Growth kinetics of vanadium pentoxide nanostructures under hydrothermal conditions

The work reported here involved a study of the growth kinetics of V2O5nH2O nanostructures under hydrothermal conditions. The coarsening process of V2O5nH2O nanoribbons was followed by subjecting the as-prepared suspensions to hydrothermal treatments at 80 °C for periods ranging from 0 to 7200 min. X-ray diffraction (XRD) confirms that the hydrothermal treatments at 80 °C caused no significant modification of the long-range order structure of samples subjected to different periods of hydrothermal treatment. Field emission scanning transmission electron microscope (FE-STEM) was used to analyze the morphology and width distribution of the nanostructures. The results indicated that the crystal growth mechanism in the [1 0 0] direction of vanadium pentoxide 1D nanostructure under hydrothermal conditions is well described by the oriented attachment (OA) mechanism. This evidence was supported by HRTEM images showing the existence of defects at the interface between nanostructures, which is characteristic of the oriented attachment (OA) mechanism.FAPESPCNPqLNL

An efficient synthesis route of 'Na IND.2''V IND.6''O IND.16.n''H IND.2'O nanowires in hydrothermal conditions

Na2V6O16·nH2O nanowires were synthesized using an environmentally friendly and one-step low-temperature hydrothermal route. The synthesis involved the hydrothermal reaction between V2O5, H2O2 and NaOH, without the addition of any organic surfactants or inorganic ions. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and thermal gravimetric analysis (TGA) techniques were used to characterize the structure, morphology, chemical composition and thermal stability of the nanostructured samples. High purity hydrated Na2V6O16·nH2O nanowires of diameters around 20–30 nm can be more efficiently obtained when subject to hydrothermal treatment at 140 °C for 24 h. The variation in the electronic and local atomic structure was analyzed using X-ray absorption spectroscopy (XAS). Based on the results obtained from the present study, a mechanism for the formation of Na2V6O16·nH2O nanowires in hydrothermal conditions was proposed.FAPESPCNP

Obtenção de filmes finos de TiO2 nanoestruturado pelo método dos precursores poliméricos

This work focuses in optimizing setup for obtaining TiO2 thin films by polymeric precursor route due to its advantages on stoichiometric and morphological control. Precursor stoichiometry, synthesis pH, solids concentration and rotation speed at deposition were optimized evaluating thin films morphology and thickness. Thermogravimetry and RMN were applied for precursor's characterization and AFM, XRD and ellipsometry for thin films evaluation. Results showed successful attainment of homogeneous nanocrystalline anatase TiO2 thin films with outstanding control over morphological characteristics, mean grain size of 17 nm, packing densities between 57 and 75%, estimated surface areas of 90 m²/g and monolayers thickness within 20 and 128 nm

Immobilization of biomolecules on natural clay minerals for medical applications

Biomolecules are a group of organic entities that are important in many areas of research on nanomaterials and for biomedical and pharmaceutical applications. Advanced systems have been developed to attempt to protect the activity of biomolecules from rapid degradation and instability. Among these techniques, the incorporation or immobilization of biomolecules has become popular in the development of biocomposites. As such, clay minerals appear to be promising materials; combining a nanometer-scale size with their adsorptive capacity, lack of toxicity, and biocompatibility would result in enhanced biomaterial properties. This mini?review discusses the recent advances concerning biological molecules immobilized on clay minerals and their biomedical applications as biosensors, in regenerative medicine, and even as controlled delivery systems

Transferência de calor através de paineis aglomerados de bagaço de cana, pinus e eucalipto : Heat transfer through against panels of sugar cane, pinus and eucaliptus

O objetivo deste trabalho foi determinar a transferência de calor, a temperatura de combustão e o calor específico de painéis de aglomerado feitos de bagaço de cana, pinus e eucalipto. Os painéis foram expostos a uma fonte de calor até a combustão e mantido por 30 minutos o fluxo de calor entre os materiais. Os resultados mostraram que a transferência de energia durante o aquecimento é maior para os painéis feitos de bagaço de cana-de-açúcar em comparação com os demais materiais

Amorphization Effects on the Basic Sites of Nanometric Magnesium Oxide

The paper reports the catalytic action of the basic sites of nanocrystalline particles of rare earth-doped magnesium oxide in the aldolization reaction between acetone and methanol leading to the C–C bond formation of an a,b-unsaturated compound (methyl vinyl ketone), also forming methyl ethyl ketone and isopropyl alcohol. Undoped and doped MgO samples were prepared by high-energy mechanical milling of commercial Mg, Y and Ce oxide powders. Catalytic activity and surface basicity of these compounds were strongly influenced by doping and the time of mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. Influence of mechanical processing of these compounds was investigated by means of N2 adsorption (BET), X-ray diffraction (XRD), TEM, CO2 chemisorption and room temperature photoluminescence emission. Strong changes of polar groups such as hydroxyl groups on the surface of the solid were directly related to the photoluminescence emission observed

Characterization of the physical properties of NdNiO3 nanotubes.

Neodymium nickelate (NdNiO3) is a correlated oxide that exhibits a metal–insulator transition (MIT) close to 200K and is of interest for advanced electronics and optoelectronics. In this work, we have synthesized NdNiO3 nanotubes using a template-assisted method. For this, precursor solution with stoichiometric amounts of Nd-Ni was prepared by polymeric precursor route, than this solution was deposited in commercial anodized aluminum mesoporous membranes. All samples were heat treated at temperatures ranging from 350 to 750°C under oxygen pressure of 1 and 100 bar. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and magnetization as a function of temperature (M(T)).FAPESPCAPESUFAB

Ischemic stroke caused by large-artery atherosclerosis: a red flag for subclinical coronary artery disease

BackgroundThe coronary calcium score (CAC) measured on chest computerized tomography is a risk marker of cardiac events and mortality. We compared CAC scores in two multiethnic groups without symptomatic coronary artery disease: subjects in the chronic phase after stroke or transient ischemic attack and at least one symptomatic stenosis ≥50% in the carotid or vertebrobasilar territories (Groupathero) and a control group (Groupcontrol).MethodsIn this cross-sectional study, Groupathero included two subgroups: GroupExtraorIntra, with stenoses in either cervical or intracranial arteries, and GroupExtra&Intra, with stenoses in at least one cervical and one intracranial artery. Groupcontrol had no history of prior stroke/transient ischemic attacks and no stenoses ≥50% in cervical or intracranial arteries. Age and sex were comparable in all groups. Frequencies of CAC ≥100 and CAC > 0 were compared between Groupathero and Groupcontrol, as well as between GroupExtraorIntr, GroupExtra&Intra, and Groupcontrol, with bivariate logistic regressions. Multivariate analyses were also performed.ResultsA total of 120 patients were included: 80 in Groupathero and 40 in Groupcontrol. CAC >0 was significantly more frequent in Groupathero (85%) than Groupcontrol (OR, 4.19; 1.74–10.07; p = 0.001). Rates of CAC ≥100 were not significantly different between Groupathero and Groupcontrol but were significantly greater in GroupExtra&Intra (n = 13) when compared to Groupcontrol (OR 4.67; 1.21–18.04; p = 0.025). In multivariate-adjusted analyses, “Groupathero” and “GroupExtra&Intra” were significantly associated with CAC.ConclusionThe frequency of coronary calcification was higher in subjects with stroke caused by large-artery atherosclerosis than in controls