Síntese e caracterização de nanopartículas de óxidos de ferro e sua mistura com resíduos da cana-de-açúcar (bagaço e palha) para emprego nos processos de adsorção e fotocatálise heterogênea

Abstract

Iron oxide nanoparticles have gained great prominence over the years due to their numerous applications in different areas of knowledge. In addition, the microwave-mediated synthesis route has been widely used, mainly due to the shorter reaction time, lower material consumption and production of nanometer-scale iron oxides. In this context, the combination of the characteristics of these materials with those of agro-industrial waste, such as sugarcane bagasse and straw; it can result in a new material with greater added value and with improved properties for application in a given process. The objective of this work is to obtain iron oxide nanoparticles and composites, from synthesis, with microwave-assisted heating aiming at adsorption and heterogeneous photocatalysis. The iron (III) nitrate salt was heated in a muffle furnace by microwaves at temperatures from 200 to 5000C for 10 minutes. Hematite nanoparticles (-Fe2O3) were obtained, being amorphous at 200 and 3000C and crystalline with a rhombohedral structure at 400 and 5000C, according to the results of X-ray Diffraction and Infrared Spectroscopy with Fourier Transform. The morphological properties were determined by Scanning Electron Microscopy and Transmission Electron Microscopy, verifying the obtaining of nanoparticles with average sizes predominantly around 50 nm. The Ultraviolet/Visible Diffuse Reflectance Spectroscopy was used to determine the band gap with values of 1,87 eV and 2,01 eV. The photocatalytic performance of iron oxides was evaluated using solutions of methylene blue, methyl orange and crystal violet dyes, obtaining a high percentage of discoloration, with samples characterized as amorphous hematite being the most promising with superior results of up to 98% conversion. The mixture of hematite nanoparticles at 2000C with sugarcane residues and thermally treated in the muffle furnace by microwaves at temperatures of 200 and 3000C, resulted in carbonaceous material/iron oxide composites, in which they presented maghemite and/or magnetite phases, as determined by X-ray Diffraction. The results of heterogeneous photocatalysis and adsorption tests of methylene blue (with values of up to 90%) showed that the composite materials are efficient photocatalysts and adsorbents for use in the treatment of wastewater contaminated by dyes.