Enhanced photocatalytic NO_x decomposition of visible-light responsive F-TiO₂/(N,C)-TiO₂ by charge transfer between F-TiO₂ and (N,C)-TiO₂ through their doping levels

Composite type photocatalyst F-TiO₂/(N,C)-TiO₂ consisted of anatase-type TiO₂ with fluorine-doping (F-TiO₂) and TiO₂ with nitrogen and carbon-doping ((N,C)-TiO₂) was prepared by simple physical mixing to exhibit higher visible-light responsive photocatalytic nitrogen oxide (NO_x) decomposition activity than those of F-TiO₂ and (N,C)-TiO₂. Transient absorption measurement clarified that the composite possessed longer carrier lifetime compared to that of each material (F-TiO₂ or (N,C)-TiO₂), resulting in higher photocatalytic activity. In the composite, photoexcited holes and electrons, which are not in impurity level but in valence and conduction band, respectively, should photocatalytically decompose NO_x, judging from the redox potential of O₂/O₂^･− and the band positions of F-TiO₂ and (N,C)-TiO₂. The mechanism for higher visible-light photocatalytic activity, or longer carrier lifetime can be explained by charge transfer between F-TiO₂ and (N,C)-TiO₂ through their impurity levels. The charge transfer should make photoexcited carries spatially separated to enhance the photocatalytic activity.