Synthesis of highly magnetic graphite-encapsulated FeCo nanoparticles using a hydrothermal process

The graphite encapsulation of metal alloy magnetic nanoparticles has attracted attention for biological applications because of the high magnetization of the encapsulated particles. However, most of the synthetic methods have limitations in terms of scalability and economics because of the demanding synthetic conditions and low yields. Here, we show that well controlled graphite-encapsulated FeCo core-shell nanoparticles can be synthesized by a hydrothermal method, simply by mixing Fe/Co with sucrose as a carbon source. Various Fe/Co metal ratios were used to determine the compositional dependence of the saturation magnetization and relaxivity coefficient. Transmission electron microscopy indicated that the particle sizes were 7 nm. In order to test the capability of graphite-encapsulated FeCo nanoparticles as magnetic resonance imaging (MRI) contrast agents, these nanoparticles were solubilized in water by the nonspecific physical adsorption of sodium dodecylbenzene sulfonate.     

热处理工艺对尖晶石型Ni0.5Zn0.45Co0.05Fe2O4静磁性能的影响

利用溶胶凝胶法制备了尖晶石型 Ni0.5Zn0.45Co0.05Fe2O4 纳米颗粒,设置了3种热处理工艺,发现随着热处理温度的提高,热处理时间的延长,颗粒长大,静磁性能提高。当热处理温度为800℃,保温8h,材料具有比较好的静磁性能（Ms=30.241Oe,Hc=73.261 emg/g,μi=0.210）。另外,将前驱体在磁场条件下热处理,得到颗粒尺寸比同种热处理工艺未加磁场条件下的大,并且静磁性能有了比较大的提高,其比饱和磁化强度甚至比在更高热处理温度,更长热处理时间下制备的NiZnCo铁氧体大。     

Hydrothermal synthesis and characterization of monodisperse α-Fe2O3 nanoparticles

Monodisperse α-Fe₂O₃ nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl₃, CH₃COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe₂O₃ nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g.     

Deposition feature of Ni nanoparticles on halloysite template and magnetic properties of the composite

A novel cermet composite with Ni nanoparticles deposited on a hollow cylindrical halloysite template is fabricated by electroless plating. Ni nanoparticles have a uniform distribution on the template, and their average diameter is mainly in the range of 20-30 nm. The halloysite template will be beneficial to make the Ni nanoparticles achieve high stability and well-dispersed state. Different heat treatment temperatures have a great effect on the crystal structure of Ni nanoparticles and the magnetic properties of the composite. With the heat-treated temperature increase, Ni nanoparticles gradually become crystallized, and the composite values of inherent coercive force (iHc), saturated magnetization (Ms), and residual magnetization (Mr) increase respectively. After complete crystallization of Ni nanoparticles at 673 K, the composite has the maximum values of iHc (253.6 Oe), Ms (57.37 emu/g), and Mr (21.64 emu/g). The sum contribution of the magneto-crystalline anisotropy, single magnetic domain effect, and the pinning effect of multiple-twinned planar defects in Ni nanoparticles would result in the high value of iHc. The new nanosized cermet composite will be at such an advantage for its practicable fabrication method, higher coercive force, high stability, and low cost that it would have great potential to be utilized to design and prepare magnetic materials.     

Air stable Fe nanostructures with high magnetization prepared by reductive annealing

Monodispersed Fe nanospindles and nanoparticles were successfully synthesized through environmentfriendly reductive annealing ?-Fe OOH nanorods. Effects of annealing temperature and reaction atmosphere on microstructure, phase, and magnetic property of Fe nanostructures were investigated.The as-obtained pure Fe nanoparticles with mean size of 45 nm had a high saturation magnetization up to 207 emu/g, close to that of bulk material(218 emu/g), which exhibited high air stability. After exposing in air for 2 and 7 days, the as synthesized Fe nanoparticles still showed high magnetization of 182 and141 emu/g, respectively.     

Fabrication and magnetic properties of Co-Ni-P rod-shaped hollow structures based on Bacillus template

A new type of Co-Ni-P rod-shaped hollow structures was prepared by electroless deposition based on Bacillus template. The metal plating layer was deposited on the surface of Bacillus, which is a kind of rod-shaped bacteria. The composition, microstructure, phase structures and magnetic properties of the hollow structures were studied. The results clearly demonstrated that the Bacillus were coated by Co-Ni-P metal plating layer and the thickness of the metal layer was around 150-200 nm. The average contents of Co, Ni, and P element of the metal layer were about 18.73 wt.%, 74.43 wt.% and 3.04 wt.%, respectively. The values of saturation magnetization (Ms), remnants magnetization (Mr) and coercivity (Hc) of the hollow structures were about 92.5 emu/g, 29.7 emu/g, and 768.7 Oe, respectively.     

