Can you imagine bathrooms or buildings that clean themselves without external power? Can you imagine a mirror that never becomes fogged? Can you imagine a car window that retains its visibility even when it rains? TOTO Ltd., the leading Japanese manufacturer of sanitary equipment, has developed a product that has made these imaginations real with "photocatalysts", a new technology developed in Japan.
A photocatalyst is a substance that uses light energy to facilitate a chemical reaction. Since its property was discovered in 1968, titanium dioxide (TiO2) has been the primary photocatalyst used in various applications in industry. When
exposed to enough ultraviolet light, it can utilize the energy to decompose water molecules into hydroxide and oxygen radicals, or organic compounds into water and carbon dioxide. This can be thought of as the reverse process of
photosynthesis, where chlorophyll uses visible light energy to combine water and carbon dioxide into a simple sugar.
Titanium dioxide is a naturally occurring oxide of titanium, and is approved by the U.S. Food and Drug Administration (FDA) as harmless to humans. In most forms, titanium dioxide is not reactive in normally occurring ambient light, so it is commonly used as an opacifier, thickener or white pigment in industrial materials, electronic components, cosmetics and even foods.
Because the activated photocatalyst can break down organic compounds, it is often added to paints and coating materials as a sterilizer and deodorizer. When used on windows and other building surfaces, it prevents build-up of mould and dirt, and breaks down harmful organic chemicals such as formaldehyde. It also effectively breaks down nitrogen oxides and sulfur oxides.
Photocatalyst coating technology has made possible building materials with advanced properties; that is, sterilization, deodorization, and anti-fouling. TOTO has been collaborating with Dr Akira Fujishima, Professor Emeritus of
the University of Tokyo and Chairman of the Kanagawa Academy of Science and Technology. Dr Fujishima was one of the original members in photocatalyst research, and with his help, TOTO has identified a novel phenomenon: when the
surface of photocatalytic film is exposed to light, the contact angle of the photocatalyst surface with water is gradually reduced. After enough exposure, the surface reaches super-hydrophilicity. In other words, it ceases to repel
water, so that the water spreads flat on the surface of the photocatalyst rather than forming a drop. This photocatalytic superhydrophilicity technology has wide applications, such as anti-fogging and self-cleaning properties, in addition to
the photocatalyst technology already known.
Anti-fogging glass. Generally, when moist air comes in contact with glass, small droplets of water are formed and the glass becomes fogged. On titanium dioxide coated glass, the water forms a continuous flat sheet, so that there is no fogging.
<Self-cleaning by rainfall>
It is very difficult to remove oil from resins with just water. With the super-hydrophilic coating, however, oil can be removed easily from the surface, because the surface has so
much more affinity to water than oil. Oil on the super-hydrophilic surface is easily removed by soaking the
material in water. Titanium dioxide can be coated on many building materials and the resulting film exhibits a self-cleaning effect due to the strong oxidizing properties.
Rainwater spreads uniformly over the tile surface and lifts away grime, for self-cleaning functionality. Over time, it saves on cleaning and maintenance costs, and maintains the appearance of buildings with no work at all.
<Anti-fogging property>
Regular mirrors and glass fog easily when cold, because moisture in the air condenses on its surface and numerous water drops form. With
the super-hydrophilic coating, though, the water cannot exist in the shape of a drop, but spreads flat on the super-hydrophilic surface.
The super-hydrophilicity coating makes water droplets on the mirror and window form into a continuous flat sheet, and this gives
the driver a clear view when it rains.
Treating mirrors with the super-hydrophilicity coating prevents water droplets from forming on the surface resulting in a safer driving experience.
<Other applications>
The hydroxyl radicals produced by the photocatalyst kill bacteria, and odor-causing organic compounds
are broken down. The superhydrophilicity makes it hard for grime and mould to stay on surfaces treated with titanium
dioxide coating, so bathrooms virtually clean themselves. The mirrors won¡Çt fog up, either!
Washroom treated with the super-hyprophilicity coating repel bacteria and grime.
<Cool buildings>
When buildings are coated with photocatalysts and wetted to create a thin film o y heat off the buildings
and effectively cool them down. This may help keep our cities cooler during the hot season.
Ryuji Matsubara of TOTO's Public Relations Department says that TOTO expects the photocatalyst technology
business to expand in the worldwide market. Besides its own products, TOTO is actively promoting patent licensing to
many companies in the world. By 2005, TOTO had registered four basic patents and eighty application patents in Japan
and overseas. According to a study by the Photocatalytic Products Forum, the exterior and interior construction materials sectors are the largest markets for photocatalytic products.
In future, development of the photocatalytic technology will further respond to society's needs: environmental protection,
enhanced aesthetic value, and longer life span for buildings. The most remarkable contribution for our future will be that the decomposition properties of photocatalytic surfaces cleans the air of nitrogen oxides and sulfur oxides. As
photocatalysis is an environmentally friendly "natural" technology that uses solar energy, its use is expected to
expand in the future.
Company Profile :
Main Office 2-1-1 Nakashima, Kokurakuta-ku Kitakyusyu-shi, Fukuoka JAPAN 802-8616
802-8616