Spectroscopic studies are very important to characterize the structure of amorphous mesoporous silica. In this study, mesoporous silica was obtained by hydrolytic polycondensation of octahydridooctasilsesquioxane and tetraethoxysilane. Infrared spectra of the reaction products and commercially available different forms of amorphous silica were measured. Spectra were analyzed directly and after the decomposition process using a band fitting procedure. In a hydrolytic polycondensation process both, alkoxy groups in tetraethoxysilane and hydrogen atoms in octahydridooctasilsesquioxane are transformed to reactive SiOH groups which can subsequently condense forming SiOSi bridges. However, as evidenced, not all SiOH groups react. The main bands in the spectra of the obtained xerogels are due to the vibrations of SiO 4 group: ν as SiOSi, ν s SiOSi and δOSiO. The bands due to SiH and SiOH vibrations are also observed.
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