Properties of TiO2 prepared by acid treatment of BaTiO3

TiO3 powders were prepared by acid treatment of BaTiO3 and their properties were investigated. The BaTiO3 powder was subjected to HNO3 in concentrations ranging from 10(-3) to 8 M at 90 degrees C for 0.5-6 h. Dissolution of BaTiO3 and precipitation of TiO2 occurred at acid concentrations of 2-5 M. BaTiO3 dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH4OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (S-BET). With increasing HNO3 concentration, the SBET value increased from 100 to 170 m(2)/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and S-BET values of about 270 m(2)/g (higher than the rutile samples). The photocatalytic activity of these TiO3 was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 degrees C. The photocatalytic activity of the TiO3 was found to depend more strongly on the sample crystallite size than on S-BET. (C) 2006 Elsevier Ltd. All rights reserved.