Synthesis of Fine Micro-sized BaZrO3 Powders Based on a Decaoctahedron Shape by the Microwave-Assisted Hydrothermal Method

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efficient microwave-assisted hydrothermal synthesis of CuO sea urchin-like architectures via a mesoscale self-assembly

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

An efficient microwave-assisted hydrothermal synthesis of BaZrO3 microcrystals: growth mechanism and photoluminescence emissions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

An eco-friendly protocol for synthesis of thiourea derivatives: 1-benzoyl-3-benzylguanidine and 1-benzoyl-3-benzyl-O-ethylisourea. A possible non-purely thermal microwave assisted reaction

1-Benzoyl-3-benzylguanidine and 1-benzoyl-3-benzyl-O-ethylisourea were synthesized in good yields (68 and 76%, respectively) from 1-benzoyl-3-benzylthiourea and benzoyl-ethylthiocarbamate in dry media conditions using KF-Al2O3 under microwave irradiation. Strong nucleophilic amines promoted the sulfur elimination by attack on the thiocarbonyl group in both thiourea and thiocarbamates to afford guanidines and isourea, respectively. Transesterification products were obtained from p-TsOH catalyzed reaction of thiocarbamate with alcohols under MW-solvent-free conditions. Very important non-purely thermal MW specific effects were evidenced and attributed to stabilization by coulombic interactions between materials and waves. (c) 2005 Elsevier Ltd. All rights reserved.

Microwave-assisted hydrothermal synthesis of nanocrystalline SnO powders

Tin oxide (SnO) powders were obtained by the microwave-assisted hydrothermal synthesis technique using SnCl2 center dot 2H(2)O as a precursor. By changing the hydrothermal processing time, temperature, the type of mineralizing agent (NaOH, KOH or NH4 OH) and its concentration, SnO crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (X-ray), Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM) and Selected Area Electron Diffraction (SAED). The results showed that plate-like form is the characteristic morphology of growth and the TEM analyses indicate the growth direction as (200). (c) 2007 Elsevier B.V. All rights reserved.

Microwave-assisted hydrothermal synthesis of ZnO powders with different reagents

In this work, zinc oxide powders were synthesized by microwave-assisted hydrothermal method in basic medium. These powders were analyzed by X-ray diffraction (XRD), Field-emisson gum scanning electron microscopy (FEG-SEM), Ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD pattern confirmed that the pure ZnO phases were obtained after MH processing performed at 130°C/ 1h. FEG-SEM micrographs reveals that these nanostructures are made up of ZnO plates. UV-vis results were employed to determine the optical band gap these materials. Also, it showed existence of photoluminescence (PL) in the different zinc powders. An orange PL emission when excited by 350 nm wavelength at room temperature was observad in the different powders.

Synthesis of wurtzite ZnS nanoparticles using the microwave assisted solvothermal method

In this article, we report the development of an efficient and rapid microwave assisted solvothermal (MAS) method to prepare wurtzite ZnS nanoparticles at 413 K using different precursors. The materials obtained were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (MET) ultraviolet-visible (UV-vis) and photoluminescence (PL) measurements. The structure, surface chemical composition and optical properties were investigated as a function of the precursor. In addition, effects as well as merits of microwave heating on the processing and characteristics of ZnS nanoparticles obtained are reported. The possible formation mechanism and optical properties of these nanoparticles were also reported. © 2012 Elsevier B.V. All rights reserved.

Microwave-assisted hydrothermal synthesis of magnetite nanoparticles with potential use as anode in lithium ion batteries

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Long-range and short-range structures of cube-like shape SrTiO3 powders: microwave-assisted hydrothermal synthesis and photocatalytic activity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Microwave-assisted hydrothermal synthesis of NiO-Ce1-XEuxO2-δ powders for fuel cell catalytic anodes

CeO2-based materials doped with rare earth (TR +3) can be used as alternative to traditional NiO-YSZ anodes in solid oxide fuel cells as they have higher ionic conductivity and lower ohmic losses compared to YSZ. Moreover, they allow fuel cell operation at lower temperatures (500-800°C). In the anode composition, the concentration of NiO acting as catalyst in YSZ provides high electrical conductivity and high electrochemical activity of reactions, promoting internal reform in the cell. In this work, NiO - Ce1-xEuxO2-δ compounds (x = 0.1, 0.2 and 0.3) have been synthesized by microwave-assisted hydrothermal method. The materials were characterized by TG, XRD, TPR and SEM-FEG techniques. The refinement of data obtained by X-ray diffraction showed the presence of ceria doped with europium crystallized in a cubic phase with fluorite structure, in addition to the presence of NiO. The microwave-assisted hydrothermal method showed significant reduction in the average particle size and good mass control of phase compositions compared to other chemical synthesis techniques.

