Elaboration et étude des propriétés des couches minces d’oxydes et de nanocomposites à base de TiO2.

Abstract

The present work consists in studying the structural, optical and photocatalytic properties of thin layers of oxide and nanocomposites based on TiO2 elaborated by the sol-gel method. The different samples are characterized by means of several techniques: X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), m_lines spectroscopy (optical guidance), UV-Visible spectrophotometry, and photoluminescence. The XRD results show that the pure TiO2 layers, prepared by using two different precursors, crystallize in a tetragonal anatase structure, and that the intensity of the diffraction peaks increases with the growth of the thickness of the layers. The pure SnO2 layers crystallize in the rutile phase (cassiterite). The micro-Raman analysis shows that the TiO2: SnO2 nanocomposites are characterized by the two phase-vibration modes anatase TiO2 and rutile TiO2. While the addition of SnO2 oxide leads to a decrease of the vibration modes of the TiO2 anatase phase and an increase in the intensity of the signals associated with the rutile TiO2. This means that SnO2 promotes and facilitates the growth of the TiO2 rutile at low temperatures, due to the fact that the TiO2 rutile has a structure identical to that of the SnO2 cassiterite phase. The SEM observations confirm the results obtained by Raman spectroscopie. The results obtained using UV-Visible spectrophotometry show that all the films are transparent in the visible and opaque in the UV, the transmission and the number of interference fringes of the TiO2: SnO2 layers decrease with increasing SnO2 concentration. The waveguiding measurements record the excitation of a single guided mode for the two polarizations TE0 and TM0 for all the samples. A decreasing profile of refractive index and of thickness is observed as the content of SnO2 increases. Photocatalytic tests are carried out on the degradation of the methylene blue (BM) under UV radiation. The obtained results show that the degradation efficiency of thin TiO2: SnO2 (8: 2) films is greater than that of pure TiO2 and SnO2 oxide films. Photoelectrochemical measurements show that the film of the SnO2: TiO2 (8: 2) nanocomposite exhibits the highest photocurrent response.