Fotocatalisadores do tipo α-Fe2O3/ZnO e α-Fe2O3/CeO2 aplicados na degradação do corante Azul de Metileno

Abstract

Advanced oxidation processes (AOPs) have emerged as promising alternative methods for treating wastewater and industrial effluents. Among the AOPs, the photolysis process stands out, which involves the activation of a semiconductor by artificial or sunlight. Thus, the present work developed efficient photocatalysts applied in the Fenton-like degradation process of the Methylene Blue (MB) dye. The degradation study was conducted at pH 3.0; 6.6 and 9.0 using zinc oxide (ZnO) and cerium oxide (CeO2) based catalysts decorated with 2.5%; 5.0%; 10% and 15% hematite (α-Fe2O3). The catalysts were synthesized by the co-precipitation method. All catalysts were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM/FEG), N2(g) physisorption analysis, Fourier transform infrared spectroscopy (FTIR), point of zero charge (pHPZC) and diffuse reflectance spectroscopy (DRS). The degradation experiments were carried out in a single compartment reactor containing a water recirculation system and a controlled temperature of 25 ºC, and the reaction was processed under agitation for 60 min. Samples of MB solution (50 mg L-1) were collected at specific times and subjected to absorbance decay analysis by UV-vis spectrophotometry. Initially, it was found that when the photo-Fenton process was applied, the MB dye removal efficiency was 96.2 and 94.0% when using catalysts with a composition of 5.0% α-Fe2O3/ZnO and 5.0% α-Fe2O3/CeO2, respectively. The high catalytic efficiency of color removal is due to the synergism between Fe3+ ions with Zn2+ or Ce4+ ions, presenting high promotion of photoradical species due to the combination with the Fenton effect. For this experiments, 50 mg of catalyst, 500 µL of H2O2, pH 6.6 and a 250 W Hg lamp (UVA radiation) were used initially. The optimization studies of the degradation parameters showed that there was no significant difference in the MB color removal when varying these parameters. Thus, the optimization parameters chosen were 10 mg of catalyst, pH 6.6, H2O2 volume of 100 µL and MB dye concentration of 10 mg L-1. Real water samples were used as a source of dye contamination, and little interference from the medium was observed, achieving high color removal (~100%). It was also shown that, after the photo-Fenton degradation, the by-products formed during the process did not present high toxicity when in contact with the Lactuca sativa L. specie. The reuse of the 5.0% α-Fe2O3/ZnO and 5.0% α Fe2O3/CeO2, showed high catalytic stability after eight consecutive cycles of degradation when the photo-Fenton process was applied, as well as there was no significant spectral change in the FTIR after the application of the catalysts.