Photoassisted Dinitrogen Fixation on TiO2 (Rutile) Surfaces
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).