Navegando por Autor "Oliveira, Aline A. S."
Agora exibindo 1 - 3 de 3
Resultados por página
Opções de Ordenação
Item Facile preparation of carbon coated magnetic Fe3O4 particles by a combined reduction/CVD process.(2011) Tristão, Juliana Cristina; Oliveira, Aline A. S.; Ardisson, José Domingos; Dias, Anderson; Lago, Rochel MonteroIn this work, we report a simple method for the preparation of magnetic carbon coated Fe3O4 particles by a single step combined reduction of Fe2O3 together with a Chemical Vapor Deposition process using methane. The temperature programmed reactionmonitored by Mo¨ ssbauer, X-ray Diffraction and Raman analyses showed that Fe2O3 is directly reduced by methane at temperatures between 600 and 900 8C to produce mainly Fe3O4 particles coated with up to 4 wt% of amorphous carbon. Thesemagneticmaterials can be separated into two fractions by simple dispersion in water, i.e., a settled material composed of large magnetic particles and a suspended material composed of nanoparticles with an average size of 100–200 nm as revealed by Scanning Electron Microscopy and High-resolution Transmission Electron Microscopy. Different uses for these materials, e.g., adsorbents, catalyst supports, rapid coagulation systems, are proposed.Item Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix : effect on water-oil interfaces.(2010) Oliveira, Aline A. S.; Teixeira, Ivo Freitas; Ribeiro, Leandro Passos; Tristão, Juliana Cristina; Dias, Anderson; Lago, Rochel MonteroNovos compósitos magnéticos anfifílicos foram preparados pelo crescimento de nanotubos e nanofibras de carbono contendo partículas magnéticas através de deposição química de vapor (CVD), utilizando etanol como fonte de carbono e lama vermelha (RM, subproduto do processo Bayer de produção de alumina) como suporte e catalisador. Monitoramento da reação CVD à temperatura programada (TPCVD), difração de raios X (XRD), espectroscopia Mössbauer, espectroscopia de energia dispersiva (EDS), espectroscopia Raman, termogravimetria (TG/DTA), análise elementar (CHN), determinação de área superficial (BET), microscopia eletrônica de varredura (SEM) e de transmissão (TEM) e medidas magnéticas mostraram que etanol reduz íons de ferro na RM para formar fases magnéticas, por exemplo Fe3O4 e Fe0, e depósitos de carbono (5-42 wt.%) na forma de nanotubos e nanofibras. A combinação de nanoestruturas hidrofóbicas de carbono com óxidos hidrofílicos de Al, Si e Ti presentes na lama vermelha produziu materiais anfifílicos com excelente interação com a interface água-óleo. Misturas de óleo de soja ou de decalina com água (completamente imiscíveis) foram emulsificadas facilmente na presença dos compósitos anfifílicos. Quando os compósitos foram adicionados a uma emulsão água-biodiesel estável, as partículas anfifílicas difundiram-se para a interface água- óleo. As partículas do compósito foram atraídas por ímãs e carregaram com elas as gotas de óleo, levando à completa desemulsificação e separação entre biodiesel e água.Item Production of nanostructured magnetic composites based on Fe0 nuclei coated with carbon nanofibers and nanotubes from red mud waste and ethanol.(2011) Oliveira, Aline A. S.; Tristão, Juliana Cristina; Ardisson, José Domingos; Dias, Anderson; Lago, Rochel MonteroIn this work, a catalytic CVD process using ethanol as carbon source was used to convert an iron rich waste, i.e. red mud (RM), in a magnetic composite. TPCVD (temperature programmed CVD), XRD, Mössbauer, EDS, magnetic measurements, TG/DTA, CHN, BET, Raman, SEM and TEM showed that ethanol gradually reduces the iron phases in the RM to Fe3O4 at 500 ◦C and to Fe1−xO at 600 ◦C. At higher temperatures Fe0 and Fe carbide are the main phases produced with the formation of large amounts of carbon (30–50 wt%) especially as nanotubes and nanofibers. These magnetic materials can be separated into two fractions by simple dispersion in water, i.e. a settled material composed of large magnetic particles and the suspended material composed of nanoparticles with average size of 10–100 nm. The carbon in the composites can be activated with CO2 increasing the surface area from 79 to 185m2 g−1. The magnetic composites were used as adsorbent of model dyes methylene blue and indigo carmine showing excellent results. The composites were also used as support to produce a recyclable Pd catalyst. Tests for the 1,5-cyclooctadiene hydrogenation showed that the catalyst can be easily magnetically separated from the reaction medium and reused for five consecutive times with no deactivation or change in selectivity.