Estudo da modificação da fotoluminescência em α-Bi2O3 após tratamento térmico assistido por pressão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influência do tratamento térmico assistido por pressão nas propriedades óptica e elétrica do trióxido de tungstênio

Pós-graduação em Química - IQ

Sintesi di leganti ciclopentadienonici e piridilimidazolici per complessi metallici. Metodo classico e microonde a confronto

In questo elaborato è stata messa a punto una procedura sintetica, semplice e veloce che sfrutta la tecnica microonde per la sintesi di tetraarilciclopentadienoni variamente sostituiti mediante una condensazione bis-aldolica tra 1,3 difenilacetone con dichetoni aromatici variamente sostituiti. Questa nuova tecnica consente di ottenere tetraarilciclopentadienoni con rese da basse a buone in 25 minuti a 70°C. La stessa procedura sintetica è stata valutata per ottenere leganti piridilimidazolici, usando come fonte di azoto NH4OAc. Basse rese e la formazione di svariati sottoprodotti ha diretto lo studio verso un approccio classico per la sintesi di questi sistemi. I leganti piridilimidazolici sono stati poi impiegati per la sintesi di complessi di Zn(II) luminescenti, i quali sono stati caratterizzati anche da un punto di vista fotofisico.

Low cost synthesis of cathode and anode materials for lithium-ion batteries

Dans cette thèse, nous démontrons des travaux sur la synthèse à faible coût des matériaux de cathode et l'anode pour les piles lithium-ion. Pour les cathodes, nous avons utilisé des précurseurs à faible coût pour préparer LiFePO4 et LiFe0.3Mn0.7PO4 en utilisant une méthode hydrothermale. Tout d'abord, des matériaux composites (LiFePO4/C) ont été synthétisés à partir d'un précurseur de Fe2O3 par une procédé hydrothermique pour faire LiFePO4(OH) dans une première étape suivie d'une calcination rapide pour le revêtement de carbone. Deuxièmement, LiFePO4 avec une bonne cristallinité et une grande pureté a été synthétisé en une seule étape, avec Fe2O3 par voie hydrothermale. Troisièmement, LiFe0.3Mn0.7PO4 a été préparé en utilisant Fe2O3 et MnO comme des précurseurs de bas coûts au sein d'une méthode hydrothermale synthétique. Pour les matériaux d'anode, nous avons nos efforts concentré sur un matériau d'anode à faible coût α-Fe2O3 avec deux types de synthèse hydrothermales, une a base de micro-ondes (MAH) l’autre plus conventionnelles (CH). La nouveauté de cette thèse est que pour la première fois le LiFePO4 a été préparé par une méthode hydrothermale en utilisant un précurseur Fe3+ (Fe2O3). Le Fe2O3 est un précurseur à faible coût et en combinant ses coûts avec les conditions de synthèse à basse température nous avons réalisé une réduction considérable des coûts de production pour le LiFePO4, menant ainsi à une meilleure commercialisation du LiFePO4 comme matériaux de cathode dans les piles lithium-ion. Par cette méthode de préparation, le LiFePO4/C procure une capacité de décharge et une stabilité de cycle accrue par rapport une synthétisation par la méthode à l'état solide pour les mêmes précurseurs Les résultats sont résumés dans deux articles qui ont été récemment soumis dans des revues scientifiques.

Morphology and Blue Photoluminescence Emission of PbMoO(4) Processed in Conventional Hydrothermal

PbMoO(4) micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120 degrees C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO(4) micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points, out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO(4)] and [PbO(8)] clusters into the lattice.

Photoluminescence properties of PZT 52/48 synthesized by microwave hydrothermal method using PVA with template

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

High-efficient microwave synthesis and characterisation of SrSnO3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Copper-organic frameworks assembled from in situ generated 5-(4-pyridyl) tetrazole building blocks: synthesis, structural features, topological analysis and catalytic oxidation of alcohols

