Optically modulated charge transfer in TiO₂-Au nano-complexes

Highly ordered TiO₂ nanotube array (TNA) films were fabricated by anodic oxidation of Ti foil. Au nanoparticles (NPs) are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. The steady-state photoluminescence (PL) spectra, as well as x-ray photoelectron spectroscopy (XPS) and Raman analysis, confirm the presence of Ti³⁺ valence states in the prepared TNA films. The UV–vis absorption spectra show that the photo-response of as-prepared samples is extended from UV to the visible light region. From the nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra, Ti³⁺-related PL intensity is observed to vary distinctly with the deposition time of Au NPs. Such a phenomenon could be explained by considering the modulation of oxygen vacancy densities and charge states in TNA films by surface loading Au NPs. The enhanced visible-light photocatalytic activities of the Au-TNA composite were evaluated through the photodegradation of methyl orange (MO) in aqueous solution by UV–vis absorption spectrometry. The decoration of Au NPs plays an essential role in enhancing visible-light photocatalytic activity, because energetic photoelectrons are able to inject to the conduction band of TiO₂ owing to the surface plasmon resonance (SPR) effect. It is hoped that our current work will provide a simple strategy to synthesize defect-related composite for photocatalytic applications. (paper)