Abstract
This article reports on the characterization of four superparamagnetic iron oxide nanoparticles stabilized with dimercaptosuccinic acid, which are suitable candidates for reference materials for magnetic properties. Particles p1 and p2 are single-core particles, while p3 and p4 are multi-core particles. Small-angle X-ray scattering analysis reveals a lognormal type of size distribution for the iron oxide cores of the particles. Their mean radii are 6.9 nm (p1), 10.6 nm (p2), 5.5 nm (p3) and 4.1 nm (p4), with narrow relative distribution widths of 0.08, 0.13, 0.08 and 0.12. The cores are arranged as a clustered network in the form of dense mass fractals with a fractal dimension of 2.9 in the multi-core particles p3 and p4, but the cores are well separated from each other by a protecting organic shell. The radii of gyration of the mass fractals are 48 and 44 nm, and each network contains 117 and 186 primary particles, respectively. The radius distributions of the primary particle were confirmed with transmission electron microscopy. All particles contain purely maghemite, as shown by X-ray absorption fine structure spectroscopy.
Highlights
The synthesis, protection, functionalization and application of magnetic nanoparticles (MNPs) is a mature topic in nanochemistry (Lu et al, 2007)
Rg,LS is the radius of gyration derived from static light scattering data, R is the mean radius of the core of the primary particle, /R is the relative width of the size distribution, r0 is the mean radius of a primary particle of core and shell within a multi-core particle, is the cutoff length for the fractal correlation, D is the mass fractal dimension of the multi-core particles, and Nagg is the aggregation number of a multi-core particle
small-angle X-ray scattering (SAXS) gave a thorough characterization of single-core and multi-core MNPs in terms of core size and size distribution, while XANES proved that the desired crystalline structure and oxidation state of the iron ions was achieved
Summary
The synthesis, protection, functionalization and application of magnetic nanoparticles (MNPs) is a mature topic in nanochemistry (Lu et al, 2007). It is still under debate which of the many magnetic properties characterizes an MNP system most accurately for a specific application, but almost every one of them is related to the magnetic core size. One can obtain the magnetic core sizes and their distribution from the analysis of magnetic data, for example, by analysing the high-field section of magnetization curves employing the Langevin function and assumed size distributions and shapes (Yoon, 2015) This information should be verified by complementary methods. Since the magnetism of nanoparticles depends strongly on core sizes, shapes and crystalline structure, as well as aggregation behaviour, the reproducibility and reliable characterization of these parameters must be addressed first
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