Synthesis,characterization and magnetic properties of MFe2O4 (M=Co,Mg, Mn,Ni) nanoparticles using ricin oil as capping agent

We focused on obtaining MFe₂O₄ nanoparticles using ricin oil solution as surfactant and on their structural characterization and magnetic properties. The annealed samples at 500 °C in air for 6 h were analyzed for the crystal phase identification by powder X-ray diffraction using CuKα radiation. The particle size, the chemical composition and the morphology of the calcinated powders were characterized by scanning electron microscopy. All sintered samples contain only one phase, which has a cubic structure with crystallite sizes of 12–21 nm. From the infrared spectra of all samples were observed two strong bands around 600 and 400 cm⁻¹, which correspond to the intrinsic lattice vibrations of octahedral and tetrahedral sites of the spinel structure, respectively, and characteristic vibration for capping agent. The magnetic properties of fine powders were investigated at room temperature by using a vibrating sample magnetometer. The room temperature M–H hysteresis loops show ferromagnetic behavior of the calcined samples, with specific saturation magnetization (M_s) values ranging between 11 and 53 emu/g.     

Growth of nano Co encapsulated in carbon-shell

Nanostructured cobalt is one of the key elements in catalysis and therapeutic drug delivery. To design and prepare nanosize-controllable cobalt, a better understanding of its growth mechanism is essential. Growth of Co nanoparticles encapsulated in carbon-shell (Co@C) during temperature-programmed carbonization of the Co²⁺-β-cyclodextrin (CD) complex at 363–573 K was, therefore, studied by in situ synchrotron small-angel X-ray scattering and X-ray absorption near edge structure spectroscopy. The carbon-shell having a thickness of about 2 nm can prevent the core Co from being aggregated and oxidized. A relatively slow reduction of Co(II) to Co is observed at 393–423 K (stage I) prior to a particle growth transition-state possessing Co of 2.2 nm in diameter at 423–483 K. At 483–513 K (stage II), an increasing Co(II) reduction rate coupled with a rapid fusion and coalescence of Co nanoparticles is found. The average growth rates of Co at stages I and II are about 27 and 98 atoms/min, respectively. The most-probable particle diameter of the ripened Co is 5.9 nm. The carbon-shell can be removed by steam reforming to yield the Co nanoparticles. This work also exemplifies the possible temperature-controllable growth of Co@C, especially in the Co size range of 2–6 nm in diameter.     

Ag‐nanoparticle‐modified single Ag nanowire for detection of melamine by surface‐enhanced Raman spectroscopy

Silver nanowires synthesized by a solvothermal method were used as templates for fabricating silver‐nanoparticle‐decorated silver (AgNP/Ag) nanowires. The number density and particle size of Ag nanoparticles can be controlled by varying the concentration of Ag precursor. Single AgNP/Ag nanowire exhibited strong surface‐enhanced Raman scattering effect. Detection of melamine molecules at concentrations as low as 1.0 × 10⁻⁸ M was used as an example to show the possible applications of such AgNP/Ag nanowires. Their application in rapid detection of melamine in milk solution was further demonstrated. It was shown that melamine in milk solution at a low concentration of 5.0 × 10⁻⁸ M can be easily detected with little sample pretreatment. The results demonstrate the potential of single AgNP/Ag nanowire as a surface‐enhanced Raman scattering substrate for convenient and sensitive detection of trace amounts of melamine in a complex mixture. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanoparticle with a ferrimagnetic interlayer coupling in the presence of single-ion anisotropis

The magnetic properties of a nanoparticle described by the transverse Ising model with single-ion anisotropis, which consists of a concentric spin-3/2 core and a hexagonal ring spin-5/2 shell coupled with a ferrimamagnetic interlayer coupling, are studied by the effective-field theory with self-spin correlations. Particular emphasis is given to the effects of the both the transverse field and the single-ion anisotropis on the longitudinal and transverse magnetizations, phase diagrams of the nanoparticle. We have found that, for appropriate values of the system parameters, one or two compensation points may be obtained in the present systems.     

Magnetization plateaus of a ferrimagnetic nanoparticle in the presence of single-ion anisotropies

The magnetization of a ferrimagnetic mixed-spin nanoparticle for a series of different single-ion anisotropies D1 and D2 with increasing external magnetic field is studied by the use of the effective-field theory with correlations. At low temperature, the magnetization exhibits an obvious step effect for different anisotropies, exchange couplings, and external magnetic field. The results show that the positive single-ion anisotropy D1 (or D2) is a necessary element for the emergence of the accessional magnetization plateaus for the ferrimagnetic mixed-spin nanoparticle. However, for the stronger D2 the magnetization plateaus dissatisfy the 2S+1 criterion in such a ferrimagnetic nanoparticle system.     

