Microemulsions as Nanoreactors to Obtain Bimetallic Nanoparticles

Microemulsions are frequently used as nanoreactors for the synthesis of bimetallic nanoparticles. The ability to manipulate the metal distribution in bimetallic nanoparticles is essential for optimizing applications, and it requires a deeper understanding of how compartmentalization of reaction medium affects nanoparticle synthesis. A simulation model was developed to predict the atomic structure of bimetallic nanoparticles prepared via microemulsion in terms of metals employed and microemulsion composition. The model was successfully proved by comparing theoretical and experimental Au/Pt STEM profiles. On this basis, the model becomes a strong tool to further enhance our knowledge of the complex mechanisms governing reactions in microemulsions and its impact on final nanostructures. The purpose of this study is to perform a comprehensive kinetic analysis of coreduction of different couple of metals in the light of the interplay between three kinetic parameters: intermicellar exchange rate, chemical reduction rates of the two metals, and reactants concentration. The particular combination of these factors determines the reaction rate of each metal, which in turn determines the final metal arrangement

Insight into the surface composition of bimetallic nanocatalysts obtained from microemulsions

The enhancement of catalysts efficiency of bimetallic nanoparticles depends on the ability to exert control over surface composition. However, results relating surface composition and feeding solution of bimetallic nanoparticles synthesized in microemulsions are controversial and apparently contradictory. In order to comprehend how the resulting surface can be modified under different synthesis conditions and for different pairs of metals, a computer simulation study was carried out. The resulting surface compositions are explained based on the relative rates of deposition of the two metals, which depend on the particular metal pair, the concentration of reactants and the microemulsion composition. This study provides a satisfactory understanding of experimental results and allows us to identify the main factors affecting the nanoparticle’s surface composition. Consequently, concrete and practical guidelines can be established to facilitate the experimental synthesis of bimetallic nanoparticles with tailored surfacesThis work was supported by Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia, Spain (Grupos Ref. Comp. ED431C 2017/22; and AEMAT ED431E2018/08), “la Caixa” Foundation-Ref: LCF/PR/PR12/11070003”)S

Core-Shell Nanocatalysts Obtained in Reverse Micelles: Structural and Kinetic Aspects

Ability to control the metal arrangement in bimetallic nanocatalysts is the key to improving their catalytic activity. To investigate how metal distribution in nanostructures can be modified, we developed a computer simulation model on the synthesis of bimetallic nanoparticles obtained in microemulsions by a one-pot method. The calculations allow predicting the metal arrangement in nanoparticle under different experimental conditions. We present results for two couples of metals, Au/Pt (Δε=0.26 V) and Au/Ag (Δε=0.19 V), but conclusions can be generalized to other bimetallic pairs with similar difference in standard reduction potentials. It was proved that both surface and interior compositions can be controlled at nanometer resolution easily by changing the initial reactant concentration inside micelles. Kinetic analysis demonstrates that the confinement of reactants inside micelles has a strong effect on the reaction rates of the metal precursors. As a result, the final nanocatalyst shows a more mixed core and a better defined shell as concentration is higher

The influence of colloidal parameters on the specific power absorption of PAA-coated magnetite nanoparticles

The suitability of magnetic nanoparticles (MNPs) to act as heat nano-sources by application of an alternating magnetic field has recently been studied due to their promising applications in biomedicine. The understanding of the magnetic relaxation mechanism in biocompatible nanoparticle systems is crucial in order to optimize the magnetic properties and maximize the specific absorption rate (SAR). With this aim, the SAR of magnetic dispersions containing superparamagnetic magnetite nanoparticles bio-coated with polyacrylic acid of an average particle size of ≈10 nm has been evaluated separately by changing colloidal parameters such as the MNP concentration and the viscosity of the solvent. A remarkable decrease of the SAR values with increasing particle concentration and solvent viscosity was found. These behaviours have been discussed on the basis of the magnetic relaxation mechanisms involved

ROTDR signal enhancement via deep convolutional denoising autoencoders trained with domain randomization

