Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

Synthesis of single-crystalline alpha-FeOOH nanorods with semi-hard magnetic property

Goethite (α-FeOOH) nanorods were synthesized via hydrothermal method. The experimental results indicate that the uniform α-FeOOH nanorods, with length up to nearly 1 μm and diameter of ca. 50 nm, demonstrate perfect crystallinity and the growth direction of [001]. Owing to the characteristics of single-crystalline structure and high purity, the hysteresis loop of the resulting products shows semi-hard magnetic behavior compared to antiferromagnetic bulk with high-coercivity in nature.     

Fe3O4纳米粒子修饰碳纳米管的制备及其磁学性能（英文）

通过FeCl2.4H2O和FeCl3.6H2O混合共沉淀,合成平均粒径为6 nm和10 nm的Fe3O4纳米粒子。然后将两种Fe3O4纳米粒子分别与经HNO3氧化处理的多壁碳纳米管(MWCNTs)置于乙醇水溶液(水和乙醇的体积比为1∶1)中,在超声波作用下制备Fe3O4/MWCNT复合材料。用高分辨透射电子显微镜、X-射线光电子能谱、振动样品磁强计、X射线衍射仪、热重分析仪对所制备的Fe3O4/MWCNT复合材料进行表征。结果表明:由6 nm和10 nm Fe3O4纳米粒子所制备的Fe3O4/MWCNT复合材料中,Fe3O4的质量分数分别为26.65%和29.3%,相应的磁饱和强度分别为16.5 emug-1和7.5 emug-1。     

Synthesis and magnetic property of FeMoO4 nanorods

Monoclinic FeMoO₄ nanorods have been prepared by the hydrothermal method in an acid aqueous solution. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrum, X-ray photoelectron spectra and differential scanning calorimetry are used to characterize the structure, morphology and composition of the sample. The FeMoO₄ nanorods exhibit a ferromagnetic property at room temperature with the coercivity of 31.1 Oe and remnant magnetization of 4.09 × 10⁻³ emu/g, respectively. The magnetic mechanism has been discussed according to the calculated results of electron density of states for FeMoO₄ with consideration of oxygen vacancies by using the Vienna ab initio simulation package.     

Facile route to the synthesis of porous α-Fe2O3 nanorods

The requirements of simple and reliable protocols for the synthesis of anisotropic structures with controlled morphology continue to be a major challenge in nanoscience. In this paper we describe the facile synthesis of porous hematite (α-Fe₂O₃) nanorods using anionic surfactant as a rod-like template. α-FeOOH nanorods with diameters of 170–210 nm and lengths up to 3–5 μm were synthesized in high yield via hydrothermal method using sodium dodecyl sulphate as a template. The porous α-Fe₂O₃ was obtained after solvent extraction and calcining the as-obtained α-FeOOH nanorods at 500 °C for 6 h. Even after removal of template by solvent extraction and calcination the shape of the nanorods was intact except the generation of pores on the nanorods. The porous nanorods were analysed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission and high-resolution transmission electron microscopy (TEM & HRTEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) measurements. SEM and TEM images showed that the morphology of hematite nanostructure is homogeneous in the shape of rods and full of porosity and magnetization measurements of the porous α-Fe₂O₃ nanorods showed weak ferromagnetic behavior. The surfactant SDS (sodium dodecyl sulphate) plays a key role in controlling the nucleation and growth of the nanorods and their use as a new class of inorganic scaffolds for the synthesis of nanomaterials are salient features of the work with implications in crystal engineering and nanocomposites design for various applications.     

