Titanium Dioxide Photocatalysis in Atmospheric Chemistry

Titanium dioxide is a relatively inexpensive, nontoxic, and easy to handle material, which is of great interest, as evidenced by the wide number of applications as well as the number of publications that have appeared in the past 20 years. Although anatase is often noted as being the most photoactive polymorph, there are numerous studies showing that rutile has comparable or even greater photoactivities than anatase. When excited with light of wavelength equal to or greater than the band gap energy, there is the generation of electronhole pairs in the conduction and valence bands, respectively. It is noteworthy that, due to the limitation of techniques for aerosol particle characterization, there are few studies that have simultaneously detected the size, composition, and phase of small atmospheric particles. It is generally assumed that metals detected in the aerosols are attributed to their corresponding metal oxides with no or limited knowledge of the exact phase.