Estudos de misturas binárias água/acetonitrila empregando sondas eletroativas

• Ano de defesa: 2016
• Autor(a) principal: Batista, Fabio Henrique Ferreira [UNIFESP]
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de São Paulo
• Palavras-chave em Português: Electroactive probes; Microelectrode; Computer simulation; Microheterogeneous system; Interfacial phenomena; Sondas eletroativas; Microeletrodo; Simulação computacional; Sistema micro-heterogêneo; Fenômenos de interface
• Link de acesso: https://sucupira.capes.gov.br/sucupira/public/consultas/coleta/trabalhoConclusao/viewTrabalhoConclusao.jsf?popup=true&id_trabalho=3325376; https://repositorio.unifesp.br/handle/11600/46715

Mixtures of water and acetonitrile form microheterogeneous systems, i.e., in the bulk, both species are not uniformly distributed at molecular level. To extract informations about these systems, systematic studies were performed to evaluate how the presence of acetonitrile, in different proportions, affects the electrochemical behaviour of the electroactive probes (potassium ferricyanide and ferrocyanide, hexaammineruthenium(III) chloride, potassium iodide and hydroquinone) in binary mixtures with water using microelectrode voltammetry. The diffusion coefficients (D) and the half-wave potentials (E1/2) were calculated from the voltammograms registered in mixtures with different ratios between water and acetonitrile for each probe. Those parameters were used to evaluate the affinity of each probe with the solvent molecules. In general, with the increase of acetonitrile content in the mixture, the values of D decreased; the greatest variations on D values were observed for potassium iodide and hexaammineruthenium(III) chloride. Shifts on half-wave potential (E1/2) values were also observed and, then, explained in terms of preferential interaction of the probe with water or acetonitrile molecules; the greatest variations on E1/2 values were observed for hydroquinone. In the specific case of the catodic reduction of ferricyanide, a change in the voltammetric profile in mixtures containing 50 mol% acetonitrile with the formation of an anodic peak was observed, suggesting the adsorption of some material in the electrode, evidenced by the electrochemical quartz crystal microbalance studies. Molecular Dynamics Computer Simulations suggest the formation of microdomains in the bulk of the binary mixture and an accumulation of acetonitrile on working electrode interface, explaining the occurrence of adsorptive processes for ferricyanide experiments, the shift E1/2 values in the voltammograms for the studied probes and the fact of D values change in function of the hydrodynamic radius of each specie.