The effects of trace elements on the crystal properties of TiO2

The effects of trace element doping of TiO2 on the crystal growth and on the anatase-to-rutile phase transformation of TiO2 were investigated. The co-precipitation process, from sulfate solution, of doped (Cr, Fe, V, Nb, Si, P) TiO2 was also studied. The heating temperatures were 473, 673, 873, 993, 1133 K and a higher temperature needed to achieve a rutile content of 98-99%. Traces of reduced titanium were found in freshly calcined anatase by X-ray diffraction. Pure anatase structure was found in 85% of the samples heated below 1000 K. Anatase-to-rutile transformation was accelerated by the mmol% content of Nb, Cr, Si, and Fe in TiO2. Interaction of co-precipitated or impregnated cations was found critical in the phase transformation process. Nb retarded the crystal growth during calcination. Sulfate ions minimized the specific surface area of TiO2 heated at low temperatures. These results of doped TiO2 serve to promote the development of new high-technology TiO2 products for photocatalytic purposes. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.