Adsorption of organic layers over electrodeposited magnetite (Fe3O4) thin films

The formation of monolayers of two organic compounds (oleic acid and dodecanethiol) over magnetite films was studied. Magnetite films ranging from 80 nm to 3.75 μm-thick were electrodeposited on Au on glass substrates under galvanostatic control, with deposition parameters optimized for minimum surface roughness. Films were characterised by SEM and AFM, showing granular deposits with a low rms roughness of 5–40 nm measured over an area of 1 μm². The growth rate was estimated by measuring cross-sections of the thin films. Pure magnetite with an fcc structure is observed in XRD diffractograms. The adsorption of both oleic acid and dodecanethiol on the magnetite films was tested by immersing them in ethanol solutions containing the organic molecules, for different deposition time, temperature and cleaning procedure. Monolayer formation in both cases was studied by contact angle and voltammetric measurements, as well as XPS.     

Synthesis of core-shell structured PS/Fe3O4 microbeads and their magnetorheology

Most magnetic materials possess serious sedimentation problem due to their large density when they are adopted as magnetorheological (MR) materials. In this communication, we fabricated novel core-shell structured polystyrene(PS)/Fe₃O₄ microbeads via a facile method. Porous morphology of the PS obtained by etching silica particles and the loaded Fe₃O₄ was observed via both SEM and TEM images. XRD pattern confirms crystalline structure of the synthesized iron species. VSM data indicate the change in saturation magnetization before and after introducing organic PS core. Finally, MR performances of the PS/Fe₃O₄ based MR fluid were investigated via a rotational rheometer and sedimentation stability was found to be improved with a decreased density of the synthesized microbeads.     

Synthesis of water dispersible magnetite nanoparticles in the presence of hydrophilic polymers

Water dispersible magnetite nanoparticles (Fe₃O₄) were synthesized by thermal decomposition of iron (III) acetylacetonate (Fe(acac)₃) in the presence of carboxylic acid-terminated poly(ethylene glycol) (mPEG acid), poly(vinyl alcohol) and NH₂-containing polyether. Crystal structure was investigated using X-ray diffractometry (XRD) and it showed that the as-synthesized particles had high crystallinity with distinct lattices. Particle size of the nanoparticles was investigated using XRD (15.32 nm), transmission electron microscopy (18.8 nm) and photo correlation spectroscopy (32 nm) techniques. Vibrating sample magnetometry indicated that magnetite nanoparticles exhibited superparamagnetic behavior at room temperature. Influence of each functional group on magnetic properties of the particles was also examined. These magnetite nanoparticles remained dispersible in aqueous dispersions with only 5% particles aggregating after 1 month of preparing.     

Resistance switching in electrodeposited polycrystalline Fe3O4 films

Resistance random access memory (RRAM) is an emerging nonvolatile memory that offers advantages of scalability, fast switching, and low voltages. Magnetite, Fe₃O₄, has been shown to exhibit resistance switching in nanoscale architectures such as superlattices. Here, we show that electrodeposited polycrystalline films of Fe₃O₄ exhibit multistate resistance switching. Experiments suggest that the insulator-to-metal transition may be facilitated by the presence of a thin nano-crystalline layer which is critical for resistance switching to occur at lower bias. We also show that the switching behavior can be tuned through the applied deposition potential. The multiple resistance states accessible in these simple architectures open up new possibilities for multi-bit data storage and retrieval.     

Water-soluble,mesoporous Fe3O4: Synthesis,characterization, and properties

Water-soluble, mesoporous Fe₃O₄ nanopowder is successfully prepared by one-step thermal decomposition of an iron-urea complex ([Fe(NH₂CONH₂)₆](NO₃)₃) in triethylene glycol (TEG). The formation of Fe₃O₄ is confirmed from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED) measurements. The morphological and structural properties of the Fe₃O₄ nanopowder are characterized by transmission electron microscopy (TEM), nitrogen adsorption–desorption, and thermogravimetric analysis (TGA). Monodisperse, nearly spherical and highly crystalline Fe₃O₄ nanoparticles are obtained by this method. The Fe₃O₄ nanopowder is well dispersed in water and ethanol with a mesoporous structure, average pore size of 3.6 nm, and Brunauner–Emmett–Teller (BET) surface area of 122 m²/g. The room temperature magnetization hysteresis curve exhibits barely measurable values for coercivity and remanence, suggesting that the Fe₃O₄ nanopowder possesses superparamagnetic characteristics.     

