Fe3O4 Nanocrystals Research Articles

Structural characterization and functional correlation of Fe3O4 nanocrystals obtained using 2-ethyl-1,3-hexanediol as innovative reactive solvent in non-hydrolytic sol-gel synthesis

An original non-hydrolytic sol-gel approach, using 2-ethyl-1,3-hexanediol as reactive solvent, was proposed to synthetize nanostructured magnetite. Iron-oxide nanoparticles were prepared and studied as a function of the precursor-to-solvent ratio. The crystallization degree of nanoparticles was followed by the combined Rietveld and Reference Intensity Ratio method. This procedure has allowed the determination of both amorphous and crystalline content of nanomagnetite, using hematite as suitable internal standard. The results of Rietveld method show that the crystalline content decreases as the precursor-to-solvent is increased, ranging from 67 to 60 wt%. Information on the crystallite size-strain distribution and microstructural evolution of nanocrystals was supplied by line profile analysis of the powder diffraction patterns, employing the Whole Powder Pattern Modeling analysis: the obtained log-normal distribution curves become increasingly narrow and symmetrical, while nanoparticle microstrain increases as the precursor concentration is increased. The dimensional analysis of the Transmission Electron Microscopy images has allowed to obtain the nanoparticle grain-size distribution. Nanoparticle dimensions decreases from 15 to 9 nm increasing the precursor concentration. The comparison between the results of X-ray diffraction and microscopic characterization techniques highlighted the effect of several factors, such as size, shape and microstructure of magnetite nanoparticles, on their functional magnetic response. Magnetic characterizations show that magnetite nanoparticles are not in the superparamagnetic phase even at room temperature, independent of the precursor concentration. On the other hand, the room-temperature saturation magnetization, ranging from 73 to 60 emu/g, is a function of the nanoparticle average size, decreasing as the precursor concentration increases.

The Outside-In Approach To Construct Fe3O4 Nanocrystals/Mesoporous Carbon Hollow Spheres Core–Shell Hybrids toward Microwave Absorption

It is widely accepted that building a core–shell structure is an effective way to modify impedance matching behavior and induce interfacial polarization relaxtion. In this work, we adopted a novel impregnation process and subsequent calcination treatment to construct Fe3O4 nanocrystals/mesoporous carbon hollow spheres (MCHS) core–shell hybrids. From the perspective of microwave absorption, MCHS possess favorable dielectric loss ability and lightweight features. Fe3O4 could produce magnetic loss and regulate impedance matching characteristics. Besides, hollow voids and mesopores facilitate microwave absorption, while multiple interfacial polarization induced between Fe3O4 nanocrystals and MCHS contributes to microwave attenuation. Combining these advantages, a maximum reflection loss value of −60.2 dB at 15.5 GHz and a broad effective bandwidth of 5.7 GHz can be achieved for the as-prepared sample at a thickness of 2.3 mm. Furthermore, the excellent microwave absorption properties with a ultrawide bandwidt...

Fine-Tuning the Wall Thickness of Ordered Mesoporous Graphene by Exploiting Ligand Exchange of Colloidal Nanocrystals.

Because of their unique physical properties, three-dimensional (3D) graphene has attracted enormous attention over the past years. However, it is still a challenge to precisely control the layer thickness of 3D graphene. Here, we report a novel strategy to rationally adjust the wall thickness of ordered mesoporous graphene (OMG). By taking advantage of ligand exchange capability of colloidal Fe3O4 nanocrystals, we are able to fine-tune the wall thickness of OMG from 2 to 6 layers of graphene. When evaluated as electrocatalyst for oxygen reduction reaction upon S and N doping, the 4-layer OMG is found to show better catalytic performance compared with their 2- and 6-layer counterparts, which we attribute to the enhanced exposure of active sites arising from the thin wall thickness and high surface area.

