E. R. Leite

Universidade Federal de São Carlos, São Carlos do Pinhal, São Paulo, Brazil

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Publications (451)737.23 Total impact

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    ABSTRACT: A new magnetically recoverable nanocatalyst was prepared by coating magnetite with niobium oxide (Fe3O4@Nb2O5) by using a simple wet impregnation method. The Fe3O4@Nb2O5 nanocatalyst was fully characterized, and its catalytic activity was evaluated by using the one-pot, three-component Biginelli reaction, with the aim to synthesize 1,4-dihydropyrimidinones, a class of compounds with diverse pharmacological properties. The developed protocol was applied to a wide range of aliphatic and aromatic substrates, and structurally diverse products were obtained in excellent yields. Compared with copper and nickel nanocatalysts, the Fe3O4@Nb2O5 nanocatalyst demonstrated superior catalytic activity at a remarkably low catalyst loading (0.1 mol %). This niobium nanocatalyst could be easily separated from the reaction mixture with an external magnet and was reused several times without any loss of its catalytic activity. Moreover, although the Biginelli reaction is a century-old reaction, its mechanism is still a controversial subject, and our investigation provided an insight into the reaction mechanism.
    ChemCatChem 10/2014; · 5.18 Impact Factor
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    ABSTRACT: We have studied the experimental conditions needed to produce LaNiO3 (LNO) nanostructures using a template-assisted method. In this route, a mesoporous anodic aluminum oxide template was filled with a chemical solution that had been prepared with polymeric precursors route. The precursor solutions and synthesized samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis, infrared spectroscopy and high-resolution scanning electron microscopy (HRSEM). The XRD results for the samples that were heat-treated at 700 degrees C revealed that these samples crystallize in a perovskite-like LaNiO3 structure. HRSEM images revealed that the samples prepared with different deposition times (0.5, 1 and 2 h) promoted the formation of LaNiO3 nanotubes with different wall thicknesses.
    Journal of Nanoscience and Nanotechnology 06/2014; 14(6):4431-6. · 1.15 Impact Factor
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    ABSTRACT: This work reports the analysis of the distribution of Gd atoms and the quantification of O vacancies applied to individual CeO2 and Gd-doped CeO2 nanocrystals by electron energy-loss spectroscopy. The concentration of O vacancies measured on the undoped system (6.3±2.6 %) matches the expected value given the typical Ce3+ content previously reported for CeO2 nanoparticles. The doped nanoparticles have an uneven distribution of dopant atoms and an atypical amount of O vacant sites (37.7±4.1 %). The measured decrease of the O content induced by Gd doping cannot be explained solely by the charge balance including Ce3+ and Gd3+ ions.
    Chemistry 05/2014; 20(21). · 5.93 Impact Factor
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    ABSTRACT: The catalytic CH4 dry reforming reaction is a means of fixing CO2 producing syngas and carbon nanotubes. This study shows that it is possible to match a large consumption of CO2 with the formation of a large amount of carbon nanotubes.
    Chinese Journal of Catalysis 04/2014; 35(4):514–523. · 1.30 Impact Factor
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    ABSTRACT: Layered molybdenum disulfide (MoS2) is deposited by microwave heating on a reduced graphene oxide (RGO). Three concentrations of MoS2 are loaded on RGO, and the structure and morphology are characterized. The first layers of MoS2 are detected as being directly bonded with the oxygen of the RGO by covalent chemical bonds (Mo-O-C). Electrochemical characterizations indicate that this electroactive material can be cycled reversibly between 0.25 and 0.8 V in 1 m HClO4 solution for hybrids with low concentrations of MoS2 layers (LCMoS2/RGO) and between 0.25 and 0.65 V for medium (MCMoS2/RGO) and high concentrations (HCMoS2/RGO) of MoS2 layers on graphene. The specific capacitance measured values at 10 mV s−1 are 128, 265, and 148 Fg−1 for the MoS2/RGO with low, medium, and high concentrations of MoS2, respectively, and the calculated energy density is 63 W h kg−1 for the LCMoS2/RGO hybrid. This supercapacitor electrode also exhibits superior cyclic stability with 92% of the specific capacitance retained after 1000 cycles.
