Izaskun Gil de Muro

Chemically Induced Permanent Magnetism in Au, Ag, and Cu Nanoparticles: Localization of the Magnetism by Element Selective Techniques

We report a direct observation of the intrinsic magnetization behavior of Au in thiol-capped gold nanoparticles with permanent magnetism at room temperature. Two element specific techniques have been used for this purpose: X-ray magnetic circular dichroism on the L edges of the Au and 197Au Mössbauer spectroscopy. Besides, we show that silver and copper nanoparticles synthesized by the same chemical procedure also present room-temperature permanent magnetism. The observed permanent magnetism at room temperature in Ag and Cu dodecanethiol-capped nanoparticles proves that the physical mechanisms associated to this magnetization process can be extended to more elements, opening the way to new and still not-discovered applications and to new possibilities to research basic questions of magnetism.

High voltage cathode materials for Na-ion batteries of general formula Na3V2O2x(PO4)2F3−2x

Different samples of the sodium–vanadium fluorophosphate cathodic materials have been synthesized via the hydrothermal method, varying the type and content of carbon used in the synthesis. Structural characterization of the composites was performed by powder X-ray diffraction. Magnetic susceptibility measurements and EPR (Electron Paramagnetic Resonance) polycrystalline spectra indicate that some of the samples exhibit V3+/V4+ mixed valence, with the general formula Na3V2O2x(PO4)2F3−2x where 0 ≤ x < 1. The morphology of the materials was analyzed by Transmission Electron Microscopy (TEM). A correlation between the type and content of carbon with the electrochemical behavior of the different samples was established. Electrochemical measurements conducted using Swagelok-type cells showed two voltage plateaux at 3.6 and 4.1 V vs. Na/Na+. The best performing sample, which comprised a moderate percentage of electrochemical grade carbon as additive, exhibited specific capacity values of about 100 mA h g−1 at 1C (≈80% of theoretical specific capacity). Cyclability tests at 1C proved good reversibility of the material that maintained 98% of initial specific capacity for 30 cycles.

Cation only conduction in new polymer–SiO2 nanohybrids: Na+ electrolytes

Hybrid nanoparticles are functionalized with delocalized covalent anions to form poly-salts for novel electrolytes for use in Li-ion or Na-ion batteries. These redox- and hydrolysis- stable electrolytes can avoid concentration gradients and still maintain the mechanical advantage of nanofillers with conductivities of around 10−5 S cm−1 at 25 °C.

A novel one step synthesized Co-free perovskite/brownmillerite nanocomposite for solid oxide fuel cells

Cobalt-free perovskite oxides Pr1−xCaxFe0.8Ni0.2O3 (PCFN) were investigated as novel cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). Ca and Ni substitution in the PrFeO3 material shows that a wide range of perovskites Pr1−xCaxFe0.8Ni0.2O3 (0 < x < 0.9) can be prepared by sintering in air at 600 °C. Perovskites with 0 < x < 0.4 exhibit orthorhombic single phases (Pnma space group), whereas 0.4 < x < 0.9 show a coexistence of the perovskite and the brownmillerite-type structure (Ca2Fe2O5). The structure of the polycrystalline powders was analyzed by X-ray powder diffraction, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The analysis on the synthesized powders shows the presence of clusters formed by 30–100 nm nanoparticles. High-Resolution TEM (HRTEM) studies were carried out to confirm the existence of Ca2Fe2O5. The dc four-probe measurement exhibits a total electrical conductivity, over 100 S cm−1 at T ≥ 600 °C when 0 < x < 0.6, pointing out that strontium can be substituted for calcium without modifying the electrochemical properties. The Pr0.4Ca0.6Fe0.8Ni0.2O3/Ca2Fe2O5 composite cathode presents the better performance in electrochemical measurements, showing an area specific resistance value of 0.09 ohm cm2 at 850 °C.

A straightforward synthesis of carbon nanotube–perovskite composites for solid oxide fuel cells

A powerful non-difficult and economical route based on the addition of carbon nanotubes (CNTs) is presented for the synthesis of nanostructured materials. For the first time, CNTs have been used as composite materials with a perovskite-type oxide for SOFC devices giving rise to an improved electrochemical behavior at intermediate temperatures.

High-voltage cathode materials for lithium-ion batteries: freeze-dried LiMn0.8Fe0.1M0.1PO4/C (M = Fe, Co, Ni, Cu) nanocomposites.

Four LiMn0.8Fe0.1M0.1PO4/C (M = Fe, Co, Ni, Cu) cathode materials have been synthesized via a freeze-drying method. The samples have been characterized by powder X-ray diffraction, transmission electron microscopy, magnetic susceptibility, and electrochemical measurements. The composition and effective insertion of the transition-metal substituents in LiMnPO4 have been corroborated by elemental analysis, the evolution of the crystallographic parameters, and the magnetic properties. The morphological characterization of the composites has demonstrated that the phosphate nanoparticles are enclosed in a matrix of amorphous carbon. Among them, LiMn0.8Fe0.1Ni0.1PO4/C is the most promising cathode material, providing a good electrochemical performance in all aspects: high voltage and specific capacity values, excellent cyclability, and good rate capability. This result has been attributed to several factors, such as the suitable morphology of the sample, the good connection afforded by the in situ generated carbon, and the amelioration of the structural stress provided by the presence of Ni(2+) and Fe(2+) in the olivine structure.

