Sensitization of NaMO3 (M: Nb and Ta) Photocatalysts with Wide Band Gaps to Visible Light by Ir Doping

NiO/NaNbO3 (BG: 3.5 eV) showed photocatalytic activity for water splitting into H-2 and O-2 under UV irradiation. When NaMO3 (M: Nb and Ta) was codoped with iridium ions and alkaline earth metal ions or lanthanum ions, a new visible-light absorption band was observed in addition to the band gap absorption band of the host material. The codopants of alkaline earth metal and lanthanum ions contributed to maintaining the charge balance and forming of fine crystals of the NaMO3 powder. These NaNbO3 and NaTaO3 codoped with iridium ions and alkaline earth metal ions or lanthanum ions showed photocatalytic activities for H-2 or O-2 evolution from an aqueous solution containing a sacrificial reagent under visible light irradiation.