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Graphical abstract Highlights • Deep gap states of TiO 2 nanorod array were identified by cyclic voltammetries. • Spatial location, energy position, and chemical entity of gap states were revealed. • High sub-band gap response was observed in photoelectrochemical water oxidation. Abstract Developing new methods to use visible light is important for TiO 2 photocatalysis. This research reported that the TiO 2 rutile nanorod (NR) array shows high sub-band gap visible light response. By means of electrochemical cyclic voltammetries, the intrinsic occupied gap states of TiO 2 NR array were identified. It was seen that the gap states can be switched from filled states to empty states by visible light illumination, which play the role of relay in promoting electrons from the valence band to the conduction band of TiO 2 NRs after absorbing two visible photons. In a consequence, the TiO 2 NR array shows the obvious anodic photocurrents for water photoelectrochemical oxidation and the photocatalytic degradation of methyl orange under visible light illumination. This study revealed the significance of the deep occupied gap states of TiO 2 NR arrays, which are usually considered as recombination centers. Different from conventional photocatalysis arising from inter-band electron transition, the present research shows a different pathway to use visible light in TiO 2 photocatalysis effectively, which should be highly meaningful for designing visibly-active TiO 2 photocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: A novel photocatalyst (Ce, C-codoped titania) was synthesized through a modified sol–gel method under mild condition. The as-prepared sample was investigated by XRD, SEM, DRS and XPS. It was found that the as-prepared photocatalyst was composed of spheroidal particles, which were smaller than undoped ones. The absorbance spectrum of Ce, C-codoped TiO2 exhibited significant red-shift to visible region. It can be ascribed to appearance of a new electronic state in the middle of the TiO2 band-gap. Furthermore, cerium doping could slow the radiative recombination process of photogenerated electrons and holes in TiO2. Accordingly, for degradation of dye Reactive Brillint Red X-3B (C.I. reactive red 2) under visible light, the photocatalytic activity of Ce, C-codoped TiO2 improved much compared to other samples (C-doped TiO2, undoped TiO2 and P25). [Copyright &y& Elsevier]