Synthesis and characterization of NaNbO3 mesostructure by a microwave-assisted hydrothermal method

In the present work, we report the synthesis and characterization of NaNbO3 particles obtained by microwave-assisted hydrothermal method from Nb2O5 and NaOH. The synthesis was made at different periods at 180 °C and 300W. The crystallization of NaNbO3 structures produced Na2Nb2O6.H2O in the intermediate phase with fiber-like morphology, and this is associated with the synthesis time. Pure orthorhombic NaNbO3 with cube-like morphology originates after synthesizing for 240 minutes. To verify the remnant polarization of particles, films were obtained by electrophoresis process and sintered at 800°C for 10 minutes in a microwave furnace. The films characterization indicated that films of niobate with fiber-like morphology present remaining polarization, and the morphology of cubes did not show remaining polarization. Considering these results, it can be concluded that the morphology implemented ferroelectric property of NaNbO3.

Synthesis of Bi-based superconductor by microwave-assisted hydrothermal method

In this work we studied the synthesis of BSCCO-2212 superconducting phase associating a quite similar method developed by Pechini with the microwave-assisted hydrothermal method. To study the influence of the microwaves on the properties of BSCCO system, we synthesized two samples by such method. For one sample we used carbonates and for the other one we used nitrates as chemical reagents. We also produced a reference sample just using carbonates by Pechini's method to compare their morphological and superconducting properties. The structural properties of the samples were analyzed by scanning electron microscopy and X-ray diffraction. The Bi-2212 phase is predominant in all samples and despites the nitrates-like sample has a broader distribution of grain size in comparison with the reference sample, its magnetic behaviour is closer to that presented by the reference one.

Microwave-assisted enzymatic synthesis of beef tallow biodiesel

Optimal conditions for the microwave-assisted enzymatic synthesis of biodiesel have been developed by a full 2(2) factorial design leading to a set of seven runs with different combinations of molar ratio and temperature. The main goal was to reduce the reaction time preliminarily established by a process of conventional heating. Reactions yielding biodiesel, in which beef tallow and ethanol used as raw materials were catalyzed by lipase from Burkholderia cepacia immobilized on silica-PVA and microwave irradiations within the range of 8-15 W were performed to reach the reaction temperature. Under optimized conditions (1:6 molar ratio of beef tallow to ethanol molar ratio at 50A degrees C) almost total conversion of the fatty acid presented in the original beef tallow was converted into ethyl esters in a reaction that required 8 h, i.e., a productivity of about 92 mg ethyl esters g(-1) h(-1). This represents an increase of sixfold for the process carried out under conventional heating. In general, the process promises low energy demand and higher biodiesel productivity. The microwave assistance speeds up the enzyme catalyzed reactions, decreases the destructive effects on the enzyme of the operational conditions such as, higher temperature, stability, and specificity to its substrate, and allows the entire reaction medium to be heated uniformly.

Microwave-assisted wet chemical (MAWC) synthesis of lithium iron phosphate

LiFePO4 is a Co-free battery material. Its advantages of low cost, non-toxic and flat discharge plateau show promising for vehicle propulsion applications. A major problem associated with this material is its low electrical conductivity. Use of nanosized LiFePO4 coated with carbon is considered a solution because the nanosized particles have much shorter path for L+ ions to travel from the LiFePO4 crystal lattice to electrolytes. As other nano material powders, however, nano LiFePO4 could have processing and health issues. In order to achieve high electrical conductivity while maintaining a satisfactory manufacturability, the particles should possess both of the nano- and the microcharacteristics correspondingly. These two contradictory requirements could only be fulfilled if the LiFePO4 powders have a hierarchical structure: micron-sized parent particles assembled by nanosized crystallites with appropriate electrolyte communication channels. This study addressed the issue by study of the formation and development mechanisms of the LiFePO4 crystallites and their microstructures. Microwaveassisted wet chemical (MAWC) synthesis approach was employed in order to facilitate the evolvement of the nanostructures. The results reveal that the LiFePO4 crystallites were directly nucleated from amorphous precursors by competition against other low temperature phases, Li3PO4 and Fe3(PO4)2•8H2O. Growth of the crystalline LiFePO4 particles went through oriented attachment first, followed by revised Ostwald ripening and then recrystallization. While recrystallization played the role in growth of well crystallized particles, oriented attachment and revised Ostwald ripening were responsible for formation of the straight edge and plate-like shaped LiFePO4 particles comprised of nanoscale substructure. Oriented attachment and revised Ostwald ripening seemed to be also responsible for clustering the plate-like LiFePO4 particles into a high-level aggregated structure. The finding from this study indicates a hope for obtaining the hierarchical structure of LiFePO4 particles that could exhibit the both micro- and nano- scale characteristics. Future study is proposed to further advance the understanding of the structural development mechanisms, so that they can be manipulated for new LiFePO4 structures ideal for battery application.