NiFe2O4/SiO2纳米复合体的制备及其磁性能

通过溶胶-凝胶法将NiFe2O4纳米颗粒分散于SiO2基体中, 制得NiFe2O4/SiO2纳米复合体. 利用XRD, DSC, TEM和VSM对合成的(NiFe2O4)wSiO2(1-w)(5%≤w≤55%)纳米复合体进行了表征. 研究结果显示: w＜15%的纳米复合体均以非晶态存在, 在15%≤w≤50%的范围内, 随着w的增加, NiFe2O4的晶粒尺寸从2.nm增长到25.nm, w进一步增加则会导致材料中NiFe2O4晶粒尺寸减小. 所制备的NiFe2O4/SiO2纳米复合体的饱和磁场强度随晶粒尺寸增加而增加, 变化范围为3.7～11.0.A·m2·kg-1; 矫顽力值最大可以达到2.49×104.A·m-1, 是纯NiFe2O4大块材料矫顽力值的4倍以上.     

Magneto-optical properties of magnetic nanocomposites

The magnetotransport, optical, and magneto-optical (MO) properties of (CoFeZr) _X (Al₂O₃)_100?X nanocomposites in the as-deposited state and after annealing have been studied. It is shown that the MO response of the nanocomposites increases in the vicinity of the percolation threshold. New features have been observed in the samples with X ≥ 45% after annealing. The permittivity tensor ε of the nanocomposites has been calculated and the simulation in the framework of the effective-medium approximation was made. It is supposed that the new features appearing in both the MO spectra and permittivity tensor ε after annealing are caused by the excitation of surface plasma resonances.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Spherical granular structures of Ag/Co nanoparticles: Synthesis, characterization and magnetic properties

Ag/Co bimetallic nanoparticles in the form of hierarchical spherical structures were prepared by the polyol process using oleic acid and oleylamine as surfactants. The Ag/Co nanoparticles so obtained were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), UV-vis spectroscopy (UV-Vis), small angle X-ray scattering (SAXS), vibrating sample magnetometer (VSM) and super-conducting quantum interference device (SQUID). The XRD results in complement with the UV-vis studies indicated the absence of Ag-Co alloy formation during the synthesis. The FESEM observations depicted dense and uniform spherical granular structures for the Ag/Co nanoparticles; while the TEM studies apparently revealed a bimodal distribution of nanoparticles exist in the Ag/Co samples. The SAXS analysis on the Ag/Co colloids further validated the TEM results. The VSM studies showed typical ferromagnetic characteristics for the Ag/Co nanoparticles at room temperature; whereas the SQUID measurements demonstrated superparamagnetic nature for these nanoclusters with a blocking temperature close to 250 K. The synthetic route presented in this work represents a simple means of producing bimetallic composite superstructures of Ag/Co nanoparticles in the form of spherical granules on a large scale. These spherical aggregates have the potential to be important building blocks for more complex nanostructures and would be interesting for magnetic studies and catalytic applications.     

Maghemite polymer nanocomposites with modulated magnetic properties

A method is presented for the production of maghemite polymer nanocomposites with modulated magnetic properties. Magnetic nanocomposites prepared using this method show regular variation in the magnetic blocking temperature from 2 K to 300 K, and variation in the saturation magnetization from 0 to 50 emu g⁻¹ (Fe₂O₃). The method is based on the in situ formation of maghemite nanoparticles in nitrogen-base polymer matrixes. The particle size can be varied regularly from 1.5 nm to 16 nm by changing the ratio of iron loading in the polymer and/or the Fe(II)/Fe(III) ratios. The particles are isolated and uniformly distributed within the matrix. The materials were characterized by electron microscopy, electron energy loss spectroscopy, Mössbauer spectroscopy, infrared spectroscopy, small angle X-ray scattering, wide angle X-ray scattering and magnetic measurements. The nanocomposites obtained are useful model material for the study of the magnetic behavior of magnetic nanoparticles, as well as for use in many industrial and biomedical applications.     

Synthesis, characterization and magnetic properties of La added Mg-Cd ferrites prepared by oxalate co-precipitation method

Nanosized powders of Mg-Cd-La ferrite synthesized by oxalate co-precipitation method using high purity sulphates are presented. The powder has been characterized by X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The phase identification of powder reveals biphasic nature of materials. The lattice constant, X-ray and physical density, porosity, crystallite size, site radii and bond length were directly affected by addition of rare earth ion (La³⁺) in Mg-Cd ferrite. The crystallite size of the samples lies in the range 25.67-30.55 nm. FT-IR spectra show two absorption bands in the frequency range from 3.5 × 10⁴ to 8.0 × 10⁴ m⁻¹ which are attributed to stretching vibration of tetrahedral and octahedral complex Fe³⁺-O²⁻ respectively. The addition of La³⁺ alters the characters of powder and decreases the grain size which suppresses the abnormal grain growth. The addition of La³⁺ resulted increase in saturation magnetization, remnant magnetization, 4πM_s and coercivity. Coercivity shows size dependent behavior. Such results are promising ones for high frequency applications.     

