Micro-Raman Spectroscopy of Fresh and Aged Silica Gels

Abstract

ABSTRACTRaman spectra were obtained from fresh and aged silica gels using micro-Raman techniques. Comparison of the spectra from wet and dried gels reveals the stages of reaction in the ethanol-TEOS-water system and the gradual development of the silica structure. The steady disappearance of bands assigned to ethanol and the appearance of bands assigned to silatious species can be traced during the drying process. Increases in either acid concentration or water level increase reaction rates to give gels in a more advanced stage of polymerization. Gels tend to develop fluorescence upon aging for several months. The source of this fluorescent could not be determined, but it's development can be prevented by heating freshly dried gels to about 155°C.