Flávia C.C. Moura

Controlled reduction of red mud waste to produce active systems for environmental applications: Heterogeneous Fenton reaction and reduction of Cr(VI)

In this work, controlled reduction of red mud with H(2) was used to produce active systems for two different environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Mössbauer, powder X-ray diffraction, thermal analyses and scanning electron microscopy analyses showed that at different temperatures, i.e. 300, 400, 500 and 600 degrees C, H(2) reduces red mud to different phases, mainly Fe(3)O(4), Fe(0)/Fe(3)O(4) and Fe(0). These Fe phases are dispersed on Al, Si and Ti oxides present in the red mud and show high reactivity towards two environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Reduction with H(2) at 400 degrees C showed the best results for the oxidation of the model dye methylene blue with H(2)O(2) at neutral pH due to the presence of the composite Fe(0)/Fe(3)O(4). The reduced red mud at 500-600 degrees C produced Fe(0) highly active for the reduction of Cr(VI) in aqueous medium. Another feature of these red mud based system is that after deactivation due to extensive use they can be completely regenerated by simple treatment with H(2).

Iron: a versatile element to produce materials for environmental applications

Iron is a versatile element forming several phases with different oxidation states and structures, such as Feo, FeO, Fe3O4, γ-Fe2O3, α-Fe2O3 and FeOOH. All these phases have unique physicochemical properties which can be used for different applications. In this work, it is described the use of different iron compounds, synthetic and also from natural and waste sources, in environmental and technological applications. Two main research areas are described. The first one is related to strategies to increase the reactivity of Fe phases, mainly by the formation of Feo/iron oxide composites and by the introduction of new metals in the iron oxide structure to promote new surface reactions. The second area is the use of the magnetic properties of some iron phases to produce versatile magnetic materials with focus in adsorption, catalysis and emulsions.

Nanostructured vanadium-doped iron oxide: catalytic oxidation of methylene blue dye

V-doped iron oxides are used as heterogeneous catalysts to oxidize the dye methylene blue in an aqueous medium containing hydrogen peroxide. XRD and Mossbauer spectroscopy reveal that vanadium is incorporated into the iron oxide structure. The H2O2 pretreatment of the solid catalyst promotes important surface and structural changes in the iron oxides primarily due to the formation of peroxo-vanadium complexes, which specifically enhance the catalytic properties of the material. Transmission electron microscope images show that the H2O2 treatment also tends to decrease the mean particle size of the material grains. V-doped iron oxides were found to play an important role as solid catalysts in H2O2 reactions. The prepared vanadium containing iron oxide was confirmed to exhibit remarkable catalytic activity for the oxidation of methylene blue, an important contaminant from textile industry. In fact, the ESI-MS spectrum obtained for methylene blue after reaction with the V-doped oxide shows hydroxylation by hydroxyl radicals in solution forming species with m/z = 130 and m/z = 110.

Investigation of the solid state reaction of LaMnO3 with Feº and its effect on the catalytic reactions with H2O2

In this work, the reaction of the perovskite LaMnO3.15 with Feo has been promoted by thermal treatment of the mixture Feo/LaMnO3.15 at 200, 400 and 600 oC. Mossbauer spectroscopy, X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed desorption (O2-TPD) analyses suggested that at 400 and 600 oC oxygen from perovskite is transferred to Feo to produce an oxygen deficient perovskite, LaMnO3-d, and highly dispersed iron oxides, mainly Fe3O4 and FeO. XRD lattice parameters and crystallite size showed that LaMnO3 suffers a strong lattice distortion after reaction but no collapse of the perovskite structure. Reactivity studies pointed to a special interface effect of Feo/LaMO3 towards two reactions with H2O2, the decomposition to O2 and the oxidation of the model molecule, the methylene blue dye. As the treatment temperature of the Feo/LaMnO3.15 increased, the activity for H2O2 decomposition decreased, whereas the activity for the dye oxidation increased. These results are discussed in terms of a decrease in the concentration of Mn4+surf and Mn3+surf species, active for the H2O2 decomposition, with the formation of Mn2+surf and Fe2+surf species, active for the Fenton reaction.

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.

Magnetic composites based on metallic nickel and molybdenum carbide: A potential material for pollutants removal

New magnetic composites based on metallic nickel and molybdenum carbide, Ni/Mo(2)C, have been produced via catalytic chemical vapor deposition from ethanol. Scanning electron microscopy, thermal analysis, Raman spectroscopy and X-ray diffraction studies suggest that the CVD process occurs in a single step. This process involves the reduction of NiMo oxides at different temperatures (700, 800 and 900°C) with catalytic deposition of carbon from ethanol producing molybdenum carbide on Ni surface. In the absence of molybdenum the formation of Ni/C was observed. The magnetic molybdenum carbide was successfully used as pollutants removal by adsorption of sulfur and nitrogen compounds from liquid fuels and model dyes such as methylene blue and indigo carmine. The dibenzothiofene adsorption process over Ni/Mo(2)C reached approximately 20 mg g(-1), notably higher than other materials described in the literature and also removed almost all methylene blue dye. The great advantage of these carbide composites is that they may be easily recovered magnetically and reused.

A novel floating photocatalyst device based on cloth canvas impregnated with iron oxide

In this paper an innovative and versatile design for a catalytic photoreactor is presented. The photoreactor is based on a floating Polypropylene non-woven fabric canvas (NWF) impregnated with particles of a mixture of iron oxides and oxyhydroxides adhered to the surface of microfibers. The canvas was characterized with different techniques including Mossbauer spectroscopy, Raman scattering, FTIR, and SEM. UV-Vis spectroscopy showed that the impregnated particles presented an average gap of 2.2 eV. The activity and efficiency of the photocatalyst was tested by photodegradation of rhodamine-B (Rh-B) and the results showed that the floating photocatalyst has a high catalytic activity and maintains its efficiency even after five reuse tests at intervals of 90 min with a small average residual concentration of 6.2% Rhodamine-B in each reuse cycle.

Unique catalytic behaviour of Ir4 clusters for the selective hydrogenation of 1,5-cyclooctadiene

Abstract In this work we compare the unique catalytic behaviour of Ir 4 clusters on the selective hydrogenation of 1,5-cyclooctadiene to cyclooctene with the mono and dinuclear Ir precursors which produce exclusively the total hydrogenation product cyclooctane.

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.

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.