六角相NaYF4纳米粒子的合成及粒子尺寸对Tb3+,Er3+下转换效率的影响

采用热溶剂法制备了NaYF4∶Tb3+,Er3+六角相纳米粒子,分析了合成条件对六角相粒子形成的影响。较高的反应温度有利于六角相NaYF4晶体的形成。实验结果表明:六角相是热力学更稳定和更有序的结构,从立方相到六角相的转变是从无序到有序结构的转变。随着尺寸的减小,纳米粒子的下转换效率明显降低。为进一步比较,制备了NaYF4∶Tb3+,Er3+核壳结构的纳米粒子。包覆后的纳米粒子的下转换效率明显提高,其原因是包覆减少了表面缺陷进而降低了表面激发能量的猝灭。     

倒置器件结构及局域等离子体效应对CdSe量子点LED发光性能的改进

研究了倒置器件结构以及CdSe量子点发光材料与金属纳米粒子之间的相互作用对量子点的电致发光性能的影响。利用TiO₂作为电子传输/注入层,成功地制备了倒置结构的量子点电致发光器件。通过对单载流子器件电压-电流特性的分析,证明了ITO作为阴极到TiO₂的电子注入特性与Al作为阴极时的效果几乎相同。观察到金属纳米粒子产生的局域等离子体效应提高了器件的效率,使得效率随电流增大而降低的速度明显减小。在电流密度为200 mA/cm²时,电致发光器件的效率大约提高了42%。     

Voltammetric Determination of Epinephrine in the Presence of Uric Acid Based on Aminated Graphene and Ag NPs Hybrid Membrane Modified Electrode

A hybrid membrane consisted of aminated graphene and Ag nanoparticles（Ag NPs） was prepared on the surface of glassy carbon electrode（GCE） by cyclic voltammetry（CV） with aminated graphene（GR-NH2） as matrix for immobilizing Ag NPs.The morphology and electrochemical properties of this hybrid membrane were characterized by scanning electron microscopy（SEM） and CV,respectively,and on this membrane,the voltammetric behaviors of epinephrine（EP） were studied in detail.The membrane exhibited excellent eletro-catalytic activities for the redox of EP,and could resolve the electrochemical response of EP and uric acid（UA） into two oxidation peaks.The peak current of EP was linear with its concentration in the ranges of 0.916-18.3 μmol/L and 18.3-184 μmol/L.The detection limit was 2.0 nmol/L（S/N=3）.The proposed modified electrode retained the advantages of easy fabrication,high sensitivity and good repeatability for the determination of EP.     

Preparation and Investigation of Arsenic Trioxide-loaded Polylactic Acid/Magnetic Hybrid Nanoparticles

In order to improve the therapeutic index and reduce the side effects of As2O3 so as to expand its clinical utility to solid tumors,As2O3-loaded polylactic acid（PLA）/magnetic nanoparticles（PAMNs） were prepared and the preparation conditions were optimized by the improved double emulsion solvent-evaporation method to obtain as a drug delivery system with a high As2O3 encapsulation efficiency and homogeneous nanosized particles.Successful loading of magnetic nanoparticles into the nanoparticles was confirmed by Fourier transform infrared（FTIR） spectroscopy.The drug loading,encapsulation efficiency and releasing properties of As2O3 in PAMNs were investigated by atomic fluorescence spectrometer analysis.Subsequently,the in vitro antitumor efficacy of free As2O3 and As2O3-PAMNs against SMMC-7721 cell line was investigated.Finally,confocal fluorescence microscopy was conducted to reveal the celluar uptake of As2O3-loaded PAMNs by SMMC-7721 cell line.     

配位自还原法制备纳米银及其电催化活性

Pt是质子交换膜燃料电池(PEMFC)阴极氧还原最好的催化剂,但价格昂贵,且易被渗透到阴极的燃料分子及中间体毒化,导致电池性能降低。 本文以乙二胺四甲叉膦酸(EDTMP)为配位剂和还原剂,采用配位自还原法快速合成银纳米粒子(Ag NPs),并研究了其对氧还原的电催化性能。 透射电子显微镜(TEM)、X射线衍射(XRD)等测试结果表明,Ag NPs分散性好且粒径均一,还原反应6 h所得Ag NPs的平均粒径约6 nm;循环伏安法(CV)等电化学测试发现,在碱性条件下此种合成方法制得的银作为电催化氧还原反应(ORR)的催化剂具有良好的催化活性,通过EDTMP配位自还原得到的Ag NPs对氧还原的半波电位(E1/2)比传统的NaBH4直接还原所制得Ag NPs的E1/2正移60 mV。