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首页> 外文会议>International Conference on Surface and Colloid Science; 200309; Brazil >Synthesis and characterization of silica-coated magnetic nanoparticles
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Synthesis and characterization of silica-coated magnetic nanoparticles

机译：二氧化硅包覆的磁性纳米粒子的合成与表征

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The present work reports on the synthesis and properties of magnetic nanoparticles based on magnetite coated by a silica layer. A series of conditions was tested to allow the synthesis of the nanoparticles, usually performed in an aqueous medium, and could be efficiently coupled with the silica sol-gel process. The resulting particles were characterized by means of X-ray diffraction, transmission electron microscopy associated with electron energy loss spectra and electron spectroscopy imaging, Fourier transform IR, Moessbauer and magnetization measurements. Initially, magnetite particles with an average crystalline grain size of about 100 A and a polydispersion of 30%, as revealed by X-ray diffraction and transmission electron microscopy analyses, respectively, were obtained with a mixture of FeCl_2 and FeCl_3 in aqueous and acid solution. The magnetization measurements, at room temperature, show that the particles are in the superparamag-netic regime. Magnetite was also synthesized in acid solutions in an alcoholic environment (25% metha-nol-to-base ratio), a medium that allows us to proceed with silica-coating by the sol-gel process in a one pot reaction. The resulting particles present size dispersion ranging from around 15 A to about 200-300 A as evidenced by electron micrographs. The superparamagnet-ic behavior is preserved, although its saturation magnetization value decreases from about 92 to about 50 emu g~(-1), probably owing to the contribution of the smallest particles as well as to the surface spin disorder induced by addition of methanol to the synthesis medium. For higher values of the alcohol-to-base ratio, the resulting particles are amorphous, becoming crystalline under thermal treatment. When tetraethyl-orthosilicate is added to a solution containing 25% of methanol to base, iron oxides are SiO_2-coated at room temperature, as evidenced by electron spectroscopy imaging and Fourier transform IR spectroscopy. The magnetization results are dependent on the Si-to-Fe volume ratio, in such a way that the values decrease as the SiO_2 amount increases, reflecting the nanoparticle coating.
机译：本工作报道了基于被二氧化硅层覆盖的磁铁矿的磁性纳米粒子的合成和性能。测试了一系列条件以允许通常在水性介质中进行的纳米颗粒的合成，并且可以与二氧化硅溶胶-凝胶工艺有效结合。通过X射线衍射，与电子能量损失谱和电子光谱成像相关的透射电子显微镜，傅里叶变换IR，Moessbauer和磁化测量来表征所得颗粒。最初，分别通过X射线衍射和透射电镜分析得到的磁铁矿颗粒的平均结晶粒径约为100 A，多分散度为30％，该混合物是在水溶液和酸溶液中用FeCl_2和FeCl_3的混合物制得的。 。在室温下的磁化强度测量表明颗粒处于超顺磁性状态。磁铁矿也可以在酒精环境（25％的甲基苯酚与碱的比率）的酸性溶液中合成，这种介质使我们能够通过溶胶-凝胶法在一锅反应中进行二氧化硅涂层。如电子显微照片所证明的，所得颗粒的尺寸分散范围为约15A至约200-300A。尽管其饱和磁化强度值从约92 eMg〜（-1）降低到约59 emu g〜（-1），但仍保留了超顺磁性行为，这可能是由于最小的颗粒以及加入甲醇引起的表面自旋无序所致。合成介质。对于更高的醇/碱比值，所得颗粒是无定形的，在热处理下变为结晶。当将原硅酸四乙酯添加到含25％甲醇的碱溶液中时，如电子光谱成像和傅里叶变换红外光谱所证明的，氧化铁在室温下被SiO_2涂覆。磁化结果取决于Si与Fe的体积比，其方式是随着SiO_2量的增加而降低，从而反映出纳米颗粒的涂层。

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