15); and (iii) micro-mesoporous materials, in which pillared clays (PILCs) obtained with different metals (Al, Si, Fe and Zr) were studied. To apply the αs-plot method, several standard isotherms previously reported by other authors were considered for the analysis of microporous and mesoporous materials. Furthermore, a series of four reference materials for PILCs were synthesized and their high-resolution nitrogen adsorption isotherms were measured and reported. The results obtained by the αs-plot method are consistent with those obtained by DFT methods. This consistency highlights the importance of the use of this reliable and versatile method, where the correct selection of the standard isotherm is the most critical aspect to be considered.