It has been thought that many novel properties and potential applications would emerge from monodisperse materials with small dimensions. Therefore, the synthesis of monodisperse nanoparticles has been intensively pursued for their technological and fundamental scientific importance. The synthesis of nanostructured magnetic materials has become a particularly important area of research and is attracting a growing interest because of the potential applications such materials have in ferrofluids, advanced magnetic materials, catalysts, colored pigments, high-density magnetic recording media, and medical diagnostics. Spinel ferrites (MFe2O4; M = Fe, Mn, Zn, or Co) are among the most important magnetic materials and have been widely used in electronic devices, information storage, magnetic resonance imaging (MRI), and drug-delivery technology. 14] Magnetite (Fe3O4) has recently been considered an ideal candidate for biological applications, both as a tag for sensing and imaging, and as an activity agent for antitumor therapy. For high performance in function-specific biological applications, magnetic particles must be spherical and have smooth surfaces, narrow size distributions, large surface areas (for maximal protein or enzyme binding), high magnetic saturation (ss) to provide maximum signal, and good dispersion in liquid media. 18,19] After Sugimoto and Matijević reported the preparation of magnetite particles with a narrow size distribution in the early 1980s, monodisperse ferrite has been fabricated by various chemistry-based synthetic methods, including coprecipitation, the reverse micelle method, microwave plasma synthesis, solgel techniques, freeze drying, ultrasound irradiation, hydrothermal methods, laser pyrolysis techniques, and thermal decomposition of organometallic and coordination compounds. 9,14, 18, 20–27] However, most of these approaches were focused on the synthesis of ferrite particles limited to diameters below 30 nm. There are no reports on the synthesis of well-crystallized ferrite nanoparticles with sizes similar to protein molecules. The development of a facile and economic synthetic strategy for the synthesis of hydrophilic, biocompatible magnetite nanoparticles would benefit their technical use in biomedical fields, especially for applications in vivo. Herein we report a general approach for the fabrication of monodisperse, hydrophilic, and single-crystalline ferrite microspheres by a solvothermal reduction method. To the best of our knowledge, this is the first report on the synthesis of single-crystalline magnetic microspheres. The ferrite spheres had monodisperse diameters that were tunable in the range of 200–800 nm. This work resulted in an important method for obtaining various monodisperse, magnetic, and single-crystalline microspheres, and provided an opportunity to further apply these promising materials. Typical syntheses of Fe3O4 and ferrite microspheres were carried out in a solvothermal system by modified reduction reactions between FeCl3 and ethylene glycol. We confirmed the production of Fe3O4 by conducting controlled oxidation reactions in which aand g-Fe2O3 were produced (Supporting Information). 28–29] The crystalline structures of MFe2O4 were characterized by XRD. As shown in Figure 1, the

Monodisperse magnetic single-crystal ferrite microspheres.

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

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Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Much progress has been made over the past ten years on the synthesis of monodisperse spherical nanocrystals. Mechanistic studies have shown that monodisperse nanocrystals are produced when the burst of nucleation that enables separation of the nucleation and growth processes is combined with the subsequent diffusion-controlled growth process through which the crystal size is determined. Several chemical methods have been used to synthesize uniform nanocrystals of metals, metal oxides, and metal chalcogenides. Monodisperse nanocrystals of CdSe, Co, and other materials have been generated in surfactant solution by nucleation induced at high temperature, and subsequent aging and size selection. Monodisperse nanocrystals of many metals and metal oxides, including magnetic ferrites, have been synthesized directly by thermal decomposition of metal-surfactant complexes prepared from the metal precursors and surfactants. Nonhydrolytic sol-gel reactions have been used to synthesize various transition-metal-oxide nanocrystals. Monodisperse gold nanocrystals have been obtained from polydisperse samples by digestive-ripening processes. Uniform-sized nanocrystals of gold, silver, platinum, and palladium have been synthesized by polyol processes in which metal salts are reduced by alcohols in the presence of appropriate surfactants.

Synthesis of monodisperse spherical nanocrystals.

https://iopscience.iop.org/article/10.1088/1468-6996/16/2/023501/pdf

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications.

Inorganic nanocrystals with tailored geometries exhibit unique shape-dependent phenomena and subsequent utilization of them as building blocks for the fabrication of nanodevices is of significant interest. Herein, we review the recent developments in the shape control of colloidal nanocrystals with a focus on the scientifically and technologically important semiconductor and metal oxide nanocrystals obtained by nonhydrolytic synthetic methods. Many structurally unprecedented motifs have been discovered including polyhedrons, rods and wires, plates and prisms, and other advanced shapes such as branched rods, stars, inorganic dendrites, and dumbbells. The currently proposed shape-guiding mechanisms are presented and the important pioneering studies on the assembly of shape-controlled nanocrystals into ordered superlattices and the fabrication of prototype advanced nanodevices are discussed.

Shape Control of Semiconductor and Metal Oxide Nanocrystals through Nonhydrolytic Colloidal Routes

Easy preparation of iron oxide nanoparticles [5- and 11-nm maghemite (γ-Fe2O3) and 19-nm magnetite (Fe3O4)] by thermal decomposition of Fe(CO)5 in the presence of residual oxygen of the system and by consecutive aeration were investigated by TEM/HRTEM, XRD, and Mossbauer spectroscopy. Also, the magnetic properties of the nanoparticles were studied by SQUID magnetometer and optical microscopy. It was suggested that the intermediate iron oxide nanoparticles (before aeration) were formed by the competing processes of oxidation and crystal growth after decomposition of Fe(CO)5. At room temperature, the aerated 5-nm particles were superparamagnetic without interaction among the particles, whereas the 19-nm particles were ferrimagnetic. The 11-nm iron oxide nanoparticles were superparamagnetic with some interactions among the particles.

/pdf/easy-synthesis-and-magnetic-properties-of-iron-oxide-5e5z0chapb.pdf

Easy Synthesis and Magnetic Properties of Iron Oxide Nanoparticles

Magnetic nanoparticles have been investigated for use as biomedical purposes for several years. For biomedical applications the use of particles that present superparamagnetic behavior at room temperature is preferred [1-4]. To control the magnetic materials by magnetic field is essential locate particle to the suitable destination on feeding by injection. In order to use them properly, the particles should be nano size. However there are many difficulties in applications, because there is lack of identifications in nano magnetic properties. In our studies, structural and magnetic properties of iron oxide nanoparticles were investigated by XRD, VSM, TEM, and Mossbauer spectroscopy. At 13 K, hyperfine fields of γ-Fe₂O₃ were 516 kOe and 490 kOe, that of Fe₃O₄ were 517 kOe and 482 kOe. The saturation magnetizations were 21.42 emu/g and 39.42 emu/g. The particle size of powders is 5~19 ㎚.

/pdf/crystallographic-and-magnetic-properties-of-iron-oxide-4yif53vvwu.pdf

Sang Won Lee

Papers

Easy Synthesis and Magnetic Properties of Iron Oxide Nanoparticles

Crystallographic and Magnetic Properties of Iron Oxide Nanoparticles for Applications in Biomedicine

Hysteresis Loss in Self-temperature Rising of Magnetic Nanoparticles for Hyperthermia Applications