Editing Titanium dioxide (section)

====Hydroxyl radical formation====
Although nanosized anatase TiO<sub>2</sub> does not absorb visible light, it does strongly absorb [[ultraviolet]] (UV) radiation (''hv''), leading to the formation of hydroxyl radicals.<ref name=":1">{{cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last1=Jones|first1=Tony|last2=Egerton|first2=Terry A.|date=2000|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-23896-6|language=en|chapter=Titanium Compounds, Inorganic|doi=10.1002/0471238961.0914151805070518.a01.pub3}}</ref> This occurs when photo-induced valence bond holes (h<sup>+</sup><sub>vb</sub>) are trapped at the surface of TiO<sub>2</sub> leading to the formation of trapped holes (h<sup>+</sup><sub>tr</sub>) that cannot oxidize water.<ref name=":8">{{cite journal |last1=Hirakawa|first1=Tsutomu|last2=Nosaka|first2=Yoshio|date=23 January 2002|title=Properties of O2•-and OH• formed in TiO<sub>2</sub> aqueous suspensions by photocatalytic reaction and the influence of H2O2 and some ions|journal=Langmuir|volume=18|issue=8|pages=3247–3254|doi=10.1021/la015685a}}</ref>

: TiO<sub>2</sub> + ''hv'' → e<sup>&minus;</sup> + h<sup>+</sup><sub>vb</sub>
: h<sup>+</sup><sub>vb</sub> → h<sup>+</sup><sub>tr</sub>
: O<sub>2</sub> + e<sup>&minus;</sup> → O<sub>2</sub><sup>•&minus;</sup>
: O<sub>2</sub><sup>•&minus;</sup> + O<sub>2</sub><sup>•&minus;</sup>+ 2{{H+}} → H<sub>2</sub>O<sub>2</sub> + O<sub>2</sub>
: O<sub>2</sub><sup>•&minus;</sup> + h<sup>+</sup><sub>vb</sub> → O<sub>2</sub>
: O<sub>2</sub><sup>•&minus;</sup> + h<sup>+</sup><sub>tr</sub> → O<sub>2</sub>
: {{OH-}} + h<sup>+</sup><sub>vb</sub> → HO•
: e<sup>&minus;</sup> + h<sup>+</sup><sub>tr</sub> → recombination
: Note: Wavelength (λ)= 387 nm<ref name=":8"/> This reaction has been found to mineralize and decompose undesirable compounds in the environment, specifically the air and in wastewater.<ref name=":8"/>

[[File:TiO2crystals.JPG|thumb|Synthetic single crystals of TiO<sub>2</sub>, c. 2–3 mm in size, cut from a larger plate]]