Crystallization of anatase from amorphous titania using the hydrothermal technique: Effects of starting material and temperature

The crystallization of anatase from amorphous titania has been controlled u sing the hydrothermal technique. Crystallite size and surface area can be c ontrolled by careful alterations of the hydrothermal conditions. The cataly tic effect of the water on crystallization has been demonstrated, and the c rystallization mechanism has been shown to change from a solid-state type t o dissolution precipitation as the temperature is increased. The influence of the amorphous precursor preparation route has been examined in order to evaluate the effect of contaminant ions on the crystallization process. It has been shown that the chloride ion accelerates the nucleation of the anat ase, even under dry conditions. The effects of acidic and basic solutions h ave been studied. Acidic conditions result in the formation of anatase, bro okite, and rutile, whereas basic conditions accelerate the production of an atase. The mechanisms for the hydrothermal crystallization of anatase and r utile are discussed.