I. Gil de Muro

Functionalized Fe3O4@Au superparamagnetic nanoparticles: in vitro bioactivity

The interaction of nanoparticles with cells has been a focus of interest during the past decade. We report the fabrication and characterization of hydrosoluble Fe₃O₄@Au nanoparticles functionalized with biocompatible and fluorescent molecules and their interaction with cell cultures by visualizing them with confocal microscopy. Gold covered iron oxide nanoparticles were synthesized by reducing metal salts in the presence of oleylamine and oleic acid. The functionalization of these particles with an amphiphilic polymer provides a water soluble corona as well as the possibility to incorporate different molecules relevant for bio-applications such as poly(ethylene glycol), glucose or a cadaverine derived dye. The particle size, and the presence of polymer layers and conjugated molecules were characterized and confirmed by transmission electron microscopy, thermogravimetric measurements and infrared spectroscopy. A complete magnetic study was performed, showing that gold provides an optimum coating, which enhances the superparamagnetic behaviour observed above 10-15 K in this kind of nanoparticle. The interaction with cells and the cytotoxicity of the Fe₃O₄@Au preparations were determined upon incubation with the HeLa cell line. These nanoparticles showed no cytotoxicity when evaluated by the MTT assay and it was demonstrated that nanoparticles clearly interacted with the cells, showing a higher level of accumulation in the cells for glucose conjugated nanoparticles.

Influence of Carbon Content on LiFePO4 / C Samples Synthesized by Freeze-Drying Process

The influence of the carbon content in LiFeP0 4 /C composites synthesized by the freeze-drying method was studied by varying the citric acid (chelating agent): Fe ratio. Diminishing this ratio from 1:1 to 0.33:1 led to a gradual reduction of the carbon content from 16.1 to 7.2% wt and different morphologies. Transmission electron microscopy micrographs of the composite with the greatest carbon percentage (16%) show mainly 30 nm LiFeP0 4 particles homogeneously embedded in a carbon network. Samples containing less carbon exhibit only one type of morphology, 200-700 nm aggregates made up of an intimate mixture of LiFeP0 4 particles and carbon. Galvanostatic cycling from 2 to 4 V vs Li/Li + evidences the typical LiFePO 4 redox behavior at 3.4 V, and a second contribution at 2.65 V probably related to the carbon content. At a high rate, a good specific capacity value is observed for the nanoparticulate sample (16% wt C), whereas poorer performance is observed for low carbon content samples (11 and 7.2 wt % C). Heterogeneous and insufficient carbon covering together with phosphate particle aggregation in these latter samples can account for this behavior. Two carbon distribution models are proposed to explain different electrochemical responses. In all cases, a good capacity retention is observed after prolonged cycling.

Effect of Carbon Coating on the Physicochemical and Electrochemical Properties of Fe2O3 Nanoparticles for Anode Application in High Performance Lithium Ion Batteries

Nanoparticulate Fe2O3 and Fe2O3/C composites with different carbon proportions have been prepared for anode application in lithium ion batteries (LIBs). Morphological studies revealed that particles of Fe2O3 in the composites were well-dispersed in the matrix of amorphous carbon. The properties of the γ-Fe2O3 nanoparticles and the correlation with the particle size and connectivity were studied by electron paramagnetic resonance, magnetic, and Mössbauer measurements. The electrochemical study revealed that composites with carbon have promising electrochemical performances. These samples yielded specific discharge capacities of 1200 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 γ-Fe2O3 nanoparticles in the in situ generated amorphous carbon matrix.

Magnetic and structural characterization of thiol capped ferromagnetic Ag nanoparticles

Dodecanethiol capped Ag nanoparticles (NPs) have been independently synthesized by the well-known Brust method under the same physical-chemical conditions. The obtained NP present similar sizes (∼2 nm) but different magnetic behaviors. The extended x-ray absorption fine structure analyses at the K-edge of Ag did not reveal any noticeable structural nor topological differences among the samples. In clear contrast with the structure provided for thiol capped ferromagnetic Au NPs, the analysis also brings out the existence of Ag–S bonds in a diffuse region surrounding a reduced Ag core where the magnetism of the Ag NPs would be located.

