TiO ₂ coating of high surface area silica gel by chemical vapor deposition of TiCl ₄ in a fluidized-bed reactor

TiO ₂ was deposited on high surface area porous silica gel (400 m ²g ^-1) in a fluidized bed reactor. Chemical vapor deposition was employed for the coating under vacuum conditions with TiCl ₄ as precursor. Nitrogen physisorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy were applied to characterize the obtained TiO ₂-SiO ₂ composites with different Ti loadings up to 5 wt%. Only a slight decrease in the specific surface area was detected at low Ti loadings. At a Ti loading of 2 wt%, TiO ₂ was found to be highly dispersed on the SiO ₂ surface likely in form of a thin film. At higher Ti loadings, two weak reflections corresponding to anatase TiO ₂ were observed in the diffraction patterns indicating the presence of crystalline bulk TiO ₂. High resolution XPS clearly distinguished two types of Ti species, i.e., Ti-O-Si at the interface and Ti-O-Ti in bulk TiO ₂. The presence of polymeric TiOx species at low Ti loadings was confirmed by a blue shift in the UV-vis spectra as compared to bulk TiO ₂. All these results point to a strong interaction between the TiO ₂ deposit and the porous SiO ₂ substrate especially at low Ti loadings.