Success in Development of Novel Photocatalyst with High Activity in Visible Light

2008.07.10

National Institute for Materials Science

the development of novel photocatalytic materials, the Photocatalytic Materials Center of the National Institute for Materials Science succeeded in the development of a stable solid solution photocatalyst (Ag0.75Sr0.25) (Nb0.75Ti0.25)O3 which displays high performance in the decomposition of organic pollutants under irradiation with visible light by applying a method of synthesizing a solid solution of different compound oxides.

Abstract

  1. In the development of novel photocatalytic materials, the Photocatalytic Materials Center (Managing Director: Jinhua Ye) of the National Institute for Materials Science (President: Teruo Kishi) succeeded in the development of a stable solid solution photocatalyst (Ag0.75Sr0.25) (Nb0.75Ti0.25)O3 which displays high performance in the decomposition of organic pollutants under irradiation with visible light by applying a method of synthesizing a solid solution of different compound oxides.
  2. Elimination of air and water pollutants, decomposition of harmful chemical substances, and solution of other similar environmental problems are indispensable to the creation of a sustainable society. As an environmental protection technology, the photocatalytic reaction, which occurs at normal temperature using only the energy of sunlight, places minimal new loads on the environment, and thus has attracted intense interest as a key to solving this type of environmental problem. TiO2 has been extensively researched as a photocatalyst, but the photocatalytic reaction involving this substance occurs only in ultraviolet light, which comprises about 4% of sunlight. Therefore, for effective use of photocatalytic technology, it is considered necessary to develop a photocatalytic material with high visible light activity, which can effectively utilize the visible light that makes up roughly 43% of sunlight, and construct a system for its use.
  3. In the present work, two perovskite-type oxides, SrTiO3 and AgNbO3, were selected as the starting materials, referring to theoretical calculations, and material development was carried out by an oxide solid solution synthesis method. One of the starting materials, SrTiO3, has a large bandgap and strong oxidation-reduction power, but does not display visible light activity. On the other hand, AgNbO3 has a small bandgap and possesses visible light responsiveness, but the potential of its valence band and conduction band does not have adequate redox power and its visible light activity is weak. According to a theoretical prediction, in a solid solution, the two substances were expected to compensate for these mutual weaknesses. Specifically, simultaneously with optimization of the bandgap for visible light absorption, appropriate redox power was predicted in both the valence band and the conduction band.
  4. Based on these development guidelines, an (Ag0.75Sr0.25) (Nb0.75Ti0.25)O3 photocatalyst was actually synthesized and used in an acetaldehyde decomposition experiment under visible light irradiation. In comparison with nitrogen-doped TiO2, which has been applied practically as a visible light responsive photocatalyst, the newly-developed photocatalyst showed excellent performance, displaying more than 3 times higher quantum efficiency (approximately 1.5% when measured with 440nm visible light), in spite of the fact that its specific area is smaller than several tenth of TiO2. Thus, the developed substance is considered a extremely promising photocatalyst for environmental purification, even under indoor lighting.
  5. Filing of a patent application for the results of this research as a substance basic patent has already been completed (title of patent: Visible light responsive photocatalyst, application number: 2006-177194, filing date: June 27, 2006). Detailed presentations, including further development after the patent application, are scheduled for the NIMS Conference 2008 (Epochal Tsukuba) to be held July 14-16, 2008 and the 8th Workshop on Photocatalysis Research (University of Tokyo, Research Center for Advanced Science and Technology) on July 16.