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The 6th (2006) Yamazaki-Teiichi Prize Winner Material

Environmental Materials Using TiO2 Photocatalyst with Solar Energy

winner Winner
Kazuhito Hashimoto
History
Mar. 1980 Completed Master's Course at Graduate School of Science, The Univ. of Tokyo
Apr. 1980 Technical official w/ the Ministry of Education, Institute for Molecular Science
Sep. 1989 Lecturer at Faculty of Engineering, The Univ. of Tokyo
Nov. 1991 Assistant Professor, Faculty of Engineering, The Univ. of Tokyo
Jun. 1997 Professer, Faculty of Engineering, The Univ. of Tokyo
Jul. 1997 Professor, Research Center for Advanced Science and Technology, The Univ. of Tokyo
Apr. 2004 Director, Professor, Research Center for Advanced Science and Technology
Present

winner Winner
Toshiya Watanabe
History
Mar. 1984 Completed Master's Course at Graduate School of Science and Engineering, Tokyo Institute of Technology
May 1984 Joined TOTO Ltd. Research Laboratory
Oct. 1996 TOTO Ltd , Sub-Manager, Optical Frontier Business Div.
Apr. 1997 TOTO Ltd., Senior Researcher, Research Laboratory
Apr. 2001 Professor, Research Center for Advanced Science & Technology, The Univ. of Tokyo
Present

Reason for award

Full-fledged practical application of photocatalysts began in 1990, when Kazuhito Hashimoto transferred from Institute for Molecular Science to The Fujishima Laboratory of Synthetic Chemistry of Engineering at the University of Tokyo and began joint research with TOTO Ltd. The first discovery was the development of TiO2 thin-film coating technology: with thin films, organic matter on the surface of the thin film could be decomposed even with weak ultraviolet (UV) rays, such as those from fluorescent light (this is known as "photoinduced oxidative decomposition function"). Toshiya Watanabe, who was chief of TOTO Basic Research Laboratory at that time, noticed, while going to the Fujishima Lab, that the photocatalysts were effective for inhibiting bacterial growth and dirt and linked it to the commercialization of antibacterial tiles.

The second result gleaned from the academic-industrial joint research conducted by Messrs. Hashimoto and Watanabe was the establishment of photoinduced hydrophilic function (superhydrophilicity; reported in Nature in 1995 and 1997). With this phenomenon, the surface of TiO2 coatings develops a ready affinity to water through UV light irradiation so that surface water drops spread thinly all over. In addition to the primary function, decomposing dirt, the superhydrophilicity, which is secondary, makes dirt easy to remove; thus, self-cleaning building materials that enabled dirt to be removed by sunlight and rainwater could be perfected. Thereafter, the research progressed so that the application formats for TiO2 photocatalysts could branch out from tiles to sheets, cloth, and coating materials; to soil-resistant, deodorizing, antibacterial and mildew-resistant materials; and to products that incorporate them (toothbrushes, bathtubs, fluorescent lights, etc.). With global market scale exceeding \80 billion in FY 2004, high growth potential approaching 20% annually is visible. Although pure TiO2 catalytic action is limited to the UV region below 380 nanometers (nm), many materials that respond with visible light are emerging, and with further improvements in performance and expanded usage purposes, a market of over ¥1 trillion is expected to be a reality, not a dream.

TiO2 photocatalysts secured a solid position as environmental materials because they could be developed into air-cleanup systems to handle the public hazard of air pollution and pollution from expressways, with their removal of NOx presumed. In addition, their application to the decomposition of volatile organic compounds (VOCs), which induce sick house syndrome, and the decomposition and removal of toxic substances from industrial and agricultural waste water and the like is steadily expanding their use as measures against air pollution and water contamination.

