Hybrid Organic−Inorganic Xerogel Access to Meso- and Microporous Silica by Thermal and Chemical Treatment

Hybrid xerogels of general formula (O)1,5Si−C⋮C−(CH2) n −C⋮C−Si(O)1,5 were prepared by sol−gel polycondensation in THF of the corresponding precursors (H3CO)3Si−C⋮C−(CH2) n −C⋮C−Si(OCH3)3, without catalyst. Treatment of the hybrid xerogels was with methanol and water in the presence of 2.0% of ammonium fluoride as catalyst. For 2 < n < 4, elimination of the organic spacer was quantitatively achieved and the organic spacer was recovered in high yield. For n = 5, 6, and 8, increasing the length of the spacer results in a decreasing efficiency of this chemical treatment. Thermal oxidation at 600−680 °C of the hybrid xerogels was also performed and elimination of the organic spacer was obtained in all the cases. Mesoporous silica with a narrow pore-size distribution was obtained by chemical treatment of the xerogel with n = 2−4. Microporous silica was obtained by thermal treatment of the xerogel at 680 °C. All the materials were characterized by SAXS, BET, and spectroscopy analysis.