Preparation of colloidal Fe3O4 ultrafine particles in microemulsions

The preparation of magnetite particles is reported from the precipitation of Fe²⁺/Fe³⁺ with NH₄OH in several kinds of microemulsions: AOT/n-heptane/water microemulsions and a new non-toxic microemulsion system whose phase behaviour and structure has been recently studied. It is shown that both the droplet size and the presence of interactions in the dispersed phase greatly influence the final size of the obtained particles. In addition, the size of the particles can be increased by successive repetition of the reaction inside the droplets of the microemulsion.     

花瓣状Fe_3O_4/Bi_2O_3复合粒子的制备及光催化活性

用共沉淀法制备的Fe3O4纳米粒子作为种子,通过水热法获得了微米尺寸的Fe3O4/Bi2O3复合粒子。X射线衍射和X光电子能谱表征结果说明复合粒子是由Fe3O4和Bi2O3组成。扫描电子显微镜照片表明复合粒子形貌基本呈规则球形,并且具有花瓣状的三维多级结构。以罗丹明B的催化降解实验为模型考察了不同反应组成、不同反应介质、不同反应温度条件下制备的复合粒子的催化活性。结果表明,当反应条件中m(Bi(NO3)3·5H2O)/m(Fe3O4)为1.9 g∶0.2 g,水作反应介质在160℃时,所制备的复合粒子催化活性最高,对罗丹明B的降解率达95.4%。降解完成后,用磁铁吸附,Fe3O4/Bi2O3很快从体系中分离,可以重新催化降解罗丹明B,实现磁场控制的循环催化。实验发现,Fe3O4/Bi2O3经6次循环利用后,对罗丹明B的降解率仍达88.5%。     

Alignment under Magnetic Field of Mixed Fe2O3/SiO2 Colloidal Mesoporous Particles Induced by Shape Anisotropy

When using the bottom‐up approach with anisotropic building‐blocks, an important goal is to find simple methods to elaborate nanocomposite materials with a truly macroscopic anisotropy. Here, micrometer size colloidal mesoporous particles with a highly anisotropic rod‐like shape (aspect ratio ≈ 10) have been fabricated from silica (SiO₂) and iron oxide (Fe₂O₃). When dispersed in a solvent, these particles can be easily oriented using a magnetic field (≈200 mT). A macroscopic orientation of the particles is achieved, with their long axis parallel to the field, due to the shape anisotropy of the magnetic component of the particles. The iron oxide nanocrystals are confined inside the porosity and they form columns in the nanochannels. Two different polymorphs of Fe₂O₃ iron oxide have been stabilized, the superparamagnetic γ‐phase and the rarest multiferroic ε‐phase. The phase transformation between these two polymorphs occurs around 900 °C. Because growth occurs under confinement, a preferred crystallographic orientation of iron oxide is obtained, and structural relationships between the two polymorphs are revealed. These findings open completely new possibilities for the design of macroscopically oriented mesoporous nanocomposites, using such strongly anisotropic Fe₂O₃/silica particles. Moreover, in the case of the ε‐phase, nanocomposites with original anisotropic magnetic properties are in view.     

Fe3O4/PMMA纳米复合材料的制备及其磁流变性能

采用水热法以简单原料一步合成出Fe3O4/PMMA纳米复合材料，由于聚甲基丙烯酸甲酯（PMMA）的作用，Fe3O4由十几纳米部分聚集形成几百纳米的粒子，并在PMMA中分散较为均匀．复合粒子具有较高的饱和磁化强度，为超顺磁性。由合成的复合粒子制备得到的磁流变液具有较高的剪切屈服应力和储能模量，分别可达十几kPa和几MPa，其值随外加磁场的增大而增大。     

