7. Conclusion

H2 reduction treatment enhanced the photocatalytic activity and PEC properties of rutile TiO2 with large particle size. One of the most important factors deciding the photocatalytic activity of reduced TiO2 is the density of electrons in shallow traps and conduction band, rather than the density of oxygen vacancies. H2 treatment at 500C created Ti3+ ions (trapped electrons), while treatment at 700C increased the density of conduction electrons, resulting in an improvement of the electrical conductivity of the TiO2 by 2–3 orders of magnitude. The enhanced activity of the reduced TiO2 suggests that n-type conductivity governed by electron density plays an important role in suppressing fast recombination by facilitating charge transport. The suppression of recombination in the reduced TiO2 was caused by not only the high electrical conductivity but also the band bending in space charge layer. The built-in electric field facilitates charge separation and charge transfer. Thus, the surface reactivities of reduced TiO2 with large particle size were enhanced without dependence on reactions. It was demonstrated that H2-reduced rutile TiO2 exhibited photocatalytic activity higher than that of anatase TiO2 and mixed-phase TiO2.
