The Influence of the Addition of Urea in the Precipitation of Hydrous Titanium(IV) Oxide on Its Crystal Structure and Pore Structure

Abstract

The effect of added urea on the crystal structure and pore structure of hydrous titanium(W)oxide (HTiO) was investigated by X-ray diffractometry, electronmicroscopic observation, and N 2 adsorption desorption at -196°C. HTiO was prepared by the thermal hydrolysis from titanium( IV) chloride solution with or without urea. The rate of the precipitation of HTiO was not affected by the addition of urea. The precipitation rate was extremely high compared with the decomposition rate of urea. In the absence of urea, the precipitates obtained after an hour heating at 80°C was a mixture of rutile and anatase type, and had mesopores around 4 nm radius. The anatase type HTiO was gradually converted into rutile and the mesopores disappeared by the subsequent heating at 80°C. In the presence of urea, anatase type HTiO with mesopores around 4 nm radius was obtained by an hour heating at 80°C. Both the crystal structure and pore volume scarcely changed by the subsequent heating for 6 hours at 80°C. When titanium(IV) chloride was hydrolyzed at high temperatures, HTiO with large crystallite size and pore volume was obtained. The influence of the hydrolysis temperature on the crystal structure and po re structure was not so remarkable in the presence of urea as in the absence of urea.