Anatase nanoparticles from hydrated titania gels

The growth of anatase particles during annealing up to 1000 °C of the dried precipitates prepared by neutralization of TiOSO4 aqueous solutions with aqueous ammonia until desired pH value at temperatures 0–80 °C was studied. The crystallinity of the precipitates depends significantly on the precipitation temperature; the precipitates prepared at low temperatures were almost amorphous whereas the higher precipitation temperature leads to more crystalline samples. Heating the sample results in crystallization of the amorphous part and above ∼400–500 °C the sample is fully crystalline. Contemporary with the crystallization of the amorphous part significant decrease of the crystal cell volume was observed in the same temperature region. Above this temperature monotonous changes in crystal lattice constants (growth of the a and decrease of the c parameter) resulting in decrease of the crystal cell size was observed. Growth of anatase nanocrystals and disappearance of surface amorphous layer was observed above 600 °C. All samples were highly photoactive. The fastest 4-chlorophenol decomposition corresponding to highest photocatalytic activity was found at samples annealed at the temperature around 800–850 °C corresponding to the particles ∼70 nm in diameter.