Some perovskite structured catalysts have narrower forbidden band widths than pure TiO_2,and they have been widely used in a number of photo-catalytic reactions.The ions in the perovskite may be replaced by other ions while maintaining the structure unchanged for its tailorable character.Bi—Ti—O can form into the typical perovskite composite oxide BiTiO_3under specific preparation conditions.The regulation of the energy gap of the perovskite BaTiO_3can be realized by substituting Bi for Ba to form the Bi_xB...