Transition Metal-Based Thiometallates as Surface Ligands for Functionalization of All-Inorganic Nanocrystals

We report a new family of inorganic ligands, namely, transition metal-based thiometallates, for the surface functionalization of colloidal nanocrystals (NCs). We synthesized Pt-, Fe-, Co-, and Ni-based thiometallates, in which transition metal ions were complexed with polysulfides. These inorganic anions easily exchanged the surface organic ligands of various nanocrystals of metal, semiconductor, and oxide materials, without affecting the NCs’ primary structural and optical characteristics. Furthermore, upon heating, these complexes were decomposed and transformed into crystalline phases of metal sulfides or pure metals, accompanied by the evaporation of S. Based on this effect, we selectively synthesized homogeneously distributed atomic Pt clusters or Pt nanoparticles on Fe3O4 nanomaterials by heating thioplatinate-capped Fe3O4 NCs. As a model application, we tested the prepared Pt-functionalized Fe3O4 nanomaterial as a heterogeneous catalyst for CO oxidation reaction and Pt–Fe3O4 catalysts exhibited the high turnover frequency due to the homogeneous distribution of atomic Pt over Fe3O4 and the corresponding strong metal–support interaction. This approach opens up a new avenue to functionalize nanocrystals for catalytic applications.

Self-Assembly and Directed Assembly of Polymer Grafted Nanocrystals via Solvent Annealing

Polymer grafted nanocrystals (PGNCs) incarnate a duality of powerful attributes: their inorganic crystal cores hold promise to design nanocrystal solids from superlattice assemblies while their polymeric ligands exhibit the soft colloidal properties of star polymers. From their star polymer analogues, PGNC derive two important, yet sometimes less-exploited attributes: (1) swollen PGNCs are mobile and can be solvent annealed toward thermodynamic equilibrium, and (2) in the semidiluted regime in good solvents, PGNCs display a richer phase diagram compared to that of hard-sphere colloids which can be accessed by controlling the solvent intake during solvent annealing. Here we study the self-assembly of ∼4 nm Fe3O4 nanocrystals capped with polystyrene ligands under solvent annealing. We confirm swelling behavior and even a phase transition to a hexatic phase, in agreement with models for star polymers. We exploit the polymeric properties of the PGNCs to perform directed self-assembly using thinly textured pat...

Field Effect of a Chemically Assembled Fe3O4 Nanocrystal Film Single‐Electron Transistor

The gate voltage dependence of the source‐drain current of a chemically assembled Fe3O4 nanocrystal film single‐electron transistor reflects the energy level splitting of the minority spin 3d band due to two‐electron Coulomb repulsion in each nanocrystal. Using the Langmuir–Blodgett technique, a Fe3O4 nanocrystal self‐assembled film was deposited on a quartz substrate where a three‐terminal electrode made of Au was prefabricated. At 300 K in a magnetic field of 0.2 T, the source‐drain current peaked near the source‐drain bias voltage of 100 V at a gate voltage of +1 to +3 V. At a bias voltage of 100 V, a gate voltage of +1 V amplified the current 13 times more than at a gate voltage of 0 V. Upon increasing the gate voltage to +5 V, the amplification of the current declined to less than three times more than at 0 V. At the optimized gate voltage, by adjusting the empty upper band energy of each Fe3O4 nanocrystal over the gate electrode to match the filled lower band energy outside of the gate electrode, the tunneling current can be greatly increased, because electron transport via the empty state of each nanocrystal over the gate electrode requires no extra energy cost.

High-Performance Oxygen Evolution Anode from Stainless Steel via Controlled Surface Oxidation and Cr Removal

Improving the water oxidation performance of abundantly available materials, such as stainless steel (SS), with notable intrinsic electrocatalytic oxygen evolution reaction (OER) activity due to the presence of Ni and Fe is highly anticipated in water splitting. A new method for promoting the corrosion of stainless steel (304) was found which assisted the uniform formation of oxygen evolution reaction (OER) enhancing NiO incorporated Fe2O3 nanocrystals with the simultaneous reduction in the surface distribution of OER inactive Cr. An equimolar combination of KOH and hypochlorite was used as the corroding agent at 180 °C. The effect of corrosion time on the OER activity was studied and found that better water oxidation performance was observed when the corrosion time was 12 h (SS-12). The SS-12 showed an abnormal enhancement in OER activity compared to the untreated SS and other optimized versions of the same by requiring very low overpotentials of 260, 302, and 340 mV at the current densities of 10, 100, ...

Controllable synthesis of Fe3O4 polyhedron possessing excellent high-rate electrochemical performance for lithium-ion batteries

Fe3O4 nanocrystals (NCs) composed of different proportion of {100} and {111} facets were prepared using oleic acid and decanoic acid as surfactant to mediate their growth process. It has been found that the morphology of Fe3O4 NCs can be tuned by changing the ratio of oleic acid and decanoic acid. When tested as the anode materials in LIBs, the Fe3O4 octahedrons obtained after annealing at 450°C was found to exhibit superior electrochemical performances with a high reversible capacity of 882.6mAhg−1 at 1Ag−1 over 200 cycles, whereas the Fe3O4 cubooctahedron and cubes bearing poor electrochemical performances. The present results prove that the surface structure of Fe3O4 polyhedrons significantly influence the utilization of Fe3O4 active materials and hence their electrochemical performance although the morphology will be destroyed during cycling.

