BaMoO(4) powders processed in domestic microwave-hydrothermal: Synthesis, characterization and photoluminescence at room temperature

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização textural e estrutural de V 2O 5/TiO 2 obtidos via sol-gel: Comparação entre secagem convencional e supercrítica

This work describes a modified sol-gel method for the preparation of V 2O 5/TiO 2 catalysts. The samples have been characterized by N 2 adsorption at 77K, x-ray diffractometry (XRD) and Fourier Transform Infrared (FT-IR). The surface area increases with the vanadia loading from 24 m 2 g -1, for pure TiO 2, to 87 m 2 g -1 for 9wt.% of V 2O 5. The rutile form is predominant for pure TiO 2 but became enriched with anatase phase when vanadia loading is increased. No crystalline V 2O 5 phase was observed in the catalysts diffractograms. Two species of surface vanadium observed by FT-IR spectroscopy a monomeric vanadyl and polymeric vanadates, the vanadyl/vanadate ratio remains practically constant.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm X 5 mm) and covered with a Mylar strip. The tip of the lightcuring unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37°C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (α=0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the lightcuring unit and by its light energy density. © Operative Dentistry.

Low-temperature synthesis of nanosized bismuth ferrite by the soft chemical method

This paper describes research on a simple low-temperature synthesis route to prepare bismuth ferrite nanopowders by the polymeric precursor method using bismuth and iron nitrates. BiFeO 3 (BFO) nanopowders were characterized by means of X-ray diffraction analyses, (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy (Raman), thermogravimnetric analyses (TG-DTA), ultra-violet/vis (UV/Vis) and field emission scanning electron microscopy (FE-SEM). XRD patterns confirmed that a pure perovskite BiFeO 3 structure with a rhombohedral distorted perovskite structure was obtained by heating at 850 °C for 4 hours. Typical FT-IR spectra for BFO powders revealed the formation of a perovskite structure at high temperatures due to a metal-oxygen bond while Raman modes indicated oxygen octahedral tilts induced by structural distortion. A homogeneous size distribution of BFO powders obtained at 850 °C for 4 hours was verified by FE-SEM analyses. © 2012 Elsevier Ltd and Techna Group S.r.l.

Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae

Background: Diminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils. Results: OAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform-near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g). Conclusions: OAFEX treatment revealed marked hemicellulose degradation, improving the cellulases ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level. © 2013 Chandel et al; licensee BioMed Central Ltd.

Altering the adsorptive and electronic properties of Pt through poly(vinyl alcohol) adsorption

In the present paper we investigated the effect of adsorbed PVA on Pt electrodes on classic electrochemical processes such as hydrogen UPD, oxygen reduction and CO electro-oxidation. Upon adsorption PVA blocks roughly 50% of the hydrogen sites and can not be removed from the Pt surface through cycling in the potential range of 0.05-1.0 V vs. RHE. Potentiodynamic experiments under controlled hydrodynamic conditions provided by rotating disk electrode experiments showed a negative impact of the adsorbed PVA on the oxygen reduction reaction (ORR). Cyclic-voltammetry results revealed that not even CO was able to remove PVA from the Pt surface. Regarding the oxidation of CO, the adsorbed polymer positively shifted the CO oxidation peak potential, therefore higher potentials are required to free the Pt surface from CO poisoning. In situ Fourier transform infrared spectroscopy evidenced that the presence of PVA shifted the linearly bound CO frequency toward higher wavenumbers, a process found to be independent of the Pt surface orientation. In situ electrochemical X-ray absorption spectroscopy results showed that PVA also impacted the electronic properties of platinum by decreasing the occupancy of the Pt conducting 5d band. Our findings clearly support the efforts toward understanding the nature of the interaction between polymers and metallic surfaces as well as the impact on technological applications (e.g. in PEMFCs). © 2013 Elsevier Ltd. All rights reserved.

A combined theoretical and experimental study of electronic structure and optical properties of β-ZnMoO4 microcrystals

In this paper, a combined theoretical and experimental study on the electronic structure and photoluminescence (PL) properties of beta zinc molybdate (β-ZnMoO4) microcrystals synthesized by the hydrothermal method has been employed. These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectroscopies. Their optical properties were investigated by ultraviolet-visible (UV-Vis) absorption spectroscopy and PL measurements. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level have been carried out. XRD patterns, Rietveld refinement, FT-Raman and FT-IR spectra showed that these crystals have a wolframite-type monoclinic structure. The Raman and IR frequencies experimental results are in reasonable agreement with theoretically calculated results. UV-Vis absorption measurements shows an optical band gap value of 3.17 eV, while the calculated band structure has a value of 3.22 eV. The density of states indicate that the main orbitals involved in the electronic structure of β-ZnMoO4 crystals are (O 2p-valence band and Mo 4d-conduction band). Finally, PL properties of β-ZnMoO4 crystals are explained by means of distortions effects in octahedral [ZnO6] and [MoO6] clusters and inhomogeneous electronic distribution into the lattice with the electron density map. © 2013 Elsevier Ltd. All rights reserved.

