Aspects Concerning the Fabrication of Magnetorheological Fluids Containing High Magnetization FeCo Nanoparticles

Recently, our collaborative work in the fabrication of a magnetorheological fluid (MRF) containing high magnetization FeCo nanoparticles (NPs, fabricated in our laboratories using the chemical reduction technique; MS = 212 Am2/kg) as magnetic fillers have resulted in a new MRF with superior performance up to 616.7 kA/m. The MRF had a yield stress value of 2729 Pa and good reversibility after a demagnetization process. This value competes with the best ones reported in the most recent literature. Nevertheless, the fabrication process of this type of fluid is not an easy task since there is a strong trend to the aggregation of the FeCo NPs due to the strong magnetic dipolar interaction among them. Thus, now we present the analysis of some aspects concerning the fabrication process of our FeCo NPs containing MRF, mainly the type of surfactant used to cover those NPs (oleic acid or aluminium stearate) and its concentration, and the procedure followed (mechanical and/or ultrasound stirring) to achieve a good dispersion of those magnetic fillers within the fluid.All the authors want to thank the financial support provided by the Basque Government under the MMMfavIN (KK-2020/00099, Elkartek program) and also the Research Groups (IT1009-16, IT1226-19 and IT1245-19) projects

High magnetization FeCo nanoparticles for magnetorheological fluids with enhanced response

We present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30–50 nm and high magnetization, 212 ± 2 A m2 kg−1. They agglomerate due to the strong magnetic dipolar interaction among them. These FeCo nanoparticles were used to synthesize a magnetorheological fluid by using oleic acid as surfactant, mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. The synthesized fluid showed a strong magnetorheological response with increasing shear stress values as the magnetic field intensity increases. Thus, we have measured a superior performance up to 616.7 kA m−1, with a yield stress value of 2729 Pa, and good reversibility after demagnetization process. This value competes with the best ones reported in the most recent literature. We have compared the obtained results with our previous reported ones by using high magnetization Fe NPs fabricated by the electrical explosion of wire method (Fe-EEW).J. Berasategi, A. Gómez and M. M. Bou-Ali would like to thank the financial support provided by the Basque Government under research project PI-2017-1-0055 and MMMfavIN (KK-2020/00099, Elkartek program). V. Vadillo, J. Gutiérrez, J.M. Barandiarán, M. Insausti and I. Gil de Muro would like to thank the financial support provided also by the Basque Government under PI-2017-1-0043, the MMMfavIN (KK-2020/00099, Elkartek program) and Research Groups (IT1245-19 and IT1226-19) research projects. A. A. and A. I. gratefully acknowledge the financial support of the Basque Government (Research Groups IT-1175-19) and the Ministerio de Economía y Competitividad (PGC2018-094548-B-I00, MCIU/AEI/FEDER, UE).Peer reviewe

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

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

Lithium Iron Phosphate/Carbon (LFP/C) Composite Using Nanocellulose as a Reducing Agent and Carbon Source

Lithium iron phosphate (LiFePO4, LFP) is the most promising cathode material for use in safe electric vehicles (EVs), due to its long cycle stability, low cost, and low toxicity, but it suffers from low conductivity and ion diffusion. In this work, we present a simple method to obtain LFP/carbon (LFP/C) composites with different types of NC: cellulose nanocrystal (CNC) and cellulose nanofiber (CNF). Microwave-assisted hydrothermal synthesis was used to obtain LFP with nanocellulose inside the vessel, and the final LFP/C composite was achieved by heating the mixture under a N2 atmosphere. The resulting LFP/C indicated that the NC in the reaction medium not only acts as the reducing agent that aqueous iron solutions need (avoiding the use of other chemicals), but also as a stabiliser of the nanoparticles produced in the hydrothermal synthesis, obtaining fewer agglomerated particles compared to synthesis without NC. The sample with the best coating—and, therefore, the best electrochemical response—was the sample with 12.6% carbon derived from CNF in the composite instead of CNC, due to its homogeneous coating. The utilisation of CNF in the reaction medium could be a promising method to obtain LFP/C in a simple, rapid, and low-cost way, avoiding the waste of unnecessary chemicals

Chemical Synthesis and Magnetic Properties of Monodisperse Nickel Ferrite Nanoparticles for Biomedical Applications

With the aim of improving the response in magnetic hyperthermia treatments and other biomedical applications, a nanoparticle system based on nickel ferrites has been investigated. Monodisperse ferrite nanoparticles with different proportions of Ni²⁺ ions and sizes have been produced by an optimized synthesis based on the thermal decomposition method and the seed-growth technique. All samples were chemically and structurally characterized by different methods, and the magnetic behavior has been analyzed by means of field and temperature dependent magnetization measurements and electronic magnetic resonance. It has been proved that low proportions of Ni²⁺ cation in the structure favors high saturation magnetization values and a reduction of the magnetic anisotropy constant. The optimized nanoparticles were transferred to water. Such nanoparticles are innocuous at concentrations up to 0.5 mg/mL and are convenient MRI contrast agents. Those samples with lower percentages of Ni²⁺ atoms and bigger particle sizes presented the highest specific absorption rate, and, for instance, they are the most adequate for magnetic hyperthermia applications

RGD-Functionalized Fe3O4 nanoparticles for magnetic hyperthermia

To improve the selectivity of magnetic nanoparticles for tumor treatment by hyperthermia, Fe3O4 nanoparticles have been functionalized with a peptide of the type arginine-glycine-aspartate (RGD) following a "click" chemistry approach. The RGD peptide was linked onto the previously coated nanoparticles in order to target αvβ3 integrin receptors over-expressed in angiogenic cancer cells. Different coatings have been analyzed to enhance the biocompatibility of magnetic nanoparticles. Monodispersed and homogeneous magnetite nanoparticles have been synthesized by the seed growth method and have been characterized using X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, transmission electron microscopy and magnetic measurements. The magnetic hyperthermia efficiency of the nanoparticles has also been investigated and cytotoxicity assays have been perfomed for functionalized nanoparticles.This work was supported by institutional funding from the Ministry of Economy Industry and Competitiveness and Basque Government under Projects MAT2016-78266-P, FEDER, GIC-IT-570-13, Fondo Social de la DGA (grupos DGA), SAF2014-54763-C2-2-R. Technical and human support provided by SGIker (UPV/EHU) is also gratefully acknowledged. A grant from Gobierno Vasco to M.S.-A. (POS_2015_2-0048) is acknowledged.Peer reviewe