65 research outputs found
Material compuesto que comprende una matriz porosa de carbón amorfo y nanopartículas de Bi obtenible mediante un procedimiento sol-gel, procedimiento de obtención y su uso.
La presente invención se refiere a un material
compuesto que comprende una matriz porosa de
carbono amorfo con un tamaño de poro comprendido
entre 2 y 1000 nm, en la que se encuentran
embebidas y distribuidas homogéneamente
nanopartículas esféricas de tamaño comprendido
entre 5 y 500 nm de al menos un elemento metálico
que es Bi en fase cristalina tetragonal, obtenible
mediante un procedimiento que comprende al menos
las siguientes etapas:a) preparar una composición líquida sol-gel en forma
de solución que contiene al menos un precursor
orgánico de la matriz en un solvente;
b) depositar la solución líquida dentro de un molde o
sobre un soporte en forma de capa o microestructura;
c) condensar la solución líquida que contiene el
precursor orgánico en el molde o en el soporte, hasta
dar lugar a un gel orgánico húmedo;d) secar el gel húmedo; y
e) someter el gel a pirólisis, en atmósfera inerte a una
temperatura igual o superior a 800°C;
donde al menos un precursor del Bi se adiciona en la
primera etapa a) disolviéndose en el solvente junto al
precursor orgánico para formar parte de la
composición sol-gel, o se adiciona en la tercera etapa
c) impregnando el gel orgánico húmedo con una
solución del precursor de Bi en un solvente antes del
secado; y donde el material presenta un área
superficial de Bi comprendida entre 2.5-102
cm2
/g y 2.5-10 5
cm2
/g, la matriz
presenta una porosidad intrínseca accesible
comprendida entre 10% y 95% respecto al carbono
amorfo no poroso.Peer reviewedConsejo Superior de Investigaciones CientíficasA1 Solicitud de patente con informe sobre el estado de la técnic
Epitaxial stabilization of ε-Fe2O3 (00l) thin films on SrTiO3 (111)
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Thin films of the metastable and elusive ε-Fe2O3 have been epitaxially stabilized on SrTiO3 (111) substrates. The ε-Fe2O3 films present a (001) orientation perpendicular to the substrate and three in-plane domains measuring a few nanometers and showing atomically sharp interfaces. We argue that this domain structure, rather than the epitaxial-strain, plays an essential role in stabilizing the ε-Fe2O3 by minimizing the energy of (100) surfaces. The ε-Fe2O3 films show a large in-plane coercivity ∼ 8 kOe which combined with the magnetoelectric character claimed for this oxide may lead to novel applications in spintronics
Electrochemically Active Thin Carbon Films with Enhanced Adhesion to Silicon Substrates
Thin carbon films deposited on technologically relevant substrates, such as silicon wafers, can be easily implemented in miniaturized electrochemical devices and used for sensing applications. However, a major issue in most carbon films is the weak film/substrate adhesion that shortens the working device lifetime. This paper describes the facile preparation of robust thin carbon films on silicon substrates by one-pot sol-gel synthesis. The improved adherence of these carbon films is based on the incorporation of silica through the controlled synthesis of a resorcinol/formaldehyde gel modified with aminopropyltriethoxysilane. The films demonstrate excellent adhesion to the silicon substrate, good homogeneity, excellent electrical conductivity and superior electrochemical performance. Moreover, this approach opens the door to the fabrication of carbon thin-film electrodes by photolithographic techniques.G. Antorrena from the Laboratorio de Microscopias Avanzadas of the Instituto de Nanociencia de Aragón is acknowledged for performing XPS analysis. This research was partially funded by, the European Union’s 7th Framework Programme (FP7/2007-2013) under grant agreement number 614155, the Spanish Ministry of Economy and Competitiveness in cofounding with the European Social Funds through the MAT2012-35324 project, the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV- 2015-0496) and the Generalitat de Catalunya (2014SGR213, 2014SGR1645). The Chinese Scholarship Council fellowship (201206240033) to P.N. and the COST Action MP1202 are also acknowledged.Peer Reviewe
Unveiling a New High-Temperature Ordered Magnetic Phase in ϵ-Fe2O3
Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-FeO is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-FeO nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2' magnetic symmetry, but only involving two of the four Fe sublattices which are ordered below T ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-FeO with a critical temperature of T ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-FeO may open the door to further expand the working range of this multifunctional iron oxide
Nanorods based on mesoporous silica containing iron oxide nanoparticles as catalytic nanomotors: study of motion dynamics
Self-propelled particles and, in particular, those based on mesoporous
silica, have raised considerable interest due to their potential applications
in the environmental and biomedical fields thanks to their biocompatibility,
tunable surface chemistry and large porosity. Although spherical particles have
been widely used to fabricate nano- and micromotors, not much attention has
been paid to other geometries, such as nanorods. Here, we report the
fabrication of self-propelled mesoporous silica nanorods (MSNRs) that move by
the catalytic decomposition of hydrogen peroxide by a sputtered Pt layer, Fe2O3
nanoparticles grown within the mesopores, or the synergistic combination of
both. We show that motion can occur in two distinct sub-populations
characterized by two different motion dynamics, namely enhanced diffusion or
directional propulsion, especially when both catalysts are used. These results
open up the possibility of using MSNRs as chassis for the fabrication of
self-propelled particles for the environmental or biomedical fields.Comment: 16 pages, 5 figures, SI with 6 pages, 8 figures, 4 video
