An easy fabrication of monodisperse oleic acid-coated Fe3O4 nanoparticles

An easy route is described for the synthesis of monodisperse oleic acid-coated Fe₃O₄ nanoparticles with uniform size and shape via a thermal decomposition of Fe(acac)₃ in the presence of oleic acid (OA). The prepared Fe₃O₄ samples are characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and vibrating sample magnetometer. The results show that the resulting OA-coated Fe₃O₄ nanoparticles have an average diameter of about 24 nm and an OA layer, around 3 nm in thickness. The magnetic saturation value of the prepared OA-coated Fe₃O₄ nanoparticles is determined to be 78.68 emu/g, indicating a well-established superparamagnetic property.     

Effect of annealing on the characteristics of Au layers grown on the high-temperature deposited Ni50Fe50 layers

80 nm-thick Ni₅₀Fe₅₀ layers were sputter-deposited on glass substrates at 400 °C and then Au layers were sputter-deposited on the Ni₅₀Fe₅₀ layers. The Au/Ni₅₀Fe₅₀ bilayer films were annealed in a vacuum of 5×10⁻⁴ Pa from 250 to 450 °C for 30 min or 90 min. The characteristics of the Au layers were studied by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and a four-point probe technique. When the annealing temperature reaches 450 °C, Fe and Ni atoms diffuse markedly into the Au layer and the Fe content is more than the Ni content. When the annealing temperature is lower than 450 °C, the grain size of the Au layers does not change markedly with annealing temperature. However, as the annealing temperature reaches 450 °C, the annealing promotes the grain growth of the Au layer. As the annealing temperature exceeds 300 °C, the resistivity of the bilayer films increases with increasing annealing temperature. The diffusion of Fe and Ni atoms into the Au layer results in an increase in the resistivity of the annealed bilayer film. Large numbers of Fe and Ni atoms diffusing into the Au layer of the annealed Au/Ni₅₀Fe₅₀ bilayer film lead to a significant decrease in the lattice constant of the Au layer.     

New heat generation material in AC magnetic field for Y3Fe5O12-based powder material synthesized by reverse coprecipitation method

We found the most promising powder material for the application of the thermal coagulation therapy for the treatment of cancerous tissues. The maximum heat generation ability (ΔT = 40-77 °C, 370 kHz, 1.77 kA·m^− 1) was obtained for the powder materials by the calcination at 1100 °C for the Y_3 − XGd_XFe₅O₁₂ system. This ΔT value is higher than ca. ΔT = 30 °C in same magnetic field for fine FeFe₂O₄ particles as the candidate material for this type of therapy. The particle growth with the formation of the cubic single phase might influence to the high heat generation. As an unexpected result, the Gd₃Fe₅O₁₂ (X = 3) has no heat generation ability in an AC magnetic field.     

Synthesis, morphology and optical properties of multi-pods Au/FeO(OH) and Au/Fe2O3 nanostructures

Multi-pods Au/FeOOH nanostructures were synthesized by a hydrothermal treatment of an aqueous solution of mixed micellar formed by gold nanoparticles, hexadecyltrimethyl ammonium bromide (CTAB), and (NH₄)₃[FeF₆] at 160 °C for 48 h and sequential calcined at 290 °C for 1.5 h, resulting in the formation of multi-pods Au/Fe₂O₃ nanostructures. The as-obtained products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy, and UV-vis spectroscopy. Surface plasmon resonance band of gold nanoparticles was observed in the multi-pods Au/FeOOH nanostructures. However, a similar behavior was not seen with multi-pods Au/Fe₂O₃ nanostructures. The critical role of F⁻ ions and CTAB molecules in the formation of FeO(OH) multipods and the probable mechanism of the formation of multi-pods Au/FeOOH and Au/Fe₂O₃ nanostructures were discussed.     

