Infrared spectroscopy as a tool for textural and structural characterization of individual and complex fumed oxides

The effects of nanoparticles size and surface content of pure silica and in complex fumed metal and metalloid oxides (FMO) on the infrared (IR) spectra in the range of Si-O-Si asymmetric stretching vibrations, were analyzed. Correlation functions were obtained linking the integral intensity of a band at νSiOSi ≈ 1200 cm−1 (w2, attributed to the surface of silica); or the ratio w2/w1 (w1 corresponds to contribution at νSiOSi ≈ 1100 cm−1 attributed to bulk transverse optical (TO) modes) with the average diameter (d) of silica nanoparticles determined from the specific surface area from nitrogen adsorption isotherms. The results of the IR spectral analyses were compared to Auger electron spectroscopy (AES) results with respect to surface content of silica in complex FMO. The nanoparticulate morphology of FMO analyzed using TEM and SEM images show a relatively broad size distribution of nanoparticles, including core-shell nanoparticles, that can affect the νSiOSi band intensity and position linked to structural features of the silica phase. Thus, the use of the correlation w2(d) or w2/w1(d) functions give appropriate results for the textural characteristics of fumed silicas and the surface content of silica in complex FMO, compared with nitrogen adsorption and AES data, respectively.