油相稳定分散Fe3O4纳米粒子的制备研究

分别采用热分解法及共沉淀油酸同步修饰法制备了2种可以在油相稳定分散的Fe3O4纳米粒子,并对热分解法制备Fe3O4纳米粒子的反应条件进行了优化,考察了热分解温度、熟化时间对颗粒粒径、形貌及磁性能的影响。通过TEM、VSM和FTIR等表征手段对2种方法制备的Fe3O4纳米粒子的油相分散稳定性、颗粒形貌及粒径、比饱和磁化强度及表面性质进行了比较。结果表明:热分解法制备的Fe3O4纳米粒子表现出更好的油相分散稳定性,共沉淀油酸同步修饰法制备的Fe3O4纳米粒子则表现出更好的磁响应性。     

Evidence of redox interactions between polypyrrole and Fe3O4 in polypyrrole-Fe3O4 composite films

The electrical properties of conducting polymers make them useful materials in a wide number of technological applications. In the last decade, an important effect on the properties of the conducting polymer when iron oxides particles are incorporated into the conductive matrix was shown. In the present study, films of polypyrrole were synthesized in the presence of magnetite particles. The effect of the magnetite particles on the structure of the polymer matrix was determined using Raman spectroscopy. Mass variations at different concentrations of Fe₃O₄ incorporated into the conducting matrix were also measured by means of quartz crystal microbalance. Additionally, the changes in the resistance of the films were evaluated over time by electrochemical impedance spectroscopy in solid state. These results show that the magnetite incorporation decreases polymeric film resistance and Raman experiments have evidenced that the incorporation of magnetite into polymeric matrix not only stabilizes the polaronic form of the polypyrrole, but also preserves the polymer from further oxidation.     

Room temperature in situ chemical synthesis of Fe3O4/graphene

A simple, cost-effective, efficient, and green approach to synthesize iron oxide/graphene (Fe₃O₄/rGO) nanocomposite using in situ deposition of Fe₃O₄ nanoparticles on reduced graphene oxide (rGO) sheets is reported. In the redox reaction, the oxidation state of iron(II) is increased to iron(III) while the graphene oxide (GO) is reduced to rGO. The GO peak is not observed in the X-ray diffraction (XRD) pattern of the nanocomposite, thus providing evidence for the reduction of the GO. The XRD spectra do have peaks that can be attributed to cubic Fe₃O_4. The field emission scanning electron microscopy (FESEM) images show Fe₃O₄ nanoparticles uniformly decorating rGO sheets. At a low concentration of Fe²⁺, there is a significant increase in the intensity of the FESEM images of the resulting rGO sheets. Elemental mapping using energy dispersive X-ray (EDX) analysis shows that these areas have a significant Fe concentration, but no morphological structure could be identified in the image. When the concentration of Fe²⁺ is increased, the Fe₃O₄ nanoparticles are formed on the rGO sheets. Separation of the Fe₃O₄/rGO nanocomposite from the solution could be achieved by applying an external magnetic field, thus demonstrating the magnetic properties of the nanocomposite. The Fe₃O₄ particle size, magnetic properties, and dispersibility of the nanocomposite could be altered by adjusting the weight ratio of GO to Fe²⁺ in the starting material.     

纳米Fe3O4稳定的Pickering型ASA乳液

利用纳米Fe₃O₄作为稳定剂和乳化剂来制备Pickering型ASA（alkenyl succinic anhydride） 施胶乳液,并研究了固体颗粒浓度、油水比、水分散相pH对乳液类型、稳定性、形态及施胶性能的影响。结果表明,纳米Fe₃O₄能够乳化制备均一稳定的Pickering型ASA乳液。乳液在室温下静置稳定,析出油相体积分数随固体颗粒用量的增加而增大,随油水比的增大而减小。油水比为2：1,水分散相浓度为0.1%（质量分数）时制备的ASA乳液稳定性最佳。固体颗粒部分吸附在油/水界面处,部分分散在分散相中,随分散相中固体颗粒浓度的增加,乳液稳定性变差。乳液静置分层之前,ASA发生部分水解。在放置1 h后用于纸页浆内施胶,随ASA乳液用量的增加,纸页表面接触角逐渐增大,且纸页表面粗糙度下降。在ASA的添加量为1.0%（质量分数）时,纸页表面接触角达到93.5°,纸页表面粗糙度为15.924 μm。     

Microstructure of selectively heated (hot spot) region in Fe3O4 powder compacts by microwave irradiation

An Fe₃O₄ powder compact was irradiated with a 2.45 GHz microwave single-mode applicator at the magnetic field maximum position. Selectively heated regions (hot spot region) having several hundred micrometers to millimeter scale were formed. They exhibited metallic color. The SEM/EDX observations showed no appreciable difference in the compositions between the hot spot regions and the matrix. However, micro-XRD revealed that the hot spot region had a larger fraction of FeO than the matrix did, although the major consisting phase was Fe₃O₄ with a little Fe₂O₃. TEM observations indicated that the observed hot spot regions comprise these oxide phases separated in nano-sized grains, which agrees with our previous report. The larger fraction of FeO phase and flat surface might be related with the metallic color of the hot spot region. Their formation mechanisms and phase constitution were discussed.     

