Síntese e avaliação das propriedades superficiais de óxidos mistos a base de ferro, lantânio, cálcio e zircônio

Abstract

Mixed oxides with perovskite structure (ABO3) and pyrochlore (A2B2O7) are promising materials as they have interesting properties for the industry, in which there is a search for cost reduction and greater efficiency in its processes, in addition to the interest in minimizing environmental impacts caused mainly by contaminants. The synthesis method, choice of metals, doping and calcination temperature are some of the main factors that can determine the formation of the desired phase. The materials LZ-9C (La2Zr2O7), LFZ-9C (La2Fe0.3Zr1.7O7), LF-9C (LaFeO3), L3C7F-9C (La0.3Ca0.7FeO3) and L7C3F-9C (La0.7Ca0.3FeO3) were synthesized by the modified proteic method using collagen as a complexing agent, followed by heat treatment at 350 °C for 2 hours and finishing with calcination at 900 °C for 2 hours. The different techniques used showed that the calcined materials obtained contain the desired phases. Another characteristic observed is that there was no uniformity on the surface of the particles. Furthermore, the infrared spectra of the non-calcined samples showed bands related to the complexing agent, which does not occur with the calcined samples, since the organic components were eliminated and metal-oxygen bond bands were identified. The specific surface area revealed relatively low values for both classes of mixed oxides due to the high calcination temperature involved during the synthesis. All materials were also prepared without the addition of a complexing agent and the analyzes indicated similar characteristics to the samples that included this component in the synthesis. The pH at the point of zero charge decreases when iron(III) is present in the oxide structure and increases when calcium is part of the composition. This event may be related to vacancies caused by dopants. Preliminary studies indicated that the adsorption of the turquoise blue (AT) dye is more effective when the pH of the medium is below 5 and when the amount of adsorbent mass used is 30 mg. In the kinetic study of AT dye removal at 30ºC, the maximum efficiency of the adsorbents were: LZ-9C (68%), LFZ-9C (87%), LF-9C (98%), L3C7F-9C (36%) and L7C3F-9C (47%) and the data best suited the Pseudo Second Order model. The reuse of adsorbents after powder drying and after calcination had positive results, with emphasis on the performance of samples LF-9C and LFZ-9C. From the waste water collected from a local textile factory, the prepared and commercial vi adsorbents were tested and the performance of dye removal efficiency from the medium showed the results: Activated carbon (25%), L3C7F-9C (13%), LF -9C (12%), L7C3F-9C (11%), Silica gel (11%), LFZ-9C (9%) and LZ-9C (7%). In a calcination regeneration cycle, the prepared adsorbents performed well in all removal cycles studied, except for active carbon, which underwent decomposition.