Ozone Formation from Illuminated Titanium Dioxide Surfaces

Abstract

The nitrogen oxides (NO(x)) decomposition on illuminated TiO(2) surfaces has been widely studied, but little is known about the subsequent formation of non-nitrogen containing products. In this study, TiO(2) coated glass surfaces and TiO(2) films with nitrate anions (either premixed with TiO(2) as KNO(3) or deposited from gaseous NO(x)) are irradiated with broad-band light. Upon irradiation, detected gas phase products include NO(2), HNO(2), and O(3). To the best of our knowledge, this is the first study that reveals the production of O(3) from TiO(2) surfaces. By surface charge transfer reactions, nitrate anions are oxidized into nitrate radicals and their photochemistry (almost in the visible) leads to O(3) formation, enhancing the oxidizing power of these surfaces.

A surface science perspective on TiO2 photocatalysis

“…Papers are emerging in the field which have examined specialized synthetic processes using TiO 2 as a photocatalyst. Examples include selective formation of certain biomolecules [1815][1816][1817], carbemide formation [1818], Cl 2 production [1819], cross-linking in fibers [1820,1821], epoxidation and selective oxidation reactions [926,929,1021,1598,[1822][1823][1824][1825][1826][1827], ozone formation [1828], hydrogen peroxide production [1486,1829,1830], selective isomerization reactions [986], nitro group addition [1831,1832], polymerization processes [1833][1834][1835][1836], urea formation [1837,1838] and a variety of other miscellaneous processes [925,1368,[1839][1840][1841][1842][1843][1844][1845][1846]. The photooxidation of alkenes to generate epoxides has been explored in the cases of several molecules, including 1-hexene [1823], 1-decene: [1823,1...…”

The Environmental Photochemistry of Oxide Surfaces and the Nature of Frozen Salt Solutions: A New in Situ XPS Approach

“…For instance, TiO 2 is a component of natural mineral dust that represents an important reactive aerosol in the atmosphere affecting the ozone budget and the climate [36]. In this context, adsorption of water and hydroxylation of the surface, which are key aspects to understand TiO 2 photocatalysis in the environment, offer still major open questions.…”

On the underlying mechanisms of the low observed nitrate selectivity in photocatalytic NOxabatement and the importance of the oxygen reduction reaction

“…9 It can be seen that the activity of the sample is quite good, almost half of the supplied NO is converted (γ ≈ 4.4 × 10 −5 ), however, the main product of the reaction is not the desired nitrate but NO 2 (or HONO as the employed analyzer cannot distinguish between the two). [10][11][12] At the beginning of the experiment, the selectivity is already poor at approximately 32 %, followed by a sharp drop to about 23 % in the first hour of illumination with a continued less steep but steady decline afterwards. The absolute activity of NO conversion also decreases with time, while the NO 2 formation seems to be less affected by this with a barely noticeable smaller decline, resulting in the lower selectivity.…”