Barium hexaferrite nanoparticles: morphology-controlled preparation,characterization and investigation of magnetic and photocatalytic properties

In this paper, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles have been successfully synthesized via a simple co-precipitation route. Six chelating agents such as three amino acids (proline, alanine, aspartic acid) and three surfactants (SDBS, PVP, and EDTA) were used. The result showed that the amino acids decrease the particle size and the best result was observed for alanine. Besides, the photocatalyst activity of as-prepared BaFe₁₂O₁₉ nanoparticles was evaluated by degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 200 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 30 emu/g.     

碳纳米管承载纳米Fe_3O_4颗粒的制备(英文)

采用一种简单又经济的方法将Fe3O4纳米颗粒填充到碳纳米管中。透射电镜(TEM)、扫描电镜(SEM)及其能谱附件(EDX)和X射线多晶衍射(XRD)测试结果表明:Fe3O4纳米颗粒成功地填充到碳纳米管中。材料的磁性能测试结果表明:碳纳米管中填充Fe3O4纳米颗粒后,在常温下具有超顺磁性,其饱和磁化强度由0.35emu/g增大到了13.15emu/g。Fe3O4纳米颗粒填充的碳纳米管可望应用于工程和医学领域。     

Preparation and magnetic properties of hollow ferrite microspheres by a gas-phase diffusion method in an ionic liquid/H2O mixed solution

In this work, hollow ferrite microspheres were prepared using a gas-phase diffusion method with cobalt nitrate and ferric nitrate as metal salt sources, an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate and water-mixed solvent as medium and ammonium carbonate as precipitant. Their structures and magnetization were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetry, infrared spectroscopy, and vibrating sample magnetometer. The effects of reaction time, reaction temperature, precipitant loading, and mole ratio of Co to Fe n(Co/Fe) on the structures and magnetization of the microspheres were studied. The results showed that ferrite hollow microspheres with uniform morphology and high-magnetic performance were obtained at 60–80 °C for 12–16 h, while the (NH₄)₂CO₃ loading was 0.15 g/ml, n(Co/Fe) was 0.5:1, and calcination temperature was 550 °C. The obtained products consisted of CoFe₂O₄ phase accompanied by ferric oxide phase, with an average particle size about 1 μm and magnetization intensity about 10 emu/g.     

纳米Fe3O4/聚苯胺复合粒子的制备及其在交变磁场下的发热性能

用水解沉淀法合成了纳米Fe₃O₄粒子,并在其悬浮液中原位包覆聚苯胺,制备出纳米Fe₃O₄/聚苯胺复合粒子。研究了两种纳米粒子在交变磁场下的发热性能,对它们在定向集热治疗肿瘤中的应用前景进行了评价。纳米Fe₃O₄粒子的粒径为10~30nm,表面包覆聚苯胺后,复合粒子的粒径为30~50nm。纳米Fe₃O₄粒子的比饱和磁化强度为50.05Am2/kg,矫顽力为10.9kA/m;纳米Fe₃O₄/聚苯胺复合粒子的比饱和磁化强度为26.34Am2/kg,矫顽力为0。在10mg/mL的生理盐水悬浮液中,在外加交变磁场作用30min后,纳米Fe₃O₄粒子悬浮液的温度为63.6℃,纳米Fe₃O₄/聚苯胺悬浮液的温度为52.4℃,二者均达到了医学上定向集热治疗肿瘤用热籽的发热要求,是很有应用前景的医用纳米材料。      

Preparation and characterization of cobalt ferrite by the polymerized complex method

Magnetic nanoparticles of Co-ferrite were prepared by the polymerized complex method. Heating in vacuum of a precursor solution containing citric acid (CA), ethylene glycol (EG) and cobalt and iron salts with a molar ratio of Co/Fe/CA/EG=1/2/9/22.5 at 130 °C produced a brownish transparent polymeric gel, which have been characterized by IR and NMR spectroscopy. The results of both techniques suggest two types of reactions: the formation of metal-CA complexes and successive esterification reactions between CA and EG. The organic fraction was removed by controlled thermal treatments (200–800 °C) whereby the bimetallic oxide was formed. The powders obtained were characterized by X-ray diffraction (XRD), vibrational sample magnetometry (VSM) and transmission electron microscopy (TEM). XRD analysis showed the presence of CoFe₂O₄ at 400 °C. The saturation magnetization values of the samples increased as a function of calcination temperature and reached a maximum of 79.8 emu/g at 800 °C. The TEM images showed spherical nanoparticles with sizes between 20 and 40 nm.     

Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

We report the synthesis of high magnetic moment CoFe nanoparticles via the diffusion of Co and Fe in core/shell structured Co/Fe nanoparticles. In an organic solution, Co nanoparticles were coated with a layer of Fe to form a Co/Fe core/shell structure. Further raising the solution temperature led to inter-diffusion of Co and Fe and formation of CoFe alloy nanoparticles. These nanoparticles have high saturation magnetization of up to 192 emu/g CoFe and can be further stabilized by thermal annealing at 600 °C. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. These two authors made an equal contribution to the work.     

Synthesis and properties of Fe/Fe3O4 nanocomposites coated with ZnS

Multifunctional Fe/Fe₃O₄@ZnS nanocomposites were synthesized by hydrothermal method, with Fe/Fe₃O₄ doped Co ion as the magnetic core and ZnS as the luminescent shell. The morphology, structure, luminescent and magnetic properties of the nanocomposites were investigated by XRD, FESEM, photoluminescence PL and VSM. The maximum emission peak and special saturation magnetization Ms of the nanocomposites are at 467 nm and 78.6 emu/g, respectively. For the nanocomposites, it is shown that there are both better magnetic behavior and fluorescence properties.     

Synthesis of nano-sized Fe–Co alloy powders by chemical solution mixing of metal salts and hydrogen reduction (CSM-HR)

Powder mixtures of (99.9% pure) FeCl₂ and CoCl₂ were used for synthesis of nanostructured Fe–Co alloy powders by chemical solution mixing and hydrogen reduction (CSM-HR). Nano-sized Fe–Co alloy powders were successfully fabricated by CSM-HR. The CSM-HR synthesized Fe–Co powder showed an ordered α′ phase with a particle size of 45 nm. The synthesized SMHR powder exhibited a coercivity force of 36 Oe and saturation magnetization value of 214 emu/g.     

Magnetism in BiFe<Subscript>1−x</Subscript>Ni<Subscript>x</Subscript>O<Subscript>3</Subscript>: studied through electron spin resonance spectroscopy

The effect of Ni doping in BiFe_1?xNi_xO₃ (BFNO) multiferroics are studied by X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), hysteresis loop (M–H), temperature dependent magnetization (FC-ZFC) measurements and electron spin resonance (ESR) techniques. The XRD and FTIR studies indicate that the BFNO compounds remain in rhombohedral (R3c) phase without appearance of any structural transformation due to Ni doping. The XPS studies show the oxidation states of Fe ions as 3⁺, whereas Bi is found to be in a mixed valence state of 2⁺ and 3⁺ in BFNO. The Ni ion doping enhances the saturation magnetization from 0.179 emu/g (x?=?0.025) to 2.38 emu/g (x?=?0.20), which is higher than the reported values found in literature. The FC-ZFC magnetization studies suggest the presence of a magnetic phase transition from a weak ferromagnetic to a spin glass state at low temperature. The ESR studies confirm the ferromagnetic state of BFNO samples.     

Green synthesis of superparamagnetic magnetite nanoparticles: effect of natural surfactant and heat treatment on the magnetic properties

A facile and eco-friendly synthetic approach was employed to synthesize superparamagnetic magnetite (Fe₃O₄) nanoparticles with cubic lattice structure. Zucchini and pomegranate peel-extracts were used as natural stabilizer and surfactant. The X-ray diffraction patterns revealed that the green synthetic technique was successful in formation of highly distributed Fe₃O₄ nanoparticles using both of the above extracts. The infrared (IR) analysis further confirmed the phase formation and the binding of extracts with Fe₃O₄ nanoparticles. Based on UV–Vis analysis, the samples showed the characteristic of surface plasmon resonance in the presence of Fe₃O₄ nanoparticles. The as-synthesized samples were heated at 550 °C for 2 h. It was found that the particles however grew, their sizes remained in nanoscale regime, indicating their thermal stability. The VSM analysis indicated that the as-synthesized samples have a saturation magnetization of 21.4 emu/g (using zucchini peel extract) and 13.3 emu/g (using pomegranate peel extract), which increased respectively to 45.8 emu/g and 38.1 emu/g after the heating process. A negligible coercivity in the samples with the particle sizes of less than 10 nm suggests superparamagnetic behavior of the samples.     

