The Influence of Gel Preparation and Thermal Treatment on the Optical Properties of SiO2-ZnO Powders Obtained by Sol-Gel Method

The effect of gel preparation and heat treatment on the structural and optical properties of SiO2-ZnO materials prepared by the sol-gel method was investigated. Zinc acetate dehydrate, TEOS (tetraethylortosilicate), ethanol, distillated water and HCl were used as a starting material, solvent and catalyst, respectively. Four powders (G1-G4) were prepared in different ways from the starting materials mentioned above. The method of adding Zn precursors during the synthesis differed from one another. For the G1 synthesis, only Zn acetate powder was employed; for the G2 synthesis, Zn acetate was dissolved in distilled water; and for the G3 synthesis, Zn acetate was dissolved in ethanol. When synthesizing G4, TEOS was added last, after Zn acetate had been combined with water and ethanol. The SiO2-ZnO materials were dried at 200 degrees C and then heat-treated at 700 degrees C and 900 degrees C. All samples were investigated by X-ray diffraction and infrared spectroscopy in order to investigate their structure. SEM measurements were performed to investigate the morphology of materials. Optical properties were influenced by gel preparation and heat treatments. A reflectance of over 60% was obtained for G3 and G4 powders, while for G1 and G2, the reflectance was below 30%. In conclusion, synthesis steps and heat treatment can control the structure and properties of the powders.