Navegando por Assunto "silica"
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Item Síntese e caracterização de nanopartículas de maguemita recobertas com sílica funcionalizada com grupos amina(Universidade Federal de Goiás, 2008-11-25) ALMEIDA, Michelly Patrícia Santana de; SARTORATTO, Patrícia Pommé Confessori; http://lattes.cnpq.br/9777959525393785Magnetic nanoparticles coated with several kinds of materials have been the focus of intense research due to their potential applications in biomedicine. This type of material contains a magnetic core that is involved by a shell of different composition. The coating of magnetic nanoparticles with amino-functionalized silica is particularly important because of its reactivity which allows the coupling with biological molecules such as fragments of DNA, antibodies, proteins, among others. In this work, maghemite nanoparticles were coated with silica and with amino-functionalized silica, the incorporation of them being achieved by using tetraethoxysilane (TEOS) and aminopropyltrimethoxysilane (APTS) as the precursors of the sol-gel system. Firstly, the magnetic fluids of maghemita were prepared and afterwards they were employed in the silica-coating procedures which were based on the Stöber method. Some experimental parameters were varied, such as the number of maghemita nanoparticles, pH of the reaction medium, time of reaction and amount of TEOS, with the aim of modulating the characteristics of the solids and obtaining stable aqueous suspensions of the materials. All products were analyzed by the following techniques: X- ray diffraction, diffuse reflectance infrared spectroscopy, dynamic light scattering, electrophoretic mobility (zeta potential) and transmission electron microscopy.Item Síntese e caracterização de compósitos mesoporosos de sílica-óxido de cobalto e avaliação catalítica na reação de redução de no com CO(Universidade Federal de Goiás, 2010-08-31) SANTOS, Gustavo Amorim; SARTORATTO, Patrícia Pommé Confessori; http://lattes.cnpq.br/9777959525393785In this work, a methodology for the synthesis of silica-cobalt oxide-based composites was developed by modifying the well known Stöber sol-gel method. The main novelty of the procedure was the use of colloidal suspensions of cobalt oxide or cobalt hydroxide nanoparticles (Co3O4,Co(OH)2), which were previously prepared from the precipitation of Co2+ ions in alkaline medium. The silica-cobalt composites having cobalt contents (w/w) around 8.4 to 11% were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG/DTA), temperature programmed reduction (TPR) and adsorption /desorption of nitrogen. The characteristics of the composites which were prepared by employing the colloidal suspensions were compared to those exhibited by other composites which were obtained from cobalt nitrate solution. The influence of cerium nitrate and citric acid was also evaluated. The methodology employed in the synthesis of nanoparticles and composites were reproducible and the prepared materials showed surface areas (300 to 567 cm3/g) and pore diameters (3.8 to 8.1 nm) values which were considered appropriate to use them as catalysts. The calcined composites which were prepared using colloidal suspensions of Co3O4 nanoparticles showed TPR curves with maximum picks at relatively low temperatures, in the range of 275 to 520 oC, suggesting the existence of weak silica-cobalt interactions. The average diameter of Co3O4 crystallites varied from 22 to 30 nm. However, the use of citric acid as a pore-forming agent in the sol-gel synthesis led to composites with enhanced silica-cobalt interactions as a result of the dissolution of the cobalt oxide particles and formation of cobalt silicate. The incorporation of cerium nitrate in the sol-gel mixture did not modify the textural properties of the composites but the reduction of cobalt oxide to metallic cobalt was retarded. The composite which was obtained from the cobalt hydroxide, β-Co(OH)2, colloidal suspension showed weak silica-cobalt interactions as well as intermediate ones, the average diameter of Co3O4 crystallites being 12 nm. Differently from the composites obtained from colloidal suspensions, those which were synthesized using a cobalt nitrate aqueous solution presented mainly cobalt silicate and a low quantity of Co3O4 particles of 11 and 17 nm. The TPR curves of these composites indicated very strong silica-cobalt interactions, as expected. The composites were evaluated as catalysts in the reduction reaction of NO to N2 with the oxidation of CO to CO2. The composites which were prepared from Co3O4 colloidal suspensions without the use of citric acid as pore-forming agent showed maximum conversions as high as 90% for both NO to N2 and CO to CO2, at temperatures above 600°C. On the other hand, the composite prepared using critic acid showed much lower conversions (60 %) at the same temperature.Item Parâmetros físico-ambientais para compartimentação geoambiental e delimitação da ocorrência de solos coesos na depressão do São Francisco, BA(Universidade Federal de Goiás, 2014-09-02) Santos, Joildes Brasil; Castro, Selma Simões de; http://lattes.cnpq.br/4460827622247417; Chrem, Luis Felipe Soares; http://lattes.cnpq.br/8363108286297687; Momoli, Renata Santos; http://lattes.cnpq.br/4153268939426905; Castro, Selma Simões de; http://lattes.cnpq.br/4460827622247417Studies on cohesive soils in Brazil and worldwide indicate that cohesion in the soil is a factor of natural limitation to agricultural use. However, in the region of the Coastal Tablelands in Northeast Brazil these soils are used through use and management techniques adapted to their natural limitations, such as high resistance to penetration, hard when dry and friable when moist, with high density and reduced effective depth, depending of dense horizon. As for the cohesion process in the soil, would be related to the accumulation clay soil filling the pores and increase its density, making them more resistant to penetration of roots. The silicification process could also be related to the formation of cohesive horizon because that silica is one of the principal cementing agents in this process in various regions of the planet. In addition, climate alternating between dry season and wet season this would also enhance soil compaction. In this study we discuss the presence of soils with cohesive horizon in Oxisols and Ultisols Yellow Yellows geomorphological unit called Depression of the San Francisco-BA, focusing on the area of the snail farm that featured a soil survey in detail. From a geo-environmental partitioning was presented a summary with the main features of the landscape, in order to understand the environment in which this type of soil occurs. And with the help of physical and environmental parameters of the relief (hipsometria, slope and curvature of the sides), use and vegetation and soil properties (isovalue of clay and silica content), it was possible to create a map with the location of the area with potential occurrence of cohesive soils for Farm Caracol, which certainly extends outside its boundaries.