The photocatalysis with tio2 describes a chemical reaction, which is accelerated by visible and UV light thanks in part to the average size of the Tio2 nanoparticle crystals of 5 ~ 8 nanometers.
A photocatalyst is a substance that causes this reaction, without getting involved or deteriorating in it. A photocatalyst coating is a coating that contains photocatalysts as ingredients, which can be applied in environments interiors and exteriors .
Titanium dioxide (TiO2) is a semiconductor with an energy band of 3.2eV. When the titanium dioxide (TiO2) of the photocatalyst une2 absorb radiation from sunlight or visible light, produce pairs of electrons and holes. The electron of the valence band of titanium dioxide is excited when it is illuminated by light. The excess energy of this excited electron promoted the electron to the conduction band of titanium dioxide, thus creating the pair of negative (e-) and positive (h +) electrons.
The positive hole of titanium dioxide breaks the water molecule to form hydrogen and a hydroxyl radical. The negative electron reacts with the oxygen molecule to form a super-oxidizing anion. These reaction oxygen species (ROS) damage the structure and disrupt the biochemistry of bacteria and viruses. In the presence of the hydroxyl radical and the molecular oxygen, the organic compounds are finally oxidized to carbon dioxide and water. This cycle is continuous and unlimited when light is available.