Titanium dioxide, also known as titania, is the naturally occurring oxide of titanium, chemical formula TiO2. Approved by the food testing laboratory of the United States Food and Drug Administration (FDA), Titanium Dioxide is considered a safe substance and harmless to human. It is commonly used in paint, printing ink, plastics, paper, synthetic fibers, rubber, condensers, painting colors and crayons, ceramics, electronic components along with food and cosmetics. Many studies have been published on the use of titanium dioxide as a photocatalyst for the decomposition of organic compounds. After illuminated by light, titanium dioxide produces hydroxyl radicals, which react with the organic matters in the air to form non-toxic inorganic matters.
Titanium Dioxide molecules contain electrons that are confined to relatively narrow energy bands. The band of highest energy that contains electrons is the valence band, while the band lying above the valence band, i.e. the conduction band, has very few electrons. The difference in energies between the highest energy of the valence band and the lowest energy of the conduction band is termed the band gap energy. When a semiconductor absorbs a photon of energy equal to or greater than its band gap, an electron may be promoted from the valence band to the conduction band leaving behind an electron vacancy or “hole” in the valence band. If charge separation is maintained, the electron and the hole may migrate to the catalyst surface where they participate in redox reaction with sorbed species.