ZnFe2O4 thin films from a single source precursor by aerosol assisted chemical vapour deposition

A single source heterobimetallic complex [Fe₂(acac)₄(dmaeH)₂][ZnCl₄] (1) (acac = 2,4-pentanedionate, dmaeH = N,N-dimethylaminoethanol), was synthesized in high yield. The complex was analyzed by melting point, Fourier transfer infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The structure of the cation was established by single crystal X-ray analysis on a derivative, [Fe₂(acac)₄(dmaeH)₂][ZnCl₃(THF)]₂·THF (1a) (THF = tetrahydrofuran). TGA analysis showed that complex (1) undergoes facile thermal decomposition at 450 °C to give ZnFe₂O₄ residue. In-house designed aerosol assisted chemical vapour deposition equipment was used to deposit thin films of ZnFe₂O₄ on fluorine doped SnO₂ coated conducting glass substrate at 450 °C. X-ray diffraction analysis proved the formation of crystalline ZnFe₂O₄ phase and scanning electron microscopy revealed the film morphology with well defined crystalline particles evenly distributed in the range 150-200 nm. The indirect and direct bandgap energies of the thin films were estimated to be 1.76 and 2.10 eV, respectively.     

Strong adsorption of chlorotetracycline on magnetite nanoparticles

In this work, environmentally friendly magnetite nanoparticles (Fe₃O₄ MNPs) were used to adsorb chlorotetracycline (CTC) from aqueous media. Fe₃O₄ MNPs exhibit ultrahigh adsorption ability to this widely used antibiotic. The adsorption behavior of CTC on Fe₃O₄ MNPs fitted the pseudo-second-order kinetics model, and the adsorption equilibrium was achieved within 10 h. The maximum Langmuir adsorption capacity of CTC on Fe₃O₄ (476 mg g⁻¹) was obtained at pH 6.5. Thermodynamic parameters calculated from the adsorption data at different temperature showed that the adsorption reaction was endothermic and spontaneous. Low concentration of NaCl and foreign divalent cations hardly affected the adsorption. Negative effect of coexisting humic acid (HA) on CTC adsorption was also observed when the concentration of HA was lower than 20 mg L⁻¹. But high concentration of HA (>20 mg L⁻¹) increased the CTC adsorption on Fe₃O₄ MNPs. The matrix effect of several environmental water samples on CTC adsorption was not evident. Fe₃O₄ MNPs were regenerated by treatment with H₂O₂ or calcination at 400 °C in N₂ atmosphere after separation from water solution by an external magnet. This research provided a high efficient and reusable adsorbent to remove CTC selectively from aqueous media.     

Preparation and characterization of bio-functionalized iron oxide nanoparticles for biomedical application

Amine modified iron oxide (Fe₃O₄) nanoparticles were synthesized by thermal decomposition method and were further used to bio-functionalize by grafting of N-hydroxysuccinimide (NHS) ester of folate and ethylenediaminetetraacetate (EDTA). Fe₃O₄ nanoparticles of ~ 22 nm were confirmed from X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. FT-IR studies indicated two bands at 1515 cm^− 1and 1646 cm^− 1, which can be attributed to carboxylic group and the amide linkage respectively, revealing the conjugation of folate with Fe₃O₄. The conjugation of the chelating agent showed strong C=O stretch and Fe-O vibrations at 1647 and 588 cm^− 1 respectively. The value of saturation magnetization for Fe₃O₄ nanoparticles was found to be 88 emu/g, which further reduced to 18 and 32% upon functionalization with EDTA and NHS ester folate, respectively. These amine modified Fe₃O₄ nanoparticles can also be functionalized with other bifunctional chelators, such as amino acids based diethylene triamine pentaacetic acid (DTPA), and thus find potential applications in radio-labeling, biosensors and cancer detection, etc.     

