Raman spectroscopic investigations on the kinetics of gelation and densification of Cd2+- and Pb2+-doped silica glasses under basic conditions

In the present work, the evolution of the gelation of undoped and Cd2+-and Pb2+-doped silica sols has been studied. Tetramethyl orthosilicate and cadmium and lead nitrates were selected as suitable precursors for the synthesis of nanoporous undoped and doped silica systems. Raman spectroscopy was used both to follow the different species formed and the structural changes occurring at various stages of the sol–gel transformation. The combination of information obtained from Raman spectra and from textural measurements using nitrogen adsorption–desorption served to investigate the effects of doping metal ion on the structure of both the gels and on the resulting nanoporous silica glasses. Results showed that doping silica materials with different concentrations of Cd2+ or Pb2+ makes it possible both to decrease the densification time and to control the porosity of the resulting gels and glasses.