Abstract
The size, size distribution and magnetic properties of magnetite nanoparticles (NPs) prepared by co-precipitation without citrate, in the presence of citrate and citrate adsorbed post-synthesis were studied by X-ray Diffraction (XRD), Dynamic Light Scattering (DLS), Electron Paramagnetic Resonance (EPR) and magnetization measurements. The aim of this investigation was to clarify the effect of citrate ions on the size and magnetic properties of magnetite NPs. The size of the primary NPs, as determined by analysing the width of diffraction peaks using various methods, was ca. 10 nm for bare magnetite NPs and with citrate adsorbed post-synthesis, whereas it was around 5 nm for the NPs co-precipitated in the presence of citrate. DLS measurements show that the three types of NPs form aggregates (100–200 nm in diameter) but the dispersions of the citrate-coated NPs are more stable against sedimentation than those of bare NPs. The sizes and size distributions determined by XRD are in good agreement with those of the magnetic domains obtained by fitting of the magnetization vs. magnetic field intensity curves. Magnetization vs. magnetic field intensity curves show that the three kinds of sample are superparamagnetic.
Highlights
Iron oxide nanoparticles (NPs) are interesting in view of their applications ranging from biomedical field to environmental remediation
The formation of clusters of individual NPs limits the colloidal stability of magnetite NP dispersions and influences the magnetic properties of these clusters in which the NPs are in close proximity
We investigated by means of X-ray Diffraction (XRD), Dynamic Light Scattering (DLS), magnetization measurements and Electron Paramagnetic Resonance (EPR) the size and magnetic properties of magnetite NPs prepared by co-precipitation without and with citrate under various conditions
Summary
Iron oxide nanoparticles (NPs) are interesting in view of their applications ranging from biomedical field to environmental remediation. We investigated by means of X-ray Diffraction (XRD), Dynamic Light Scattering (DLS), magnetization measurements and Electron Paramagnetic Resonance (EPR) the size and magnetic properties of magnetite NPs prepared by co-precipitation without and with citrate under various conditions. A study of the particle size, PSD, aggregation of the NPs and their effect on the magnetic properties of magnetite NPs is of fundamental relevance to tailor the preparation procedures in view of the applications of these NPs. In order to clarify the effect of citrate on particle size and PSD, the coating with citrate was carried out by co-precipitation of magnetite NPs in the presence of citrate (in situ) and by adsorbing citrate ions on the NPs after synthesis (ex situ). Zero Field Cooling/Field Cooling (ZFC/FC) curves and EPR spectra were measured in order to derive information about the interactions between bare and citrate-coated (prepared in both ways) magnetite NPs
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