Densification and polymorphic transition of multiphase Y2O3 nanoparticles during spark plasma sintering

Multiphase (MP) monoclinic and cubic Y₂O₃ nanoparticles, 40 nm in diameter, were densified by spark plasma sintering for 5-15 min and100 MPa at 1000 °C, 1100 °C, and 1500 °C. Densification started with pressure increase at room temperature. Densification stagnated during heating compared to the high shrinkage rate in cubic single-phase reference nanopowder. The limited densification of the MP nanopowder originated from the vermicular structure (skeleton) formed during the heating. Interface controlled monoclinic to cubic polymorphic transformation above 980 °C led to the formation of large spherical cubic grains within the vermicular matrix. This resulted in the loss of the nanocrystalline character and low final density.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Au/Fe3O4磁性纳米粒子的合成及表征

报道了一种合成具有巯基官能团修饰的Au/Fe_3O_4磁性纳米粒子的新方法。采用共沉淀法制备Fe_3O_4磁性纳米颗粒,并在此基础上用聚(烯丙胺)溶液还原HAuCl4,制得Au/Fe_3O_4磁性核壳纳米颗粒,再用3-巯基-1-丙磺酸钠修饰Au/Fe_3O_4磁性纳米粒子,最后得到具有巯基官能团稳定的Au/Fe_3O_4磁性纳米粒子。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能谱仪(EDS)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)、振动样品磁强计(VSM)分别对产物的微观结构及磁性特征进行表征。     

Structural stability of ZnFe2O4 nanoparticles under different annealing conditions

We study the structural stability of surfactant coated ZnFe₂O₄ (ZF) nanoparticles of average particle size 10 nm annealed under different environments. The X-ray diffraction studies in oleic acid coated ZF (OC-ZF) show distinctly different phase transitions under different annealing conditions. The OC-ZF is reduced to α-Fe/ZnO phase under vacuum while it forms FeO/ZnO under argon whereas the ZnFe₂O₄ phase remains stable under air annealing. The simultaneous thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) coupled mass spectra (MS) in OC-ZF under argon atmosphere suggests that the residual carbon removes oxygen from the lattice to reduce the ZnFe₂O₄ phase into FeO/ZnO during argon annealing. Apart from CO and CO₂ gas evolution at high temperature under argon annealing, creation of oxygen vacancies due to the random removal of oxygen under vacuum annealing, leads to direct interaction between Fe–Fe and the formation of metal Fe. It appears that the residual carbon aids the reduction of ZF and the formation of α-Fe/ZnO during vacuum annealing. After annealing at 1000 °C in vacuum, the magnetization is increased abruptly from 13.8 to 106.5 emu g⁻¹. In sharp contrast, the air and argon annealed samples show a diminished magnetization of 1 emu g⁻¹. The field cooled (FC) and zero FC magnetization of vacuum and argon annealed samples exhibit superparamagnetic and spin-glass type behavior respectively. Our results offer possibilities to switch a magnetically inactive material to an active one.     

Temperature dependence of magnetic property and photocatalytic activity of Fe3O4/hydroxyapatite nanoparticles

Fe₃O₄/hydroxyapatite (HAP) nanoparticles have been developed as a novel photocatalyst support, based on the embedment of magnetic Fe₃O₄ particles into HAP shell via homogeneous precipitation method. The resultant nanoparticles were characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD). These particles were almost spherical in shape, rather monodisperse and have a unique size of about 25 nm in diameter. The effect of calcination temperature on magnetic property and photocatalytic activity of Fe₃O₄/HAP nanoparticles was investigated in detail. The obtained results showed that the Fe₃O₄/HAP nanoparticles calcined at 400 °C possessed good magnetism and photocatalytic activity in comparison with that calcined at other temperatures.     

Synthesis and spectroscopic investigations of Mn3O4 nanoparticles

Trimanganese tetraoxide (Mn₃O₄) nanoparticles have been synthesized via hydrothermal process. Nevertheless, homogeneous nanoparticles of Mn₃O₄ with platelet lozange shape were obtained. The crystallite size ranged from 40 to 70 nm. The Mn₃O₄ product was investigated by X-ray diffraction, transmission electron microscopy (MET), and impedance spectroscopy. Electrical conductivity measurements showed that the as-synthesized Mn₃O₄ nanomaterial has a conductivity value which goes from 1.8 10⁻⁷ Ω⁻¹ cm⁻¹ at 298 K, to 23 10⁻⁵ Ω⁻¹ cm⁻¹ at 493 K. The temperature dependence of the conductivity between 298 and 493 K obeys to Arrhenius law with an activation energy of 0.48 eV.     

