SPECTROSCOPIC, PHOTOCONDUCTIVITY, AND PHOTOCATALYTIC STUDIES OF TIO2 COLLOIDS - NAKED AND WITH THE LATTICE DOPED WITH CR3+, FE3+, AND V5+ CATIONS

Colloidal TiO2 particulates have been prepared using a low-temperature (0-degrees-C) method by controlled hydrolysis of TiCl4; TiO2 particulates doped in the lattice with Cr3+ (0.5, 5, and 10 wt % -relative to weight of TiO2-from aqueous CrCl3), with Fe3+ (10 wt % from aqueous FeCl3) and with V5+ ( 10 wt% from aqueous NH4VO3) were also synthesized by an analogous procedure. These particulates were examined spectroscopically and by photoconductivity measurements to assess the photosensitization of titania (anatase) by incorporated metal dopants. Visible absorption bands in metal-doped particulates parallel those observed for aqueous metal cations at all levels of doping (up to 20 wt %); these bands are not reproduced in the action spectra of photoconductivity vs wavelength, except for the absorption threshold of the TiO2 system in all cases. Their photocatalytic activity was determined by standard photoreduction (of water, H-2 evolution) and photooxidation (of oxalic acid) reactions to assess the influence of metal dopants in heterogeneous photocatalysis.