Preparation and characterization of anatase powders

Anatase powders have been prepared by precipitation and by sol-gel methods. In the former, titania was continuously precipitated at 25 degrees C, pH 1.97 in a stirred reactor by mixing TiOSO4 and potassium hydroxide so as to keep solution supersaturation constant throughout the precipitation process. The preparations were performed in the absence and in the presence of Li+, Nb5+ and W6+ ions. In all cases anatase was the sole phase forming. The presence of these metal ions (1-7 x 10(-5) M) did not influence the precipitation kinetics, which was controlled by surface integration. XPS analysis showed that the dopant ions were incorporated into the anatase lattice for the preparations in supersaturated solutions. Microelectrophoresis experiments did not show any differentiation of the electric charge of the preparations in the presence and in the absence of these ions. The relatively high specific surface area (SSA) of the anatase obtained (135 m(3) g(-1)) increased (up to 250 m(2) g(-1)) by the incorporation of the dopant ions. In the sol-gel preparations the process was found to depend on the supersaturation of the sol with respect to the solid phase forming. A threshold sol composition corresponding to a total titanium concentration of C-Ti = 0.06 M (25 degrees C, pH = 2.5-3.0) was found to be critical for the formation of the gel. Anatase was exclusively formed both in the absence and in the presence of dopant ions in the gel. The SSA obtained was low although it increased in the presence of dopant metal ions. Electrokinetic measurements of the solids formed by the sol-gel method, suggested that the dopant ions tend to accumulate on the surface of the anatase particles.