Surface structure and chemistry of high surface area silica gels

Combined Raman and ²⁹Si NMR investigations of high surface area silica gels indicate that dehydroxylation of the a-SiO₂ surface results preferentially in the formation of cyclic trisiloxanes (3-membered rings). Estimates of the maximum experimentally observed concentration of 3-membered rings correspond to a surface coverage of about 28–58%. Two consequences of 3-membered rings on the a-SiO₂ surface are enhanced hydrolysis rates and increased skeletal densities.