Doutorado em Física

URI Permanente para esta coleção

http://repositorio.ufes.br/handle/10/17493

Nível: Doutorado
Ano de início: 2003
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1509

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Navegando Doutorado em Física por Assunto "Activated carbon"

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    Obtenção e caracterização de nanopartículas magnéticas inseridas em materiais carbonosos porosos a partir da decomposição do pentacarbonil ferro
    (Universidade Federal do Espírito Santo, 2009-09-25) Schettino Junior, Miguel Angelo; Nunes Filho, Evaristo; Freitas, Jair Carlos Checon de; Takeuchi, Armando; Fernandes, Antonio Alberto Ribeiro
    This work is concerned with the synthesis and characterization of iron oxide nanoparticles embedded into an activated carbon, giving rise to nanocomposites with magnetic properties. The samples were prepared starting from the mixture of the organometallic compound iron pentacarbonyl and the activated carbon, with various reactant ratios, under argon or ambient atmosphere. The experimental techniques used for the characterization of the products were: Mössbauer spectroscopy, X-ray diffraction - with conventional or synchrotron radiation -, X-ray photoelectron spectroscopy, scanning electron microscopy, textural analysis using nitrogen adsorption, measurements of magnetic properties, elemental analysis and thermogravimety. The results showed that the iron contents in the as prepared samples reached values up to ca. 32 wt.%. The nanoparticles were identified as iron oxides homogeneously dispersed into the activated carbon, with average crystallite sizes in the range 4-6 nm and exhibiting superparamagnetic behaviour at room temperature. The samples prepared under ambient atmosphere showed the predominance of hematite and magnetite, whereas only magnetite was detected in the samples prepared under argon atmosphere. The specific surface area and the total pore volume of the activated carbon showed a reduction of 40 and 50%, respectively, after the formation of the nanoparticles. Heat treatments carried out under inert atmosphere led to the growth of the iron oxide crystallites; the reduction of the iron oxidation state started at ca. 400?C, up to temperatures close to 700 oC. The samples heat treated at 900 oC exhibited the presence of metallic iron as the dominant phase, besides the formation of iron carbides. High-temperature X-ray diffraction experiments performed in situ during the heat treatments revealed the appearance of wüstite as an intermediate phase previous to the formation of metallic iron. The thermal expansion coefficients found for the nanocrystalline iron oxides were considerably higher than the values expected for the bulk phases, an effect associated with the large fraction of surface atoms in the nanoparticles. The results of this work showed that the followed methods of synthesis and subsequent heat treatments allow the achievement of magnetic iron-containing nanoparticles dispersed into the activated carbon matrix. The nature and the average size of these particles depend on the specific experimental conditions, such as the atmosphere of synthesis, the temperature and the time of heat treatment.
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    Utilização de RMN no estado sólido em uma abordagem multinuclear para estudo de materiais carbonosos porosos.
    (Universidade Federal do Espírito Santo, 2017-09-06) Lopes, Thierry Ramos; Freitas, Jair Carlos Checon de; Scopel, Wanderlã Luis; Bueno, Thiago Eduardo Pedreira; Alfonso, Jorge Luis Gonzalez; Bonagamba Tito José; Gontijo, Leonardo Cabral
    This work is concerned with a study of activated carbons prepared by physical and chemical activation, using solid-state nuclear magnetic resonance (NMR) spectroscopy in a multinuclear approach. The activated carbons were obtained starting from the endocarp of babassu coconut (EB), either by physical activation (with steam named as EBF samples) or by chemical activation (using H3P O4 named as EBP samples). The activated carbons exhibited high speci c surface area, with values depending on the experimental conditions used in each synthesis. The 1H NMR spectra of the EBF samples showed two major peaks with chemical shifts changing as a function of the activation temperature. The broader peak was associated with 1H nuclei in aromatic groups, the other being associated with adsorbed water. In order to better understand these results, hydrated samples of milled graphites were also studied by 1H NMR, allowing the identi cation of a signi cant variation of the chemical shift of the peak due to adsorbed water as a function of the increase in the milling time (which caused structural changes in the milled graphites). The chemical nature of the phosphorus-containing species in the EBP samples was studied by 1H, 13C and 31P solid-state NMR spectroscopy, including 2D 1H -31 P correlation experiments, which allowed the detection of the formation of di erent phosphorus compounds (mostly containing phosphate groups) embedded into the porous carbon network. Due to the natural occurrence of silicon compounds in the endocarp of babassu coconut, the chemical activation with H3P O4 was found to produce silicon pyrophosphate nanocrystals. Nanocomposites containing nanostructured Al compounds were obtained by impregnation of EBF and EBP samples with Al(NO3)9H2O, followed by heat treatments at di erent temperatures; 27Al NMR spectra were used to analyze the coordination type of the Al3+ cations present in each sample, which was changed depending on the heat treatment temperature.