Microwave-Assisted Synthesis of Fe3O4 Nanocrystals with Predominantly Exposed Facets and Their Heterogeneous UVA/Fenton Catalytic Activity.

Fe3O4 nanocrystals with five different morphologies (i.e., nanospheres, nanorods, nanocubes, nano-octahedrons, and nanoplates) were acquired using a simple, efficient, and economic microwave-assisted oxidation technique. The microstructure, morphology, predominant exposed facets, and iron atom local environment of Fe3O4 were revealed by powder X-ray diffraction (PXRD), scanning transmission electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometer (XPS), and Mössbauer spectrum. We demonstrated that the heterogeneous UVA/Fenton catalytic activities of Fe3O4 nanocrystals are morphology/facets dependent. Under UVA irradiation, the catalytic activity of the as-prepared Fe3O4 was in the sequence of nanospheres > nanoplates > nano-octahedrons ≈ nanocubes > nanorods > nano-octahedrons (by coprecipitation). The dominating factor for the catalytic performance was the particle size and BET specific surface area; moreover, the exposed {111} facets, which contained more Fe2+ species, on the nanocrystal surface led to a stronger UVA/Fenton catalytic activity. Both •OH and O2•- radicals participated in the UVA/Fenton degradation process, and •OH played the dominant role. These morphology-controlled nanomagnetites showed great potential in applications as heterogeneous UVA/Fenton catalysts for effectively treating nonbiodegradable organic pollutants.

Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals

We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the 1H NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261±0.002ppm benzene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to exchange interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm3 sample volume is in the 107Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media.

Effects of amount of benzyl ether and reaction time on the shape and magnetic properties of Fe3O4 nanocrystals

Magnetite Fe3O4 nanoparticles (NPs) have attracted much interest due to their low toxicity, good biological compatibility and fast response to an external magnetic field. The magnetite Fe3O4NPs with different shapes and sizes were successfully prepared by the thermal decomposition method. The effects of the amount of solvent and the reaction time on the morphologies and the magnetic properties of magnetite Fe3O4 NPs were investigated comprehensively. A series of testing methods including X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectrum testified that the as-obtained samples were pure magnetite phase. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) indicated the amount of solvent and the reaction time could tune the shape and size of Fe3O4 NPs. The truncated cube and octahedron were the intergradations for the cube. The oleic acid played an important role in inhibiting the crystal growth along the 〈100〉 direction and accelerating that along the 〈111〉 direction of magnetite. The variation trend of the saturation magnetization (Ms) was in agreement with that of the particle size, which was attributed the contribution from the small-size effect or surface effect. The variation of the coercivity (Hc) depended on that of the magnetic anisotropy, the surface anisotropy or the shape anisotropy.

Erratum to: Four-electron oxygen reduction from mesoporous carbon modified with Fe2O3 nanocrystals

Erratum to: Four-electron oxygen reduction from mesoporous carbon modified with Fe2O3 nanocrystals

Luminescent/magnetic PLGA-based hybrid nanocomposites: a smart nanocarrier system for targeted codelivery and dual-modality imaging in cancer theranostics.

