Ozone Formation from Illuminated Titanium Dioxide Surfaces

The nitrogen oxides (NOx) decomposition on illuminated TiO2 surfaces has been widely studied, but little is known about the subsequent formation of non-nitrogen containing products. In this study, TiO2 coated glass surfaces and TiO2 films with nitrate anions (either premixed with TiO2 as KNO3 or deposited from gaseous NOx) are irradiated with broad-band light. Upon irradiation, detected gas phase products include NO2, HNO2, and O3. To the best of our knowledge, this is the first study that reveals the production of O3 from TiO2 surfaces. By surface charge transfer reactions, nitrate anions are oxidized into nitrate radicals and their photochemistry (almost in the visible) leads to O3 formation, enhancing the oxidizing power of these surfaces.