Structural studies of gel phases. Part 1.—Infrared spectroscopic study of silica monoliths; the effect of thermal history on structure

Abstract

Fourier-transform mid-infrared (FTIR) and near-infrared (NIR) spectroscopies have been used to investigate the effects of thermal history on the bulk and surface structure of monolithic silica gels and glasses prepared by the sol–gel route. Effective dehydroxylation occurs above 700 °C with consolidation of the bulk structure leaving some residual silanol groups and water molecules within glasses treated above 1000 °C. Above this temperature, both functionalities are perturbed by the silica matrix and do not undergo rehydration. New assignments of bands in the first and second overtone regions have been made and used to assess silanol levels and functionality (first overtone region) and water levels (second overtone region).