Abstract
Magnetite nanoparticles are of great importance in nanotechnology and nanomedicine and have found manifold applications. Here, the effect of coating of magnetite nanoparticles with organic stabilizers, such as O-phosphoryl ethanolamine, glycerol phosphate, phospho-l-ascorbic acid, phospho-d,l-serine, glycolic acid, lactic acid, d,l-malic acid, and d,l-mandelic acid was studied. Remarkably, this procedure led to an improvement of saturation magnetization in three cases rather than to an unfavorable decrease as usually observed. Detailed X-ray powder diffraction investigations revealed that changes in the average crystallite occurred in the coating process. Surprisingly, changes of the average crystallite sizes in either direction were further observed, when the exposure time to the stabilizer was increased. These results imply a new mechanism for the well-known coating of magnetite nanoparticles with stabilizers. Instead of the hitherto accepted simple anchoring of the stabilizers to the magnetite nanoparticle surfaces, a more complex recrystallization mechanism is likely, wherein partial re-dispersion of magnetite moieties from the nanoparticles and re-deposition are involved. The results can help producers and users of magnetite nanoparticles to obtain optimal results in the production of core shell magnetite nanoparticles.
Highlights
Magnetic nanoparticles with tailored properties have found various important applications in nanomedicine, electronics, separation technology, catalysis, and in magnetic sealing
Various studies revealed that coating with stabilizers can affect the size, the shape, and the magnetism of the magnetite (Fe3O4) nanoparticles (MNPs) as can other factors such as temperature, concentration, type of anions, ionic strength, and pH or exposure to an external magnetic field [1,4,5,10,11,12,13,14]
MNP 1, the following stabilizer were added after 1 h: O-phosphoryl ethanolamine 2a [17], glycerol phosphate 2b [18], phospho-L-ascorbic acid 2c [18], phospho-D,L-serine 2d, glycolic acid 2e [19,20], D,L-lactic acid 2f, malic acid 2g, and D,L-mandelic acid 2h (Scheme 1)
Summary
Magnetic nanoparticles with tailored properties have found various important applications in nanomedicine, electronics, separation technology, catalysis, and in magnetic sealing. Magnetite (Fe3O4) nanoparticles (MNPs) are most prominent [1,2,3,4,5,6]. They are easy to prepare at low costs and are much less toxic than other magnetic nanoparticles [7,8]. For all applications, they must meet crucial property requirements, such as colloidal and chemical stability and, in particular, a high magnetization. Information about the effect of coating on the crystallite structure found in the magnetite cores are still missing. The results further allow understanding the process of surface coating of MNP in a hitherto unknown way
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