A Comparison of Nitrogen Adsorption and Thermogravimetric Methods in the Assessment of the Pore Size Distribution of Mesoporous Silica Gels

The pore dimensions are determined by using adsorption and thermogravimetry methods for unmodified silica gel Si-100 and silanized silica gel Lichrosorb RP-18. Thermal desorption measurements for various liquids were performed under quasi-isothermal conditions. Methanol, acetone, benzene and n-hexane were used as a wetting liquids. Pore size distributions and total pore volumes derived from thermal desorption compare reasonably well with results obtained from the analysis of adsorption isotherms of nitrogen. For different types of adsorbates the effects connected with the presence of the surface liquid film are discussed. The presence of long alkyl chains on the silica surface strongly influences the pore diameter calculated from thermogravimetric data.