Physico-Chemical and Electrochemical Properties of Nanoparticulate NiO/C Composites for High Performance Lithium and Sodium Ion Battery Anodes

Nanoparticulate NiO and NiO/C composites with different carbon proportions have been prepared for anode application in lithium and sodium ion batteries. Structural characterization demonstrated the presence of metallic Ni in the composites. Morphological study revealed that the NiO and Ni nanoparticles were well dispersed in the matrix of amorphous carbon. The electrochemical study showed that the lithium ion batteries (LIBs), containing composites with carbon, have promising electrochemical performances, delivering specific discharge capacities of 550 mAh/g after operating for 100 cycles at 1C. These excellent results could be explained by the homogeneity of particle size and structure, as well as the uniform distribution of NiO/Ni nanoparticles in the in situ generated amorphous carbon matrix. On the other hand, the sodium ion battery (NIB) with the NiO/C composite revealed a poor cycling stability. Post-mortem analyses revealed that this fact could be ascribed to the absence of a stable Solid Electrolyte Interface (SEI) or passivation layer upon cycling.

Tailoring biocompatible Fe3O4 nanoparticles for applications to magnetic hyperthermia

Magnetite based nanoparticles functionalized with different ligands have been obtained by optimization of two synthetic methods. Gold surrounded Fe3O4 nanoparticles capped with oleic acid and oleylamine were achieved by thermal decomposition of metallo-organic precursors. By this way nanoparticles with perfectly defined size within 3.5 nm to 7 nm in diameter and organic content from 16.1% to 40.9 % were obtained. Precipitation of iron(II) chloride in basic solution yield magnetite nanoparticles between 20 and 40 nm with contents of organic ligands of 3 - 12 %. The samples have been characterized by X-ray diffraction, transmission electron microscopy and thermogravimetric measurements. A complete magnetic study has been performed by means of a SQUID magnetometer and electron magnetic resonance (EMR), showing the influence of capping covering on the superparamagnetic behaviour. The citotoxicity and interaction with HeLa cells was evaluated for some of the preparations. Finally, the specific absorption rate (SAR) was calculated to compare the efficiency of heating each sample for the various applied magnetic fields.

Exploring Reaction Conditions to Improve the Magnetic Response of Cobalt-Doped Ferrite Nanoparticles

With the aim of studying the influence of synthesis parameters in structural and magnetic properties of cobalt-doped magnetite nanoparticles, Fe3−xCoxO4 (0 < x < 0.15) samples were synthetized by thermal decomposition method at different reaction times (30–120 min). The Co ferrite nanoparticles are monodisperse with diameters between 6 and 11 nm and morphologies depending on reaction times, varying from spheric, cuboctahedral, to cubic. Chemical analysis and X-ray diffraction were used to confirm the composition, high crystallinity, and pure-phase structure. The investigation of the magnetic properties, both magnetization and electronic magnetic resonance, has led the conditions to improve the magnetic response of doped nanoparticles. Magnetization values of 86 emu·g−1 at room temperature (R.T.) have been obtained for the sample with the highest Co content and the highest reflux time. Magnetic characterization also displays a dependence of the magnetic anisotropy constant with the varying cobalt content.

Synthesis, physical and microwave absorption properties of Barium ferrite - P(VDF-TrFE) nanocomposites

We present results concerning the synthesis, magnetic, dielectric and microwave absorption properties of BaFe12O19 / P(VDF-TrFE) nanocomposites. First, barium ferrite nanopowders were prepared by the hydrothermal synthesis method. Structural and morphological properties of the prepared powders were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing as result a good quality spherical plus platelet-like shaped nanoparticles. Afterwards, composite films with filler nanoparticles of barium ferrite BaFe12O19 (BaFO, nominal 5-20 wt.%) dispersed within P(VDF-TrFE) acting as polymeric matrix have been prepared by solvent evaporation. Magnetic properties were examined by the vibrating sample magnetometry (VSM), and a direct comparison of results obtained for the composites respect to the pure nanopowder allow us to obtain the true nanofiller content value, different from the initially nominal one. Dielectric properties have been measured up to 2 MHz and show the typical behaviour of Maxwell-Wagner type interfacial polarization. From 10 kHz up, permittivity of the composites remains almost unchanged, with values that show a smooth increase as the %wt. of BaFe12O19 does. Finally, microwave absorption properties were analyzed by using ESR technique operating at X-band. All obtained results are discussed in terms of size and quantity of the composites BaFe12O19 filler nanoparticles.