E. R. Leite

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

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Publications (457)982.65 Total impact

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    ABSTRACT: One of the primary challenges in obtaining heterostructures is control of the morphology and surface features of the components that are suitable for a specific application. In this sense, the use of preformed nanoparticles as building blocks is interesting. However, to create heterojunctions between preformed nanoparticles, a further calcination step is usually needed that can result in changes in nanoparticle morphology and surface chemistry. Therefore, the main goal of this study was to explore collision-induced heteroaggregation and oriented attachment under hydrothermal conditions to obtain heterostructures from preformed nanoparticles without further thermal treatment or addition of capping agents. We use anatase TiO2 and rutile SnO2 nanoparticles as a model system. A kinetic model based on a diffusion-controlled reaction is adapted to describe the process. For tracking charge migration across the interface and, consequently, heterojunction formation, we employ an indirect method based on the detection of hydroxyl radicals formed over a semiconductor during UV radiation. The rate of hydroxyl radical formation is directly proportional to the photogenerated charge lifetime, which, in turn, depends on the number of heterojunctions formed. The insights presented here suggest the possibility of obtaining the benefits of heterostructures by using nanoparticles with controlled morphology and surface characteristics.
    01/2015; 3(5). DOI:10.1039/C4TA05926C
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    ABSTRACT: a b s t r a c t This paper investigates the near-infrared emission and structural properties of Er 3+ -doped zirconium oxide thin films modified with a fixed content of zinc oxide. The films were obtained by electron beam deposition on Si(1 0 0) substrates, followed by a thermal treatment with or without a controlled oxygen flow. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) was used to eval-uate the surface morphology, distributions and size of the grains in the films. The results confirmed sig-nificant changes in these films from thermal treatment with or without oxygen flow. Fourier transform infrared spectroscopy (FTIR) was used to analyze the absorption bands of the films. The photolumines-cence (PL) measurement and 4 I 13/2 ? 4 I 15/2 lifetime was measured under 980 nm near-infrared excitation. The effects of thermal treatment as well as the concentration of Er 2 O 3 on the PL emission intensity and lifetime in the near-infrared region (from the 4 I 13/2 ? 4 I 15/2 radiative transition) were studied. Thermal treatment under a controlled atmosphere increased the PL emission intensity due to a diminution of the residual OH groups, as confirmed by the XPS and analysis and FTIR spectroscopy. The film modified with 3 mol% of Er 2 O 3 content annealed in oxygen flow shows an emission intensity of two orders of mag-nitude greater than the annealed film without oxygen flow at 1550 nm, nevertheless, the bandwidth was practically the same (7.6 nm) in both cases. Published by Elsevier B.V.
    Journal of Alloys and Compounds 01/2015; 619:800-806. DOI:10.1016/j.jallcom.2014.09.007 · 2.73 Impact Factor
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    ABSTRACT: Pure (Bi 12 TiO 20) and niobium-doped (Bi 12 Ti 1-x Nb x O 20 , with ''x'' up to 0.15) bismuth titanates were prepared by the oxidant peroxide method (OPM) and used to photodegradate rhodamine b (RhB) under UV and visible radiation. Rietveld refinements showed samples consisting mainly of sillenite structure with small amounts of a perovskite secondary phase in the Nb-doped materials. These bismuth-based catalysts exhibited superior performance than the commercial TiO 2 , with band gaps ranging from 2.53 of pure Bi 12 TiO 20 to 2.73 eV depending on the amount of niobium added, which seems to be responsible for the improved photoactivity of the doped catalysts under UV radiation.
    Journal of Nanoparticle Research 12/2014; 16(113):2653. DOI:10.1007/s11051-014-2653-2 · 2.18 Impact Factor
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    ABSTRACT: Surface-modified silica nanoparticles have a plenty of applications, such as coatings, dyes or biomarkers, catalysts and encapsulated products. When modified with 3-(trimethoxysilyl)propyl methacrylate (SiO2-MPS) or covered with a polymeric shell obtained from a reaction between divinylbenzene and styrene (SiO2-Pol), these SiO2 nanoparticles induced distinct arrangements in polymer nanocomposites (PNC) prepared with commercial carboxylated nitrile rubber (XNBR). The hydrophilicity character of the modified SiO2 nanoparticles was also altered, improving their interaction with the XNBR macromolecules. Consequently, choosing the PNC properties for different conditions and applications became possible due to the adjustment of the nanoparticle surface characteristics. Although the final characteristics of the nanocomposites films varied according to the nanoparticle used, the PNC prepared with SiO2-Pol presented better homogeneity than those with SiO2-MPS. 2014 Elsevier B.V. All rights reserved.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 11/2014; 462:45–51. DOI:10.1016/j.colsurfa.2014.08.012 · 2.35 Impact Factor
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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; 6(12). DOI:10.1002/cctc.201402689 · 5.18 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 09/2014; 364:18–23. DOI:10.1016/j.jmmm.2014.04.014 · 2.00 Impact Factor
  • Microscopy and Microanalysis 08/2014; 20(S3):178-179. DOI:10.1017/S143192761400261X · 1.76 Impact Factor
  • Ricardo H. Gonçalves, Edson R. Leite
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    ABSTRACT: Much research has been devoted to improving the water splitting efficiency of hematite photoanodes. In this study, we demonstrate a significant advance in the colloidal nanocrystal deposition (CND) process to obtain hematite thin films with high photoelectrochemical performance. For this approach, we designed the magnetic field-assisted dip coating process to achieve homogeneous hematite thin films by using magnetic nanocrystals (maghemite) as the precursor. Using this non-aqueous deposition route, we produced undoped and Sn-doped hematite photoanodes with excellent photocurrents of 1.4 mA cm−2 at 1.23 VRHE and 2.7 mA cm−2 at 1.23 VRHE, respectively, using a standard AM1.5 G solar light simulator.
    Energy & Environmental Science 07/2014; 7(7):2250. DOI:10.1039/c4ee00335g · 15.49 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. DOI:10.1166/jnn.2014.8253 · 1.34 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 - A European Journal 05/2014; 20(21). DOI:10.1002/chem.201400412 · 5.93 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 05/2014; 75(5):583–587. DOI:10.1016/j.jpcs.2014.01.003 · 1.59 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). DOI:10.1002/aenm.201301380 · 14.39 Impact Factor
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    ABSTRACT: A factorial experimental design was combined with response surface methodology (RSM) to optimize the catalyzed CO2 consumption by coke deposition and syngas production during the dry reforming of CH4. The CH4/CO2 feed ratio and the reaction temperature were chosen as the variables, and the selected responses were CH4 and CO2 conversion, the H-2 /CO ratio, and coke deposition. The optimal reaction conditions were found to be a CH4/CO2 feed ratio of approximately 3 at 700 degrees C, producing a large quantity of coke and realizing high CO2 conversion. Furthermore, Raman results showed that the CH4/CO2 ratio and reaction temperature affect the system's response, particularly the characteristics of the coke produced, which indicates the formation of carbon nanotubes and amorphous carbon.
    Chinese Journal of Catalysis 04/2014; 35(4):514–523. DOI:10.1016/S1872-2067(14)60018-8 · 1.55 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 02/2014; 415:89–94. DOI:10.1016/j.jcis.2013.10.010 · 3.55 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-. DOI:10.1088/0268-1242/29/1/015001 · 2.21 Impact Factor
  • Cerâmica 01/2014; 60(353):154-159. DOI:10.1590/S0366-69132014000100021
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    ABSTRACT: Strontium titanate (SrTiO3) is an n-type semiconductor with high chemical and photochemical stability. This wide band gap oxide has a band gap energy of about 3.2 eV as well as a favorable energy for photocatalysis. In this study, we demonstrate an alternative and superior method to produce Nb-doped and undoped SrTiO3 photoanode thin films based on a colloidal deposition process which possess good activity under standard solar illumination conditions. Methanol was used as “hole scavenger,” and the results showed that the semiconductor-liquid junction (SCLJ) charge accumulation is not an important mechanism to control the photocurrent density and overpotential. In addition, experimental results suggest that the dominance of photocurrent density is controlled by the potential at the surface space charge layer for the Nb-doped SrTiO3 and by recombination at the depletion layer for the undoped oxide.
    RSC Advances 01/2014; 4(4):2029. DOI:10.1039/c3ra45066j · 3.71 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). DOI:10.1088/0022-3727/47/4/045301 · 2.52 Impact Factor
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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 12/2013; 114(24):243705-243705-6. DOI:10.1063/1.4857035 · 2.19 Impact Factor
  • 15th Brazilian Meeting on Organic Synthesis; 12/2013

