Estudo do comportamento térmico das nanopartículas de Fe3O4 funcionalizadas
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Data
2023-02-28
Autores
Baldini Fumis, Daniel
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Universidade Estadual Paulista (Unesp)
Resumo
A mistura entre os íons de ferro Fe3+ e Fe2+ em uma proporção molar 2:1 leva a formação de óxido de ferro Fe3O4 comumente conhecido como magnetita, a partir da síntese por co-precipitação. As nanopartículas desses óxidos possuem uma superfície muito reativa, podendo sofrer oxidação para estruturas γ-Fe2O3 (maghmita) e α-Fe2O3 (hematita). Com base nisso, é muito importante evitar o processo de oxidação dessas nanopartículas e uma das estratégias para isso é a funcionalização da superfície com moléculas orgânicas ou inorgânicas. Deste modo, no presente trabalho, foi estudado o comportamento térmico das nanopartículas sintetizadas de Fe3O4 e Fe3O4@EDTA, obtidas a partir do método de co-precipitação seguida da funcionalização com EDTA, numa única etapa sintética. As nanopartículas foram caracterizadas com a termogravimetria (TG/DTG), análise térmica diferencial (DTA), calorimetria exploratória diferencial (DSC), difratometria de raios-X (DRX), microscopia eletrônica de varredura (MEV) e de transmissão (MET) e espectroscopia dispersiva de energia de raios X (EDS). Os resultados da análise térmica mostraram um intermediário de reação, γ-Fe2O3, na reação de decomposição das nanopartículas de Fe3O4 e Fe3O4-EDTA, conforme confirmado pelas curvas TG-DTA, DSC e DRX. A formação de α-Fe2O3 ocorreu nas para as duas nanopartículas, porém na nanopartícula funcionalizada o evento térmico foi deslocado para maiores temperaturas, indicando que a funcionalização está estabilizando termicamente está nanopartícula. Os resultados da variação da energia de ativação para a reação de formação de α-Fe2O3 foram maiores para a nanopartícula funcionalizadas o que concorda com os resultados da análise térmica. Além disso, a funcionalização da superfície das nanopartículas alterou o mecanismo de formação de α-Fe2O3 de processo auto-catalítica para Fe3O4 para os processos auto-catálitico (α até 48,2% ) e difusional ( acima de α 48,2%) para a nanopartícula de Fe3O4-EDTA.
The mixture between Fe3+ and Fe2+ iron ions in a 2:1 molar ratio leads to the formation of iron oxide Fe3O4 commonly known as magnetite, from synthesis by co-precipitation. The nanoparticles of these oxides have a very reactive surface and may be oxidized to γ-Fe2O3 (maghmite) and α-Fe2O3 (hematite) structures. Based on this, it is very important to avoid the oxidation process of these nanoparticles and one of the strategies for this is surface functionalization with organic or inorganic molecules. In the present work, the thermal behavior of synthesized nanoparticles of Fe3O4 and Fe3O4@EDTA, obtained from the co-precipitation method followed by functionalization with EDTA, in a single synthetic step, was studied. The nanoparticles were characterized with thermogravimetry (TG/DTG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray diffraction (DRX), scanning electron microscopy (SEM) and transmission (TEM) and X-ray energy dispersive spectroscopy (EDS). The thermal analysis results showed a reaction intermediate, γ-Fe2O3 , in the decomposition reaction of Fe3O4 and Fe3O4-EDTA nanoparticles, as confirmed by the TG-DTA, DSC and DRX curves. The formation of α-Fe2O3 occurred in both nanoparticles, but in the functionalized nanoparticle the thermal event was shifted to higher temperatures, indicating that the functionalization is thermally stabilizing this nanoparticle. The results of the activation energy variation for the α-Fe2O3 formation reaction were higher for the functionalized nanoparticle, which agrees with the results of the thermal analysis. Furthermore, the surface functionalization of the nanoparticles altered the mechanism of formation of α-Fe2O3 from the auto-catalytic process to Fe3O4 for the auto-catalytic (α up to 48.2%) and diffusional (above α 48.2%) processes. for the Fe3O4-EDTA nanoparticle
The mixture between Fe3+ and Fe2+ iron ions in a 2:1 molar ratio leads to the formation of iron oxide Fe3O4 commonly known as magnetite, from synthesis by co-precipitation. The nanoparticles of these oxides have a very reactive surface and may be oxidized to γ-Fe2O3 (maghmite) and α-Fe2O3 (hematite) structures. Based on this, it is very important to avoid the oxidation process of these nanoparticles and one of the strategies for this is surface functionalization with organic or inorganic molecules. In the present work, the thermal behavior of synthesized nanoparticles of Fe3O4 and Fe3O4@EDTA, obtained from the co-precipitation method followed by functionalization with EDTA, in a single synthetic step, was studied. The nanoparticles were characterized with thermogravimetry (TG/DTG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray diffraction (DRX), scanning electron microscopy (SEM) and transmission (TEM) and X-ray energy dispersive spectroscopy (EDS). The thermal analysis results showed a reaction intermediate, γ-Fe2O3 , in the decomposition reaction of Fe3O4 and Fe3O4-EDTA nanoparticles, as confirmed by the TG-DTA, DSC and DRX curves. The formation of α-Fe2O3 occurred in both nanoparticles, but in the functionalized nanoparticle the thermal event was shifted to higher temperatures, indicating that the functionalization is thermally stabilizing this nanoparticle. The results of the activation energy variation for the α-Fe2O3 formation reaction were higher for the functionalized nanoparticle, which agrees with the results of the thermal analysis. Furthermore, the surface functionalization of the nanoparticles altered the mechanism of formation of α-Fe2O3 from the auto-catalytic process to Fe3O4 for the auto-catalytic (α up to 48.2%) and diffusional (above α 48.2%) processes. for the Fe3O4-EDTA nanoparticle
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Palavras-chave
Magnetita, Maghmita, Cinética não-isotérmica, Magnetite, Non isothermal kinetics, Thermal analysis