Fe3O4 Nanocubes Research Articles

Coaxial Fe3O4/CuO hybrid nanowires as ultra fast charge/discharge lithium-ion battery anodes

We report the facile, template free electrochemical fabrication of hierarchical Fe3O4/CuO hybrid wires, grown directly on a copper substrate. The electrodes are produced by the electrochemical deposition of Fe3O4 on CuO nanoneedle arrays, fabricated by anodization. The Fe3O4/CuO hybrid anodes displayed ultrafast charging/discharging properties and high rate capabilities, superior to those of their individual building blocks Fe3O4 and CuO. For example, at a current density of 820 mA g−1, the Fe3O4/CuO hybrid wires delivered high reversible specific capacity, good cycling stability (delivering 953 mA h g−1 discharge capacity with 98.7% Coulombic efficiency after 100 cycles) and excellent rate capability (319 mA h g−1 at 8200 mA g−1). The excellent performance of the Fe3O4/CuO hybrids comes from the intelligent integration of the two compatible components into unique hierarchical architectures with a high specific capacity, with one-dimensional CuO nanoneedle arrays electrochemically coated with mesoporous Fe3O4 nanocubes.

L-Serine-Assisted Synthesis of Superparamagnetic Fe3O4Nanocubes for Lithuium Ion Batteries

Monodisperse superparamagnetic Fe3O4 nanocubes with the edge length up to approximately 16 nm were synthesized by using a biomolecule-assisted solvothermal approach. The Fe3O4 nanocubes are characterized by X-ray powder diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The magnetic properties of the Fe3O4 nanocubes are studied by zero-field cooling (ZFC) and field cooling (FC) procedures, i.e., M–T and M–H curves. The electrochemical behavior of the Fe3O4 nanocubes was tested in lithium ion batteries, which presents high specific capacitance of 695.1 mA·h/g at a current rate of 0.2 C, higher than that of commonly used graphite electrode (372 mA·h/g), as well as excellent Coulombic efficiency of above 95% after the 11th cycle in the subsequent cycles.

Shape-Controlled Growth and Shape-Dependent Cation Site Occupancy of Monodisperse Fe3O4 Nanoparticles

The shape control and formation mechanism of Fe3O4 nanoparticles (NPs) synthesized by a modified hot-injection method were investigated. Monodisperse Fe3O4 nanocubes terminated at {100} planes with the average size of 16.1 ± 0.9 nm were synthesized by injecting Fe precursor into reaction solution at 290 °C with a slow injection rate of 10 mL/h. When we increased the monomer concentration in solution by increasing the injection rate to 20 mL/h or doubling the precursor concentration with the same reaction time, the main terminated planes of Fe3O4 NPs became {100} and {110} planes leading to a rhombicuboctahedral shape. The shape of NPs was strongly affected by the monomer concentration and the intrinsic surface energy of Fe3O4. The shape-induced crystallographic orientation-ordered superlattices were obtained in both cubic and rhombicuboctahedral Fe3O4 NPs. On the other hand, the shape-dependent occupancy of the cation sites was clearly observed, measured by using X-ray magnetic circular dichroism (XMCD) spectra. The octahedral sites were occupied by more ferric ions, Fe3+, when the shape of Fe3O4 NPs became cubic.

Surface Plasmon Enhanced Third-Order Nonlinear Optical Effects in Ag−Fe3O4 Nanocomposites

We report an approach to enhance the third-order nonlinear optical properties of a nanocrystal through the attachment of another metallic nanoparticle. Both two-photon absorption (TPA) cross section and nonlinear refractive (NR) cross section of a Fe3O4 nanocube with and without the attachment of an Ag nanoparticle are characterized by using the Z-scan technique. As compared to pristine Fe3O4 nanocube, the TPA and NR cross section of Ag-particle-attached Fe3O4 nanocube is increased by several folds at light frequencies far below the surface plasmon resonance of Ag particle, with precise values depending on the size of the Ag particle. These enhanced values are in agreement with the theoretically calculated enhancement by discrete dipole approximation modeling, which reveals that the local electric field induced by the metal nanoparticle should play an essential role in the enhancement.

Shape-Controlled Synthesis and Magnetic Properties of Monodisperse Fe3O4 Nanocubes

Monodisperse Fe3O4 nanocubes have been successfully synthesized by a facile solvothermal method at 260 °C in the presence of oleic acid and oleylamine. Well-defined assembly of uniform Fe3O4 nanocubes with an average size of 12 nm could be obtained without a size-selection process. The shape of as-prepared Fe3O4 nanoparticles could be reversibly interchanged between spheres and cubes by adjusting the reaction parameters. The phase structures, morphologies, and sizes of as-prepared products were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The magnetic properties of Fe3O4 nanocubes were measured by using a quantum design superconducting quantum interference device (SQUID). The magnetic study reveals that the as-synthesized nanocubes are ferromagnetic at 2 K while they are superparamagnetic at 300 K.