Cancer diagnosis and treatment represent an urgent medical need given the rising cancer incidence over the past few decades. Cancer theranostics, namely, the combination of diagnostics and therapeutics within a single agent, are being developed using various anticancer drug-, siRNA-, or inorganic materials-loaded nanocarriers. Herein, we demonstrate a strategy of encapsulating quantum dots, superparamagnetic Fe3O4 nanocrystals, and doxorubicin (DOX) into biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) polymeric nanocomposites using the double emulsion solvent evaporation method, followed by coupling to the amine group of polyethyleneimine premodified with polyethylene glycol-folic acid (PEI-PEG-FA [PPF]) segments and adsorption of vascular endothelial growth factor (VEGF)-targeted small hairpin RNA (shRNA). VEGF is important for tumor growth, progression, and metastasis. These drug-loaded luminescent/magnetic PLGA-based hybrid nanocomposites (LDM-PLGA/PPF/VEGF shRNA) were fabricated for tumor-specific targeting, drug/gene delivery, and cancer imaging. The data showed that LDM-PLGA/PPF/VEGF shRNA nanocomposites can codeliver DOX and VEGF shRNA into tumor cells and effectively suppress VEGF expression, exhibiting remarkable synergistic antitumor effects both in vitro and in vivo. The cell viability waŝ14% when treated with LDM-PLGA/PPF/VEGF shRNA nanocomposites ([DOX] =25 μg/mL), and in vivo tumor growth data showed that the tumor volume decreased by 81% compared with the saline group at 21 days postinjection. Magnetic resonance and fluorescence imaging data revealed that the luminescent/magnetic hybrid nanocomposites may also be used as an efficient nanoprobe for enhanced T2-weighted magnetic resonance and fluorescence imaging in vitro and in vivo. The present work validates the great potential of the developed multifunctional LDM-PLGA/PPF/VEGF shRNA nanocomposites as effective theranostic agents through the codelivery of drugs/genes and dual-modality imaging in cancer treatment.

Four-electron oxygen reduction from mesoporous carbon modified with Fe2O3 nanocrystals

Synthesis and characterization of a cost-effective electrocatalyst for oxygen reduction reaction (ORR) are attempted for sustainable development in energy storage protocol. Ordered mesoporous carbon (OMC) has emerged as a promising candidate for such purposes, particularly in alkaline conditions. However, the scarceness of active sites is responsible for considerably lower catalytic performance of OMC. Herein, we report a new facile route to synthesize α-Fe2O3 nanoparticles supported on ordered mesoporous carbons forming a new hybrid ORR catalyst. This catalyst displayed excellent catalytic properties, long-term stability and impressive methanol tolerance.

An efficientfficient, controllable and facile two-step synthesis strategy: Fe3O4@RGO composites with various Fe3O4 nanoparticles and their supercapacitance properties

An efficient, controllable, and facile two-step synthetic strategy to prepare graphene-based nanocomposites is proposed. A series of Fe3O4-decorated reduced graphene oxide (Fe3O4@RGO) nanocomposites incorporating Fe3O4 nanocrystals of various sizes were prepared by an ethanothermal method using graphene oxide (GO) and monodisperse Fe3O4 nanocrystals with diameters ranging from 4 to 10 nm. The morphologies and microstructures of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, nitrogen adsorption measurements, and transmission electron microscopy. The results show that GO can be reduced to graphene during the ethanothermal process, and that the Fe3O4 nanocrystals are well dispersed on the graphene sheets generated in the process. The analysis of the electrochemical properties of the Fe3O4@RGO materials shows that nanocomposites prepared with Fe3O4 nanocrystals of different sizes exhibit different electrochemical performances. Among all samples, Fe3O4@RGO prepared with Fe3O4 nanocrystals of 6 nm diameter possessed the highest specific capacitance of 481 F/g at 1 A/g, highlighting the excellent capability of this material. This work illustrates a promising route to develop graphene-based nanocomposite materials with a wide range of potential applications.

High yield production of graphene-Fe2O3 nano-composites via electrochemical intercalation of nitromethane and iron chloride, and their application in lithium storage

We demonstrate a facile, scalable and tunable method to produce a composite material based on graphene multilayers and Fe2O3, combining the good conductivity and 2D layered structure of the former and the lithium storage capacity of the latter. The composite was obtained directly from bulk graphite, exploiting the fast electrochemical intercalation of tetrachloroferrate (III) anions (FeCl4−) and nitromethane molecules between the graphene sheets. Then, irradiation with microwaves triggered the simultaneous exfoliation of graphite and its functionalization with Fe2O3 nanocrystals, produced by the thermal hydrolysis of the FeCl4−. This process was monitored in real time using thermal gravimetry and mass spectrometry. X-rays diffraction, Raman spectroscopy, scanning electron and transmission microscopies confirmed the final structure of the composite formed by conductive 2D nanosheets coated by Fe2O3 crystals, featuring both high crystallinity and nanometric size. The composite could be used directly as an anode in Li-ion batteries, demonstrating the viability of this approach for high yield and scalable production of graphene/metal oxide composites.