Intense photoluminescence emission at room temperature in calcium copper titanate powders

A study was undertaken about the structural and photoluminescent properties at room temperature of CaCu3Ti4O12 (CCTO) powders synthesized by a soft chemical method and heat treated between 300 and 800 °C. The decomposition of precursor powder was followed by thermogravimetric analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and photoluminescence (PL) measurements. XRD analyses revealed that the powders annealed at 800 °C are becoming ordered and crystallize in the cubic structure. The most intense PL emission was obtained for the sample calcined at 700 °C, which is not highly disordered (300-500 °C) and neither completely ordered (800 °C). From the spectrum it is clearly visible that the lowest wavelength peak is placed around 480 nm and the highest wavelength peak at about 590 nm. The UV/vis absorption spectroscopy measurements showed the presence of intermediate energy levels in the band gap of structurally disordered powders. © 2012 Elsevier Ltd and Techna Group S.r.l.

Effect of soaking time on the photoluminescence properties of cerium oxide nanoparticles

The structural and photoluminescence properties at room temperature of CeO2 nanoparticles synthesized by a microwave-assisted hydrothermal method (MAH) under different soaking times on KOH mineralizer added to a cerium ammonium nitrate aqueous solution were undertaken. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and photoluminescence (PL) measurements were employed. XRD revealed that the nanoparticles are free of secondary phases and crystallize in the cubic structure. The UV/vis absorption spectroscopy suggested the presence of intermediate energy levels in the band gap of structurally ordered powders. The most intense PL emission was obtained for nanoparticles which represent a lower particle size. © 2013 Elsevier Ltd and Techna Group S.r.l.

Antimicrobial Brazilian propolis (EPP-AF) containing biocellulose membranes as promising biomaterial for skin wound healing

Among remarkable discoveries concerning propolis, such as antifungal, antiviral, and antioxidant activities, its anti-inflammatory, and mainly its antibacterial, properties deserve special attention when skin wound healing is concerned. Based on this and knowing the distinctive performance of bacterial (BC) membranes on wound healing, in this work it is proposed to demonstrate the potent antimicrobial activity and wound healing properties of a novel propolis containing biocellulose membrane. The obtained propolis/BC membrane was able to adsorb propolis not only on the surface, but also in its interstices demonstrated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, and thermogravidimetric assays. Additionally, the polyphenolic compounds determination and the prominent antibacterial activity in the membrane are demonstrated to be dose dependent, supporting the possibility of obtaining propolis/BC membranes at the desired concentrations, taking into consideration its application and its skin residence time. Finally, it could be suggested that propolis/BC membrane may favor tissue repair in less time and more effectively in contaminated wounds. © 2013 Hernane da Silva Barud et al.

Rietveld refinement, morphology and optical properties of (Ba 1-xSrx)MoO4 crystals

In this article, the structural refinement, morphology and optical properties of barium strontium molybdate [(Ba1-x Sr x )MoO4 with x = 0, 0.25, 0.50, 0.75 and 1] crystals, synthesized by the co-precipitation (drop-by-drop) method, are reported. The crystals obtained were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, and Fourier transform-Raman (FT-Raman) and Fourier transform-infrared (FT-IR) spectroscopies. The shapes of the crystals were observed by means of field-emission scanning electron microscopy (FE-SEM). The optical properties were investigated using ultraviolet-visible (UV-Vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns, Rietveld refinement, and FT-Raman and FT-IR spectra showed that all of the crystals are monophasic with a scheelite-type tetragonal structure. The refined lattice parameters and atomic positions were employed to model the [BaO8], [SrO8] and [MoO4] clusters in the tetragonal lattices. The FE-SEM images indicate that increased x content produces a decrease in the crystal size and modifications in the crystal shape. UV-Vis spectra indicated a decrease in the optical band gap with an increase in x in the (Ba1-x Sr x )MoO4 crystals. Finally, a decrease in the intensity of PL emission is apparent with an increase in x up to 0.75 in the (Ba1-x Sr x )MoO4 crystal lattice when excited by a wavelength of 350nm, probably associated with the degree of structural order-disorder. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

Photoluminescence properties of praseodymium doped cerium oxide nanoparticles

The structural and photoluminescent properties at room temperature of CeO2 nanoparticles synthesized by a Microwave-Assisted Hydrothermal Method (MAH) under different praseodymium contents was undertaken. X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), UV-vis Spectroscopy (UV-vis), Fourier Transform Raman (FT-Raman) and Photoluminescence (PL) measurements were employed. XRD revealed that the nanoparticles are free of secondary phases and crystallize in the cubic structure while FT-Raman revealed a typical scattering mode of fluorite type. The UV/vis absorption spectroscopy suggested the presence of intermediate energy levels in the band gap of structurally ordered powders. The most intense PL emission was obtained for nanoparticles which represent a lower particle size. © 2013 Elsevier Ltd and Techna Group S.r.l.

Um método para detecção e classificação de curtos-circuitos em redes de distribuição de energia elétrica baseado na transformada de Fourier e em redes neurais artificiais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem estocástica de opções de câmbio no Brasil: aplicação de transformada rápida de Fourier e expansão assintótica ao modelo de Heston

Pós-graduação em Física - IFT

Influência da composição de resinas compostas no grau de conversão e degradação hidrolítica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)