Phase transformation of FeO/Fe3O4 core/shell nanocubes and facile synthesis of Fe3O4 nanocubes

A phase transformation induced by reduction in the γ-Fe2O3 nanocubes synthesized by oxidizing the corresponding FeO/Fe3O4 nanocubes was achieved in solution. Results from x-ray diffraction (XRD), color indication, and magnetic analysis strongly support this phase transformation. The γ-Fe2O3 nanocubes were transformed to Fe3O4 nanocubes within 260–300 °C range and the FeO/Fe3O4 nanospheres at 350 °C. The change in shape of the nanoparticles within the γ-Fe2O3→Fe3O4 transformation as observed from the transmission electron microscopy images was representative for entire the nanoparticles systems as confirmed by the XRD patterns of these nanoparticles in assembled state, suggesting a simple and novel route for synthesis of Fe3O4 nanocubes.

Facile Synthesis, Phase Transfer, and Magnetic Properties of Monodisperse Magnetite Nanocubes

The monodisperse Fe3O4 nanocubes with controllable sizes from 6.5 to 30.0 nm have been synthesized in organic phase. By the formation of surfactant bilayers with charged hydrophilic ions of alpha -cyclodextrin, Fe3O4 nanocubes were successfully ldquopulledrdquo into water from hexane for a possible biomedical application. The Fe3O4 nanocubes with the surfactant bilayers show a good stability in aqueous solution compared with those in aqueous solution which were transferred from organic phase by ligand exchange using PVP with strong binding group. The hysteresis loop at 300 K of Fe3O4 nanocubes with different sizes reveals that a size-dependent behavior of saturation magnetization and the nanocubes with a size less than 25 nm show a typical superparamagnetic behavior at room temperature. The comparison of magnetization of the hydrophilic Fe3O4 nanocubes in CD and PVP aqueous solution reveals that the surfactant bilayers can provide a good stability of magnetization.

Shape control of new FexO–Fe3O4and Fe1–yMnyO–Fe3–zMnzO4 nanostructures

AbstractNew nanoparticle shapes of iron oxide (FexOFe3O4, where 0.8 < x < 1) and iron‐manganese oxide (Fe1–yMnyOFe3–zMnzO4, where 0 < y < 1, and 0 < z < 3) were synthesized by decomposition of the corresponding metal formates in tri‐n‐octylamine/oleic acid mixtures at elevated temperatures (ca. 370 °C), under an inert atmosphere. Details of the syntheses leading to the various shapes of nanoparticles are provided as a function of the reactions parameters, that is, precursor type and concentration, surfactant concentration, water concentration, reaction time, and temperature. Different electron microscopy techniques were used to characterize the crystal phases and the novel shapes of these nanostructures. Nanoparticles of FexOFe3O4 were produced with different shapes, that is spheres, hexagons, and cubes, depending on the reaction conditions. By tuning the conditions, iron oxide nanocubes with concave faces were produced exclusively. Electron and X‐ray diffraction data reveal these nanocubes to be single‐crystal FexO (wüstite) with small amounts of Fe3O4 (magnetite). For the mixed metal system, solid solutions of Fe1–yMnyO with very small amounts of Fe3–zMnzO4 were observed, in which the produced oxide had a larger Fe:Mn ratio than present in the starting reagents. Adjusting the iron to manganese ratio in the mixed‐metal nanoparticles resulted in different shapes. Nanoparticles with ca. 1:1 (Fe:Mn) ratios displayed a ‘dog‐bone‐like’ morphology, which can be considered a shape in between a pure FexOFe3O4 nanocube and the rod‐like nanostructures previously reported for the manganese oxide system. In general, higher Fe:Mn ratios (e.g., 9:1) in the product resulted in nanostructures with cubic shapes, while lower Fe:Mn values (e.g., 2:8) resulted in long (ca. 200 nm) rod‐like nanostructures with flared ends. All of the nanostructures reported here exhibit internal structures that suggest a growth mechanism with etching on negatively curved rough crystal faces. Oxidation of the nanoparticles occurred with retention of their original shape.

Synthesis and magnetic properties of monodisperse magnetite nanocubes

The monodisperse Fe3O4 nanocubes with controllable sizes from 6.5to30.0nm have been synthesized in one pot. The shape-induced texture of the self-assembled nanocube superlattices has been deposited onto substrates by a convective assembly technique. The cubelike shapes affect the crystalline orientation of individual particles within the self-assembled superlattices compared with the nanoparticles with an isotropic spherical shape. The nanocubes with a size less than 25nm show a typical superparamagnetic behavior at room temperature. Comparison of the hysteresis loop at 5K of cubes with different sizes reveals a size-dependent behavior of saturation magnetization and coercivity.