Two new metal- organic compounds {[Cu-3(mu(3)-4-(p)tz)(4)(mu(2)-N-3)(2)(DMF)(2)](DMF)(2)}(n) (1) and {[Cu(4ptz) (2)(H2O)(2)]}(n) (2) {4-ptz = 5-(4-pyridyl)tetrazolate} with 3D and 2D coordination networks, respectively, have been synthesized while studying the effect of reaction conditions on the coordination modes of 4-pytz by employing the [2 + 3] cycloaddition as a tool for generating in situ the 5-substituted tetrazole ligands from 4-pyridinecarbonitrile and NaN3 in the presence of a copper(II) salt. The obtained compounds have been structurally characterized and the topological analysis of 1 discloses a topologically unique trinodal 3,5,6-connected 3D network which, upon further simplification, results in a uninodal 8-connected underlying net with the bcu (body centred cubic) topology driven by the [Cu-3(mu(2)-N-3)(2)] cluster nodes and mu(3)-4-ptz linkers. In contrast, the 2D metal-organic network in 2 has been classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology assembled from the Cu nodes and mu(2)-4-ptz linkers. The catalytic investigations disclosed that 1 and 2 act as active catalyst precursors towards the microwave-assisted homogeneous oxidation of secondary alcohols (1-phenylethanol, cyclohexanol, 2-hexanol, 3-hexanol, 2-octanol and 3-octanol) with tert-butylhydroperoxide, leading to the yields of the corresponding ketones up to 86% (TOF = 430 h(-1)) and 58% (TOF = 290 h(-1)) in the oxidation of 1-phenylethanol and cyclohexanol, respectively, after 1 h under low power ( 10 W) microwave irradiation, and in the absence of any added solvent or additive.

Synthesis and characterization of sugar containing hydrophilic and hydrophobic polymers with potential application in medicine

Dissertation toobtaina Master of Science degree in Bioorganics

Palladium(II) and platinum(II) complexes with tridentate iminophosphine ligands; synthesis and structural studies

The previously synthesised Schiff-base ligands 2-(2-Ph2PC6H4N = CH) - R' - C6H3OH (R' = 3-OCH3, HL1; 5-OCH3, HL2; 5-Br, HL3; 5-Cl, HL4) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino) aniline with the appropriate substituted salicylaldehyde. HL1-4 react directly with (MCl2)-Cl-II (M = Pd, Pt) or (PtI2)-I-II(cod) affording neutral square-planar complexes of general formula [(MCl)-Cl-II(eta(3)-L1-4)] (M = Pd, Pt, 1 - 8) and [(PtI)-I-II(eta(3)-L1-4)] (M = Pd, Pt, 9 - 12). Reaction of complexes 1 - 4 with the triarylphosphines PR3 (R = Ph, p-tolyl) gave the novel ionic complexes [Pd-II(PR3)(eta(3)- L1-4)] ClO4 (13 - 20). Substituted platinum complexes of the type [Pt-II(PR3)(eta(3)- L1-4)] ClO4 (R = P(CH2CH2CN)(3) 21 - 24) and [Pt-II( P(p-tolyl)(3))(eta(3)-L-3,L-4)] ClO4 ( 25 and 26) were synthesised from the appropriate [(PtCl)-Cl-II(eta(3)-L1-4)] complex (5 - 8) and PR3. The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O, N, P donor set together with one further atom which is trans to the central nitrogen atom.

Electronic structure and optical properties of BaMoO(4) powders

Barium molybdate (BaMoO(4)) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 degrees C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm(-1), which is associated to the Mo-O antisymmetric stretching vibrations into the [MoO(4)] clusters. UV-vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap. (C) 2009 Elsevier B.V. All rights reserved.

Otimização do processamento para obtenção de compósitos polímero/cerâmica com propriedades piezo e piroelétricas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Titanato de Bário e cálcio: influência da substituição parcial d modificador de rede nas propriedades fotoluminescentes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Towards controlled synthesis and better understanding of blue shift of the CaS crystals

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Urea-Based Synthesis of Zinc Oxide Nanostructures at Low Temperature

The preparation of nanometer-sized structures of zinc oxide (ZnO) from zinc acetate and urea as raw materials was performed using conventional water bath heating and a microwave hydrothermal (MH) method in an aqueous solution. The oxide formation is controlled by decomposition of the added urea in the sealed autoclave. The influence of urea and the synthesis method on the final product formation are discussed. Broadband photoluminescence (PL) behavior in visible-range spectra was observed with a maximum peak centered in the green region which was attributed to different defects and the structural changes involved with ZnO crystals which were produced during the nucleation process.