Avaliação do efeito sinérgico entre metais: óxidos de ferro magnéticos dopados com terra rara como potenciais catalisadores redox

Abstract

Iron oxides are used as catalysts and adsorbents to remove organic and inorganic compounds in water. Among the oxides are magnetite, maghemite, goethite and hematite. In order to increase the catalysis action, iron oxides are modified by other metals such as Cerium with high redox potential and Oxygen vacancies at the oxide surface, allowing the redox cycle of Fe 2+ /Fe 3+ and Ce 3+ /Ce 4+ to be repeated and, therefore, increase the catalytic potential. In addition, Cerium has large affinity to Sulfur, Nitrogen and Oxygen compounds increasing, therefore, removal of organic contaminants. At this research, iron oxides were prepared using the synthetic protocol to obtain the magnetite phase doped with Ce +3 , in order to evaluate doping effects at nucleation process, formation and possible phase transition among the bi-metalic Fe-Ce oxides. The catalysts were applied in order to degrade the methylene blue compound. Besides that, another synthesis route was performed with magnetite doped with Ce 4 + to create vacancies and be used as catalysts to degrade the reactive red model molecule. All products were characterized chemically, morphological and structural through analysis such as FTIR, Raman, XRD, TG, DSC, TPR, XPS, Mössbauer, adsorption-desorption N2 isotherms and ICP-OES. The doped iron oxides by Ce 3+ and Ce 4+ were identified as mixed oxides formed by magnetite and goethite phases. The products were submitted to the experimental design (temperature, organic compound concentration, catalytic mass and oxidant volume) and they were very important to optimize the experimental conditions. The catalyst FexCe0,1O (doped with Ce 3+ ) presented satisfactory results to degrade the methylene blue when compared to pure magnetite; temperature was the dependent factor for this process. The catalyst presented the potential of 97% to degrade the methylene blue. The catalyst FexCe0,2(IV)O (doped with Ce 4+ ) presented the potential of 92% to degrade the reactive red dye. In addition, the products developed at this research can potentially adsorb red reactive. They were very active to remove organic compounds in water.