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

Abstract

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.