Carbon microspheres with embedded magnetic iron oxide nanoparticles

Narrow-size disperse porous carbon microspheres with embedded magnetite nanoparticles were prepared by annealing Fe(III)-containing microspheres composed of a copolymer of acrylic acid and divinylbenzene at 800 °C under inert atmosphere. The Fe(III)-containing microspheres were prepared by uptake of Fe²⁺ ions through ion exchange process by poly(acrylic acid-divinylbenzene) microspheres that were prepared by distillation-precipitation polymerization, followed by annealing at 250 °C at ambient atmosphere. The carbonization of the microspheres created micropores with a maximum pore diameter of about 0.38 nm and a BET surface area of ~ 200 m²/g. The saturation magnetization of the magnetic carbon microspheres was 31.5 emu/g with a low remnant magnetization and coercivity.     

Synthesis of silver/silica nanocomposites anchored by polymer via in situ reduction

Silver/silica nanocomposites were synthesized by in situ reduction of silver salt and anchorage of the formed silver nanoparticles to silica nanospheres using a polymer anchor. Synthesis conditions including reductants, anchor polymers, and surfactants were determined. The successful formation of the nanocomposites was governed by the reduction of silver nitrate in citrate aqueous solution by sodium borohydride and adsorption onto polyvinylpyrrolidone coated silica nanospheres. The size and structure of the nanocomposites were observed by light scattering measurement and scanning electron microscopy, respectively. Optical properties of the nanocomposites were determined by UV-visible absorption spectra.     

Mechanosynthesis and magnetic properties of nanocrystalline LaFeO3 using different iron oxides

The synthesis of the orthoferrite LaFeO₃ using high-energy ball-milling of La₂O₃ and Fe₃O₄ or α-Fe₂O₃ oxides and subsequent thermal treatments of resulting powders was studied. The phase evolution during the mechanical treatment was analyzed by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). Also, magnetic properties of the obtained materials were measured at room temperature by vibrating sample magnetometry (VSM). From 30 min of mechanochemical activation the gradual disappearance of reactants and the formation of LaFeO₃ were observed. For both reactive mixtures the reaction was completed after 3 h of milling. Magnetic hysteresis loops of these mechanoactivated samples showed a significant ferromagnetic component in LaFeO₃. This behavior was interpreted on the basis of a spin-canting effect induced by the mechanochemical treatment. Thermal treatments allowed the relaxation of the distorted structure, resulting in the formation of the conventional antiferromagnetic LaFeO₃ phase.     

Improvement of magnetic characteristics and electrical properties of FeCoHfO/AlOx multilayered films

High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, effective uniaxial anisotropic field should be as low as possible. A multilayered technique (laminating the magnetic layers with oxide spacers) was exploited to improve the magnetic properties of thick films. The FeCoHfO/AlO_x multilayered films were fabricated by dc reactive magnetron sputtering. Inserting an insulator (AlO_x) layer can decrease the magneto-elastic anisotropy by reducing the residual stress of the FeCoHfO magnetic films. The anisotropic field and resistivity of the FeCoHfO/AlO_x multilayered films were evidently improved by multilayered coating. With this optimum configuration of 9 layers structure [FeCoHfO (133 nm)/AlO_x (10 nm)]₉, low anisotropic field (H_K = 65 Oe) and high resistivity (ρ ∼ 1350) μΩ cm were achieved.     

Synthesis of magnetically separable Sn doped magnetite/silica core-shell structure and photocatalytic property

Sn doped Fe₃O₄/SiO₂ core-shell structures with the magnetic and photocatalytic properties have been successfully synthesized using Fe₃O₄ microspheres as the precursor. The morphology, phase and structure of the bifunctional products were investigated by X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction, high-resolution transmission electron microscopy, energy dispersive spectroscopy, and scanning electron microscopy. The effects of the amount and hydrolysis rate of tetraethyl orthosilicate on the preparation of the Fe₃O₄/SiO₂ core-shell structures were investigated. Low concentration and slow hydrolysis rate of tetraethyl orthosilicate were useful to obtain the uniform silica coated Fe₃O₄. The magnetic measurements indicated that the Sn doped Fe₃O₄/SiO₂ core-shell structures showed ferromagnetic property and the magnetic saturation value slightly decreased after coated the silica layer. The magnetic Sn doped Fe₃O₄/SiO₂ core-shell structures exhibited good photocatalytic activity in the degradation of methyl orange and could be separated by applying an appropriate magnetic field.     