Fe3O4/BSA纳米磁性复合颗粒的磁响应性能

利用化学液相共沉淀法制备出不同尺寸、具有超顺磁性的纳米磁性Fe3O4/BSA颗粒,经分散后包覆蛋白使其具备良好的生物兼容性,该颗粒可长期、稳定地分散在溶液中。在外加交变磁场(414kA/m,50Hz)下纪录不同颗粒的浊度变化率,并利用光透射性可即时测得介质中浑浊程度与时间的关系,结合浊度-浓度拟合曲线,计算出在外加磁场作用下,磁性纳米复合颗粒对外加磁场的响应程度,半定量计算出相同时间下不同尺寸的微粒吸附在管壁上的质量百分比。结果显示,稳定在介质中的纳米磁性颗粒在外加磁场后,磁响应性随颗粒尺寸增大而增大,颗粒大小分别为10、108和210nm,所对应的磁响应性分别为6%、10%和12%;在外加磁场30s后,该磁性纳米复合颗粒在管壁附着的质量百分比分别为39.9%、70.4%及86.7%。     

Fabricating mono-dispersed Fe3O4-SiO2 core-shell particles with help of triboelectrification

For years, it has been widely held that triboelectrification is not the sought-after technique to develop innovative materials with enhanced functionalities. In this study, we tried to break such a traditional concept and find its ever-expanding roles in material science. In our strategy, triboelectrification brought adequate charge to particles, so as to achieve their mono-dispersity in solutions. Following this strategy, the synthesis of mono-dispersed Fe₃O₄-SiO₂ core-shell particles involved two-stage triboelectrification treatment. In the first-stage treatment, positive triboelectric charges on Fe₃O₄ cores ensured their uniform SiO₂ coating and well-defined core-shell structure. In the second-stage treatment, positive triboelectric charges on Fe₃O₄-SiO₂ core-shell particles guaranteed their mono-dispersity for further biological use. The Zeta potential of these triboelectrically-treated Fe₃O₄-SiO₂ core-shell particles still maintained at ca. +55 mV after standing for two months, and their conglomeration was negligible owing to their limited increase in hydrodynamic size. Besides, their excellent linearity between relaxivities and iron concentration, and their virtually unchanged r₂/r₁ ratio within two months manifested that triboelectrification can be a promising technique in fabricating advanced materials.     

Microwave absorption behavior of ZnO whisker modified by nanosized Fe3O4 particles

Tetra-needle-like ZnO whisker was magnetic modified through in situ synthesis of nanosized Fe3O4 particles on the surface of the whisker, and the microwave absorption behavior of the as-prepared product was investigated in detail. The result of the comparative microwave absorbing experiment showed that the magnetic modified ZnO whisker appeared more superior property of microwave absorption than that of the original ZnO whisker in 2-18 GHz. Further investigation indicated that the microwave absorption behavior of the product was influenced by ferrite content and Fe3O4 particles' distribution in the product. When the ferrite content of the product changed from 2 wt% to 9 wt%, the microwave absorbing ability of the product was increased; then, the microwave absorbing ability of the product decreased with the further increasing of ferrite content from 9 wt% to 16 wt%. The product with uniform distribution of Fe3O4 particles showed better microwave absorption property than that with irregular distribution of Fe3O4 particles, and this result inferred that the biphase interface between ZnO and Fe3O4 contributed to microwave absorption through interface polarization.     

Influence of process control agent type on the mechanosynthesis of Fe3O4 particles

The influence of the nature of the process control agent (PCA) used in the mechanosynthesis of the magnetite nanoparticles has been studied. The two-step route used here for obtaining nanocrystalline/nanoparticles Fe₃O₄ consists of a heat treatment, to prepare well-crystallised magnetite, followed by the mechanosynthesis process. Dry milled magnetite samples have been obtained as a reference, using the same conditions (duration and energy), to determine the influence of the process control agents (PCA). Three different PCAs have been used: benzene, ethanol and oleic acid. The characterisation of the magnetite particles has been performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), magnetic measurements M(H), differential scanning calorimetry (DSC) and thermogravimetric (TG) measurements and Scanning Electron Microscopy (SEM). XRD and SEM analysis revealed a different processing mechanism for the two milling modes, wet and dry. In the case of dry milling, even for short milling times, iron contamination and formation of a wüstite – FeO phase is noticed. The use of the PCA during the milling process limits the above-mentioned contamination. Ethanol and benzene uses as PCA lead to synthesis of fine uniform sized particles. SEM images reveal the presence on nanoparticles. In the case of oleic acid, DSC, TG and magnetic measurements revealed the presence of a thin layer of oleic acid adsorbed on the particles. FTIR analysis highlighted the presence of both free and bonded oleic acid. The magnetisation of the samples was found to be linked to the powder contamination (FeO or oleic acid), structural defects or finite size effects.     

