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

Ag-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 degrees 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 m(2)/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. (C) 2018 Elsevier B.V. All rights reserved.