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Amino-modified Fe₃O₄ magnetic nanocomposite particles were prepared by one-step glycothermal method. The shape and morphology of Fe₃O₄ particles change when a small amount of water is added as a co-solvent in the glycothermal method. The morphology and structure of the sample were characterized and measured by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. TEM images show that the morphology of the samples is from irregular polyhedron to spherical particles. Average diameter of particles is approximately 70/40/10 nm and more evenly distributed. XRD results show that the samples are cubic spinel structure. FTIR results show that a chemical bonds combination exists between the amino and iron oxide, nano-iron oxide are modified by the amino.

A biomimetic and facile approach for integrating Fe₃O₄ and Au with polydopamine (PDA) was proposed to construct gold-coated Fe₃O₄ nanoparticles (Fe₃O₄@Au–PDA) with a core–shell structure by coupling in situ reduction with a seed-mediated method in aqueous solution at room temperature. The morphology, structure and composition of the core–shell structured Fe₃O₄@Au–PDA nanoparticles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS). The formation process of Au shell was assessed using a UV-Vis spectrophotometer. More importantly, according to investigating changes in PDA molecules by Fourier transform infrared spectroscopy (FTIR) and in preparation process of the zeta-potential data of nanoparticles, the mechanism of core–shell structure formation was proposed. Firstly, PDA-coated Fe₃O₄ are obtained using dopamine (DA) self-polymerization to form thin and surface-adherent PDA films onto the surface of a Fe₃O₄ "core". Then, Au seeds are attached on the surface of PDA-coated Fe₃O₄ via electrostatic interaction in order to serve as nucleation centers catalyzing the reduction of Au³⁺ to Au⁰ by the catechol groups in PDA. Accompanied by the deposition of Au, PDA films transfer from the surface of Fe₃O₄ to that of Au as stabilizing agent. In order to confirm the reasonableness of this mechanism, two verification experiments were conducted. The presence of PDA on the surface of Fe₃O₄@Au–PDA nanoparticles was confirmed by the finding that glycine or ethylenediamine could be grafted onto Fe₃O₄@Au–PDA nanoparticles through Schiff base reaction. In addition, Fe₃O₄@Au–DA nanoparticles, in which DA was substituted for PDA, were prepared using the same method as that for Fe₃O₄@Au–PDA nanoparticles and characterized by UV-Vis, TEM and FTIR. The results validated that DA possesses multiple functions of attaching Au seeds as well as acting as both reductant and stabilizing agent, the same functions as those of PDA.

Fe₃O₄–SiO₂ core–shell structure nanoparticles containing magnetic properties were investigated for their potential use in drug delivery. The Fe₃O₄–SiO₂ core–shell structure nanoparticles were successfully synthesized by a simple and convenient way. The Fe₃O₄–SiO₂ nanoparticles showed superparamagnetic behavior, indicating a great application potential in separation technologies. From the application point of view, the prepared nanoparticles were found to act as an efficient drug carrier. Specifically, the surface of the core–shell nanoparticles was modified with amino groups by use of silane coupling agent 3-aminopropyltriethoxysilane (APTS). Doxorubicin (DOX) was successfully grafted to the surface of the core–shell nanoparticles after the decoration with the carboxyl acid groups on the surface of amino-modified core–shell structure nanoparticles. Moreover, the nanocomposite showed a good drug delivery performance in the DOX-loading efficiency and drug release experiments, confirming that the materials had a great application potential in drug delivery. It is envisioned that the prepared materials are the ideal agent for application in medical diagnosis and therapy.

In this work, Fe₃O₄ with nanosized triangle plates and capsule-like nanoparticles were prepared by solvothermal approach (Fe₃O₄-S) and hydrothermal approach (Fe₃O₄-H), respectively and their catalytic performance as a heterogeneous Fenton-like catalyst are investigated. Excellent ferromagnetic properties are obtained in both Fe₃O₄-S nanoplates and Fe₃O₄-H nanoparticles. The Fe₃O₄-S nanoplates exhibited better catalytic performance than Fe₃O₄-H nanoparticles in the degradation of Rhodamine B (RhB) with hydrogen peroxide. The relatively high catalytic activity of Fe₃O₄-S can be ascribed to its high specific surface area and high degree of crystallinity. Fe₃O₄-S nanoplates also exhibit good catalytic stability and reusability and do not generate significant loss of catalytic activity after four cycles of degradation.

Fe₃O₄–graphene nanocomposites were prepared via a simple hydrothermal method. Ultrafine Fe₃O₄ nanoparticles were evenly anchored on graphene substrates. As anode material for Li-ion batteries (LIB), the nanocomposite showed high initial discharge and charge capacities of 1456mAhg^-1 and 739.9mAhg^-1 at high current density of 500mAg^-1. Additionally, the charge capacity was also retained at 698.3mAhg^-1 after 200 cycles, thereby indicating excellent cycling stability. The results suggested that the as-prepared Fe₃O₄–graphene nanocomposite is a promising candidate for practical application as a Li-ion battery anode material.