Assessment of reliability of the Horvath–Kawazoe pore size analysis method using argon adsorption isotherms on ordered mesoporous silicas

A set of argon adsorption isotherms measured on MCM-41 ordered mesoporous silicas of different pore sizes was used to assess the reliability of the Horvath–Kawazoe (HK) method for mesopore size analysis. It was shown that for small mesopores the HK-type relation between the pore size and argon condensation pressure for cylindrical oxide-type pores underestimates the pore width of MCM-41 materials but this underestimation is much smaller than that obtained from nitrogen adsorption data. In contrast, the relation established on the basis of well-defined argon/MCM-41 adsorption systems allows for a correct evaluation of the pore width of MCM-41 but does not improve the shape of the pore size distribution (PSD). Both aforementioned pore width-condensation pressure relations underestimated the PSD height because of the appearance of an artificial tail in the range of fine pores. This artificial tail erroneously suggests the presence of micropores for all MCM-41 samples studied. Therefore, the recognition of the artificial nature of this tail is crucial for avoiding gross misinterpretations of the HK PSDs.