Development of novel visible light sensitive photocatalysts has attracted much attention to use solar energy and indoor light effectively. Numerous studies have reported the sensitization to visible light with respect to TiO₂-based photocatalysts [1]. However, up to now, it seems that they have insufficient activities, especially under visible light. We are investigating now to enhance the activities by focusing on the overlap of the introduced anion p-orbital with O 2p-orbiral, constituting the valence band of TiO₂.
With the exception of TiO₂-based materials, several researchers have examined oxide or oxynitride materials that are sensitive to visible light for the oxidative decomposition of organic compounds. We have investigated various such novel photocatalysts, controlling electronic band structures and crystalline structures. For example, we have already reported Ag⁺-inserted NbO₂F with a ReO₃ structure and a-AgGaO₂ with a delafossite structure utilizing Ag⁺ [2]. Ag⁺ cation in a 4d¹⁰ configuration mixes the O2p orbitals, forming the highly dispersed upper valence band. This can be favorable for visible light sensitivity and high photocatalytic activity, because mixing Ag4d with O2p decreases in the band-gap energy and the dispersed valence band leads to high mobility of photo-generated holes. The key factors in realizing high-efficiency visible light sensitive photocatalysts are modulation of the closed shell with ligand O2p orbitals and finding crystal structure favorable for holes’ mobility. The details will be introduced at the conference.
[1] e.g., R. Asahi et al., Science, 293, 269 (2001). [2] e.g., H.Irie et al., J. Phys. Chem. B., 110, 23274 (2006).