This document aims provide a detailed explanation of the chemical science behind the self cleaning and pollution converting properties of TiO2 nanocoatings.
What's So Special about TiO2?
TiO2, (Titanium Dioxide) is a chemical made up from one titanium atom and two oxygen atoms, it is used as a white pigment in many products such as paint, paper, inks and cosmetics. At first you might think that this is a pretty mundane chemical, but the interesting thing is that when TiO2 in anatase form is ground to nano-sized particles (increasing the it's surface area) the photocatalytic properties are increased dramatically, and hence it's ability to convert unwanted chemicals is increased.
Breaking Down Unwanted Chemicals
The self cleaning and pollution reducing properties of a TiO2 coating arise from its ability to break down unwanted chemicals such as algae and fungi (self-cleaning) or noxious gases such as nitrogen dioxide and benzene.
Firstly ozone and water react with the aid of light to produce oxyhydride (OH) free radicals. Subsequent reactions then occur between these free radicals and our unwanted pollutants, oxidising them to harmless chemicals which are then washed away by rainwater, or released into the air (see diagram).
As you can see from the diagram TiO2 just catalyses the reaction and therefore does not get 'used up' in the reactions - so the effects don't reduce with age!
