Sol-gel synthesis of Ag-loaded TiO2-ZnO thin films with enhanced photocatalytic activity

g-loaded TiO2-ZnO thin films, with low ZnO content, were synthesized by a one-step sol-gel process. The Ag content varied in the interval 0?4?mol% Ag. The films were deposited on glass substrates and post-annealed at 500?C to induce crystallinity. By using the Tauc model, it was determined that the higher the Ag concentration the higher the optical band-gap energy of the films, a result attributed to the Burstein-Moss effect. Images obtained by scanning electron microscopy and transmission electron microscopy depicted aggregated particles with grain size close to 20?25?nm for the oxides with no Ag, whereas the particle size decreased with the addition of Ag. X-ray photoelectron spectroscopy measurements indicated the formation of the Ti4+ and Zn2+ oxidation states, while Ag was found in the metallic state. A depth profile analysis, performed by secondary ion mass spectrometry, confirmed the presence of Ti, Zn, and Ag in the films. X-ray diffraction patterns displayed the anatase phase of TiO2. For (TiO2)0.95-(ZnO)0.05 thin films, a BET analysis showed that the specific surface area increased from 4.56 up to 48.84?m2/g as a consequence of Ag doping. The photocatalytic degradation of the materials under UV irradiation was assessed by using methylene blue as a model pollutant. For (TiO2)1-x-(ZnO)x compounds with no Ag, the highest response corresponded to x?=?0.05. In addition, the optimum photodegradation was found for (TiO2)0.95-(ZnO)0.05 thin films with 2?mol% Ag.