Characterization of the porosity and surface chemistry of mesoporous silicas by quasi-equilibrated thermodesorption of 1-butanol and n-nonane

Mesoporous silicas MCM-41 and SBA-15 were studied using the quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA) of n-nonane and 1-butanol. The QE-TPDA profiles of n-nonane containing one desorption maximum were typical for the mesoporous materials. The pore size distributions from the thermodesorption data were similar to those calculated from N2 adsorption isotherms. The QE-TPDA profiles of 1-butanol exhibited low temperature maxima (below 70 °C) resulting from desorption of the adsorbate filling the mesopores and high temperature maxima (at ca. 100 °C) attributed to desorption of the molecules specifically adsorbed on the hydrogen-bonded silanols. These findings were confirmed by IR measurements. Hydrothermal treatment of MCM-41 resulted in increase of the H-bonded silanol concentration, while for SBA-15 an inverse effect was observed.