Comparison of molecular orbital calculations with spectroscopy on sol-gel silica-titania glass

摘要

Using Intermediate Neglect of Differential Overlap (INDO) Molecular Orbital (MO) calculations, a four membered tetrahedral ring was modelled. Using a pure cyclotetrasiloxane cluster at a base line, one titanium atom was substituted for one silicon atom in the ring structure. The resulting model cluster of silica doped with titanium shows an increase in the bond lengths and an increase in the Ti-O-Ti angle. These computational results compare favorably with experimental studies that indicate a weaker bond for Ti-O over Si-O. Spectroscopically, sol-gel silica doped with titania shows a shift in the Fourier transform infrared (FTIR) peaks that correspond to these lengthened bonds. Shifts in the ultraviolet cutoff also compares favorably with the models. Finally, the structural density of the titania doped sol-gel silica is compared to acid catalyzed sol-gel silica as the processing temperature is increased. The observed differences between pure and titania doped sol-gel silica compare well with the results from the INDO MO model.