    Advanced Energy Materials 04/2014; 4(6). · 14.39 Impact Factor
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    ABSTRACT: Electronic properties of self-assembled high crystalline quality fluorine-doped tin oxide (FTO) nanobelts were studied. We report the experimental transport data of a thin film made using a dispersion of these single-crystal nanobelts. We have shown that the theory of weak localization in a weak disorder regime provides a reasonable description of the observed electrons’ transport characteristics of fluorine doped tin oxide nanobelts thin films. Also, our results suggest that the macroscopic extrinsic disorder, related to the random distribution of nanobelts, does not give a noticeable contribution to the whole transport mechanism.
    Journal of Physics and Chemistry of Solids 01/2014; 75(5):583–587. · 1.53 Impact Factor
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    ABSTRACT: Multiferroic laminated ceramic composites consisting of piezoelectric (BaTiO3, phase B)-magnetostrictive (La0.7Ba0.3MnO3, phase L) materials were synthesized by the Pechini method. The composites were sintered separately and in the form of L–B–L, in order to compare the properties of the separate phases and the laminated material. X-ray diffraction analysis of the separate phases revealed a tetragonal structure with the P4/mm space group for the B phase, and an orthorhombic structure with the R-3cH space group for the L phase. The dielectric and magnetic properties, as well as the magnetoelectric coupling coefficients (αMEαME), were measured as a function of frequency. The dielectric constants at 1 kHz were 1560 for the separate B phase and 2970 for the L–B–L sample. Magnetization measurement of the L–B–L pellet showed that the ferromagnetic transition temperature (TCTC) was around 304 K. Transverse (α31ME) and longitudinal (α33ME) magnetoelectric coupling coefficients were measured for the L–B–L sample at room temperature, and the maximum values obtained were 0.55 and 0.52 mV cm−1 Oe−1, respectively.
    Journal of Magnetism and Magnetic Materials 01/2014; 364:18–23. · 2.00 Impact Factor
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    ABSTRACT: Bismuth titanate (Bi4Ti3O12 and Bi12TiO20) powders were synthesized by the Oxidant Peroxide Method (OPM), and the effect of temperatures on physical and chemical properties of particles was investigated. The results showed that the morphology and average particle size of materials can be successfully controlled by adjusting the temperature. The samples after calcination were characterized by X-ray diffractometry, transmission electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy, and BET isotherms. The photocatalytic activity of materials was also evaluated by studying the degradation of 10 ppm aqueous rhodamine B dye under ultraviolet radiation.
    Journal of Colloid and Interface Science 01/2014; 415:89–94. · 3.55 Impact Factor
  • Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2014; 462:45–51. · 2.11 Impact Factor
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    ABSTRACT: Single crystalline Zn3P2 nanowires were synthesized on Si substrates via vapour phase deposition catalysed by In-Au seeds. Single nanowire devices were fabricated and the metal-Zn3P2 nanowire contacts were studied using a model based on two Schottky barriers as a function of temperature. As far we know, these are the first reported values of Schottky barriers of Ti/Zn3P2 nanowire contacts. The obtained values showed no significant dependence on the temperature, indicating that the defects at the nanowire's surfaces did not affect the device characteristics. We found evidence of an acceptor level at 49 meV, also indicating that the dominant transport mechanism is the thermal activation of carriers as is found in the bulk Zn3P2. It seems that the p-type behaviour is independent of the dimensionality of the Zn3P2 samples and primarily associated with the phosphorous interstitial atoms.
    Semiconductor Science and Technology 01/2014; 29(1):5001-. · 1.92 Impact Factor
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    ABSTRACT: Fluorine doped SnO2 (FTO) nanobelts were synthesized and their transport properties, such as conduction mechanism, mobility, carrier density and density of states (DOS) were investigated. Variable range hopping was observed as the dominant mechanism in a large range of temperature (40-260 K). Through these data we estimated the localization length and hopping distance at 300 K of FTO nanobelts exhibiting a three-dimensional character for carrier transport. The carrier mobility was calculated to be 48 cm2 V-1 s-1 for samples with carrier density of 2 × 1018 cm-3. Taking into account the parameters obtained from temperature-dependent resistivity and the above data, the characteristic DOS at Fermi level in our samples was found.
    Journal of Physics D Applied Physics 12/2013; 47(4). · 2.53 Impact Factor
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    ABSTRACT: A theoretical approach aiming at the prediction of segregation of dopant atoms on nanocrystalline systems is discussed here. It considers the free energy minimization argument in order to provide the most likely dopant distribution as a function of the total doping level. For this, it requires as input (i) a fixed polyhedral geometry with defined facets, and (ii) a set of functions that describe the surface energy as a function of dopant content for different crystallographic planes. Two Sb-doped SnO2 nanocrystalline systems with different morphology and dopant content were selected as a case study, and the calculation of the dopant distributions expected for them is presented in detail. The obtained results were compared to previously reported characterization of this system by a combination of HRTEM and surface energy calculations, and both methods are shown to be equivalent. Considering its application pre-requisites, the present theoretical approach can provide a first estimation of doping atom distribution for a wide range of nanocrystalline systems. We expect that its use will support the reduction of experimental effort for the characterization of doped nanocrystals, and also provide a solution to the characterization of systems where even state-of-art analytical techniques are limited.
