Highly selective photocatalytic reduction of NO2 in air to NO using Cu2+-loaded TiO2 thin films

We have discovered that Cu2+-loaded TiO2 films (1.5 μm thick) exhibit a high activity of selective reduction of NO2 to NO in air under UV light illumination (1 mW cm−2). This effect is associated with a reduced NO oxidation to HNO3. For an increasing amount of Cu2+ ions the NO reductions become more stable. Cu2+ ions are responsible for the high redox property, playing an important role in adsorption of NO2/NO2−, electron transfer from the TiO2 to NO2/NO2−, and recombination center for positive holes.