Al2O3 and Al2O3-ZrO2 Fibers Obtained by Biotemplete with Low Thermal Conductivity

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Experimental and theoretical studies of photoluminescence in Zns obtained by microwave-assisted solvothermal method

A shift of the photoluminescence (PL) emission was observed in ZnS prepared by microwave assisted solvothermal method with the increase of the time in microwave. In this work we reported a study of the optical behavior linking with the structural disorder according to XRD and FEG-TEM results. The reduction of intrinsic defects in the lattice is responsible for the decrease of electronic levels in the band gap changing the PL profile. This effect was confirmed by electronic structure calculations

Interfacial photoluminescence emission properties of core/shell Al2O3/ZrO2

This research investigated the synthesis of the Al2O3/ZrO2 core-shell system using a polymeric precursor method. The interfacial features emission show the possibility for control of the luminescence behaviour. X-ray diffraction (XRD) patterns are well defined for alpha-Al2O3 and for gamma-Al2O3, core structures and a zirconia shell phase for high concentrations. Photoluminescence (PL) spectra (lambda(exc) = 350.7 nm) reveal that the effect of the zirconia coating on the alumina was more effective for alpha-Al2O3 than for gamma-Al2O3 which may be related to the zirconia coating process on alumina. The image transmission electron microscopy (TEM) shows an amorphous region of 10 nm which is attributed to a ZrO2 shell layer.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Photocatalytic activity of semiconductor sulfide heterostructures

This paper reports a theoretical and experimental study of the heterostructure photocatalytic activity in a CdS or ZnS and CdS@ZnS decorated system prepared by a microwave assisted solvothermal (MAS) method. A theoretical model of the decorated system was created in order to analyze the electronic transition mainly in their interface. The results show that CdS and ZnS interfaces produce an electron charge transfer from the CdS electron-populated clusters to the ZnS hole-populated clusters which helps to enhance the photocatalytic activity of the CdS@ZnS decorated system. © 2013 The Royal Society of Chemistry

Sintering of porous alumina obtained by biotemplate fibers for low thermal conductivity applications

In this research report, a sintering process of porous ceramic materials based on Al2O3 was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100-1600°C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14m2/g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al2O3 in the sintered samples. Thermal properties of the sintered Al2O3 fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al2O3 and therefore improved its potential use as an insulating material. © 2012 Elsevier Ltd

Europium doped zinc sulfide: a correlation between experimental and theoretical calculations

This paper presents the correlation among electronic and optical property effects induced by the addition of different concentrations of europium (Eu3+) in zinc sulfide (ZnS) by microwave-assisted solvothermal (MAS) method. A shift of the photoluminescence (PL) emission was observed with the increase of Eu3+. The periodic DFT calculations with the B3LYP hybrid functional were performed using the CRYS TAL computer code. The UV-vis spectra and theoretical results indicate a decrease in behavior of the energy gap as a function of dopant concentration. Therefore, new localized states are generated in the forbidden band gap region, the new states increase the probability of less energy transitions which may be responsible for a red shift in the PL bands spectrum.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Gadolinium-doped cerium oxide nanorods: novel active catalysts for ethanol reforming

The gadolinium-doped ceria nanorods (Gd(0.2)Ce(0.8)O(2-x) ) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd(0.2)Ce(0.8)O(2-x) nanorods were more catalytically active than commercial CeO(2) in the ethanol reforming reaction.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

YbF3/SiO2 Fillers as Radiopacifiers in a Dental Adhesive Resin

The objective of this study was to evaluate the effect of functionalizing a dental adhesive resin with YbF3/SiO2 fillers for use as radiopacifiers. Particles of YbF3/SiO2 were obtained with the high-energy mechanical milling method and characterized by both physical and chemical methods. After characterization, the particles were sieved and silanized prior to being incorporated into an adhesive resin. The stability of the particle suspension was then evaluated. After light activation, the radiopacity, degree of conversion, flexural strength and elastic modulus were determined. The dental adhesive resins with 10 and 15 wt% of filler provided satisfactory radiopacity, while flexural strength and elastic modulus were not affected. The degree of conversion was statistically lower than that of the control (p<0.05). The method used for incorporating the tested ytterbium fluoride/silicon dioxide particles at concentrations of 10 and 15 wt% was shown to be feasible for the development of a radiopaque dental adhesive system

SnO2 nanoparticles functionalized in amorphous silica and glass

Two different routes to obtain SnO2 nanoparticles, undoped and doped with rare earth metals (Eu or Pr), are described herein. The first route was based on the polymeric precursor method that led to the obtainment of SnO2 nanoparticles dispersed in amorphous silica. The second route was simply the impregnation with SnCl4 aqueous solution of SiO2-CaO glass microparticles functionalized with hydroxyl (-OH) groups. The materials were characterized by N-2 physisorption, XRD, EDS and TEM analyses. We also present the results of catalytic experiments involving the nanocrystalline composites in ethanol steam reforming. The catalytic properties of the undoped composites with SnO2 supported on SiO2-CaO glass differ from their doped analogues, however, they were both selective towards ethylene formation, in contrast to the doped composite obtained by the polymeric precursor method. (c) 2009 Elsevier B.V. All rights reservedConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

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.FAPESPCNPqCAPESGeneralitat Valenciana (Prometeo/2009/053)MICINN (CTQ2009-14541-C02)Programa de Cooperación Científica con IberoaméricaMECD (PHB2009-0065-PC