Polyphosphate hybrid materials: photochemistry, (di)electric characterization and its application in electrochemical capacitors / Materiais hÃbridos de polifosfatos: fotoquÃmica, caracterizaÃÃo (di)elÃtrica e sua utilizaÃÃo em capacitores eletroquÃmicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The synergy between the properties of two substances, an organic and another inorganic, can be obtained in a single material by the sol-gel process. The low temperature processing allow the incorporation of organic substances in inorganic matrices. These hybrid materials can have covalent interactions between host and guest (C1), or weak interactions, like van der Waals, hydrogen bonds and electrostatics. These materials present single properties, like mechanical resistance of the inorganic matrix and photoluminescence of the organic phase. In this spirit, the goal of this dissertation was to develop, characterize and apply hybrid materials with luminescence, conductivity and capacitance, where the inorganic matrix resides in the polyphosphate gel. The first system obtained consisted of a hybrid material where the organic molecule was rhodamine B. Such molecule experienced a slow photodegradation under visible light, resulting in a material with strong green luminescence. Chemical tests provided sufficient information to conclude that the dye undergoes N-deethylation by oxygenated radicals photo-produced. In this way, the polyphosphate matrix was utilized to obtain hybrid materials with electrical properties by photochemical method. Hybrids with polyaniline and polypyrrole were obtained. The polypyrrole was synthesized by chemical way, using an oxidizing matrix of ferric polyphosphate, while the polyaniline was photochemically prepared by UV and gamma radiation. All the polymers were in the conducting form, according UVVis- NIR absorption spectroscopy. Chronoamperometric measurements showed that more pyrrole and radiation, in the aniline case, imply in a major electronic conductivity in the final material. Strong space charge polarization was observed in all materials, result of the high ionic strength of the polyphosphate matrix. While the ionic conductivity diminished in the polypyrrole composites, probably due to the water loss, a gain in the protonic conductivity was observed on the polyaniline hybrids. By graphite incorporation on the aluminum and iron polyphosphate matrix, was obtained a material that acted as electrode for electrochemical capacitor. Such device presented lower volumetric capacitance with relation to the same composite, but added of polyaniline polymerized inside the inorganic matrix. Itâs due to the pseudocapacitance of the polyaniline redox processes

ASSUNTO(S)

fotoquÃmica rhodamine rodamina conducting polymers photochemistry relaxaÃÃo dielÃtrica capacitores eletroquÃmicos electrochemical capacitors polÃmeros condutores dielectric relaxatio quimica

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