    Physical Chemistry Chemical Physics 11/2013; · 4.20 Impact Factor
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    ABSTRACT: This work presents the morphological characterization of CeO2 nanocrystals by the analysis of single unfiltered high-angle annular dark-field (HAADF)-high-resolution scanning transmission electron microscopy (HRSTEM) images. The thickness of each individual atomic column is estimated by the classification of its HAADF integrated intensity using a Gaussian mixture model. The resulting thickness maps obtained from two example nanocrystals with distinct morphology were analyzed with aid of the symmetry from the CeO2 crystallographic structure, providing an approximation for their 3-D morphology with high spatial resolution. A confidence level of +/-1 atom per atomic column along the viewing direction on the thickness estimation is indicated by the use of multislice image simulation. The described characterization procedure stands out as a simple approach for retrieving morphological parameters of individual nanocrystals, such as volume and specific surface areas for different crystalline planes. The procedure is an alternative to the tilt-series tomography technique for a number of nanocrystalline systems, since its application does not require the acquisition of multiple images from the same nanocrystal along different zone axes.
    Nanoscale Research Letters 11/2013; 8(1):475. · 2.52 Impact Factor
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    ABSTRACT: Cerium oxide (ceria) has attracted attention because of its important applications such as solid oxide fuel cells, catalysts for automobile exhaust gas, catalysts to obtain hydrogen, UV blockers, biomaterials, etc.. Control methods for synthesis of ceria are of great importance to explain or predict these properties. Thus, the objective of this work was to study the growth of cerium oxide nanobelts in a microwave-assisted hydrothermal system, where in 8 min 330 nm nanobelts were obtained at 130 ºC and 3 atm. The results collaborate to the research on reformers for ethanol and/or solid oxide fuel cells anode.
    Cerâmica 09/2013; 59(351):426-430.
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    ABSTRACT: In this Chapter we review some of our latest results regarding the growth, characterization and magnetic properties of bulk samples (composite fibers) of the optimally doped La 1-x Ce x MnO 3 manganites by using the Laser Heated Pedestal Growth technique. It has been widely recognized that, in comparison with the hole doped manganite (like, e.g., La 1-x Ca x MnO 3), its electron doped counterpart La 1-x Ce x MnO 3 is a metastable phase. That is why, before optimizing the growth conditions, we were able to grow polycrystalline multiphase fibers. Their composition and granularity were verified through Scanning Electron Microcopy with Energy Dispersive X-ray analysis. The magnetic behavior of the fibers was probed by AC susceptibility and magnetization measurements as a function of temperature. Several ferromagnetic transitions were identified. In addition to a weak transition at T C0 =45K (due to MnO 2 impurities), three more transitions with Curie temperatures T C1 =126K, T C2 =180K, and T C,max =300K were observed and linked to fiber regions with cerium concentration of x=0.063, x=0.13, and x=0.3,respectively.
