Proceedings of nanoGe Fall Meeting19 (NFM19)
Publication date: 18th July 2019
Photocatalytic reactions at the surface of titanium dioxide (TiO2) under UV light irradiation have been attracting much attention in view of their practical applications to environmental cleaning such as self cleaning of tiles, glasses, and windows. It has been reported that the doping of nitrogen into TiO2 contributes to band gap narrowing to provide visible-light response. In the present study, nitrogen doped TiO2 photocatalysts were prepared by nitrogen implantation method, and investigated the chemical states of the surface of the samples mainly by soft X-ray spectroscopies.
Nitrogen ions were implanted into TiO2 at 5 or 50 keV at room temperature. Photocatalytic activity of the N+-implanted sample was evaluated by the decomposition reaction of methylene-blue solution under visible-light irradiation. The photocatalytic activity changed with the amount of implanted nitrogen, and the photocatalytic active and inactive N+-implanted samples were obtained.
O K-edge and Ti L2,3-edge of XANES analysis exhibited the formation of Ti3+ species in both photocatalytic active and inactive samples (A-cat and I-cat). The Ti3+ species would be formed by the displacement effect of oxygen atoms during the N+ implantation. On the other hand, in N K-edge XANES spectra, a double-peak structure around 400 eV was observed for the photocatalytic active sample while the XANES spectrum of the photocatalytic inactive sample showed a distinct single peak around 401 eV. These results suggested two types of chemical states of nitrogen, i.e., the photocatalytic active N substituting the O sites and the inactive NO2 species. In the valence band photoelectron spectrum of the photocatalytic active sample, the additional electronic states were observed just above the valence band edge of a TiO2. The electronic state would be originated from the substituting nitrogen and be responsible for the band gap narrowing, i.e., visible light response of TiO2 photocatalysts.
This study was supported by JSPS KAKENHI Grant Number JP16H06440 (Synthesis of Mixed Anion Compounds toward Novel Functionalities).
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