Martín E. Saleta

Preparation of iron oxide nanoparticles stabilized with biomolecules: experimental and mechanistic issues.

Nanoparticles (NPs) with magnetic properties based on magnetite (Fe(3)O(4), MAG) modified with oleic acid (OA), chitosan (CS) and bovine serum albumin (BSA) have been prepared. A versatile method of synthesis was employed, involving two steps: (i) co-precipitation of MAG; and (ii) nanoprecipitation of macromolecules on as-formed MAG NPs. Experimental variables have been explored to determine the set of conditions that ensure suitable properties of NPs in terms of their size, functionality and magnetic properties. It was found that the presence of OA in Fe(+2)/Fe(+3) solutions yields MAG NPs with lower aggregation levels, while increasing initial amounts of OA may change the capability of NPs to disperse in aqueous or organic media by modifying the stabilization mechanism. Incorporation of CS was verified through Fourier transform IR spectroscopy. This biopolymer stabilizes NPs by electrostatic repulsions leading to stable ferrofluids and minimal fraction of recoverable solid NPs. BSA was successfully added to NP formulations, increasing their functionality and probably their biocompatibility. In this case too stable ferrofluids were obtained, where BSA acts as a polyelectrolyte. From the proposed methodology it is possible to achieve a wide range of NPs magnetically active intended for several applications. The required properties may be obtained by varying experimental conditions.

Origin of magnetic anisotropy in ZnO/CoFe2O4 and CoO/CoFe2O4 core/shell nanoparticle systems

ZnO-core/CoFe2O4-shell nanoparticles of 7.4 nm average size have been synthesized and their magnetic properties have been compared to those of CoO-core/CoFe2O4-shell nanoparticles with similar morphology. The coercive field values are much lower than those for CoO/CoFe2O4 nanoparticles (e.g., at 5 K: Hc = 7.8 kOe for ZnO/CoFe2O4; Hc = 27.8 kOe for CoO/CoFe2O4). The nature of the coercive field values is explained by a phenomenological model for the free energy of a non-magnetic core, or an antiferromagnetic core, encapsulated by a hard ferrimagnetic shell.

Strong reduction of V4+ amount in vanadium oxide/hexadecylamine nanotubes by doping with Co2+ and Ni2+ ions: Electron paramagnetic resonance and magnetic studies

In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VOx/Hexa NT’s) doped with Co2+ and Ni2+ ions. The morphology of the NT’s has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co2+, S = 3/2 and Ni2+, S = 1) decreases notably the amount of V4+ ions in the system, from 14−16% (nondoped case) to 2%−4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V4+ in the nanotub...

Metal oxides: crystallographic characterizations for high-temperature electrochemistry applications

The strong relationship between the crystallographic structure and defects with the electronic and transport properties of a certain material is a key figure in most of the research conducted in materials science. The properties of an oxide in particular (transport, electrochemical, thermal, etc.) can be affected by several factors including the synthesis method and environmental conditions such as pressure, temperature, atmosphere, electrical current and field, magnetic field, etc. Therefore, it is important to go beyond the limited information obtained through the traditional ex-situ characterization techniques toward the more exhaustive ones provided by the in-situ or in-operando experiments, where it is possible the study of a device under nonambient working conditions.

Sowing crystals: crystal growth activities in Bariloche, Argentina

Adriana Serquis1, Virginia Tognoli2, Martin Saleta2, Dina Tobia2, Mauricio D Arce1, Morena Robles3, Jordana Dorfman3, Patricia Mateos3 1Materials Characterization Department CNEA-CONICET, Bariloche, Argentina, 2Magnetic Resonance Department CNEA CONICET, Bariloche, Argentina, 3Sección Divulgación Científica y Tecnológica, CAB-IB CNEA CUYO, Bariloche, Argentina E-mail: aserquis@cab.cnea.gov.ar