Lengthy one-dimensional magnetite (Fe3O4) sub-microfibers with excellent electrochemical performance

One dimensional Fe3O4 sub-microfibers with an average diameter of about 920nm and length of about 25μm were prepared by hydrothermal synthesis in the presence of sodium citrate (Na3cit). The physicochemical properties were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). It was found that Fe3O4 crystal nuclei were generated from different Fe2+−citrate complexes under hydrothermal conditions and Na3cit as a capping agent promoted the formation of Fe3O4 microfibers. The Fe3O4 nanocrystals grew along the (110) axis on the exposed (111) facet, and then further formed microfibers via an oriented attachment mechanism during the collisions. Polyvinylpyrrolidine (PVP) was more conducive to microfibers growth in comparison to polyethyleneglycol 4000 (PEG-4000), cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The electrochemical measurements show that the Fe3O4 sub-microfibers had a specific capacitance of 117.6Fg−1 with good cycling performance.

A Novel Hydrothermal Approach for the Synthesis of Flower-Like Fe2O3/Fe Foam Nanocrystals and Their Superior Performance in Fisher–Tropsch Synthesis

A novel and facile hydrothermal approach was developed for the synthesis of three-dimensional flower-like α-Fe2O3 nanocrystals grown directly on Fe substrate using Fe(NO3)3 and hexamethylenetetramine as precursors in aqueous medium. A reaction mechanism for the synthesis and growth of the flower-like α-Fe2O3 nanocrystals was proposed to explain the effects of reaction time and temperature on the morphology and structure of the as-synthesized nanocrystals. Moreover, cube-like shapes of Fe2O3 nanocrystals were produced when urea used as hydrolysis reagent during the synthesis process. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were employed to confirm the unique morphology, high crystallinity and pure phase structure. The as-synthesized flower-like α-Fe2O3 nanocrystals displayed a higher activity and C2–4 olefin/paraffin ratio in Fisher–Tropsch synthesis than the cube-like shape of α-Fe2O3 nanocrystals, possibly due to their high specific surface area as well as diversity of catalytic active sites. The produced flower-like Fe2O3 nanocrystals sample displayed high catalytic activity and C2-4 olefin/paraffin over the cube-like Fe2O3 nanocrystals for Fischer-Tropsch synthesis, due to the high specific surface area and diversity of catalytic active sites.

Shape-dependent magnetic and microwave absorption properties of iron oxide nanocrystals

Synthesis of uniform magnetic nanocrystals with tunable shape is valuable to investigate the microwave absorption properties that depend closely on the shape and size. In this study, we utilize an efficient method to synthesize nano-sized iron oxide nanocrystals with different shapes through thermal decomposition of Fe(acac)3 in oleylamine. While the spherical Fe3O4 nanocrystals display a typical superparamagnetic behavior at room temperature, the triangular nanoplates exhibit a blocking behavior at an unexpected high temperature. The antiferromagnetic-ferrimagnetic core-shell structure of FeO@Fe3O4 nanocubes presents exchange bias behavior. We also investigate the high frequency properties of all samples by a network analyzer. Compared to spherical and cubic shapes, the triangular Fe3O4 nanoplates exhibit significantly enhanced microwave absorption performance in terms of strong reflection loss and wide bandwidth. Moreover, the triangular Fe3O4 nanoplates have obvious dielectric and magnetic resonance behaviors responding to the microwave at the frequency range of 2–18 GHz. The dielectric and magnetic resonance behaviors may be derived from the interface polarization and exchange resonance. The minimum reflection loss of triangular Fe3O4 nanoplates reaches −32.1 dB at 11.7 GHz and the bandwidth less than −10 dB is from 10.6 to 13.3 GHz at a thickness of 2.5 mm.

New opportunities in the preparation of nanocomposites for biomedical applications: revised mechanosynthesis of magnetite–silica nanocomposites

Environmentally friendly preparation of functionalized magnetite-silica (Fe3O4/SiO2) nanocomposites (NCs) with different SiO2 content (6, 20 and 50 wt%) using revised mechanosynthesis is reported. High-energy ball milling of α-Fe2O3, Si and SiO2 mixtures was followed by hydrolysis and condensation of 3-aminopropyl-triethoxysilane.X-ray powder diffraction and transmission electron microscopy showed the formation of almost spherical Fe3O4 nanocrystals with a narrow size distribution (4–6 nm) uniformly dispersed in the amorphous 100–200 nm SiO2 agglomerates. Scanning electron microscopy and energy dispersive spectroscopy were used to study the elemental distribution in the sample. Fourier transform infrared spectroscopy confirmed the NC surface functionalization with amino groups. Magnetic properties were also explored, indicating a homogeneous distribution of magnetic nanoparticles in the silica matrix.