Catalisadores nanoestruturados com ordenamento core-shell: o efeito do meio de síntese na eficiência catalítica

Abstract

Metal oxides are known for their importance as catalysts in the most diverse sectors, from reaction of industrial interest to environmental remediation. The performance of these oxides in heterogeneous catalysis depends largely on their nature, size, shape and surface area, and the relationship between these factors is crucial to determine their potential in catalytic activities. In view of the above and the need to improve wastewater treatment techniques, core-shell materials already become an increasingly interesting alternative for obtaining not only stable catalysts, but also catalysts that present different properties, which can be studied for other application areas. Therefore, this work aims to develop nanostructured materials with a core-shell ordering, the shell being a polymer. Iron oxides were synthesized in pure magnetite phase and coated with polyethylene glycol (PEG) and polyvinyl alcohol (PVA). The synthesis occurred by the method of coprecipitation with a modification of the reaction medium by adding the polymers to the reaction medium. Through X-ray diffraction analysis (XRD) it was possible to show the existence of nanomaterials in the magnetite phase, with the materials MagPEG20000 – 2% and MagPVA – 2% standing out for presenting an even smaller size than the others. In addition, both materials showed greater dispersion of particles by surface morphology and this is related to the proportion of the polymer and to the size of the polymeric chain. The catalytic activity and degradation mechanism were evaluated by the decomposition of hydrogen peroxide in aqueous and organic media, showing an O2 evolution equivalent to 13.55 and 14.7 mL for the best performing materials, respectively, MagPEG20000 – 2% and MagPVA – 2%, and a reduction of approximately 75% in the evolution of this volume when in an aqueous medium. The kinetic capacity of degradation and adsorption was studied by removing the color of the organic molecules methylene blue (BM), black eriochrome T (EBT) and crystal violet (VC), in which the materials modified by PEG20000 and PVA, with proportions of 2% were the ones with the best result, showing a discoloration of approximately 100% for the BM dye, 85% (for the one modified by PEG) and 90% (for the one modified by PVA) for the EBT dye, and 83% and 98% for the VC dye. In view of the results, it can be considered that the addition of PEG20000 and PVA as stabilizing polymers was successful in the proportions of 2% by mass, directly interfering in the properties of iron oxide.