喷射-共沉淀法合成纳米晶CoFe2O4及磁性能

用喷射-共沉淀法成功地制备了纳米晶CoFe2O4铁氧体粉料.研究了不同合成温度对产物晶体结构、微观形貌和磁性能影响.结果表明:喷射-共沉淀法制备的粉料颗粒细小均匀、形状完整.600℃下煅烧1.5h,样品晶粒尺寸为29nm左右,平均颗粒尺寸小于100nm.室温下,样品比饱和磁化强度随煅烧温度增加而增大.850℃煅烧1.5 h时,其比饱和磁化强度Ms为88.6A·m2·kg-1.当晶粒大小为29nm时,纳米晶CoFe2O4铁氧体矫顽力达到最大值64.5kA·m-1,随后又随晶粒尺寸增大而减小.这可能归因于纳米磁性材料存在强烈的晶粒尺寸效应.     

Synthesis and characterization of zinc ferrite nanoparticles obtained by self-propagating low-temperature combustion method

The self-propagating low-temperature combustion method was used to produce nanocrystalline particles of zinc ferrite. The products were characterized for chemical and phase composition, morphology and magnetic properties. The results obtained showed the formation of single-phase zinc ferrite nanoparticles with an average particle size of about 40 nm. As-synthesized powder displayed good magnetic property. Due to the simplicity and low cost of this process, it could also become a valuable starting point for the generation of other mixed and complex ferrites.     

CoFe_2O_4@FeCo纳米核壳颗粒的制备与磁性研究

利用化学共沉淀法合成Co Fe2O4纳米颗粒,并在氢气气氛下还原获得Co Fe2O4@Fe Co核壳结构磁性纳米颗粒。用XRD和TEM对所得样品进行结构分析,用SQUID测量样品在300 K时的磁滞回线,发现随着壳厚度的增加,核壳结构样品的矫顽力呈现先增加后减小的趋势,而其饱和磁化强度表现出逐渐增加的趋势。为了探究所制备样品的核壳磁性层之间的交换相互作用,还测量了M-T曲线以及T=5 K时的零磁场冷却(ZFC)和带磁场冷却(FC)磁滞回线。     

Effective removal of Zn (II) ions from aqueous solution by the magnetic MnFe2O4 and CoFe2O4 spinel ferrite nanoparticles with focuses on synthesis,characterization, adsorption,and desorption

In this study, the MnFe₂O₄ and CoFe₂O₄ spinel ferrites nanoparticles were synthesized via a practical co-precipitation route to investigate the zinc removal from aqueous solution. The synthesized magnetic adsorbents were characterized by XRD, VSM, FE-SEM, BET, EDS, and DLS analyses. The synthesized adsorbents had a diameter range of 20–80 nm. The specific surface areas of adsorbents were found to be 84.5 and 50.4 m²/g for MnFe₂O₄ and CoFe₂O₄, and the saturation magnetization were 61.39 and 37.54 emu/g, respectively. The effects of initial pH, contact time, metal ion concentration, and temperature on Zn (II) adsorption were precisely investigated. These nanoparticles could remove Zn (II) by following the Langmuir isotherm model at optimum pH = 6, with the high adsorption capacities of 454.5 and 384.6 mg/g for MnFe₂O₄ and CoFe₂O₄, respectively. The results of kinetics studies were well fitted by pseudo-second-order, with the determination coefficients of 0.999 for both adsorbents. The thermodynamics studies showed that the zinc (II) adsorption was an exothermic and spontaneous process. Furthermore, the reusability and the desorption capability of adsorbents were also investigated.     

