CoFe₂O₄ and CoFe₂O₄/SiO₂ Core/Shell Nanoparticles: Magnetic and Spectroscopic Study

Abstract

Spherical nanoparticles of surfactant-coated CoFe 2 O 4 (core) were prepared through thermal decomposition of metal acetylacetonates in the presence of a mixture of oleic acid and oleylamine and uniformly coated with silica shell by using tetraethylorthosilicate (TEOS) and ammonia in a micellar solution (core/shell). Transmission electron microscopy (TEM) analysis of core/shell nanoparticles evidenced the high homogeneity of the coating process in producing single core/shell nanoparticles with a narrow size distribution. The combined use of spectroscopic studies (NMR and FTIR) on core and core/shell nanoparticles pointed out that the surfactants' layer bound to the surface core nanoparticles is retained also after the silica coating process. This allows to obtaining systems with very similar magnetic behavior but weaker dipolar interparticle interactions and lower values of saturation magnetization. In view of the interest in biomedical field, the effect of the CoFe 2 O 4 nanoparticles silica coating was also studied by controlling the possible modifications in cytotoxicity by trypan blue and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assays on human cells.

Synthesis of monodisperse Ce x Zr1−x O2 nanocrystals and the size-dependent enhancement of their properties

“…Nanoscaled materials often exhibit unique sizedependent properties that are dramatically different from those of their bulk counterparts [1][2][3][4]. One of the most representative examples is gold, which is highly inert in bulk form but exhibits high catalytic activity in the form of nanoparticles [5].…”

Synthesis and Biodistribution of Cat's Eye-shaped [57Co]CoO@SiO2Nanoshell Aqueous Colloids for Single Photon Emission Computed Tomography (SPECT) Imaging Agent

“…18 Among various coating materials, amorphous silica is commonly used as coating or encapsulating materials due to its hydrophilic nature and biocompatibility. 19 After silica coating on the core material, the surface properties of the core-shell nanostructure such as the charge, reactivity, stability, dispersibility and solubility of core materials can be controlled. Moreover, the hydroxyl group on silica shell can be easily modified with suitable functional molecules by simple hydrolysis and condensation reaction.…”

Influence of aging time of oleate precursor on the magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method

“…In the case of samples at 300 K, we calculated a SQ of 0.03 for sample 2D, 0.13 for sample 14D, and 0.28 for sample 30D. A theoretical SQ value of 0.5 is attributed to single domain magnetic nanoparticles with uniaxial anisotropy, while SQ values of 0.83 indicate the presence of cubic magnetocrystalline anisotropy, as is the case of bulk cobalt ferrite [5,45,46]. In our case, the synthesized nanoparticles exhibited uniaxial magnetocrystalline anisotropy, as all samples displayed a SQ value less than 0.8, however an increase in SQ was observed with aging time of the oleate precursor.…”