S‐Doped TiSe2 Nanoplates/Fe3O4 Nanoparticles Heterostructure

2D Sulfur‐doped TiSe₂/Fe₃O₄ (named as S‐TiSe₂/Fe₃O₄) heterostructures are synthesized successfully based on a facile oil phase process. The Fe₃O₄ nanoparticles, with an average size of 8 nm, grow uniformly on the surface of S‐doped TiSe₂ (named as S‐TiSe₂) nanoplates (300 nm in diameter and 15 nm in thickness). These heterostructures combine the advantages of both S‐TiSe₂ with good electrical conductivity and Fe₃O₄ with high theoretical Li storage capacity. As demonstrated potential applications for energy storage, the S‐TiSe₂/Fe₃O₄ heterostructures possess high reversible capacities (707.4 mAh g⁻¹ at 0.1 A g⁻¹ during the 100th cycle), excellent cycling stability (432.3 mAh g⁻¹ after 200 cycles at 5 A g⁻¹), and good rate capability (e.g., 301.7 mAh g⁻¹ at 20 A g⁻¹) in lithium‐ion batteries. As for sodium‐ion batteries, the S‐TiSe₂/Fe₃O₄ heterostructures also maintain reversible capacities of 402.3 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles, and a high rate capacity of 203.3 mAh g⁻¹ at 4 A g⁻¹.     

Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.     

Investigation of adsorption properties of oxytetracycline hydrochloride on magnetic zeolite/Fe3O4 particles

Iron oxides and ferrite-supported zeolites have been successfully used in the cheap and environmentally friendly removal of organic pollutants such as antibiotics. In this study, the adsorption of Oxytetracycline hydrochloride (OTC-HCL) on zeolite/Fe₃O₄ particles synthesized from natural Manisa-Gördes clinoptilolite by co-precipitation method was investigated in the batch system at 298–323 K. Various parameters such as pH, initial antibiotic concentration, adsorbent dosage, contact time, stirring speed and temperature were examined and optimum parameters were determined according to experimental data. Adsorption isotherms were investigated with Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin models. Kinetic constants were determined according to pseudo first order, pseudo second order, intraparticle diffusion and Elovich models. OTC-HCL adsorption on zeolite/Fe₃O₄ best fitted to the Langmuir isotherm and pseudo second order kinetic models. The maximum adsorption capacity of zeolite/Fe₃O₄ was determined as 83.33 mg/g at 323 K. Adsorption of OTC-HCL on zeolite/Fe₃O₄ occurred spontaneously and endothermic. Physicochemical characterization of zeolite/Fe₃O₄ was performed before and after adsorption, by N₂ adsorption-desorption, XRD, FTIR, SEM-EDX, XPS, TEM analyses. Magnetic properties of zeolite/Fe₃O₄ were determined by VSM analysis. The BET specific surface area of zeolite/Fe₃O₄ decreased after adsorption of OTC-HCL. VSM and SEM-EDX results showed that zeolite/Fe₃O₄ had superparamagnetic property and OTC-HCL adsorbed on zeolite/Fe₃O₄ successfully.     

表面修饰磁性Fe_3O_4粒子及其在生物医学应用中的新进展

磁性材料具有独特的结构和优异的性能已被广泛的应用于生物医学领域,通过表面修饰磁性材料可使生物材料表面有更好的生物相容性。综述了磁性材料在磁共振成像、生物分离、靶向药物载体、磁流体致热治疗等方面的研究进展和应用前景。     

Magnetoresistance Intensification of Fe3O4/BaTiO3 Nanoparticle-Composite-Sinter Produced by Low Temperature Heat Treatment

We have presented the study on the magnetoresistance intensification of (Fe₃O₄)_1?X /(BaTiO₃) _X nanoparticle-composite-sinter (NPCS) produced by low temperature heat treatment. The average sizes of ??-Fe₂O₃ and BaTiO₃ nanoparticles are 30?nm and 40?nm, respectively. They were homogeneously mixed together and were sintered at 500?°C for 3?hours in the atmosphere of Ar(90%)/H₂(10%). X?of (Fe₃O₄)_1?X /(BaTiO₃) _X NPCS was varied between 0 and 0.75. With increasing?X, the electrical resistivity (ER) increases and shows the Mott??s variable-range-hopping (VRH) conduction behavior in a wide temperature region. The negative differential magnetoresistivity (ND-MR) is observed for all samples in a moderately high magnetic field region. In a low magnetic field region, the MR shows a large hysteresis. As X increases, the variation of the MR is intensified. We consider that the total number of network channels of the electrical conduction is reduced and the spin scattering is consequently intensified.     

