Hybrid organic-inorganic xerogel access to meso- and microporous silica by thermal and chemical treatment

Hybrid xerogels of general formula (O)(1,5)Si-C=C-(CH2)(n)-C=C-Si(O)(1,5) were prepared by sol-gel polycondensation in THF of the corresponding precursors (H3CO)(3)Si-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 degrees 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 degrees C. All the materials were characterized by SAXS, BET, and spectroscopy analysis.