柠檬酸钠改性的Fe3O4磁性纳米粒子的快速制备

以FeSO_4·7H_2O为单一铁源,浓氨水为沉淀剂,柠檬酸钠为表面改性剂利用简单回流法快速合成Fe_3O_4磁性纳米粒子。考察反应时间,反应温度及浓氨水加入方式对合成Fe_3O_4磁性纳米粒子的影响,并利用动态光散射仪、傅立叶红外射线光谱仪及透射扫描电镜等对合成的Fe_3O_4磁性纳米粒子进行表征。结果表明,以柠檬酸钠为表面改性剂,逐滴加入浓氨水,反应温度为(70～80)℃和反应时间为6 min时,获得的Fe_3O_4磁性纳米粒子在水中具有良好的分散性及磁响应性。Zeta电位和红外光谱同时表明,柠檬酸钠成功地吸附于Fe_3O_4磁性纳米粒子的表面(Fe_3O_4@SC),且Zeta电位值为-31.3 mV;透射扫描电镜显示获得的Fe_3O_4@SC磁性纳米粒子呈球状结构,粒径约为10 nm。     

Using a bifunctional polymer for the functionalization of Fe3O4 nanoparticles

A bifunctional maleimido-tetra(ethylene glycol)-poly(glycerol monoacrylate) (MAL-TEG-PGA) polymer was synthesized and used as a linker to couple functional biomolecules to iron oxide nanoparticles. The cell-penetrating peptide Tat was chosen as a model ligand and successfully conjugated to the surface of Fe₃O₄ nanoparticles using MAL-TEG-PGA. The Tat-conjugated Fe₃O₄ nanoparticles can be prepared simply by applying the linker to the iron oxide nanoparticles and then coupling the Tat peptide to the maleimide terminus or by coating the nanoparticles with a pre-coupled linker. Cell-uptake studies demonstrated that the Tat peptide was an efficient functional biomolecule to translocate iron oxide nanoparticles into the cell nucleus. Tat-conjugated nanoparticles thus prepared may be useful for drug or gene delivery.     

Functionalized magnetic core-shell Fe3O4@SiO2 nanoparticles as selectivity-enhanced chemosensor for Hg(II)

A colorimetric and ‘‘turn-on” fluorescent chemosensor Rho-Fe₃O₄@SiO₂ for Hg²⁺ in which N-(rhodamine-6G)lactam-ethylenediamine (Rho-en) is conjugated with the magnetic core-shell Fe₃O₄@SiO₂ NPs has been strategically designed and synthesized. The final product was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR) and UV-visible absorption and fluorescence emission. Fluorescence and UV-visible spectra results showed that the resultant multifunctional nanoparticles Rho-Fe₃O₄@SiO₂ exhibited selective ‘turn-on’ type fluorescent enhancements and distinct color changes with Hg²⁺. The selectivity of the Rho-Fe₃O₄@SiO₂ for Hg(II) ion is better than that of the Rho-en in the same conditions. In addition, the presence of magnetic Fe₃O₄ nanoparticles in the sensor Rho-Fe₃O₄@SiO₂ NPs would also facilitate the magnetic separation of the Hg(II)-Rho-Fe₃O₄@SiO₂ from the solution.     

Fe3O4 coupled BiOCl: A highly efficient magnetic photocatalyst

The magnetic photocatalyst, Fe₃O₄/BiOCl nanocomposite, was prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), physical property measurement system (PPMS). It was found that Fe₃O₄/BiOCl was an effective photocatalyst to degrade the organic dyes. Compared with the conventional core–shell magnetic photocatalysts, such as Fe₃O₄/TiO₂ system which dramatically lost their intrinsically photocatalytic activity due to the introduction of the magnetic core, the as-synthesized Fe₃O₄/BiOCl reserved as high photocatalytic activity as that of BiOCl. The high catalytic activity possibly involved in a coupled structure and the special interfaces, that is, the probability of combination of the carriers could be reduced in this system. Moreover, the superparamagnetic Fe₃O₄/BiOCl can be not only easily recycled but also fluidized by applying an external magnetic field.     