Fe_3N和Fe_4N粉状化合物的合成及其电磁特性研究

纯铁粉在氨和氢的气氛中进行固气反应合成Fe3N和Fe4N粉状化合物。研究了氨气和氢气比例、温度以及时间对固气反应产物的影响,进而分别获得纯相粉状Fe3N和Fe4N化合物。利用矢量网络分析仪测试了Fe3N和Fe4N的磁导率和介电常数,并与市售铁氧体进行了比较。发现在1MHz～1GHz频段内,Fe3N和Fe4N的磁导率低于铁氧体,介电常数均高于铁氧体,且Fe4N的电磁性能优于Fe3N。     

化学镀Co—B合金对Fe3O4吸波性能的影响

采用化学共沉淀法制备纳米Fe3O4颗粒，通过胶体钯活化敏化一步法处理后，以KBH4为还原剂、C4H4O6Na2-2H2O为络合剂进行Co-B化学镀，对包覆前后的样品进行了XRD、SEM、TEM、电磁参数等表征以及吸波性能分析。结果表明：Fe3O4表面包覆的纤维状Co-B合金以无定形形式存在，Co-B包覆Fe3O4在2．0～18GHz具有良好的吸波效果．     

纳米Fe_3O_4/Fe复合磁流变液的流变性

用化学共沉淀法合成了纳米Fe3O4粒子,平均二次粒径为51.2nm,比表面积为109.6m2/g。以合成的纳米Fe3O4粒子与羰基铁粉复合配制了纳米复合磁流变(MR)液,并测定了其流变性。结果显示:纳米复合MR液对温度比较稳定;复合MR液在接近零场的低磁场强度下表现为牛顿流体,随着磁场强度提高转变为非牛顿流体;反复加载或撤除磁场,具有"开/关"特性,响应迅速,施加磁场时的响应时间Δt约为50～100ms,撤退磁场时约为100～150ms。     

Fe3O4纳米粒子的制备与超顺磁性

采用红外光谱、X射线衍射、透射电子显微镜和振动样品磁强计对用化学共沉淀法制备出的纳米Fe3O4粒子进行了形貌、结构及磁性能表征.其中,红外和XRD测试结果表明制备出的Fe3O4粒子的物态和晶相结构;透射电子显微镜照片表明制备出的纳米四氧化三铁成球性好,且大部分四氧化三铁粒子的粒径在10nm左右;磁化曲线表明制备出的Fe3O4粒子无剩磁和矫顽力,具有超顺磁性.并且,将制备出的纳米Fe3O4粒子和块状Fe3O4的磁性能进行对比,探讨了Fe3O4由块状的亚铁磁性向纳米级的超顺磁性转变的原因.     

Fe3O4/聚苯乙烯中空微球磁性复合微粒的制备及其磁流变性能的研究

用共沉淀法在聚苯乙烯（PS）中空微球表面包覆Fe3O4，制备了Fe3O4/Ps中空微球磁性复合微粒，当磁性包覆层的厚度为30～50nm时，复合微粒的室温表现密度为1．5g/cm^3，为传统磁流变液（MRF）中所用铁粉等软磁性颗粒密度（约7．9g/cm^3）的1/5，更为接近MRF中载液的密度。复合颗粒的磁滞回线比较狭长，呈软磁性，其磁性能和Fe3O4纳米颗粒相差不大。与Fe3O4颗粒相比，Fe3O4/PS中空磁性复合微粒在水载液中的沉降稳定性大大提高，复合微粒含量越高，其沉降稳定性越好。在磁性微粒含量相同的条件下，基于Fe3O4/PS中空磁性复合微粒的MRF的磁流变性能明显优于基于Fe3O4纳米微粒的MRF。