High-temperature hydrogenation of pure and silver-decorated titanate nanotubes to increase their solar absorbance for photocatalytic applications

Titanate nanotubes (TiNTs) and silver-decorated titanate nanotubes (TiNTs@Ag) were synthesized using the hydrothermal method. In the decorated nanotubes the silver particles were obtained by the photoreduction of AgNO3 under UV light. Pure and Ag-decorated nanotubes were high-temperature heat treated at 550 degrees C in a hydrogen atmosphere and the core-shell''-structured TiO2 nanoparticles were formed. For the structural characterization of all the titanate nanostructures we used conventional and analytical transmission electron microscopy (TEM) techniques, X-ray diffraction (XRD) and Raman spectroscopy. The Ag-decorated titanate nanostructures were additionally studied by X-ray photo-electron spectroscopy (XPS), with the aim being to investigate the surface chemistry. Using UV-ViS-NIR spectroscopy we studied the photocatalytic activity on caffeine for the TiNT and TiNT@Ag samples that were high-temperature heat treated at 550 degrees C in a hydrogen atmosphere. We found that hydrogenation at high temperature of the TiNTs and TiNTs@Ag is essential to increase the absorption of light in the visible and near-IR regions. In the case of the hydrogenated TiNTs@Ag the absorption is even stronger in the visible region than in the UV, which was not observed in TiO2-based nanostructures up until now, to the best of our knowledge. The hydrogenated TiNTs@Ag sample had a two-times higher photodegradation impact on the caffeine than the hydrogenated TiNT samples, which is a consequence of the increased absorption of visible light and the synergetic effects between the silver and the TiO2 nanoparticles that increase the efficiency of the formation of electron-hole pairs and the charge transfer to the surface of the nanoparticles. (C) 2014 Elsevier B.V. All rights reserved.