Morphology of titania coatings on silica gel

Abstract

Control of the hydrolysis and condensation of soluble precursors of titanium is shown to yield oxide coatings of well-defined morphology. A ``smooth'' coating, consisting of patches of titania on silica, causes only a small increase in the surface area, from 130 m2/g for the uncoated silica gel to 154 m2/g. On the other hand, the ``rough'' coating, which consists of 3 nm diameter titania particles dispersed over the silica surface, results in an increase in the BET surface area to 350 m2/g. The specific titania surface area was determined via isopropanol dehydration activity and was found to be comparable to the BET surface area indicating that the titania phase is responsible for the increase in surface area. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) provide definitive evidence for the coating morphology while X-ray photoelectron spectroscopy (XPS) was used to determine the dispersion of the titania. The supported titania maintains its surface area upon calcination at temperatures up to 873 K while unsupported titania looses much of its surface area. Also demonstrated in this work is a novel preparation method using titanium bis-ammonium lactato dihydroxide (TALH), a water soluble precursor.