Caracterização estrutural e óptica dos cristais de CuWO4 sintetizados pelo método de coprecipitação seguido por tratamento térmico e suas propriedades sonocatalíticas para degradação do corante rodamina 6G

Abstract

In this dissertation, copper tungstate crystals (CuWO4) were synthesized by the coprecipitation method followed by heat treatment at 500 ºC for 2 h, and their structural, optical, colorimetric and sonocatalytic properties were reported. X-ray diffraction patterns and Rietveld refinement indicated that CuWO4 crystals are single-phase and present in a triclinic structure formed by distorted octahedral clusters of [CuO6] and [WO6]. The micro-Raman and infrared Fourier transform spectra indicate the presence of Raman-active (Ag) and seven infrared-active (Au) vibrational modes for pure CuWO4 crystals. The reflection spectrum in the ultraviolet-visible region showed an increase in the energy values of the optical band from 2.75 to 2.20 eV with heat treatment. The sonocatalytic properties of CuWO4 crystals were investigated for the first time in the decolorization of Rhodamine 6G (Rh6G) dye and showed an efficiency of 94% after 240 min. Finally, we investigated the influence of oxidative species such as hole (h+), electrons (e-), hydroxyl radicals (•OH), and superoxides (O2•-) on the sonodegradation process to determine the degradation mechanism. The use of isopropyl alcohol (scavenging of •OH radicals) reduced the degradation rate to 1%, benzoquinone (scavenging of O2•- radicals) to 5%, silver nitrate (scavenging e-) to 36%, and ammonium oxalate (h+ scavenger) to 30%. Therefore, the results indicated that all radicals participate in the degradation of the Rh6G dye, with the presence of •OH and O2• radicals having the most significant influence on Rh6G degradation and discoloration.