M. T. de Oliveira

Bio: M. T. de Oliveira is an academic researcher from University of São Paulo. The author has contributed to research in topics: Hematite & Maghemite. The author has an hindex of 1, co-authored 1 publications receiving 2264 citations.

Raman microspectroscopy of some iron oxides and oxyhydroxides

Abstract: Hematite (α-Fe2O3), magnetite (Fe3O4), wustite (FeO), maghemite (γ-Fe2O3), goethite (α-FeOOH), lepidocrocite (γ-FeOOH) and δ-FeOOH were studied by Raman microscopy. Such compounds have already been studied by Raman spectroscopy, but there are some disagreements in the reported data. Here, Raman microscopy was employed to investigate the laser power dependence of the spectra of these oxides and oxyhydroxides. Low laser power was used for the reference spectra in order to minimize the risks of spectral changes due to sample degradation. The results obtained show that increasing laser power causes the characteristic bands of hematite to show up in the spectra of most of the compounds studied whereas the hematite spectrum undergoes band broadening and band shifts. © 1997 John Wiley & Sons, Ltd.

Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process.

Abstract: The synthesis of highly crystalline and monodisperse γ-Fe2O3 nanocrystallites is reported. High-temperature (300 °C) aging of iron−oleic acid metal complex, which was prepared by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100 °C, was found to generate monodisperse iron nanoparticles. The resulting iron nanoparticles were transformed to monodisperse γ-Fe2O3 nanocrystallites by controlled oxidation by using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters. Transmission electron microscopic images of the particles showed 2-dimensional and 3-dimensional assembly of particles, demonstrating the uniformity of these nanoparticles. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the γ-Fe2O3 structures. Monodisperse γ-Fe2O3 nanocrystallites with a particle size of 13 nm also can be...

Graphene-Wrapped Fe(3)O(4) Anode Material with Improved Reversible Capacity and Cyclic Stability for Lithium Ion Batteries

Abstract: [Zhou, Guangmin; Li, Feng; Zhang, Lili; Li, Na; Wu, Zhong-Shuai; Wen, Lei; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Wang, Da-Wei; Lu, Gao Qing (Max)] Univ Queensland, AIBN, ARC Ctr Excellence Funct Nanomat, Brisbane, Qld 4072, Australia.;Li, F (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;fli@imr.ac.cn cheng@imr.ac.cn

Oxygen-Deficient Hematite Nanorods as High-Performance and Novel Negative Electrodes for Flexible Asymmetric Supercapacitors

Abstract: Oxygen-deficient α-Fe2 O3 nanorods with outstanding capacitive performance are developed and demonstrated as novel negative electrodes for flexible asymmetric supercapacitors. The asymmetric-supercapacitor device based on the oxygen-deficient α-Fe2 O3 nanorod negative electrode and a MnO2 positive electrode achieves a maximum energy density of 0.41 mW·h/cm(3) ; it is also capable of charging a mobile phone and powering a light-emitting diode indicator.

Effects of Fe Electrolyte Impurities on Ni(OH)2/NiOOH Structure and Oxygen Evolution Activity

Abstract: Ni-(oxy)hydroxide-based materials are promising earth-abundant catalysts for electrochemical water oxidation in basic media. Recent findings demonstrate that incorporation of trace Fe impurities from commonly used KOH electrolytes significantly improves oxygen evolution reaction (OER) activity over NiOOH electrocatalysts. Because nearly all previous studies detailing structural differences between α-Ni(OH)2/γ-NiOOH and β-Ni(OH)2/β-NiOOH were completed in unpurified electrolytes, it is unclear whether these structural changes are unique to the aging phase transition in the Ni-(oxy)hydroxide matrix or if they arise fully or in part from inadvertent Fe incorporation. Here, we report an investigation of the effects of Fe incorporation on structure–activity relationships in Ni-(oxy)hydroxide. Electrochemical, in situ Raman, X-ray photoelectron spectroscopy, and electrochemical quartz crystal microbalance measurements were employed to investigate Ni(OH)2 thin films aged in Fe-free and unpurified (reagent-grade)...

The renaissance of iron-based Fischer-Tropsch synthesis: on the multifaceted catalyst deactivation behaviour.

Abstract: Iron-based Fischer–Tropsch catalysts, which are applied in the conversion of CO and H2 into longer hydrocarbon chains, are historically amongst the most intensively studied systems in heterogeneous catalysis. Despite this, fundamental understanding of the complex and dynamic chemistry of the iron–carbon–oxygen system and its implications for the rapid deactivation of the iron-based catalysts is still a developing field. Fischer–Tropsch catalysis is characterized by its multidisciplinary nature and therefore deals with a wide variety of fundamental chemical and physical problems. This critical review will summarize the current state of knowledge of the underlying mechanisms for the activation and eventual deactivation of iron-based Fischer–Tropsch catalysts and suggest systematic approaches for relating chemical identity to performance in next generation iron-based catalyst systems (210 references).