Raman and IR investigation of silica nanoparticles structure

In the present investigation we report experimental data regarding the Raman and Infra-Red (IR) absorption activities of commercial silica nanoparticles. We compared the data of the nanoparticles with the ones acquired in the same experimental conditions for commercial bulk silica. By this comparison we highlighted that the variability of the spectral features of the matrix related Raman and IR bands in the nanoparticles is above the one observed for the bulk systems before any treatments. Furthermore, by studying nanoparticles with different sizes (diameters from 40 to 7 nm) and applying the shell-model we can suggest that the core network of the nanoparticles is close to the one encountered in the bulk materials. By contrast for the surface shell, having a thickness of about 1 nm, as suggested by previous investigations, the structure is strongly modified. In fact, from Raman and IR data it appears that the Si-O-Si angle has a lower main value than those encountered in bulk systems and that the ring statistic is shifted towards lower member rings.