Mossbauer spectra and magnetic properties study of CoFe2O4 nanoparticles prepared by hydrothermal method

用水热法在不同温度下制备结晶性较好、颗粒均一的CoFe2O4纳米颗粒,无需进一步煅烧。利用X射线衍射仪（XRD）、场发射扫描电镜（SEM）、穆斯堡尔谱仪和综合物性测量系统（PPMS）对不同温度下合成的样品进行表征。结果表明,随着合成温度的升高,CoFe2O4纳米颗粒的结晶性增强,粒径逐渐增大,样品的饱和磁化强度逐渐增强。当合成温度为500℃时,CoFe2O4纳米颗粒的饱和磁化强度达到64.1A.m2/kg,与块体的CoFe2O4（72A.m2/kg）接近。穆斯堡尔谱分析表明,当晶粒粒径超过了超顺磁性的临界尺寸,样品的超顺磁性消失,随着合成温度的升高,B位上Fe3＋离子的比例增高,磁性能增强。     

Rapid Synthesis of Nanocrystalline NiFe2O4 and CoFe2O4 Powders by a Microwave-Assisted Combustion Method

A facile and rapid microwave-assisted combustion method was applied to synthesize the nanocrystalline NiFe₂O₄ and CoFe₂O₄ powders. The results suggested that application of microwave heating to synthesize the homogeneous porous NiFe₂O₄ and CoFe₂O₄ powders was achieved in a few minutes. The structure and morphology of the as-prepared nanocrystalline powders of NiFe₂O₄ and CoFe₂O₄ were investigated by means of X-ray diffraction (XRD) and tunneling electron microscopy (TEM). The XRD spectra confirmed the formation of spinel structure with a crystallite size of 30.03 nm for NiFe₂O₄ and 36.7 nm for CoFe₂O₄ nanopowders, and TEM results indicated spherical shape of the products. Magnetic measurements revealed that at room temperature while NiFe₂O₄ is superparamagnetic, CoFe₂O₄ shows ferromagnetic behavior.     

Synthesis and characterization of nickel ferrite magnetic nanoparticles

Nickel ferrite (NiFe₂O₄) nanoparticles are prepared by a polyvinyl alcohol (PVA) assisted sol-gel auto-combustion method. The structure, composition, morphology and magnetic properties of the gel precursor are characterized by powder XRD, FT-IR, TGA, HR-SEM, TEM, HR-TEM and VSM. XRD confirms the formation of single-phase nickel ferrite with space group of Fd3m and inverse spinel structure. The vibration properties of nanoparticles are analysed by FT-IR spectrum. The thermal decomposition of the gel precursors is investigated by TGA. HR-SEM and TEM images show that the particles have spherical shape with particle size in the range of ∼30 nm and consistent with XRD result. The magnetic properties of these nanoparticles are studied for confirming the ferromagnetic behaviour at room temperature.     

CoFe2O4纳米线阵列的合成及磁性

利用多孔阳极氧化铝模板和溶胶．凝胶法制备了CoFe2O4纳米线阵列。溶胶是通过真空注入法被填充到模板的纳米孔洞中的，通过高温热处理，形成CoFe2O4纳米线阵列。利用扫描电子显微镜（SEM）、X射线衍射仪（XRD）和振动样品磁强计（VSM）对CoFe2O4纳米线阵列的形貌、结构和磁性进行了研究。CoFe2O4纳米线的直径与模板孔径相等．其具有多晶的尖晶石结构。CoFe2O4纳米线阵列未表现磁各向异性，这是由其多晶结构和较大的磁晶各向异性常数决定的．     

用CoFe2O4纳米粒子改性羰基铁粉磁流变液

用反相微乳法制备出了粒径和矫顽力不同的CoFe2O4纳米粒子,并将其添加到传统的羰基铁粉MR液中,研究了CoFe2O4纳米粒子的静磁特性和用量对改性MR液性能的影响.结果表明改性的羰基铁粉MR液的磁致剪切应力随CoFe2O4纳米粒子的粒径减少和矫顽力增大而显著提高,随CoFe2O4纳米粒子用量的增加在1.2%时取得最大值;并用MR液的结构模型解释了这些实验现象.     

