Juliana C. Tristão

Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix: effect on water-oil interfaces

Novos compositos magneticos anfifilicos foram preparados pelo crescimento de nanotubos e nanofibras de carbono contendo particulas magneticas atraves de deposicao quimica de vapor (CVD), utilizando etanol como fonte de carbono e lama vermelha (RM, subproduto do processo Bayer de producao de alumina) como suporte e catalisador. Monitoramento da reacao CVD a temperatura programada (TPCVD), difracao de raios X (XRD), espectroscopia Mossbauer, espectroscopia de energia dispersiva (EDS), espectroscopia Raman, termogravimetria (TG/DTA), analise elementar (CHN), determinacao de area superficial (BET), microscopia eletronica de varredura (SEM) e de transmissao (TEM) e medidas magneticas mostraram que etanol reduz ions de ferro na RM para formar fases magneticas, por exemplo Fe 3 O 4 e Fe 0 , e depositos de carbono (5-42 wt.%) na forma de nanotubos e nanofibras. A combinacao de nanoestruturas hidrofobicas de carbono com oxidos hidrofilicos de Al, Si e Ti presentes na lama vermelha produziu materiais anfifilicos com excelente interacao com a interface agua-oleo. Misturas de oleo de soja ou de decalina com agua (completamente imisciveis) foram emulsificadas facilmente na presenca dos compositos anfifilicos. Quando os compositos foram adicionados a uma emulsao agua-biodiesel estavel, as particulas anfifilicas difundiram-se para a interface agua- oleo. As particulas do composito foram atraidas por imas e carregaram com elas as gotas de oleo, levando a completa desemulsificacao e separacao entre biodiesel e agua. New magnetic amphiphilic composites were prepared by the catalytic carbon vapor deposition (CVD) growth of carbon nanotubes and nanofibers using ethanol as carbon source and red mud waste (RM, a by-product of the Bayer process of alumina production) as catalyst and support. Temperature-programmed CVD (TPCVD), analyses by X-ray diffractometry (XRD), Mossbauer spectroscopy, energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, thermogravimetry (TG/DTA), elemental analysis (CHN), superficial area determination (BET), scanning (SEM) and transmission (TEM) electron microscopies and magnetic measurements showed that ethanol reduces the iron ions in the red mud to form magnetic phases, e.g., Fe 3 O 4 and Fe 0 , and carbon deposits (5-42 wt.%), particularly nanotubes and nanofibers. The combination of the hydrophobic carbon nanostructures with the hydrophilic Al, Si and Ti oxides present in the RM produced amphiphilic materials with excellent interaction with the water-oil interface. Soybean oil or decalin mixtures with water (completely immiscible) were easily emulsified in the presence of the amphiphilic composites. When the composites were added to stable biodiesel-water emulsions, the amphiphilic particles diffused to the interface oil-water. These composite particles were attracted by a magnet, carrying the oil droplets with them and leading to the complete demulsification and separation of the biodiesel from the water.

Sistema RTP: uma técnica poderosa para o monitoramento da formação de nanotubos de carbono durante o processo por deposição de vapor químico

In this work, a TPR (Temperature Programmed Reduction) system is used as a powerful tool to monitor carbon nanotubes production during CVD (Chemical Vapour Deposition), The experiments were carried out using catalyst precursors based on Fe-Mo supported on Al2O3 and methane as carbon source. As methane reacts on the Fe metal surface, carbon is deposited and H2 is produced. TPR is very sensitive to the presence of H2 and affords information on the temperature where catalyst is active to form different forms of carbon, the reaction kinetics, the catalyst deactivation and carbon yields.

LaFe xMn yMo zO 3 catalysts for the oxidation of volatile aromatic organic contaminants

New mixed perovskites LaFexMnyMozO3 were prepared, characterized and investigated as catalysts for the total oxidation of the model aromatic VOC (Volatile Organic Compound), toluene. The perovskites were characterized by XRD (X-Ray Diffractometry), Mossbauer spectroscopy, TPR (Temperature Programmed Reduction) and BET surface area determination. The results suggested the formation of the perovskite phase with incorporation of all metals in the structure. The catalytic studies were carried out in a Temperature Programmed Reaction system with toluene (1000 ppm) and synthetic air in the gas phase. It was observed that the oxidation of toluene starts at temperature as low as 280 oC and that Mn is responsible for most of the catalytic activity. However, the presence of small amounts of Fe (LaFe0.27Mn0.73O3) leads to an increase in this activity. Stability studies showed that these perovskite catalysts are stable even after 100 h reaction at 400 oC with no significant structural change, as observed by XRD and Mossbauer analyses.

Controlled reduction of LaFe xMn yMo zO3/Al2O3 composites to produce highly dispersed and stable Fe0 catalysts: a Mössbauer investigation

In this work, controlled reduction of perovskites supported on Al2O3 was used to prepare thermally stable nanodispersed iron catalysts based on Fe0/La2O3/Al2O3. The perovskites composites LaFe0.90Mn0.08Mo0.02O3(25, 33 and 50 wt (%)) /Al2O3 and LaFe0.90Mn0.1O3(25 wt (%)) /Al2O3 were prepared and characterized by XRD, BET, TPR, SEM and Mossbauer spectroscopy. XRD for unsupported perovskite showed the formation of a single phase perovskite structure. The Mossbauer spectra of the perovskites were fitted with hyperfine field distribution model for the perovskite. Supported perovskites on Al2O3 showed a decrease of the hyperfine field in respect to unsupported perovskite, due to decrease of particle size and dispersion of the Fe3+ specimens on the support. Also showed broaden lines and relaxation effects due to the small particle size. To produce the Fe0 catalyst, the composite perovskite(25%)/Al2O3 was reduced with H2 at 900, 1000 and 1100 °C for 1 hour. XRD data indicated the formation of Fe0 catalyst with particles sizes of ca. 35 nm. The Mossbauer spectrum showed the formation of metallic iron and doublets corresponding to species of octahedric Fe2+ and Fe3+ sites dispersed on Al2O3. These catalysts showed improved stability towards sintering even upon treatment at 1000 and 1100 °C under H2.