In this work, a deep convolutional adaptive filter is proposed to enhance the performance of a Raman based distributed temperature sensor system by the application of domain randomization methods for its training. The improvement of the signal-to-noise ratio in the Raman backscattered signals in the training process and translation to a real scenario is demonstrated. The ability of the proposed technique to reduce signal noise effectively is proved independently of the sensor configuration and without degradation of temperature accuracy or spatial resolution of these systems. Moreover, using single trace to noise reduction in the ROTDR signals accelerates the system response avoiding the employment of many averages in a unique measurement.This work has been supported by Spanish CICYT (TEC2016-76021-C2-2-R), by ISCIII (DTS17-00055, INTRACARDIO) co-funded by EU-FEDER FUNDS and by the Spanish Ministry of Education, Culture and Sports through FPU16/05705

Microemulsións: un avance na obtención de fluídos magnéticos

Neste traballo preséntase unha vía alternativa e totalmente orixinal de síntese de nanopartículas para a preparación de fluidos magnéticos, con mellaras respecto ós métodos tradicionais. Para elo, empréganse mezclas ternarias dun disolvente orgánico, un tensioactivo e unha disolución acuosa en forma de microemulsión, para sintetizar nanopartículas magnéticas de óxidos de ferro. Estas nanopartículas, lavadas e cubertas con ácido oleico, son estabilizadas nun líquido portador, producindo un fluido magnético. Preséntanse medidas de difracción de raios-X, microscopía electrónica de transmisión e medidas de magnetización, tanto das partículas coma do líquido preparadoIn this work, an alternative and completely original route for the synthesis of magnetic fluids is presented. This method presents improvements with respect to the traditional methods. Por this purpose, ternary mixtures of organic solvent, surfactant and aqueous solution forming a microemulsion are used for the synthesis of magnetic iron oxide particles. These particles, washed and covered with oleic acid, are stabilized in a carrier liquid, producing a magnetic fluid. X-ray diffraction, transmission electron microscopy and magnetic measurements of the particles and the prepared liquid are reportedS

Elucidation of the Average Molecular Structure of Argentinian Asphaltenes

Petroleum asphaltenes were separated from three different Argentinian crude oils. The asphaltene fractions were extracted by precipitation employing n-pentane and n-heptane solvents, and the coprecipitated resins were removed via Soxhlet extraction. The asphaltenes were characterized by elemental analysis, thermogravimetric analysis, laser desorption ionization mass spectrometry, Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, powder X-ray diffraction, and Raman spectroscopy. It was found that the asphaltene fractions present both a higher content of heteroatoms and a major degree of aromaticity, when n-heptane is employed. Average structural parameters were obtained by a comprehensive analysis of the experimental data, including those describing the central polycyclic aromatic hydrocarbon (PAH) cores and lateral chains. Thus, a hypothetical average molecular structure is proposed for the Argentinian asphaltenes. The average model molecules have a nucleus of PAHs arranged as pericondensed systems of 4-6 fused aromatic rings, with naphthenic groups and/or alkyl chains of 5-10 carbon long attached.Fil: Bava, Yanina Belén. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Gerones, Mariana. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Buceta, David. Universidad de Santiago de Compostela; EspañaFil: De La Iglesia Rodríguez, Darío. Universidad de Santiago de Compostela; EspañaFil: López-Quintela, M. Arturo. Universidad de Santiago de Compostela; EspañaFil: Erben, Mauricio Federico. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; Argentin

Self-Assembly of Silver Metal Clusters of Small Atomicity on Cyclic Peptide Nanotubes

