Nanostructured titanium oxynitride porous thin films as efficient visible-active photocatalysts

Nanocrystalline mesoporous N-doped titania films have been prepared for the first time. The introduction of nitrogen into the anatase structure starts at 500 degrees C, with N bonding to titanium via oxygen substitution. Increasing the treatment temperature leads to the formation of TiN (TiN1-xOx) and N-doped rutile showing mixed-valence Ti states. Microstructural characterization shows that the ordered mesoporosity is maintained until 700 degrees C, where TiN (TiN1-xOx) begins to form. Optical characterization shows that the discrete introduction of N is able to shift the titania absorption edge. The photocatalytic tests give the best results under visible light excitation for the film nitrided at 500 degrees C. At this temperature the concentration of nitrogen in the structure is optimal since oxygen vacancies are still not important enough to promote the recombination of the photogenerated electrons and holes.