Resíduo de caulim modificado com ZnO aplicado na fotodegradação do corante aniônico amarelo de remazol

Abstract

Industrial activities generate various types of waste, including kaolin residue, whose high production has raised concerns and encouraged the search for solutions that add value to this material. By modifying it with ZnO, a naturally abundant, non-toxic and low-cost compound, the removal of waste from the environment is promoted, minimizing environmental damage. This study aimed to synthesize and characterize photocatalysts based on kaolin residue, modified with ZnO, for photocatalytic application in the decolorization/degradation of the anionic dye remazol yellow RG. The photocatalysts were synthesized by the coprecipitation method followed by calcination, in which the concentration of the active phase (ZnO) supported on the kaolin residue (RC) was varied with the intention of incorporating 10%, 20% and 30% of this phase and calcined at 500 °C for 5 hours, obtaining the photocatalysts named ZnO-RC10%, ZnO-RC-20% and ZnO-RC-30%. Subsequently, depending on the best result, the calcination temperature was also varied at 400 °C and 600 °C to study the influence of this parameter on the formation and efficiency of the photocatalysts. The photocatalytic tests were performed in a reactor with a UVC radiation lamp and the efficiency of the dye decolorization was monitored by UV-vis spectroscopy at a wavelength of 412 nm. The characterization results of the synthesized hybrids demonstrated their efficient formation, in which the XRD patterns of the synthesized photocatalysts presented, in addition to the characteristic peaks of kaolin, characteristic peaks of ZnO in 2θ regions of approximately 31.7; 34.4; 36.2; 45.5; 56.6 and 62.8. The XRF and EDS results corroborated this fact, in which the EDS spectra of all photocatalysts presented very clear signs of the presence of zinc metal and the XRF results presented ZnO percentage of 7.70%, 14.97% and 15.76% for ZnO-RC-10%, ZnO-RC-20% and ZnO-RC-30%, respectively. After performing the photocatalytic tests, it was found that the photocatalysts ZnO-RC-20% and ZnO-RC-30% presented the best photodecolorization results, 69.96% and 79.03, respectively. Therefore, it was decided to synthesize the photocatalyst ZnORC-20% at different calcination temperatures (400 and 600 °C) and evaluate the influence on the photodecolorization process. A difference in efficiency was observed according to the calcination temperature, with the photocatalyst calcined at 400 °C showing better efficiency with 78.15% of dye discoloration. The results demonstrated the possibility of valorizing the kaolin residue and the formation of promising photocatalysts, in addition to efficiency in up to three reuse cycles.