Subnanometric noble metal clusters, composed by only a few atoms, behave like molecular entities and display magnetic, luminescent and catalytic activities. However, non-covalent interactions of molecular metal clusters, lacking of any ligand or surfactant, have not been seen at work. Theoretically attractive and experimentally discernable, van der Waals forces and non-covalent interactions at the metal/organic interfaces will be crucial to understand and develop the next generation of hybrid nanomaterials. Here, we present experimental and theoretical evidence of non-covalent interactions between subnanometric metal (0) silver clusters and aromatic rings and their application in the preparation of 1D self-assembled hybrid architectures with ditopic peptide nanotubes. Atomic force microscopy, fluorescence experiments, circular dichroism and computational simulations verified the occurrence of these interactions in the clean and mild formation of a novel peptide nanotube and metal cluster hybrid materials. The findings reported here confirmed the sensitivity of silver metal clusters of small atomicity towards non-covalent interactions, a concept that could find multiple applications in nanotechnology. We conclude that induced supramolecular forces are optimal candidates for the precise spatial positioning and properties modulation of molecular metal clusters. The reported results herein outline and generalize the possibilities that non-covalent interactions will have in this emerging fieldThis work was supported by the Spanish Ministry of Economy and Competitivity (Mineco) and the ERDF [CTQ2010-15725, CTQ2013-43264-R, MAT2011-28673-C02-01, MAT2012-36754-C02-01], by the Xunta de Galicia (GRC2006/132, GRC2013/044, EM 2012/117). J.M. received a Ramón y Cajal contract from the Mineco. We also thank the ORFEO-CINCA network and Mineco through CTQ2014-51912-REDCS

¿Es generalizable la existencia de una transición de primer orden ferromagnética-paramagnética en los materiales con magnetorresistencia colosal R2/3B1/3MnO3 (R=lantanido; B=alcalinoterreo)?

En este trabajo se examina la naturaleza de la transición de fase ferromagnética de materiales de manganeso con estructura de perovskita, de gran interés tecnológico por sus enormes variaciones de resistividad eléctrica ante la presencia de un campo magnético aplicado (magnetorresistencia colosal). Se encuentra que, en contra de la opinión generalizada, no todos estos materiales presentan un comportamiento cualitativamente similar. En concreto, el carácter de primer orden de la transición ferromagnética no es un factor común. Las implicaciones físicas de este resultado son discutidasIn this work, the nature of the ferromagnetic phase transition of manganese-based materials with perovskite structure, is examined. These are materials of great technological interest due to the enormous variations of their electrical resistivity under the presence of an applied magnetic field (colossal magnetoresistance). lt is found that, contrary to the assumed belíef, not all these materials present a qualitatively similar behaviour. Concretely, the first order character of the ferromagnetic transition is not a common factor. The physical implications of this result are discussedS

Novel synthetic routes of large-pore magnetic mesoporous nanocomposites (SBA-15/Fe3O4) as potential multifunctional theranostic nanodevices

In this paper, novel magnetic silica nanocomposites were prepared by anchoring magnetite nanoparticles onto the outer surface of mesoporous SBA-15 silica; the magnetic nanoparticles were prepared by microemulsion and solvothermal methods, varying the synthesis conditions in order to control the final physicochemical, textural and magnetic properties. The morphology and mesostructure of the materials were characterized by X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption, and Transmission and Scanning Electron Microscopy (TEM and SEM). Magnetic silica nanocomposites feature a two-dimensional hexagonal arrangement constituted by a homogeneous pore channel system with diameters between 13 and 18 nm and a Brunauer–Emmett–Teller (BET) surface area higher than 260 m2 g−1. The different morphologies of the samples are given by the presence of diverse magnetic nanoparticle arrangements covalently linked onto the outer surface of the mesoporous silica rods. This confers on them a superparamagnetic behaviour with a magnetic response between 50–80 emu g−1, even though the weight percent of magnetite present in the samples does not exceed 21.7%. In addition, the magnetic nanocomposites exhibit magnetic hyperthermia with moderate Specific Absorption Rate (SAR) valuesThis work was supported in part by MINECO (Spain) and FEDER Funds (projects MAT 2015-67458-P and CTQ2016-79461-R); and the European Commission (PANA project, Call H2020-NMP-2015-two-stage, Grant 686009; and the MADIA project, Call H2020-ICT-2016-1, Grant 732678)S