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Nanopartículas de prata e prata-paládio estabilizadas pela polietilenoimina linear funcionalizada

By Kelly de Oliveira Santos

Abstract

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em QuímicaA proposta deste trabalho foi a síntese, caracterização e estudo da atividade catalítica de nanopartículas (NPs) de prata e bimetálicas prata-paládio utilizando-se a polietilenoimina linear (LPEI) funcionalizada como estabilizante. A LPEI foi funcionalizada por meio de síntese do tipo "paralela" com grupos etanólicos e octílicos. Para a seleção dos melhores estabilizantes das Ag-NPs utilizou-se uma abordagem de processamento rápido e foram selecionados dois estabilizantes: F1 (LPEI funcionalizada com 0,4 eq. cloroetanol) e F12 (LPEI funcionalizada com 0,4 eq. cloroetanol e 0,5 eq. bromoctano). Para a otimização das condições de síntese das Ag-NPs utilizou-se planejamento fatorial. Então, as NPs bimetálicas foram sintetizadas utilizando-se a banda SPR das Ag-NPs como um probe in situ. As F1-AgPd-NPs se mostraram completamente esféricas e ocas, enquanto as NPs preparadas a partir das F12-Ag-NPs se apresentam como esferas porosas. Por fim, foram determinadas as atividade catalíticas: (i) das Ag-NPs na reação de redução do p-nitrofenol utilizando-se NaBH4 como agente redutor, onde foram obtidas as maiores constantes catalíticas encontradas na literatura; e (ii) das AgPd-NPs na reação de oxidação do ácido fórmico, onde apenas o sistema F1-AgPd-NPs foi eficiente, apresentando a maior atividade por área encontrada na literatura. As NPs foram caracterizadas por meio de diversas técnicas.The goal of this work was the synthesis, characterization and catalytic study of silver and bimetallic silver-palladium nanoparticles (NPs) having the modified linear polyethylene imine (LPEI) as stabilizer. In order to achive this goal, the methodoly used was based on five steps: (i) the LPEI functionalization with chloroethanol and bromoctane; (ii) selection of the best Ag-NPs stabilizers using a high-throughput in situ screening; (iii) optimization of the conditions to synthetize the Ag-NPs using a multivariate analysis; (iv) synthesis of bimetallic NPs using the Ag-NPs SPR band as a probe in situ; e (v) determination of Ag-NPs catalytic activity over the p-nitrophenol (Nip) reaction using NaBH4 as a reducing agent and AgPd-NPs catalytic activity over the formic acid oxidation reaction. The NPs were characterized by UV-Vis, TEM, HR-TEM, EDX, XRD, SAXS e DLS techniques. The Ag-NPs were synthesized using two stabilizers: F1 (LPEI functionalized with 0.4 equivalents of chloroethanol) and F12 (LPEI functionalized with 0.4 eq. of chloroethanol and 0.5 eq. of bromoctane). For the Nip reduction reaction (used as a model for the M-NPs catalytic study) with NaBH4 and F1- and F12-Ag-NPs as catalysts the rate constant normalized to the surface area of the NPs per unit volume found were 1.66 and 0.37 s-1 m-2 L, respectively. These values are among the highest ones found in literature. A full kinetic analysis based on the Langmuir model indicates that all species are likely adsorbed and accommodated on the surface before they take part in any reaction, and the Nip molecules hava a much stronger adsorption affinity than BH4- ions for the Ag-NP surface. Finally, using the Ag-NPs as templates, the silver-palladium nanoparticles (AgPd-NPs) were obtained by adding palladium acetate in the reaction medium. These NPs were also fully characterized by the UV-Vis, TEM, HR-TEM, EDX and XRD techniques, and it was possible to verify that the F1-AgPd-NPs are spherical and hollow, while the F12-AgPd-NPs are spherical and solid. The bimetallic NPs were used as catalysts for the formic acid oxidation reaction (for further use in fuell cells), but only the F1-AgPd-NPs system was active. For this system, the electrochemically active surface area (ECSA) found was 1.28 m2 g-1, and the area activity was 61 mA cm-2, the highest value found in the literature, even when compared with nanocatalysts based only in Pd

Topics: Quimica, Nanopartículas, Catalise, Prata, Paladio
Publisher: Florianópolis
Year: 2012
OAI identifier: oai:agregador.ibict.br.RI_UFSC:oai:repositorio.ufsc.br:123456789/99481
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