Preparo e avaliação catalítica de nanopartículas de magnetita modificada com zircônia

Abstract

Catalysts and adsorbents have been used in several industrial processes. Among these, iron-based materials are used to remove organic and inorganic compounds in aqueous media. Iron oxides are naturally occurring materials, are abundant in the earth's crust and can be easily synthesized in the laboratory, such as goethite, hematite, magnetite and maghemite, which have a very interesting chemistry due to its magnetic properties . Iron oxides have great potential for application in heterogeneous catalysis and without the need for high temperatures. Among the iron oxides, magnetite (Fe3O4) attracts attention due to its electronic, magnetic, chemical properties and its high availability and ease of production, enabling a wide field of applications. In this work, magnetite was synthesized using an inverse coprecipitation method, where iron substitutions were made using 5 mol% zirconia and surface modification with 10 mol% graphite (Fe3O4, Fe2.85Zr0.15O4, GF-Fe3O4, GF-Fe2.85Zr0.15O4,) in order to increase its catalytic activity and promote changes in the crystal arrangement (isomorphic substitution), aiming at the removal of the remazol black model compound (PR). Materials containing graphite were only submitted to FTIR characterization due to the work difficulties faced due to the COVID-19 pandemic. The materials Fe3O4 and Fe2.85Zr0.15O4 were characterized by scanning electron microscopy with mapping by energy dispersive spectroscopy (SEM-EDS), differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD). Likewise, the catalytic tests of hydrogen peroxide decomposition (H2O2), adsorption and degradation using heterogeneous Fenton (catalyst/H2O2/CH2O2), were also performed only for these materials. The FTIR results indicated bands characteristic of magnetite formation and for materials containing graphite, some bands can be attributed to carbon. The SEM-EDS analysis shows that the particles are aggregated, and this suggests a magnetic attraction effect between the particles. The thermal stability of magnetite, evaluated by thermogravimetry (TG) and differential scanning calorimetry, did not demonstrate crystalline phase transitions at a temperature of 450 °C. The reflections observed in XRD materials are characteristic of the cubic ordering of the magnetite phase and with the incorporation of zirconia there was a decrease in the intensity of the reflection signal at 2Ɵ = 35.70°. The redox mechanism is processed by oxygen vacancies, as observed in the H2O2 decomposition tests. Adsorption tests showed low adsorption, indicating that the materials are not capable of adsorbing the tested dye. The degradation of PR by Fe2.85Zr0.15O4 reached 81.7% in 60 minutes, on the other hand, Fe3O4 reached this result after 120 minutes. Through the results obtained, it is not possible to conclude through the characterizations that the material has been doped, as the catalytic tests can be an indication of this, due to the improvements obtained in its catalytic activity. In order to complement the research, the second chapter presents a manuscript of a review article.