Synthesis, characterization and magnetic properties of CoFe2O4 nanorods

In this work, we demonstrated a new precursor route to synthesize CoFe₂O₄ one-dimensional (1D) nanorods. CoFe₂O₄ nanorods were prepared via the thermal decomposition of CoFe₂(C₂O₄)₃ nanorod precursor, which was prepared by solvothermal method without the assistance of template or surfactant. The microstructure and magnetic property of the obtained products were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric (TG) and differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results showed that the as-prepared CoFe₂O₄ nanorods were built by magnetic nanoparticles after calcining the precursor nanorods at different temperatures, and the size variation of magnetic nanoparticles with calcination temperatures leaded to variable magnetic properties.     

Synthesis and magnetic properties of Mn-doped ZnO nanorods via radio frequency plasma deposition

Well-aligned Mn-doped ZnO nanorods were synthesized by simple radio frequency (RF) plasma deposition in the absence of extra catalysts. The synthesized nanorods having a typical average diameter of about 25 nm, were about 310 nm in length and well-aligned along the normal direction of the substrate. Magnetic measurements indicate that the nanorods are ferromagnetic at room temperature (RT). The presence of considerable shallow donor defects in the nanorods does allow possible defect mediated mechanisms (e.g., bound magnetic polarons) for mediating exchange coupling of the dopant Mn ions resulting in RT ferromagnetism.     

Structural anisotropy of silica hydrogels prepared under magnetic field

Birefringence measurements have been carried out on the Pb-doped silica hydrogels prepared under various magnetic fields up to 5T. The silica gels prepared at 5T were used as a medium of crystal growth of PbBr₂, whose result implied the structural anisotropy; an aligned array of crystallites was obtained by transmission electron microscopy. While the samples prepared at 0, 1, and 3T have no birefringence, we found that the samples have negative birefringence on the order of magnitude 10^− 6 as if the direction of the magnetic field is the optic axis of a uniaxal crystal. To the authors' knowledge, the birefringent silica hydrogels were obtained by gelation under magnetic field for the first time. Also, scanning microscopic light scattering experiments have been performed. The results indicate that the characteristic length distribution for birefringent samples is narrower than that for non-birefringent ones.     

Synthesis, luminescent, and magnetic properties of LaVO4:Eu nanorods

The LaVO₄:Eu nanorods were synthesized successfully by an ethylenediaminetetraacetic acid (EDTA)-mediated hydrothermal method. The resulting products were characterized using XRD, TEM, HRTEM, Fluorescence Spectrometer and SQUID magnetometer. It was found that Eu³⁺ entered into the LaVO₄ crystalline host lattice and it replaced La³⁺. Consequently the unit cell parameters of LaVO₄:Eu nanorods became smaller. Further studies indicated that the rare earth ions Eu³⁺ improved the properties of the LaVO₄:Eu nanorods evidently. The Eu³⁺ ions doping in LaVO₄ nanorods led to better luminescent properties and magnetic properties than that of pure LaVO₄ nanorods.     

Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O

Copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles with mean size of about 100 nm were successfully synthesized by a simple hydrothermal method. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectra, and Fourier transform infrared spectra (FTIR). The composition and purity of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles were characterized by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic property of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles was characterized by vibrant sample magnetometer. Magnetic hysteresis curve indicate that the as-synthesized nanoparticles are of weak ferromagnetic property at room temperature.     