Thermal decomposition study of [MCu(C3H2O4)2(H2O)n] phases (M is Ca (n = 3), Sr and Ba (n = 4))

Abstract Three new compounds with the general formula [MCu(C 3 H 2 O 4 ) 2 (H 2 O) n ] (M is Ca ( n = 3), Sr and Ba ( n = 4)) have been synthesized and characterized by analytical and infrared techniques. X-ray diffraction methods have shown that all the complexes have orthorhombic unit cells. Thermal decomposition of these compounds using TGA-DSC and DTA techniques involves three consecutive steps: dehydration, ligand pyrolysis and inorganic residue evolution. Dehydration is an endothermic process with enthalpies of around 200 kJ mol −1 . Kinetic analysis of the dehydration curves has been performed and the Johnson equation gave the best correlation factors for the three complexes. Further treatments in tubular furnaces resulted in the formation of mixed oxides of formula MCuO 2 (M is Ca, Sr and Ba). The formation of small homogeneous particles in these oxides, as with metallo-organic percursors, has been observed by scanning electron microscopy.

Evolution with time of the magnetic and spectroscopic properties of the BaCuO2+δ phase. Study of Ba1−xSrxCuO2+δ solid solutions

Abstract A study of the evolution of the magnetic and spectroscopic properties of BaCuO 2+x , obtained by thermal decomposition of BaCu(edta).nH 2 O (edta = ethylenediaminetetraacetate), has been performed. The ferromagnetic behaviour of this compound is maintained with time, but a decrease in the effective magnetic number has been observed, probably due to the changes in the oxidation states of copper ions belonging to the disordered part of the structure. An axial signal was observed in EPR, which becomes rhombic with time. Solid solutions Ba 1−x Sr x CuO 2+δ have been prepared by thermal treatment of metallo-organic complexes. A diminution in the magnitude of the ferromagnetic exchange interaction appears as strontium is substituted by barium. The thermal treatment of the altered samples gives rise to their original behaviour.

Preparation of functionalized Fe1-xPdx based nanoparticles: magnetic characterization

Oleic acid/oleylamine capped Fe1-xPdx (x=0.16, 0.20, 0.25) nanoparticles have been synthesized using a diol as reducing agent in order to get nanoparticles of different average sizes and coatings. Composition and morphology were analyzed by infrared spectroscopy (IR), X-Ray Diffraction (RXD), thermogravimetry (TG) and Transmission Electron Microscopy (TEM). Well dispersed nanoparticles with uniform sizes between 3 and 8 nm and average diameters less than 6 nm were obtained. Magnetic properties were investigated by Electron Magnetic Resonance (EMR) and magnetization measurements. Most of the nanoparticles were superparamagnetic at physiological temperature with low magnetic saturation values (near 5 emu.g-1 alloy/0.4 Nβ per Fe atom). SAR measurements were also performed with the aim of carrying out hyperthermia measurements but the nanoparticles did not work as magnetic heaters.

Nanoparticles of La{sub 0.8}Ca{sub 0.2}Fe{sub 0.8}Ni{sub 0.2}O{sub 3-{delta}} perovskite for solid oxide fuel cell application

Polycrystalline samples of La0.8Ca0.2Fe0.8Ni0.2O3−δ (LCFN) with perovskite type structure have been prepared by combustion, freeze drying, citrate-gel process and liquid mix method. The analysis of X-ray powder diffraction indicated that the samples were single phase and crystallized in an orthorhombic (space group, Pnma no. 62) structure. Transmission electron microscopy (TEM) analysis on the synthesized powder at 600 °C by liquid mix method showed clusters of 150 nm formed by nanoparticles of 20 nm. Electrochemical performance of LCFN cathodes, which are used for intermediate temperature solid oxide fuel cells, were investigated. The polarization resistance was studied using two different electrolytes: Y-doped zirconia (YSZ) and Sm-doped ceria (SDC). The dc four-probe measurement exhibits a total electrical conductivity, over 100 S cm−1 at T ≥ 600 °C, pointing out that strontium can be substituted for the cheaper calcium cation without destroying the electrochemical properties. Experimental results indicate that nanoparticles have more advantages in terms of smaller particle size and better electrochemical performance.