PRISTINE AND Au-MODIFIED ZnO vs. TiO_2 NANO-POWDERS PREPARED BY SOL-GEL: SYNTHESIS, STRUCTURAL PROPERTIES AND PHOTOCATALYTIC DEGRADATION OF RHODAMINE B

摘要

ZnO nano-powders have been prepared by sol-gel method, alcoholic route, starting from zinc acetate dihydrate as Zn source. The obtained white powders where thermally treated (TT) at 400 and 500 ℃ for lh. The modification of ZnO powder with Au was performed by impregnating it with 0.2 mM aqueous solution of chloroauric acid followed by TT at 500 ℃ in air stream for 1 hour. The characterization of the ZnO powders was made by TG/ATD analysis, X-ray diffraction, FT-IR spectroscopy and Scanning Electron Microscopy. X-ray diffraction analysis of the nano-powders revealed a hexagonal wurtzite ZnO phase and the presence of Au in the Au-modified ZnO powder TT at 500 ℃. FT-IR spectra identified the Zn-0 characteristic bands and the change of shape and intensity of bands with crystallization. The temperature of 500℃ and addition of Au have positive influence on crystallization. TiO_2 was used as reference photocatalyst for photoreactivity evaluation of the ZnO-based materials, and it was synthesized also by sol-gel method starting from titanium isopropylate. According to the thermal analysis investigations, the TiO_2 powder was thermally treated at 400 ℃ for lh, leading to the crystallization into the anatase phase, as proved by XRD. SEM revealed the morphology of the TiO_2 powder and FT-IR the characteristic vibrational bands of the obtained material. Both materials, ZnO and TiO_2, have similar fine grains but with different aggregation tendency. The photocatalytic evaluation of the obtained materials was been carried out for Rhodamine B (RhB) degradation under simulated solar irradiation, by following the transformation degree of the dye in time. It was found that Au enhances the photocatalytic degradation of the RhB, the pristine ZnO having comparable activity with TiO_2.