Publication Stats

6k Citations
982.65 Total Impact Points

Institutions

  • 1996–2015
    • Universidade Federal de São Carlos
      • • Department of Chemistry
      • • Departamento de Química (DQ)
      São Carlos do Pinhal, São Paulo, Brazil
  • 2001–2012
    • CEP America
      Емеривил, California, United States
  • 2004–2010
    • Universidade Federal de São Paulo
      San Paulo, São Paulo, Brazil
    • Lehigh University
      • Department of Materials Science and Engineering
      Bethlehem, Pennsylvania, United States
  • 1997–2010
    • São Paulo State University
      • Department of Physical Chemistry
      San Paulo, São Paulo, Brazil
  • 2009
    • Brazilian Agricultural Research Corporation (EMBRAPA)
      Brasília, Federal District, Brazil
  • 2008
    • Universidade Federal de Pelotas
      São Francisco de Paula, Rio Grande do Sul, Brazil
  • 2007
    • Federal University of Maranhão
      Maranhão, Maranhão, Brazil
    • Universidade Federal de Ouro Preto
      Ouro Preto, Minas Gerais, Brazil
    • State University of Ponta Grossa
      Ponta Grossa, Paraná, Brazil
  • 2006
    • University of Pennsylvania
      • Department of Chemistry
      Philadelphia, Pennsylvania, United States
  • 2002
    • Federal University of Santa Catarina
      Nossa Senhora do Destêrro, Santa Catarina, Brazil