Fe3O4-graphene composites with three-dimensional laminated structures have been synthesised by a simple in situ hydrothermal method. From field-emission and transmission electron microscopy results, the Fe3O4 nanoparticles, around 3-15 nm in size, are highly encapsulated in a graphene nanosheet matrix. The reversible Li-cycling properties of Fe3O4-graphene have been evaluated by galvanostatic discharge-charge cycling, cyclic voltammetry and impedance spectroscopy. Results show that the Fe3O4-graphene nanocomposite with a graphene content of 38.0 wt% exhibits a stable capacity of about 650 mAh g(-1) with no noticeable fading for up to 100 cycles in the voltage range of 0.0-3.0 V. The superior performance of Fe3O4-graphene is clearly established by comparison of the results with those from bare Fe3O4. The graphene nanosheets in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe3O4.

Graphene-encapsulated Fe3O4 nanoparticles with 3D laminated structure as superior anode in lithium ion batteries.

The nano iron oxides have been synthesized by almost all the known wet chemical methods which include precipitation at ambient/elevated temperatures, surfactant mediation, emulsion/micro-emulsion, electro-deposition etc. Iron oxides in nano-scale have exhibited great potential for their applications as catalytic materials, wastewater treatment adsorbents, pigments, flocculants, coatings, gas sensors, ion exchangers, magnetic recording devices, magnetic data storage devices, toners and inks for xerography, magnetic resonance imaging, bioseparation and medicine. Nano sized magnetite Fe3O4, and maghemite γ-Fe2O3 exhibiting excellent magnetic properties find applications for biomedical purposes and as soft ferrites. Iron hydroxides and oxyhydroxides such as ferrihydrite, goethite, akaganeite, lepidocrocite are being evaluated for their applications in water purification for the removal of toxic ions. Hematite, α-Fe2O3 in the nano range has been used to obtain transparent paints. In catalysis both iron oxides and hydroxides find application in numerous synthesis processes. This review outlines the work being carried out on synthesis of iron oxides in nano form and their various applications.

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Synthesis and applications of nano-structured iron oxides/hydroxides - a review

Magnetic iron oxide nanoparticles (MIONs) have attracted enormous attention due to their wide applications, including for magnetic separation, for magnetic hyperthermia, and as contrast agents for magnetic resonance imaging (MRI). This review article introduces the methods of synthesizing MIONs, and their application as MRI contrast agents. Currently, many methods have been reported for the synthesis of MIONs. Herein, we only focus on the liquid-based synthesis methods including aqueous phase methods and organic phase methods. In addition, the MIONs larger than 10 nm can be used as negative contrast agents and the recently emerged extremely small MIONs (ES-MIONs) smaller than 5 nm are potential positive contrast agents. In this review, we focus on the ES-MIONs because ES-MIONs avoid the disadvantages of MION-based T2- and gadolinium chelate-based T1-weighted contrast agents.

Iron Oxide Nanoparticle Based Contrast Agents for Magnetic Resonance Imaging.

Hybrid nanomaterials have received voluminous interest due to the combination of unique properties of organic and inorganic component in one material. In this class, magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility. Organic–inorganic magnetic nanocomposites can be prepared by in situ, ex situ, microwave reflux, co-precipitation, melt blending, and ceramic–glass processing and plasma polymerization techniques. These nanocomposites have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents, and magnetically recoverable photocatalysts for degradation of organic pollutants. This review article is mainly focused on fabrication of magnetic polymer nanocomposites and their applications. Different types of magnetic nanoparticles, methods of their synthesis, properties, and applications have also been reviewed briefly. The review also provides detailed insight into various types of magnetic nanocomposites and their synthesis. Diverse applications of magnetic nanocomposites including environmental and biomedical uses have been discussed.

Magnetic polymer nanocomposites for environmental and biomedical applications

Magnetic nanoparticles (MNPs) are of high significance in sensing as they provide viable solutions to the enduring challenges related to lower detection limits and nonspecific effects. The rapid expansion in the applications of MNPs creates a need to overview the current state of the field of MNPs for sensing applications. In this review, the trends and concepts in the literature are critically appraised in terms of the opportunities and limitations of MNPs used for the most advanced sensing applications. The latest progress in MNP sensor technologies is overviewed with a focus on MNP structures and properties, as well as the strategies of incorporating these MNPs into devices. By looking at recent synthetic advancements, and the key challenges that face nanoparticle-based sensors, this review aims to outline how to design, synthesize, and use MNPs to make the most effective and sensitive sensors.

Advances in the Application of Magnetic Nanoparticles for Sensing.

Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.

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Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Size control of magnetite nanoparticles in hydrothermal synthesis by coexistence of lactate and sulfate ions

This study provides a facile single-step coprecipitation method for preparing size-controlled high crystalline magnetite nanoparticles in water system without using any organic solvents. In this method, an iron ions solution and an alkaline solution are simply mixed at room temperature without using any additional heating treatment. The size of obtained magnetite nanoparticles greatly depended on the coexisting anionic species in the starting solution because the coexisting anions greatly influenced both the formation of crystal nuclei and the dispersion stabilisation of formed precipitates. The size control of magnetite nanoparticles having high crystallinity and ferromagnetic property could be successfully achieved by using the effects of coexisting anions. For synthesising finer magnetite nanoparticles, the presence of lactate ion in the starting solution was effective, and coarser ones could be synthesised under higher ferrous/ferric ions molar ratios.

https://www.tandfonline.com/doi/pdf/10.1080/17458080903490731

Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature

Mechanochemical preparation of magnetite nanoparticles by coprecipitation

In a hydrothermal preparation of crystalline magnetite (Fe3O4) nanoparticles, the influence of the experimental parameters (initial molar ratio of ferrous/ferric ions, initial concentration of ferrous ions, and heating time), and their interactions, on the particle formation was studied using response surface methodology (RSM), based on a statistical design of experiments (DOE). As indices indicating particle formation and crystallization, the variation in the particle diameter and crystallite size with the synthesis conditions was examined. The crystallite size was greatly affected by both the initial ferrous/ferric ion molar ratio and the heating time, whereas the particle diameter strongly depended on the heating time, and on the interaction between the initial ferrous/ferric ion molar ratio and the initial concentration of ferrous ions. The results from a statistical analysis suggest that the polycrystalline Fe3O4 nanoparticles form via crystal growth and/or thermal aggregation, after nucleation durin...

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Naoya Mizutani

Papers

Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Size control of magnetite nanoparticles in hydrothermal synthesis by coexistence of lactate and sulfate ions

Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature

Mechanochemical preparation of magnetite nanoparticles by coprecipitation

Response Surface Methodology Study on Magnetite Nanoparticle Formation under Hydrothermal Conditions