    05/2013: pages 71-80; , ISBN: 978-1-62618-097-0
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    ABSTRACT: Much has been talking about the advantages of polymeric nanocomposites, but little is known about the influence of nanoparticles on the stability of these materials. In this sense, we studied the influence of both oxides of zirconium and titanium, known to have photocatalytic properties, as well as the influence of synthetic clay Laponite on the photodegradation of styrene–butadiene rubber (SBR). SBR nanocomposites were prepared by the colloidal route by mixing commercial polymer lattices and nanometric anatase TiO2, monoclinic ZrO2 or exfoliated Laponite clays colloidal suspensions. To better understand the degradation mechanisms that occur in these nanocomposites, the efficiency of different photocatalysts under ultraviolet radiation was monitored by FT‐IR and UV–vis spectroscopies and by differential scanning calorimetric. It was observed that TiO2 and ZrO2 nanoparticles undoubtedly acted as catalysts during the photodegradation process with different efficiencies and rates. However, when compared to pure SBR samples, the polymer degradation mechanism was unaffected. Unlike studies with nanocomposites montmorillonite, exfoliated laponite clay effectively acts as a photostabilizer of polymer UV photodegradation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 05/2013; 128(4). · 1.40 Impact Factor
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    ABSTRACT: In this research, high resolution transmission electron microscopy (HRTEM) and high angle annular dark field–scanning transmission electron microscopy (HAADF-STEM) studies of ceria(IV) oxide CeO2 nanocrystals (NCs) synthesized by a hydrothermal/two phase process were conducted. The synthesis route affords the possibility of controlling the shape of the CeO2 NCs by changing the oleic acid/cerium ([OLA]/[Ce3+]) ratio. At a relatively low [OLA]/[Ce3+] ratio of 4, a polyhedral NC morphology was obtained with {111} and {200} termination facets. Increasing the [OLA]/[Ce3+] ratio to 8, while maintaining a constant reaction time and temperature during the synthesis, truncated cube-like CeO2 NCs with {200}, {220}, and {111} termination facets was generated. These morphologies were identified by HRTEM and HAADF-STEM characterization. Fourier transform infrared (FT-IR) analysis and thermogravimetric analysis (TGA) confirm the presence of chemically bonded oleic acid (OLA) on the CeO2 NC surface. It indicates that there is a relationship between the bonded OLA and the shape of the NC. Additionally, the identification of concave surfaces on {200} facets by HAADF-STEM characterization suggests that the formation of the cube-like CeO2 morphology is a multiple step mechanism. On the basis of these observations new growth mechanisms for the CeO2 morphology variants are proposed.
    Chemistry of Materials. 05/2013; 25(10):2028–2034.
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    ABSTRACT: It has been demonstrated that the presence of oxide monolayers in semiconductor surfaces alters the electronic potential at surfaces and, consequently, can drastically affect the electronic transport features of a practical device such as a field effect transistor. In this work experimental and theoretical approaches to characterize Al/germanium nanowire Schottky devices by using samples covered with a thin oxide layer (2 nm width) were explored. It was also demonstrated that the oxide layer on Ge causes a weak dependence of the metal work function on Schottky barrier heights indicating the presence of Fermi level pinning. From theoretical calculations the pinning factor S was estimated to range between 0.52 and 0.89, indicating a weak Fermi level pinning which is induced by the presence of charge localization at all nanowires' surface coming from interface states.
    Journal of Applied Physics 01/2013; 114(24):243705-243705-6. · 2.21 Impact Factor
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Publication Stats

2k Citations
737.23 Total Impact Points

Institutions

  • 1997–2014
    • Universidade Federal de São Carlos
      • • Departamento de Química (DQ)
      • • Department of Chemistry
      • • Departamento de Física (DF)
      São Carlos do Pinhal, São Paulo, Brazil
  • 2011–2013
    • Brazilian Nanotechnology National Laboratory
      • Electron Microscopy Laboratory (LME)
      Conceição de Campinas, São Paulo, Brazil
  • 2009–2011
    • Laboratório Nacional de Luz Síncrotron
      Conceição de Campinas, São Paulo, Brazil
  • 2004–2010
    • Universidade Federal de São Paulo
      San Paulo, São Paulo, Brazil
    • Universidade Federal da Paraíba
      • Departamento de Química
      João Pessoa, Estado da Paraiba, Brazil
    • Centro Brasileiro de Pesquisas Físicas
      Rio de Janeiro, Rio de Janeiro, Brazil
    • Universidade São Francisco
      San Paulo, São Paulo, Brazil
  • 2007–2009
    • Brazilian Agricultural Research Corporation (EMBRAPA)
      Brasília, Federal District, Brazil
  • 2000–2009
    • State University of Ponta Grossa
      • Department of Dentistry
      Ponta Grossa, Estado do Parana, Brazil
  • 2008
    • Universidade Federal do Ceará
      Ceará, Ceará, Brazil
    • Universidade Federal de Pelotas
      São Francisco de Paula, Rio Grande do Sul, Brazil
  • 2001–2008
    • CEP America
      Emeryville, California, United States
  • 1997–2005
    • São Paulo State University
      • • Instituto de Química - Araraquara
      • • Departamento de Química
      São Paulo, Estado de Sao Paulo, Brazil
  • 2003–2004
    • University of São Paulo
      • Instituto de Física (IF) (São Paulo)
      San Paulo, São Paulo, Brazil
  • 1999
    • Universitat Jaume I
      • Departament de Química Física i Analítica
      Castelló de la Plana, Valencia, Spain