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Hiaz.TitaniumDioxider1.1 - 05 Jul 2005 - 13:17 - TWikiGuesttopic end

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Titanium dioxide

Titanium dioxide is a white powder, something we eat and see frequently as a whitener for paint, processed food, toothpaste, and many other products. However, it turns out that TiO2 is also a strong photocatalyst--so when it's in the sun, organic compounds (e.g. dirt, mold, mildew, bacteria) that touch it break down, without consuming the TiO2 because it's just a catalyst in the reactions. Also, it's extremely hydrophilic, so water hitting it forms a smooth sheet instead of tiny droplets, and that sheet gets under dirt to lift it off the surface and get it easily washed away. The combination of these effects makes TiO2 self-cleaning to a large extent, and it can be applied in microscopically thin coatings to building materials, glass, or even fabrics. As Nature reports, scientists in Hong Kong are developing dirt-resistant clothing with it, and a Japanese company named Toto already has ceramic tiles on the market using it. As the National Institute of Health's Environmental Health Perspectives reports,

...self-cleaning ceramic tiles...achieve a 99.9% bacterial kill rate within one hour for such strains as penicillin-resistant Staphylococcus aureus and Escherichia coli.

Japan's Mitsubishi Materials Corporation has developed a paving stone it calls "Noxer" that uses the catalytic properties of TiO2 to remove nitrogen oxide (NOx) from the air, breaking it down into more environmentally benign substances...[namely] nitric acid ions. These ions can then be washed away by rainfall or neutralized by the alkaline composition of the concrete. Results of these tests showed an 80% NOx removal rate based on an intensity of UV light of 1-12 watts per square meter (W/m2) (the UV intensity of direct sunlight in summer is 20-30 W/m2, compared to 1 W/m2 on a cloudy winter day).

...Other experiments with TiO2 involve removing the ripening hormone ethylene from areas where perishable fruits, vegetables, and cut flowers are stored; stripping organic pollutants such as trichloroethylene and methyl-tert-butyl ether from water; and degrading toxins produced by blue-green algae. It remains to be seen, however, whether the formation of undesirable intermediate products during these processes outweighs the benefits offered by TiO2's photocatalytic properties.


-- HiazHhzz - 23 Jun 2004
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