Nitrogen Incorporation in TiO₂: Does It Make a Visible Light Photo-Active Material?

The possibility of hydrogen production by photo-catalytic decomposition of water on titania has provided the incentive for intense research. Titania is the preferred semiconductor for this process, in spite of its large band gap (~3.2 eV) that restricts its utility only in the UV region. Various sensitization methodologies have been adopted to make titania to be active in the visible region. Doping of TiO 2 with nitrogen is one such method. The purpose of this presentation is to examine the state and location of nitrogen introduced in TiO 2 lattice and how far the shift of optical response to visible radiation can be beneficial for the observed photo-catalysis. The specific aspects that are discussed in this article are: (i) N-doped titania surface adopts a non-native configuration, though the bulk material is still in the native configuration of pure TiO 2 (ii) Though the nitrogen doped materials showed optical response in the visible region, the changes/improvements in photo-catalytic activity are only marginal in most of the cases. (iii) The exact chemical nature/state of the introduced nitrogen, and its location in titania lattice, substitutional and/or interstitial, is still unclear (iv) Is there a limit to the incorporation of nitrogen in the lattice of TiO 2 ?