One-step hydrothermal process to prepare highly crystalline Fe3O4 nanoparticles with improved magnetic properties

Hydrothermal process was successfully used to synthesize Fe₃O₄ powder using ferrous chloride (FeCl₂) and diamine hydrate (H₄N₂·H₂O) as starting materials by carefully controlling the reaction conditions. The as-prepared Fe₃O₄ sample was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and its magnetic properties were evaluated on a vibrating sample magnetometer (VSM). The nanoscale (40 nm) Fe₃O₄ powder obtained at 140 °C for 6 h possessed a saturation magnetization of 85.8 emu/g, a little lower than that of the correspondent bulk Fe₃O₄ (92 emu/g). It is suggested that the well-crystallized Fe₃O₄ grains formed under appropriate hydrothermal conditions should be responsible for the increased saturation magnetization in nanosized Fe₃O₄.     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Preparation of Fe3O4/PVA nanofibers via combining in-situ composite with electrospinning

A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe₃O₄/poly(vinyl alcohol) (PVA) composite nanofibers. Fe₃O₄ magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe₃O₄/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe₃O₄ nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (M_s = 2.42 emµ·g^-1) although only 4 wt.% content.     

Structure and electrochemical performance of Fe3O4/graphene nanocomposite as anode material for lithium-ion batteries

Using hydrothermal method, Fe₃O₄/graphene nanocomposite is prepared by synthesizing Fe₃O₄ particles in graphene. The synthesized Fe₃O₄ is nano-sized sphere particles (100–200 nm) and uniformly distributed on the planes of graphene. Fe₃O₄/graphene nanocomposite as anode material for lithium ion batteries shows high reversible specific capacity of 771 mAh g⁻¹ at 50th cycle and good rate capability. The excellent electrochemical performance of the nanocomposite can be attributed to the high surface area and good electronic conductivity of graphene. Due to the high surface area, graphene can prevent Fe₃O₄ nanoparticles from aggregating and provide enough space to buffer the volume change during the Li insertion/extraction processes in Fe₃O₄ nanoparticles.     

Synthesis of Co3O4 nanoparticles via the CTAB-assisted method

Cobalt oxide (Co₃O₄) nanoparticles were successfully synthesized by the cetyltrimethylammonium bromide (CTAB)-assisted method at normal pressure for the first time. The structure and morphology of the as-prepared Co₃O₄ nanoparticles were characterized by powder X-ray diffracton (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂-sorption analysis. XRD studies indicated that the as-prepared product was well-crystallized cubic phase of Co₃O₄ with a cell constant of α = 8.0722 Å. The EM images showed that the obtained Co₃O₄ sample consisted of dispersive quasi-spherical particles with the size ranged from 15 to 25 nm.     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Supercritical fluid mediated synthesis of poly(2-hydroxyethyl methacrylate)/Fe3O4 hybrid nanocomposite

Poly(2-hydroxyethyl methacrylate) (PHEMA) and magnetic nanoparticle (Fe₃O₄) hybrid nanocomposite was synthesized by dispersion polymerization in supercritical carbon dioxide (scCO₂) using a copolymeric stabilizer, poly[(2-dimethylamino)ethyl methacrylate-co-1H,1H-perfluorooctyl methacrylate] (PDMAEMA-co-PFOMA). Fe₃O₄ nanoparticles were first surface-modified with a silane coupling agent methacryloxypropyltrimethoxysilane (MPTMS), which provides a reactive CC bond and can copolymerize with 2-hydroxyethyl methacrylate (HEMA). After immobilization of the silane coupling agent, polymer chains were successfully grafted onto the surface of Fe₃O₄, resulting in the formation of core-shell nanostructure. FE-TEM pictures showed that the nanoparticles were well dispersed in the polymer matrix. The incorporation of Fe₃O₄ in the nanocomposite was confirmed by FT-IR, XRD and XPS. Thermal stability and magnetic property increase with the increasing amount of Fe₃O₄ nanoparticles in the composite. This new environmentally benign green synthetic route may offer advantages of easy separation and solvent removal.