Al2O3-supported Cu-Co bimetallic catalysts prepared with polyol process for removal of BTEX and PAH in the incineration flue gas

The polyol process is an effective method to generate well-dispersed nanoscale active sites on a support. To study the activity of catalysts prepared by polyol process, Cu_1.25Co_3.75/Al₂O₃, Cu_2.5Co_2.5/Al₂O₃, and Cu_3.75Co_1.25/Al₂O₃ were studied in a pilot-scale incinerator system to remove benzene, toluene, ethylbenzene, xylene, and polycyclic aromatic hydrocarbons, and the effect of lead in a flue gas was also discussed. The pilot-scale experiment results indicated that Cu_1.25Co_3.75/Al₂O₃ exhibited a good performance on organic compounds removal, without being poisoned by lead. The bimetal containing Cu/Co = 1/3 exhibits a better activity and stabilization on oxidation than the others. When the Cu/Co ratio was above one, the X-ray powder diffractometer, and Fourier transform infrared spectroscopy analyses results revealed that several components (Cu⁰, CuO, and CuCo₂O₄) of the spent catalysts disappeared. This may be due to the active sites that were covered with an amount of CH₃-groups.     

On the mechanical and biological properties of bredigite-magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite scaffolds

The aim of the present study was to study the mechanical and biologocal properties of the bredigite-magnetite (Ca₇MgSi₄O₁₆-Fe₃O₄) nanocomposite with various amounts of magnetite (0, 10, 20 and 30 wt%). According to the obtained results, the properties of the constructed scaffolds have an extreme dependence on the magnetite content. In this research, the bredigite-30 wt% magnetite as the optimum sample showed a fracture toughness of 2.69 MPa m^1/2 and a Young's modulus of 29 GPa. Increasing bredigite content led to the increase of pH values in the SBF solution. This was originated from the interchange/interaction of Ca²⁺ ion on the scaffold surface. The sample containing 10 wt% magnetite presented a rocky and irregular surface while that of 30 wt% illustrated a smooth and flat outer layer with coarse projections. The results confirmed that the biodegradation rate of the pure bredigite is more than that of 20 wt% sample. The event is originated from the dissolution of the Si ions of the bridigite particles in the absence of magnetite.     

Co3O4纳米颗粒的制备及其超级电容性能研究

采用简单化学沉淀法,以十六烷基三甲基溴化铵(CTAB)为模板,Co(NO3)2.6H2O和NaOH为原料,空气作为温和氧化剂,室温下合成了具有花状分级多孔结构的Co3O4纳米颗粒电极材料。X-射线衍射(XRD)表明,产物中主要成分为Co3O4;扫面电镜的结果显示,制备的材料具有菜花状分级多孔结构;电化学测试结果表明,最高比容量达250 F/g,且经过1 000次循环后,容量保持了84%,显示出良好的超级电容性能。     

Negative magnetization and exchange bias effect in Fe-doped CoCr2O4

Polycrystalline ceramics of Co(Cr_1-xFe_x)₂O₄ (0?≤?x?≤?0.12) were experimentally studied based on a series of temperature and time-dependent dc magnetic measurements using different magnetic field histories. Magnetization in field cooling process was continuously decreased for doping content x in the range of 0?≤?x?≤?0.04. Remarkable negative magnetization is observed when x reaches to 0.06 and persists up to x?=?0.1. Two-sublattice model is established and competition of the two magnetic sublattices is responsible for the phenomenon. The magnetic switching effect is realized just by changing the magnitude of the applied magnetic field and double magnetocaloric effects are obtained. These unique features under low magnetic fields show attractive for application in spintronic devices due to that the magnetic state can effectively be tuned through magnetic field or temperature. Besides, the system exhibits both positive and negative exchange bias fields which are considered to be originating from the unidirectional anisotropy of exchange coupling of antiferromagnetic/ferromagnetic phases and spin reorientation of the two sublattices magnetic moments, respectively.     

Synthesis of Fe2O3 nanoparticles for nitrogen dioxide gas sensing applications

Iron (III) oxide, Fe₂O₃, nanoparticles of approximately 40 nm diameter were synthesized by sol–gel method and their nitrogen dioxide adsorption and desorption kinetics were investigated by custom fabricated gas sensor unit. The morphology and crystal structure of Fe₂O₃ nanoparticles were studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) respectively. The roughness of film surface was investigated by atomic force microscopy (AFM). Relative sensitivity of Fe₂O₃ nanoparticles for NO₂ sensor was determined by electrical resistance measurements. Our reproducible experimental results show that Fe₂O₃ nanoparticles have a great potential for nitrogen dioxide sensing applications operating at a temperature of 200 °C.