A novel oxynitride photocatalyst system for water splitting : La2Zn1-xTi1+x(O,N)6
Résumé
The use of solar energy is of highest interest from a low environmental impact viewpoint, and nowadays the photocatalytic splitting of water under solar radiations is a challenging and promising domain of research to provide clean and renewable H2 as an alternative energy resource [1]. Current oxide photocatalysts (TiO2 , ZnO, SrTiO3 , NaTaO3 ...) are wide-gap semiconductors for which UV-light is necessary to produce electron-hole pairs by
photoexcitation. Therefore, the development of visible-light-driven photocatalysts for overall water splitting is currently attracting much attention as a potential efficient utilization of solar energy. So far the (oxy)nitride approach become attractive and promising for this specific issue as a consequence of the anionic N3-/O2- substitution results in an increase of the covalent character which is illustrated by a shift of the absorption edge towards higher wavelength values (band gap < 3 eV). However other requirements have to be considered to synthesize an efficient visible-light-driven photocatalyst such as the mobility of the photogenerated charge carriers, the crystal structure or the chemical stability. Perovskite-type oxynitrides containing lanthanides and d0 metal ions such as LaTiO2N exhibit interesting photocatalytic behavior as well as d10-type metal oxynitrides and sulfides, for instance (Zn,Ga)(O,N) and ZnS systems. Here, we have investigated a system combining these features: the monoclinic perovskite-type oxynitride system La2Zn1-xTi1+x(O,N)6. It is expected that the expanded nature of the Zn 4s band improves the mobility of the photogenerated carriers thus enhancing the photocatalytic activity of the material [2]. The effect of the Zn/Ti ratio on the photocatylic behavior of the oxynitride is investigated and the performance of this new photocatalyst will be compared to the reference material LaTiO2N.
REFERENCES
1. K. Maeda, J. Photochem. Photobiol. C: Photochem. Reviews 58-59 (2011) p. 443-446
2. J. Yin, Z. Zou, J. Ye, J. Phys. Chem. B 108 (2004) p. 12790-12794
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