Technology  >> Photocatalyst  >> Self Cleaning Theory             Self Cleaning Theory                 1) Coated a film of Nano TiO2 on concrete or wall of the buildings     2) When Nano TiO2 is subjected to light exceeding the material's band gap, it will produce electron-hole pairs     3) These electron-hole pairs react with oxygen (O2) and water molecular (H2O) to form super active substances (O2-. ‧OH, H2O2 ).                 4) When pollutants such as nitride compounds and sulfur compounds (Nox, SOX) attach to TiO2 layer, and react with super active substances, the pollutants are oxidized as NO3- & SO4+                 Due to hydrophilic property of Nano TiO2, the pollutants will be easily washed away during rainfall.             5) The objectives coated with a layer of TiO2 have ability to remove pollutants and keep their surface always clean.