The influence of antimony co-doping on the electronic structure of rutile rhodium-doped TiO2 has been investigated by X-ray photoemission spectroscopy. Rh doping leads to the appearance of new Rh 4d states above the top of the O 2p valence band and the Fermi level shifts down from a position close to the conduction band minimum in undoped TiO2 to deeper in the gap. Sb co-doping restores the Fermi level to the top of the bandgap. These changes are consistent with a change in valence state from open shell t(2g)(5) Rh(IV) to closed shell t(2g)(6) Rh(III) upon Sb co-doping. (C) 2011 Elsevier B.V. All rights reserved.