In September 2002, Ministry of Economy, Trade and Industry embarked on a movement to standardize photocatalysts. In January 2004, Volume 1 of the Japanese Industrial Standards (JIS) established "Test method for air purification performance of photocatalytic materials (JIS R 1701-1:2004)." Since then, standards pertaining to test methods for self-cleaning, water-purifying, antibacterial and mildew-resistant functions have been investigated. Additionally, based on Japan's proposal, an agreement on international standardization of test methods for photocatalysts is being worked out through International Standards Organization (ISO). In this way, photocatalysts, as environmental materials, is about to leap forward as one of the advanced technologies, of which Japan can be proud , setting a global standard as technology originating from Japan.

Background of research and development

Titanium oxide photocatalytic reaction is a technology that was developed in Japan based on the water photolysis reaction that is known as the Honda-Fujishima effect (Nature 1972). It has been the focus of widespread research around the world, as a method of capturing solar energy in the 1970s and as a water-processing and air-cleaning method since the 1980s. However, despite the long years of research, in the late 1980s, it was thought that photocatalytic reaction could never be established as practical technology. Because of sunlight's low energy density, photocatalytic reaction using sunlight was deemed inappropriate for capturing energy or processing large quantities of matter.

Achievements

Around 1990, the prizewinners came up with a completely new idea: the photocatalytic reaction of titanium oxide thin-film coatings under weak light. This creative thinking was based on the premise that by focusing the reaction only on the adsorptive materials on the surface of the titanium oxide, a sufficient amount of energy would be produced, even if the density of the photo energy from sunlight or indoor light was low. This, in turn, would enable photocatalytic reaction to become a valid practical technology. Based on this concept, photocatalytic antibacterial tiles, self-cleaning cover glass for tunnel lighting and other developments were achieved. In addition, around the mid 1990s, the prizewinners discovered a new phenomenon (now known as photoinduced hydrophilic effect) in which light irradiation makes it remarkably easy to wet the surface of titanium oxide coating materials. Until that time, the applicable range for the self-cleaning effect obtained with the photocatalytic reaction had been limited by the amount of light. However, combination with the photoinduced hydrophilic effect led to the development of groundbreaking self-cleaning materials with the added function of enabling dirt to be easily rinsed away with water, resulting in an extremely wide applicable range. In addition, water forms a thin film on the surface of hydrophilic materials, but because water drops do not adhere to them, titanium oxide coating materials have come into widespread use as antifogging materials for car rear-view mirrors and the like. They have been highly acclaimed as environmentally sound materials that function only with natural energy, such as light and rainwater, and no chemicals or electricity.

Additionally, since the end of the 1990s, the prizewinners have undertaken highly original research on the development of environmental protection systems using photocatalytic reaction, with the earth and the outer walls of buildings serving as reaction fields. They succeeded in developing materials and systems for environmental cleanup covering a multitude of fields, including purification materials for agricultural waste fluid, purification materials for soil polluted by volatile materials, and materials for saving energy and preventing urban warming. Using solar energy and rainwater only, they are the ideal sustainable environmental remediation technologies for the twenty-first century. Expectations are extremely high that they will link to the creation of genuine environment business.

Meaning of the achievements

The "discovery of the photocatalytic reaction of titanium oxide thin-film coatings under weak light" can also be considered a reversal of the concepts in the research on photochemical reaction that had been done until that time, which had been premised on using a strong light source. In keeping, it provided an entirely new vantage point for the discipline of photochemistry as a whole. Moreover, the discovery of the phenomenon of photoinduced hydrophilicity substantially overturned what had been taken as common knowledge in surface science to that time -- that extremely weak ultraviolet light substantially changes metal oxide surface properties -- to create a new academic field. In addition, this spawned active applied research in the industrial world. At present, the photocatalyst industry is producing results on the order of ¥55 billion domestically and over ¥30 billion overseas.

The discovery of titanium oxide photocatalytic reaction using the earth and the outer walls of buildings as reaction fields has advanced into technology for environmental protection and reform. Through the cooperation of national and municipal governments, universities and the industrial world, development is occurring in the form of a variety of industry-university-government cooperation projects.

Thus, the results have not been limited to academia but are having major impact on the industrial world and the general public, as well, in what can be rightly deemed highly significant ways.

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