Hydrothermal Synthesis and Characterization of CoFe2O4 Nanoparticles and Nanorods

This paper presents a low temperature (130 and 160 °C) synthesis route to prepare the spinel phase CoFe₂O₄ nanoparticles and nanorods. A one-dimensional (1-D) structure of Co-ferrite was successfully synthesized using Cetyl Trimethyl Ammonium Bromide (CTAB) as a surfactant at temperature 160 °C. Structural, electrical, and magnetic measurements have been performed using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and the Vibrating Sample Magnetometer (VSM). XRD patterns show a pure spinel (fcc) structure, showing a complete phase formation at a low temperature of 160 °C, without any subsequent sintering. Average crystallite sizes have been calculated by Sherrer’s and Williamson-Hall methods. As prepared CoFe₂O₄ nanorods exhibited a uniform shape of diameter 60–80 nm and 600–900 nm in length. The FTIR spectrum for Co-ferrite nanorods shows two intrinsic lattice absorption bands for tetrahedral and octahedral sublattices. DC electrical resistivity of CoFe₂O₄ nanorods is high up to ～10⁸ (Ω-cm), as compared to CoFe₂O₄ nanoparticles (～10⁷ Ω-cm) at 373 K. Dielectric parameters were measured using a LCR meter, in the frequency range of 1 kHz to 5 MHz. The real and imaginary part of the dielectric constant (ε′ and ε″) and dielectric loss tangent (tanδ) reduces for CoFe₂O₄ nanorods in comparison to nanoparticles, and has a value of 13.6 and 0.0416, respectively. Magnetic properties were characterized by VSM under a field of 10 kOe and showed that the 1-D structure reduces the magnetization of nanocrystalline CoFe₂O₄ from 65 emu/gm to 54 emu/gm.     

Synthesis, characterization and superparamagnetic resonance studies of ZnFe2O4 nanoparticles

Superparamagnetic nanoparticles of zinc ferrite (ZnFe2O4) were produced by a microwave induced combustion synthesis method. XRD, FT-IR, SEM, VSM and ESR were used for the structural, morphological, and magnetic investigation of the product, respectively. Average particle size of the nanoparticles was estimated by the Schérrer equation using the full-width at half maximum (FWHM) of the most intense XRD peak and found as 41 nm. Magnetization measurements have shown that the samples have a blocking temperature of 72 K which indicates a superparamagnetic behavior. Superparamagnetic resonance (SPR) spectra at room temperature show a broad line with a Landé g-factor, g(eff) approximately 2. We used a theoretical formalism based on a distribution of diameters of the nanoparticles following lognormal proposed by Berger et al. The nanoparticles behave as single magnetic domains with random orientations of magnetic moments which are subject to thermal fluctuations. A Landau-Lifshitz line shape function presents adequate results which are in good agreement with the experimental ones. At high temperatures, the SPR line shape is governed by the core anisotropy and the thermal fluctuations. By decreasing the temperature, the magnetic susceptibility of shell spins increases. As a result of this, the surface spins produce an effective field on the core leading to a decrease of resonance field, B(r). Also, the effective anisotropy increases as the shell spins begin to order. So, the results are interpreted by a simple model, in which each single-domain nanoparticle is considered as a core-shell system, with magneto-crystalline anisotropy on the core and surface anisotropy on the shell.     

Synthesis of magnetite nanoparticles by surfactant-free electrochemical method in an aqueous system

A simple surfactant-free electrochemical method is proposed for the preparation of magnetite nanoparticles using iron as the anode and plain water as the electrolyte. This study observed the effects of certain parameters on the formation of magnetite nanoparticles and their mechanism in the system, including the role of OH^? ions, the distance between electrodes and current density. We found that OH^? ions play an important role in the formation of magnetite nanoparticles. Particle size can be controlled by adjusting the current density and the distance between electrodes. Particle size increases by increasing the current density and by decreasing the distance between electrodes. Particle formation cannot be favored when the distance between electrodes is larger than a critical value. The magnetite nanoparticles produced by this method are nearly spherical with a mean size ranging from 10 to 30 nm depending on the experimental conditions. They exhibit ferromagnetic properties with a coercivity ranging from 140 to 295 Oe and a saturation magnetization ranging from 60 to 70 emu g^?1, which is lower than that of the corresponding bulk Fe₃O₄ (92 emu g^?1). This simple method appears to be promising as a synthetic route to producing magnetite nanoparticles.     

