Elaboration et étude des propriétés physiques et chimiques de nanopoudres d’oxyde de zinc pour une application en photocatalyse hétérogène.

Abstract

The objective of this thesis is firstly the study of the controlled growth of ZnO nanostructures by two methods of synthetsis, a chemical method which is the Sol-Gel ZnO-SG method and a physical method which is the Sublimation-Condensation ZnO-SPVD; and secondly, the result study aim to compare and correlate the photocatalytic efficiencies with the physicochemical properties of the catalysts synthesized with the aim of defining new efficient catalysts. The optimization of the preparation conditions for ZnO nanopowders by the sol-gel method was carried out by varying several parameters: the concentration of the precursor, the time and the temperature of the gelation. Structural and morphological characterizations were obtained using X-ray spectra, Raman spectroscopy and scanning electron microscopy (SEM). The XRD results indicate that the powders obtained from the two techniques have a hexagonal ""würtzite"" structure, a nanometric particle size. The UV-Visible spectroscopy measurements reveal that all the studied ZnO powders exhibit the absorption edge in the UV region, this result suggests that the photocatalytic activity could be better under irradiation with UV light. The obtained results indicate that the photocatalytic activity was correlated to the particle sizes of catalysts. The catalyst prepared by the physical method (ZnO-SPVD) exhibits a higher photoactivity to degrade GV dye than the catalyst prepared by the chemical method (ZnO-SG). The experiments were carried out in the presence of each of ZnO-SPVD or ZnO-SG to investigate the factors that influence the photocatalytic degradation of GV, such as the adsorption amount, pH of dye solution, electron acceptors (H2O2), and the presence of inorganic species commonly present in real wastewaters (HCO3-). The experimental results showed that the adsorption on the surface of both samples was an important parameter controlling the photocatalytic activity. For both catalysts, the degradation rate in alkaline medium was higher than in natural and acid medium. The presence of the H2O2 and HCO3- ions increased the effectiveness of the photodegradation.