Nanopartícules magnètiques en matrius de sílice
Descripció del recurs: el 21 setembre 2011En aquest treball s'han estudiat diferents aproximacions a la síntesi de compòsits de nanopartícules magnètiques en matrius de sílice de tipus aerogel o xerogel. Així, s'han obtingut materials amb propietats molt diferents tant pel que fa al seu magnetisme (materials durs o tous), a les seves propietats òptiques (transparents, opacs, anisotròpics) o la seva densitat, i se n'han estudiat algunes de les seves possibles aplicacions magnetoòptiques. Les matrius de sílice en forma de xerogel també s'han fet servir per a estabilitzar, gràcies al confinament, l'ε-Fe2O3, un polimorf metastable d'óxid de Fe (III) molt poc conegut. S'ha fet una caracterització de les propietats magnètiques del material i s'ha vist que la seva temperatura de Curie és de 510 K i que a temperatura ambient és un ferrimagnet colineal amb una imantació moderada (20 emu/g a saturació) i una anisotropia magnètica elevada que fan que la seva coercitivitat sigui molt elevada per a un òxid de Fe (20 kOe). Entre 150 i 80 K l'ε-Fe2O3 presenta una transició de fase magnètica i estructural de segon ordre que té com a resultat l'aparició d'una estructura magnètica incommensurada de tipus "ona quadrada". S'ha posat de manifest que coincidint amb aquesta transició de fase, el material presenta un acoblament magnetoelèctric.In this Thesis, different approximations to the synthesis of composites of magnetic nanoparticles in silica aerogel or xerogel matrices have been studied. In particular, we have obtained materials with a range of different properties regarding its magnetism (hard or soft magnetic materials), optical properties (transparent, opaque, anisotropic) or density and we have studied its potential magneto-optical applications. The xerogel matrices have also been used to stabilize by confinement a rare iron (III) oxide polymorph, the ε-Fe2O3, which has not been much studied so far. The magnetic properties of the polymorph have been studied in detail and it has been established that it has a Curie temperature of 510 K. At room temperature, it presents a collinear ferromagnetic order with a moderate magnetization (20 emu/g at saturation) and a large magnetic anisotropy which result in a huge coercivity of about 20 kOe. Between 150 and 80 K, ε-Fe2O3 presents a second order magnetic and structural transition to a "square-wave" incommensurate magnetic order. Concomitantly with this transition it has been shown that the material presents a magnetoelectric coupling.En este trabajo se han estudiado diferentes aproximaciones a la síntesis de composites de nanopartículas magnéticas en matrices de sílice de tipo aerogel o xerogel. Así, se han obtenido materiales con propiedades muy distintas tanto en relación a su magnetismo (materiales duros o blandos), a les sus propiedades ópticas (transparentes, opacos, anisotrópicos) o a su densidad, y se han estudiado algunas de sus posibles aplicaciones magnetoópticas. Las matrices de sílice en forma de xerogel también se han utilizado para estabilizar, gracias al confinamiento, el ε-Fe2O3, un polimorfo metaestable de óxido de Fe (III) muy poco conocido. Se ha hecho una caracterización de sus propiedades magnéticas y se ha establecido que su temperatura de Curie es de 510 K y que a temperatura ambiente es un ferrimagneto co-lineal con una imantación moderada (20 emu/g a saturación) y una anisotropía magnética elevada que hacen que su coercitividad sea muy elevada para un óxido de Fe (20 kOe). Entre 150 i 80 K el ε-Fe2O3 presenta una transición de fase magnética y estructural de segundo orden que da lugar a una estructura magnética inconmensurable de tipo "onda cuadrada". Se ha puesto de manifiesto que coincidiendo con esta transición de fase, el material presenta un acoplamiento magnetoeléctrico
Magnetic Mesoporous Silica Nanorods Loaded with Ceria and Functionalized with Fluorophores for Multimodal Imaging
Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol-gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-FeO) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assesse
Prevalence and seasonality of viral respiratory infections in a temperate climate region : A 24-year study (1997-2020)
Background: Few long-term reports have been published on the epidemiology of respiratory viruses despite their frequent involvement in extremely common infections. The aim here was to determine the frequency and distribution of respiratory viruses in a temperate climate area (Barcelona, Spain) throughout a 24-year period. Methods: We collected data on all respiratory viruses detected from 1997 to 2020 in our institution. Clinical specimens were analyzed mainly by conventional techniques, and molecular techniques were also used. Results: Of the 59,579 specimens analyzed, 21,382 (35.9%) were positive for at least one virus. The number of positive samples during cold months was significantly higher than in warm months. Respiratory virus infections were detected in patients of all ages, above all in children under 3 years of age, who were most frequently infected with the respiratory syncytial virus, whereas Influenza A virus predominated in the other groups, especially in adults. A clear demographic and seasonal pattern was established for some viruses. Circulation of other respiratory viruses during the FLUAV H1N1pdm09 and SARS-CoV-2 pandemics was observed. Conclusions: This long-term study provides new knowledge about the prevalence of respiratory viruses in a Mediterranean region. Throughout the study period, the frequency of some viruses remained constant, whereas others varied with the year. A clear demographic and seasonal pattern was established for some viruses. Patients suffering from severe respiratory infections should be examined for a range of respiratory viruses regardless of gender, age, or season
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