Synthesis and properties of nickel nanoparticles and their nanocomposites

For the first time, nickel nanoparticles are synthesized in reverse micelles by a radiation-chemical method. The particles are shown to be spherical with sizes of an order of magnitude of 1–100 nm. Nickel particles are oxidized by air oxygen to nickel oxide nanoparticles, retaining their shape and nanoscale dimensions. Adsorption of nickel-metal nanoparticles on silica is studied by spectrophotometry.

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Original Russian Text ? S.V. Gornostaeva, A.A. Revina, L.D. Belyakova, O.G. Larionov, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 4, pp. 400–403. An erratum to this article can be found online at http://dx.doi.org/.     

Preparation and formation mechanism of nanocomposites with fluorescent and magnetic properties

Fluorescent magnetic nanocomposites were successfully synthesized using the self-prepared Fe₃O₄ magnetic liquid and CdTe quantum dots (QDs) as precursors. High-resolution transmission electron microscopy, selected area electron diffraction, energy-dispersive spectroscopy and Fourier transform infrared spectroscopy were used to characterize the size, morphology, structure and composition of the nanocomposites. A fluorescent microscope was used to observe their micro-morphology. Magnetic and optical properties were characterized by a vibrating sample magnetometer and fluorescent spectrophotometer, respectively. The characterized results indicated that the Fe₃O₄ nanoparticles had been successfully combined with CdTe QDs. The products could exist stably in the aqueous phase, and had better biocompatibility. It was found that the nanocomposites, which had higher magnetization intensity and better fluorescent properties synchronously, were fabricated by the formation of chemical bond with amide structure. Thus this type of nanocomposite could be applied in various science and technology fields in the future.     

Synthesis,characterization and electrical properties of dihalogenated polyanilines

Poly(2.5-dichloroaniline), poly(2,3-dichloroaniline), poly(3,5-dichloroaniline), poly(2,5-dibromoaniline) and poly(2,6-dibromoaniline) have been synthesized from dihaloanilines in protic and aprotic media with different oxidizing agents, such as copper perchlorate, potassium dichromate and potassium permanganate. Each polymer is characterized by elemental analysis, IR and UV-Vis spectroscopy, scanning electron microscopy (SEM) and conductivity measurements. To obtain the doped polymers, they are treated with inorganic acids and then their electric properties determined. The use of different oxidants allows the obtention of polymers with different redox states which, in some cases, present semiconducting properties and are soluble in methanol and acetone. For the sake of comparison of the electrical and structural properties of the new polymers, polyaniline (PANI) has also been synthesized in a manner analogous to the poly(dihaloanilines).     

Microwave-assisted synthesis and magnetic properties of size-controlled CoNi/MWCNT nanocomposites

Size-controlled CoNi alloy nanoparticles with average diameters in the range of 15-48 nm attached on the multi-walled carbon nanotubes (MWCNTs) were prepared to form CoNi/MWCNT nanocomposites by microwave-assisted method. The size of CoNi alloy nanoparticles can be controlled through adjusting the atomic ratios of metals to carbon nanotubes in the mixed acetate solution. The as-prepared nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The results show that CoNi alloy nanoparticles are face-centered cubic structure, quasi-spherical and disperse uniformly on the surface of MWCNTs. Magnetic measurement shows that both the coercivity and the saturation magnetization of the samples increase with the increase of the particle size from 15 to 37 nm, and decrease from 37 to 48 nm.     

Sonochemical synthesis,characterization,and magnetic properties of Mn-doped ZnO nanostructures

Mn-doped ZnO samples,Zn1-xMnxO (x =0,0.01,0.03 and 0.05;mole fraction),were successfully synthesized by sonochemical method.The undoped and Mn-doped ZnO samples...     

Synthesis,characterisation and properties of Ni/PSZ and Ni/YSZ nanocomposites

Nanocrystalline partially stabilised zirconia (PSZ) and yttria-fully stabilised zirconia (YSZ) powders were prepared by solution combustion process. Nanocrystalline nature of the powders was confirmed by XRD and TEM. Nanocomposite Ni/PSZ and Ni/YSZ films were electrodeposited from a suspension of nanoparticles in nickel sulfamate solution. The strengthening of the nanocomposite due to nanoparticle incorporation was characterised by nanohardness measurements.     

Synthesis,morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe₂O₃) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ～500 nm whereas thickness is ～100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe₂O₃ particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H_C = 1140 Oe, remanent magnetization M_r = 0.125 emu/g and saturation magnetization M_S = 2.15 emu/g as well as the Morin transition at T_M ～ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.     

