The codoping effect of antimony on the photocatalytic activity of visible-light-driven SrTiO3 doped with rhodium (SrTiO3:Rh) was investigated. SrTiO3 doped with rhodium and antimony (SrTiO3:Rh/Sb) prepared by a hydrothermal method was found to be active for photocatalytic H-2 evolution from an aqueous methanol solution and O-2 evolution from an aqueous silver nitrate solution under visible light irradiation, although SrTiO3 doped with rhodium and no antimony was active only for the H-2 evolution. Photocatalytic activities of SrTiO3:Rh/Sb were strongly dependent on the ratio of codopant to dopant (Sb/Rh). Diffuse reflection spectroscopy (DRS), electron spin resonance (ESR), Raman, and action spectrum analyses revealed the contribution of rhodium and antimony to visible-light response of SrTiO3:Rh/Sb. Unstable and reversible Rh3+ ions in oxidation state were the superior species for the H-2 evolution. On the other hand, Rh3+ ions stabilized by codoping of antimony without the formation of Rh4+ ions and oxygen defects which would work as undesirable recombination sites between photogenerated electrons and holes played an important role in the O-2 evolution. Moreover, when an IrOx cocatalyst was loaded on the surface of the SrTiO3:Rh/Sb photocatalyst, the photocatalytic activity of the O-2 evolution drastically increased. The apparent quantum yield for the H-2 evolution over Pt(0.3 wt%)/SrTiO3:Rh(1%)/Sb(1%) and the O-2 evolution over IrOx(3.0 wt%)/SrTiO3:Rh(1%)/Sb(1%) at 420 nm were 0.8% and 4.5%, respectively. The Z-scheme system composed of Ru(1.0 wt%)/SrTiO3:Rh(2%) as a H-2-evolving photocatalyst, IrOx(3.0 wt%)/SrTiO3:Rh(1%)/Sb(1%) as an O-2-evolving photocatalyst, and an Fe3+/Fe2+ redox couple as an electron mediator showed photocatalytic activity for overall water splitting under visible light irradiation. (C) 2013 Elsevier B.V. All rights reserved.