Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-01-04T20:50:47Z No. of bitstreams: 1 AndreLuisLopesMoriyama_TESE.pdf: 5424215 bytes, checksum: 7e441e3f7c8e167e83a6733578cbcab5 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-01-05T22:00:58Z (GMT) No. of bitstreams: 1 AndreLuisLopesMoriyama_TESE.pdf: 5424215 bytes, checksum: 7e441e3f7c8e167e83a6733578cbcab5 (MD5) / Made available in DSpace on 2016-01-05T22:00:58Z (GMT). No. of bitstreams: 1 AndreLuisLopesMoriyama_TESE.pdf: 5424215 bytes, checksum: 7e441e3f7c8e167e83a6733578cbcab5 (MD5) Previous issue date: 2014-11-06 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / Esta tese ? parte de pesquisa sobre novos materiais para catalisadores e sensores de g?s mais ativos, sens?veis, e seletivos. O objetivo desta tese foi desenvolver e caracterizar ferrita de cobalto em diferentes morfologias, a fim de estudar sua influ?ncia sobre a resposta el?trica e a atividade catal?tica do material. Foi tamb?m de hierarquizar estes nanocristalitos para obter maior difusividade do g?s no material. Os p?s foram produzidos via hidrot?rmica e solvot?rmica, e foram caracterizados por termogravimetria, difra??o de raios X, microscopia eletr?nica de varredura, microscopia eletr?nica de transmiss?o (difra??o de el?trons, simula??es de alta resolu??o), e espectroscopia de energia dispersiva. As propriedades catal?ticas e el?tricas foram testados em presen?a dos gases CO e NO2, este ?ltimo em diferentes concentra??es (1- 100 ppm), e a diferentes temperaturas (temperatura ambiente at? 350 ?C). Nanooctaedros com tamanho m?dio de 20 nm foram obtidos por via hidrot?rmica. Determinou-se que a forma dos cristalitos est? principalmente associada ? natureza do agente precipitante e ? presen?a de ?ons OHno meio de rea??o. Por via solvot?rmico, foram preparados p?s esf?ricos de CoFe2O4 e com tamanho de cristalitos de 8 e 20 nm. Os p?s de CoFe2O4 apresentam uma resposta forte a pequenas quantidades de NO2 (10 ppm a 200 ?C). Os nanooctatedros tem maior sensibilidade do que os cristalitos esf?ricos de mesmo tamanho, e apresentam menor tempo de resposta e menor tempo de retorno. Estes resultados foram confirmados atrav?s da modelagem da cin?tica de resposta e de recupera??o do sensor. Testes iniciais de atividade catal?tica na rea??o de oxida??o do CO entre 100 ? e 350 ? C mostram que o efeito do tamanho ? predominante em rela??o ao efeito da forma no que diz respeito ? convers?o da rea??o. A morfologia dos cristalitos nanom?tricos influenciou a taxa da rea??o. Uma maior taxa de rea??o ? obtida em presen?a de nanooctaedros. A fim de melhorar as propriedades de detec??o e catal?ticas do material, n?s desenvolvemos uma metodologia de hierarquiza??o de nanocristalitos que envolve o uso de templates a base de carbono. / This thesis is part of research on new materials for catalysis and gas sensors more active, sensitive, selective. The aim of this thesis was to develop and characterize cobalt ferrite in different morphologies, in order to study their influence on the electrical response and the catalytic activity, and to hierarchize these grains for greater diffusivity of gas in the material. The powders were produced via hydrothermal and solvothermal, and were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy (electron diffraction, highresolution simulations), and energy dispersive spectroscopy. The catalytic and electrical properties were tested in the presence of CO and NO2 gases, the latter in different concentrations (1-100 ppm) and at different temperatures (room temperature to 350 ? C). Nanooctahedra with an average size of 20 nm were obtained by hydrothermal route. It has been determined that the shape of the grains is mainly linked to the nature of the precipitating agent and the presence of OH ions in the reaction medium. By solvothermal method CoFe2O4 spherical powders were prepared with grain size of 8 and 20 nm. CoFe2O4 powders exhibit a strong response to small amounts of NO2 (10 ppm to 200 ? C). The nanooctahedra have greater sensitivity than the spherical grains of the same size, and have smaller response time and shorter recovery times. These results were confirmed by modeling the kinetics of response and recovery of the sensor. Initial tests of catalytic activity in the oxidation of CO between temperatures of 100 ?C and 350 ?C show that the size effect is predominant in relation the effect of the form with respect to the conversion of the reaction. The morphology of the grains influence the rate of reaction. A higher reaction rate is obtained in the presence of nanooctahedra. In order to improve the detection and catalytic properties of the material, we have developed a methodology for hierarchizing grains which involves the use of carbonbased templates.