Co-Authors:
Polevaya, Y., Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
Samuel, J., Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
Ottolenghi, M., Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
Avnir, D., Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
Abstract:
Nitrogen adsorption at -195°C serves as routine method for the measurement of surface area of porous materials derived by sol-gel procedures. In a systematic study of the simultaneous effect of the pH and water-silane ratio of the starting solutions of preparation of SiO2 xerogels on their surface areas, it was found that conditions of high acidity and low water/silane ratio result in microporous materials, the surface of which cannot be accessed by N2 at -195°C, within a realistic time scale, but only by CO2 at 0°C. In a typical result for TMOS/water/methanol = 1/2/3 at pH=1.0, the apparent N2-area was zero, while the CO2-area was 414 m2/gr. It is recommended to recheck apparent N2-low surface areas of sol-gel materials by CO2 adsorption. The behavior of pyrene-doped xerogels of this type is in agreement with the structural characterization by adsorption. © 1995 Kluwer Academic Publishers.
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