Aline A. S. Oliveira

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.

Biphasic oxidation promoted by magnetic amphiphilic nanocomposites undergoing a reversible emulsion process

Magnetic amphiphilic nanocomposites (MANCs) based on nanoalumina and carbon nanostructures were produced and applied as catalysts for biphasic reactions. These amphiphilic composites (MANCs) exhibit an excellent interaction at the interface of systems composed of immiscible liquids and can form stable emulsions between them. Being magnetic, the composites can also be used to break other stable emulsions or make the emulsions formed reversible. In this work, we report the first use of magnetic amphiphilic nanocomposites to promote biphasic reactions undergoing a magnetically reversible emulsion process. Fe and Mo catalysts were supported on the surface of nanoalumina to grow carbon nanostructures by a CVD process. To achieve the amphiphilic property, the carbon coating on the surface of the matrix is only partial. Thus, exposed iron sites can be active to catalysis. For this reason the biphasic selective oxidation of organic contaminants by hydrogen peroxide was studied. Fe species catalyze the decomposition of H2O2 into ˙OH very close to the substrate and intensify the biphasic reaction. The oxidized compounds are then extracted by the aqueous phase by polarity. The amphiphilic nanocomposites showed a high activity for the oxidation of model contaminants, reaching 100% of removal. The composites can be recovered by a magnetic field and reused several times with good efficiency.

The combined effect between Co and carbon nanostructures grown on cordierite monoliths for the removal of organic contaminants from the liquid phase

Carbon nanostructures were grown on the surface of cordierite monoliths using Fe or Co nanoparticles by catalytic chemical vapor deposition (CCVD) using ethanol in order to intensify the interaction of this support with organic contaminants. The materials produced were extensively characterized by X-ray diffraction, thermal analysis, elemental analysis, atomic absorption spectrometry, Raman spectroscopy and scanning and transmission electron microscopies. These materials were tested in the removal of quinoline and methylene blue from liquid solutions. Promising results were attributed to the combined effect of the hydrophobic carbon nanostructures in adsorbing the organic contaminants with cobalt metal cores that are able to promote the oxidation of the adsorbed molecules via a heterogeneous Fenton process.

Magnetic amphiphilic nanocomposites based on silica–carbon for sulphur contaminant oxidation

Silica and carbon based magnetic amphiphilic nanocomposites (MANCs) were synthesized and applied for desulfurization in this work. The structure, composition, and magnetic and amphiphilic properties of the resulting MANCs were characterized in detail by physicochemical means such as XRD, elemental analysis, Raman spectroscopy, electron microscopies, thermal analysis, TPR, Mossbauer spectroscopy, magnetization measurements, and contact angle measurements. Different concentrations of Fe and Mo were supported on the surface of silica in order to catalyse the controlled growth of carbon nanotubes and nanofibers by chemical vapor deposition (CVD). The partial coating of hydrophilic silica with hydrophobic carbon nanostructures imparts amphiphilicity, which makes the composites strategic catalysts to promote emulsion formation and to act on the interface. Moreover, during the CVD process magnetic species were produced conferring magnetic properties which can facilitate the emulsion breakage by a simple magnetic process. Studies on desulfurization reactions catalysed by these nanocomposites were promising and showed that Mo plays an important role in the catalyst efficiency.