Surface chemistry of TiO2-ZnO thin films doped with Ag. Its role on the photocatalytic degradation of methylene blue

摘要

Photocatalytic Ag-loaded (TiO2)(0.95)-(ZnO)(0.05) thin films were synthesized by the sol-gel dip-coating method, with the Ag content varying in the range 1-4 mol%. The films were deposited on glass substrates at room temperature and then annealed at 500 degrees C. Raman spectroscopy disclosed basically the anatase phase of TiO2. Secondary ion mass spectrometry measurements proved the incorporation of Ag in the films, revealing its diffusion to the film surface as a consequence of thermal treatments. X-ray photoelectron spectroscopy (XPS) was used to study in detail the chemical composition and electronic structure of the samples. The O 1s, Ti 2p, and Zn 2p core level spectra indicated Ti4+ and Zn2+ states associated with TiO2 and ZnO regions. The chemical species identification was confirmed by calculating the modified Auger parameter for O, Ti, and Zn. In addition, an XPS depth profile analysis using an Ar+ ion gun showed the formation of Ti+2 and Ti+3 oxidation states as a consequence of the Ar+ bombardment. The photocatalytic activity under UV irradiation was evaluated by the degradation of methylene blue aqueous solutions, with the best response corresponding to (TiO2)(0.95)-(ZnO)(0.05) thin films doped with 2 mol% Ag.