Preparação de novos catalisadores do tipo fenton heterogêneos, à base de óxidos de ferro formados em litologia de Itabirito

Abstract

In this thesis is discussed the development of new materials based on geomaterial, formed on itabirite, to use in heterogeneous Fenton-like catalytic systems. The geomaterial studied is extremally iron oxides-rich, i. e., hematite and goethite. However, it is practically inative towards H2O2 reactions. Thus, the main objective this work was to develop active catalysts using the geomaterial as precursor. For this propose, two treatments was carried out: (1) solubilization of iron oxides from geomaterial, chemical reduction and precipitation of new iron phases (2) chemical reduction of Fe3+, in the hematite and goethite structures, through reaction with charcoal obtained from sucrose burn. In the treatment (1) the samples was dissolved with concentrated HCl, the soluble Fe3+ was chemically reduced with different Na2SO3 contents and the new iron phases precipitated using NaOH. In the treatment (2) the soil/charcoal composites was obtained from impregnation of sucrose on the geomaterial and further the materials was thermally treated at different heating temperatures in air atmosphere. The synthesized materials was characterized by chemical analysis of Fe2+ and total Fe, diffuse reflectance measurements, surface area measurements, 57Fe Mössbauer spectroscopy and X-ray diffraction. The results obtained for the treatment (1) indicated that the main products formed was a solid solution of magnetite-maghemite in all materials, beyond ferrihydrite in sample I-3, lepidocrocite in the Fe-4, feroxyhite in the I-4 and small amounts of hematite in the I-6 sample. The catalytic activity of the materials towards methylene blue degradation, used as model molecule in this study, was significatively better than unaltered sample. Kinetic studies showed that reaction order of methylene blue degradation was 1 in respect to dye and catalyst concentration and approximately 0.5 in respect to H2O2 concentration. The mechanism of methylene blue degradation proposed is similar to the heterogeneous Fenton-like and occur via free radicals. Fe2+, in the magnetite structure, and feroxyhite, was the active sites in those systems. The color removal from dye solution and conversion of organic carbon into inorganic carbon was 80 and 14%, respectively, after reaction 150 min. The results obtained to the treatment 2 showed that hematite and goethite could react with CO to form reduced species such as magnetite and wüstite. The catalytic activity of these materials showed significatively better than unaltered sample in the methylene blue degradation. Optimal heating temperature of the soil/charcoal composites was found be 600 C. Wüstite formation was induced by the increase in the charcoal content in the composites. Co-bearing composites was strongly active in the dye degradation. Cobalt had an important role in the stabilization of wüstite and avoids the sintering process during the heating of the composites. Kinetic studies showed that the reaction order is 1 in respect to methylene blue and catalyst concentration and 0.5 in respect to H2O2 concentration. Fe2+ and Co2+ species was the active sites in those systems. The mechanism of methylene blue degradation occurs via hydroxyl radical, which could be verified by some fragments in the mass spectra (ESI-MS). The materials presented a strong potential to discoloration and mineralization of methylene blue in aqueous medium.