Photoassisted Dinitrogen Fixation on TiO₂ (Rutile) Surfaces

Abstract

The ability of TiO₂ (rutile) surfaces which contain pre-adsorbed peroxide to fix molecular nitrogen oxidatively, has been reported previously by Bickley et al. (1). In a recent work (2) we have shown that oxygen photoadsorption on hydroxylated surfaces of TiO₂ occurs with the formation of adsorbed H₂O at temperature below ∼323 K. Above this temperature, adsorbed H₂O₂ molecules are thermally unstable, but the photoadsorption of O₂ continues albeit by an alternative mechanism. Some of the oxidising species which are produced are sufficiently reactive to be able to fix dinitrogen, which is released during temperature programmed desorption as NO(g) and N₂(g); NH₃(g) being undetected. These results, demonstrated the possibility of a photochemical process for photo-oxidative dinitrogen fixation on TiO₂ and materials related which could occur spontaneously in nature. The identity of the surface nitrogen species remains unclear. Independent XPS information gives a N(1s) signal from the surfaces species at a binding energy of 399.5 eV, this being consistent with the likely presence of a species such as NO⁻(ads) or N₂O ⁼₂ (ads).