Preparation of BaTi4O9 by a sol-gel method and its photocatalytic activity for water decomposition

In the development of photocatalyst materials, barium tetratitanate, BaTi4O9, with a pentagonal-prism tunnel structure was prepared by a sol-gel method and calcined in air at various temperatures from 873 to 1273 K. The changes in the structures were investigated using TG-DTA, X-ray diffraction, Raman and FTIR spectroscopies, and the photoinduced properties were examined by EPR spectroscopy. X-Ray diffraction patterns showed that crystallization occurs by calcination above 973 K. A characteristic Raman peak at 860 cm(-1), assigned to the stretching vibration of short Ti-O bonds, increased in intensity with increasing calcination temperatures. EPR signals with g = 2.018 and g = 2.004 were produced for BaTi4O9 calcined above 1173 K with UV irradiation at 77 K in the presence of oxygen. These signals are associated with an O-.- radical. Calcined BaTi4O9 was combined with RuO2, and its photocatalytic activity for water decomposition increased with increasing calcination temperatures of BaTi4O9. From the findings that the formation of the O-.- species and the photocatalytic activity are the results of high efficiency for the separation of photoexcited charges and are closely associated with crystallization of BaTi4O9, it is proposed that the crystallization develops the pentagonal-prism tunnel structure of BaTi4O9 and enhances the role of the polarization fields present in the TiO6 octahedra which facilitates the separation of photoexcited charges.