NiO/SiO2 nanostructure and the magnetic moment of NiO nanoparticles

We report on the synthesis, morphology and magnetic properties of a novel NiO/SiO₂ nanostructure. The NiO/SiO₂ nanostructure was synthesized by a method based on the contribution of sol-gel and combustion processes. X-ray powder diffraction (XRPD) showed the formation of the nanocrystalline NiO phase. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) revealed perfectly spherical NiO nanoparticles with diameter of about 5 nm. Amorphous silica shell around the NiO nanoparticles was also observed by HRTEM showing NiO/SiO₂ core-shell nanostructure. Magnetic measurements show hysteretic behavior at 2 K with coercivity H_C = 700 Oe, remanent magnetization M_r = 3.9 emu/g, saturation magnetization M_S = 28.2 emu/g and huge magnetic moment m_p ≈ 1300 μ_B of the nanoparticles.     

Synthesis of different nanostructured flower-like iron oxides and study of their performance as adsorbent

Iron oxides with different flower-like nanostructures have been successfully synthesized by decomposition of the iron alkoxide precursor at different conditions. The effect of reaction time (reflux time) and the calcination conditions on the morphology and composition of prepared iron oxides were investigated. Characterizations of the prepared powders were performed by scanning electronic microscopy, X-ray diffraction and N₂ adsorption/desorption isotherm. The results show that the prepared nanostructured iron oxides can be used as adsorbent for rapid removal of dye pollutants from water.     

Thermally induced changes in the magnetic properties of iron oxide nanoparticles under reducing and oxidizing conditions

Application of iron oxide nanoparticles in the fields of water purification, biomedicine or chemistry often requires controlled magnetic properties that can be modified by changing temperature and redox conditions. Therefore, this work investigates the changes in the magnetic properties of iron oxide nanoparticles in the FeOOH − Fe₂O₃ − Fe₃O₄ system (i.e. hematite, goethite, lepidocrocite, maghemite and magnetite) at heating under reducing and oxidizing conditions. The results show that heat treatment of hematite and goethite in the presence of a reducing agent (5% starch) leads to their conversion into high magnetic magnetite. The starting temperature of transformation is approximately 350 °C for both samples. The magnetization increases to 86 Am²/kg for hematite reduced at 700 °C and to 88 Am²/kg for goethite reduced at 900 °C. An intense reaction occurs within the first 10 min and then the conversion process decelerates. Thermal treatment of lepidocrocite under both oxidizing and reducing conditions leads to an increase in magnetization due to the formation of maghemite and magnetite, respectively. Regardless of the redox conditions, the formation of magnetic phase begins at a temperature of 250 °C and is associated with the formation of maghemite from lepidocrocite. Under oxidizing conditions, the magnetization begins to decrease at 350 °C, which is associated with the conversion of maghemite to hematite. On the contrary, under reducing conditions, the magnetization of lepidocrocite increases up to 900 °C, which is associated with the formation of magnetite. Maximum values of magnetization are 36 Am²/kg for maghemite obtained at 350 °C, and 88 Am²/kg for magnetite obtained at 900 °C from lepidocrocite. With the help of conventional heating, the magnetic properties of IONs can be altered by phase transformations in the FeOOH − Fe₂O₃ − Fe₃O₄ system. Temperature and redox conditions are the two most important factors controlling the transformation pathways and the magnetic properties of the resulting IONs.     

壳聚糖修饰氧化铁磁性纳米颗粒的制备和性能研究

通过共沉淀法制备氧化铁磁性纳米颗粒,用壳聚糖对其表面进行修饰得到样品(CS@MNPs);表征其形貌结构、尺寸、表面基团、表面电荷、磁学性质和在不同介质中的稳定性等。实验结果表明,CS@MNPs具有典型的立方反尖晶石晶体结构;粒径为16.5nm;在生理(pH值7.4)条件下拥有较高的正电荷(10mV);呈现超顺磁性,对驰豫时间T1、T2,尤其是T2*具有很强的响应;在双蒸馏水和含10%新生牛血清的RPMI 1640培养液中具有良好的稳定性,具有作为磁共振造影剂的潜力。