Synthesis and Characterization of Fucan-Coated Cobalt Ferrite Nanoparticles

This work presents some results of the synthesis and structural, microstructural, and magnetic characterization of fucan coated cobalt ferrite nanoparticles prepared by using a modified coprecipitation method. Aqueous suspensions of magnetic particles were prepared by coprecipitation of Fe(III) and Co(II) in the presence of NaOH, acid oleic and fucan polymer. The samples were characterized by X-ray diffraction (XRD), electron scanning microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), accelerated surface area, and porosimetry (ASAP/BET-Brunauer-Emmet-Teller) determination and magnetization measurements. Our results reveal that both uncoated and fucan polysaccharide coated CoFe₂O₄ nanoparticles were successfully obtained. The nanoparticles present sizes between 7 to 20 nm and saturation magnetization of the order of 40 emu/g. The nanoparticles thus obtained are suitable for future applications as a solid support for enzymes immobilization and other biotechnology applications.     

Effect of divalent metal hydroxide solubility product on the size of ferrite nanoparticles

We study the effect of divalent metal hydroxide solubility product on the size and magnetic properties of nanoparticles formed during co-precipitation. We synthesized ferrite nanoparticles by varying the solubility product from 10^− 13 to 10^− 17 by using different divalent cations of Mn, Co, Fe and Zn, where the average particle size decreased from 29.1 to 8.9 nm. The Mn, Co and Fe ferrites were magnetic in nature with saturation magnetization of 44.6, 47.38 and 56.19 emu/g respectively, whereas the Zn ferrite was paramagnetic. The increase in particle size observed with increasing solubility product of divalent metal hydroxide is in agreement with the nucleation theory.     

Processing and magnetic properties of metal-containing SiCN ceramic micro- and nano-composites

Owing to their excellent high temperature and oxidation resistance, non-oxide polymer-derived silicon-based ceramics are suitable for applications in hot and corrosive environments. The metal (Fe, Co)-containing pre-ceramic compounds combine the processability of organic polymers with the physical and chemical characteristics of the metallic component. In this study, we will introduce two different routes to embed metal particles in a SiCN ceramic matrix, derived from the commercially available polysilazane Ceraset^®. (1). Mixing and milling of metal powders (Fe, Co) with pre-crosslinked polysilazane followed by pyrolysis at 1100 °C. (2). Chemical reaction between metal carbonyl compounds, namely Fe(CO)₅ and Co₂(CO)₈, with pure polyorganosilazane followed by pyrolysis at 1100 °C. Both synthetic routes will be discussed on two particular examples, iron- and cobalt-containing samples as well as their resulting different microstructures with respect to their magnetic properties. The phases and microstructures of the metal–SiCN composites were investigated in terms of X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with EDX, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and magnetometer. Upon annealing in argon at 1100 °C, the crosslinked polysilazane blended with iron powder possesses a high saturation magnetization of about ～57 emu/g and exhibits good ferromagnetic behaviour in comparison to the one blended with cobalt. The magnetic measurements were performed within the temperature range 65–300 K.     

反应物量对燃烧合成Ni-Zn铁氧体粉的影响

为探讨燃烧合成法制备Ni0.4Zn0.6Fe2O4粉末工业化放大合成的可行性,研究不同反应物量对燃烧合成制备的Ni0.4Zn0.6Fe2O4粉体及烧结后产物的物相、微观形貌及磁性能的影响,对终产物进行XRD、SEM和EDS分析,对样品经行磁性能测试.结果表明:Fe-Fe2O3-Zn O-Ni O体系燃烧合成过程是以扩散-溶解-析出机制进行的,燃烧反应在非平衡条件下进行,燃烧产物的主要物相为Ni-Zn铁氧体,其中存在Zn O及一些铁的氧化物的杂质,产物经热处理后物相全部转变为尖晶石结构;随着反应物量的增加,产物颗粒尺寸增大,均匀度增加,反应物量的增加对产物的磁性能影响不大;随着反应物量的增加,饱和磁化强度逐渐增加,矫顽力基本不变,反应物量为1 500 g时制备的产品磁性能最佳,具有较高的饱和磁化强度Ms=63.72 emu/g和较低的矫顽力Hc=15.61 Oe.