An anatase type of TiO 2 photocatalyst containing N atoms was synthesized by a new technique using a complex of Ti 41 with a nitrogen-containing ligand as a precursor. The TiO 2 -like photocatalyst prepared by calcination of a Ti 41 -bipyridine complex exhibited high photocatalytic activity for NO x removal under both ultraviolet and visible-light (l v 645 nm) illumination. The doping of the N atom into the anatase lattice, which is expected from UV-VIS spectroscopy, XRD, and XPS, is inferred as an important factor for the visible light absorption and NO x removal activity under a wide range of visible light illumination. The bipyridine ligand acted as the source of N and C atoms and additionally inhibited sintering of the photocatalyst during heat treatment.

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A deactivating behavior of TiO2 photocatalysts in NO2 oxidation to HNO3 was studied with use of TiO2 nanoparticulate thin films (0.5−1.5 μm thick) under UV light illumination over 10 h. The photocatalytic activity was decreased with accumulation of HNO3 on the TiO2 surface. For thicker TiO2 films, the deactivation rate was found to be slower. The amount of HNO3 trapped on the TiO2 surface was increased and finally saturated, at which the largest amount of HNO3 was proportional to the thickness of the film. On the basis of the results, we concluded that the produced HNO3, inhibiting the reaction as a physical barrier, must be able to diffuse on the TiO2 surface at a rate of at least more than 1.5 μm h−1, and finally distributes homogeneously on the whole film. The maximum density of HNO3 accumulated on the TiO2 surface was estimated to be ∼2 molecules nm−2 under standard conditions. Finally, when the steady state is reached, the photocatalytic activity remained ∼8% of the initial one.

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