水热法制备CoFe2O4/石墨烯复合物及其电化学性能

本研究采用水热法制备了质量比为2∶1的CoFe2O4/石墨烯(CoFe2O4/graphene)复合物,利用XRD、FT-IR和TEM对样品的结构和形貌进行了表征,采用循环伏安法(CV)和恒电流充放电测试研究了其电化学性能。结果表明,CoFe2O4均匀的分布在石墨烯表面,粒径大约为10nm。在0.5A/g的电流密度下,比电容为105F/g。1000次循环后,电容保持率在90%以上。     

沸石基纳米磁性材料CoFe2O4制备及表征

采用水热分散法,通过分步化学反应,简便有效地制备了沸石基纳米磁性材料,并用XRD、IR和振动样品磁强计(VSM)对所得样品进行了相关测试。测试结果表明,体相CoFe2O4的磁学参数:矫顽力Hc、饱和磁化强度Ms和剩余磁化强度Mr均有较大幅度的降低。即由体相强磁性材料变为纳米非晶软磁材料,这是纳米粒子的小尺寸效应和量子尺寸效应所致,并且XRD、IR和磁滞回线表征结果也佐证此结论。     

Preparation and characterization of superconducting (YBa2Cu3O x -Ag) composites obtained by sol-gel method

For the first time a simple sol-gel method has been developed for the preparation of [YBa₂Cu₃O _x -Ag] composites using nitrates of Y, Ba, Cu, and Ag. For the two composites (with 10 and 20 wt% Ag), the electrical resistivities and magnetic susceptibilities (both alternating and direct current) show critical temperatureT _c (zero) around 90–91 K. The X-ray diffraction studies indicate no major change of lattice parameters for the orthorhombic phase. The critical current density,J _c, is found to be around 200 A cm^–2 at zero field and 80 K. The degradation ofT _c of the composites in presence of water is also very low, similar to the previous observations. This sol-gel method could be used for the large-scale production of superconducting composite powders necessary for drawing wires/tapes or targets for sputtering.     

Alginate hydrogel microbeads incorporated with Ag nanoparticles obtained by electrochemical method

An innovative method was developed for production of alginate hydrogel microbeads incorporated with silver nanoparticles (AgNPs) based on electrochemical synthesis followed by electrostatic extrusion. AgNPs were synthesized galvanostatically at different values of AgNO₃ concentration in the initial solution (0.5–3.9 mM), current density (5–50 mA cm⁻²), and implementation time (0.5–10 min). Increase in all of these parameters increased the concentration of AgNPs in alginate solution and was confirmed by TEM analysis and UV–vis spectroscopy. Cyclic voltammetry studies and Fourier transform infrared spectroscopy proved the alginate to be a good capping agent for the electrochemical synthesis of silver nanoparticles, due to coordination bonding between hydroxyl and ether groups, as well as ring oxygen atoms in uronic acid residues of alginate molecules, and Ag nanoparticles. Ag/alginate colloid solution was used for production of uniform hydrogel microbeads (with diameter of 487.75 ± 16.5 μm) by electrostatic extrusion technique. UV–vis spectroscopy confirmed retention and entrapment of AgNPs in microbeads during the production process. Alginate microbeads incorporated with AgNPs are attractive as biocompatible carriers and/or efficient donors of AgNPs as active components especially for potential biomedical applications, which was demonstrated by the antibacterial activity against Staphylococcus aureus.     

CoFe2O4-SiO2电纺纳米纤维的对喷制备技术与磁性研究

将溶胶-凝胶法和新型双喷丝头静电纺丝技术相结合,制备了CoFe2O4-SiO2电纺纳米纤维材料。利用热分析法(TG-DTA)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和振动样品磁强计(VSM)等测试手段,表征了所研制纳米纤维的晶型结构、纤维形貌以及磁学性能。研究结果表明,样品中CoFe2O4为单畴结构,纤维直径在100nm左右,非晶态SiO2的存在有效抑制了CoFe2O4晶粒的生长;煅烧温度对纤维形貌和晶型结构有较大影响,随着煅烧温度的升高,饱和磁化强度(Ms)和剩余磁化强度(Mr)均增大,但矫顽力(Hc)和剩磁比(Mr/Ms)呈波动变化。