engleski

Ag-functionalized titanate nanostructures for photocatalytic application

TiO2-based nanostructures have been extensively investigated materials over the past two decades, because of their promising physical and chemical properties, such as a high specific surface area, the low costs of synthesis, a high photo-activity and environmental stability. Because of these properties the titania nanostructures can be used for photocatalysis, in solar cells, sensors, and in the cosmetics industry. Since TiO2 has a relatively large bandgap of 3.2 eV for anatase and 3 eV for rutile, both crystal forms are photo active only under UV light irradiation. Thus, one of the key parameters essential to increase the photocatalytic activity in the visible and near-IR regions is to optimize the bandgap of TiO2-based materials. The aim of the work is to study how annealing in a reducing atmosphere of titanate nanotubes (TiNT) and Ag decorated titanate nanotubes (TiNT@Ag) influenced on their structure, morphology, phase transitions, UV-ViS- NIR absorbance and photocatalytic activity. Undoped titanate nanotubes (TiNT) and silver- doped titanate nanotubes (TiNT@Ag) were synthesized using the hydrothermal method. In the doped nanotubes the silver particles were obtained by the photoreduction of AgNO3 under UV light. For the structural characterization of the titanate nanotubes we used conventional and analytical transmission electron microscopy (TEM) techniques, X-ray diffraction (XRD) and Raman spectroscopy. The silver-doped titanate nanotubes were additionally studied by X-ray photo-electron spectroscopy (XPS) with the aim 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 previously heat treated at high- temperature of 550°C in a hydrogen atmosphere. An increase of photocatalytic activity after a heat treatment in a reducing atmosphere was observed in the TiNT and TiNT@Ag (Fig 1). We found that the hydrogenated TiNT@Ag samples had a two-times higher photodegradation impact on the caffeine than the TiNT samples, which is a consequence of the increased absorption of visible light (Fig 2) 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.

: nanostructured oxide materials; chemical synthesis; photo-catalysis; TEM; X-ray diffraction

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