New approach to evaluate pore size distributions and surface areas for hydrophobic mesoporous solids

A new approach to pore size and surface area analysis for hydrophobic mesop orous solids is proposed. Well-defined materials with strongly hydrophobic surfaces were prepared via chemical bonding of octyldimethylsilyl (ODMS) li gands to the surface of large-pore MCM-41 samples. Nitrogen statistical fil m thickness curves (t-curves) were determined for hydrophobic pores. These t-curves were fitted with the nitrogen adsorption isotherm fora macroporous silica modified with ODMS groups in order to derive the reference t-curve valid in the entire range of relative pressures. An empirical expression fo r the reference t-curve was found. The reference t-curve and the previously derived corrected form of the Kelvin equation were used to calculate pore size distributions for hydrophobic mesoporous materials, allowing to correc tly reproduce the total pore volume, average pore size, and surface area de termined using independent calculation procedures. The reference nitrogen a dsorption isotherm on hydrophobic materials is reported in a tabular form. Moreover, the accuracy of the BET specific surface area was discussed. Thus , this study allowed us to develop the methodology for accurate and consist ent characterization of hydrophobic mesoporous materials using nitrogen ads orption.