Synthesis and magnetic properties of CoPt nanoparticles

CoPt nanoparticles were prepared by simultaneous thermally reducing Co(CH3COO)2 and Pt(acac)2 in oleylamine with a small quantity of oleic acid. The composition of the particles was controlled by changing the amount of the reactants. Transmission electronic microscopy reveals that Co 48 Pt 52 particles with an average diameter of 8.4 nm are steadily dispersed in octane in the presence of oleylamine and oleic acid. Selected area electron diffraction indicates that the as-prepared particles have a face center cubic structure. Magnetic properties of these particles measured by a vibrate sample magnetometer yield a coercivity of 1.194×104 A·m-1 and a saturation magnetization of 5.3 emu·g-1 . After annealing at 650 ℃ for 2 h under the flowing Ar, the coercivity increases to 9.552×104 A·m-1 according to partly phase transformation from face center cubic structure to face center tetragonal structure for the nanoparticles.     

Synthesis,characterization, and photovoltaic properties of diketopyrrolopyrrole-oligothiophene/fullerene dyads

Low-band-gap dyad molecules containing diketopyrrolopyrole (DPP) chromophore and hexathiophene were designed and synthesized in combination with C₆₀ and C₇₀ derivatives as the electron acceptors. The effect of alkyl side chains in the donor parts on film morphology, thermal properties, and optical properties were investigated by X-ray diffraction analysis, differential scanning calorimetry, UV–vis absorption spectroscopy, and fluorescence spectroscopy. The donor part with a shorter alkyl side chain showed better packing of the π-plane and an enhancement of absorption in the longer-wavelength region, which led to higher J_SC of organic solar cells. The use of C₇₀ as the electron acceptor led to stronger absorption in the visible region, resulting in improved external quantum efficiency and J_SC compared with those of the C₆₀ derivatives. The single-component solar cell of the dyad with the methyl side chains and C₇₀ derivative showed the power conversion efficiency of 0.84% with a relatively high J_SC of 4.4 mA cm⁻² under AM 1.5 illumination (100 mW cm⁻²).     

Synthesis, characterization and electrical properties of soluble conjugated poly-Schiff bases

Four conjugated poly-Schiff bases with the same backbone but different side groups were prepared by polycondensation of 1,4-diaminobenzene with glyoxal, 2,3-butanedione, 3,4-hexanedione and 4,5-octanedione, respectively. The polymers were characterized by FT-IR, elemental analysis, etc. It was discovered that the conjugated poly-Schiff bases with alkyl side groups can be dissolved in common organic solvents. Electrical conductivities of the pristine polymers and their relationship with temperature were measured, showing that the polymers are typical semiconductors. When the polymers were doped with iodine, electrical conductivity increased by seven to nine orders of magnitude (up to 10⁻³-10⁻⁴ S/cm). The effect of side groups on the conductivity of the I₂-doped polymers is discussed.     

Synthesis,spectroscopic and magnetic properties of m–p aniline tetramers

Alternating m–p-N-hexylaniline and aniline tetramers have been synthesized via palladium-catalyzed amination reactions. The tetramers can be oxidized with m-chloroperbenzoic acid or NOBF₄ and form radical cations stable in acidic media. The magnetization measurements of oxidized N-hexylaniline or p-aniline tetramers reveal the paramagnetic-type behaviour.     

Fabrication,characterization and microwave properties of polyurethane nanocomposites reinforced with iron oxide and barium titanate nanoparticles

Polyurethane (PU) nanocomposites reinforced with magnetic iron oxide nanoparticles and/or dielectric barium titanate nanoparticles fabricated by the surface-initiated-polymerization approach were investigated. The polymer matrix incorporated with different nanoparticles shows different presenting status surrounding the nanoparticles, i.e., chemical bonding, physical entanglement and bulk polymer chain. The nanoparticles have a different effect on the thermal stability of the polymer nanocomposites. By embedding different functional nanoparticles, unique physical properties were observed, such as enlarged coercivity and larger dielectric constant (real permittivity). The synergistic effect of the binary nanoparticle reinforced PU nanocomposite was explored. The addition of the iron oxide nanoparticles does have some effect on the permittivity. However, little difference was observed in the magnetic properties and permeability after the introduction of the dielectric barium titanate nanoparticle into Fe₂O₃/PU nanocomposites. The permeability and permittivity of γ-Fe₂O₃ and BaTiO₃ nanoparticle reinforced PU nanocomposites were investigated with frequencies ranging from 10 MHz to 1 GHz. The predicted microwave properties from Bruggeman’s equation were consistent with the measured data, except for the real permittivity of Fe₂O₃/BaTiO₃/PU. The volume average method (VAM) usually used for fiber-reinforced composites with reinforcements in the thickness direction was applied in this nanocomposite system. The predicted real permittivity by VAM was found to be in better agreement with the measured data than that predicted by Bruggeman’s equation.