Structural and Magnetic Characterization of Co and Ni Silicate Hydroxides in Bulk and in Nanostructures within Silica Aerogels
Structural and Magnetic Characterization of Co and Ni Silicate Hydroxides in Bulk and in Nanostructures within Silica Aerogels
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DOI：
10.1021/cm8029714
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发表时间：
2009-03-10
影响因子：
8.6
通讯作者：
Wang, Peng
中科院分区：
文献类型：
--
作者：
Carta, Daniela;Casula, Maria F.;Wang, Peng
X射线衍射，透射电子显微镜，X射线吸收光谱，和磁性测量被用来研究高度多孔的二氧化硅气凝胶含有铁和钴或铁和镍，在450 ℃下煅烧，这是在形成CoFe 2 O 4-SiO2和NiFe 2 O 4-SiO2气凝胶纳米复合材料的中间体。还研究了不含铁和纯Co和Ni硅酸盐氢氧化物的气凝胶。含有铁和钴或铁和镍的气凝胶样品呈现两个独立的相，一个含有水铁矿形式的铁，另一个含有Co或Ni硅酸盐氢氧化物。硅酸盐氢氧化物以纳米颗粒的形式存在于气凝胶中，在电子显微镜图像中具有一维外观，因此其是各向异性纳米结构，例如纳米针或纳米片。磁性研究表明，从纯Co或Ni硅酸盐氢氧化物到仅含镍或仅含钴的气凝胶样品，颗粒的尺寸和形状极大地改变了矫顽磁力。最后，在还含有铁的样品中，总磁性行为受到水铁矿的存在和铁在硅酸盐氢氧化钴或镍的纳米结构中的可能扩散的影响。
X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy, and magnetic measurements were used to investigate highly porous silica aerogels containing iron and cobalt or iron and nickel, calcined at 450 degrees C, which are intermediates in the formation of CoFe2O4-SiO2 and NiFe2O4-SiO2 aerogel nanocomposites. Aerogels without iron and pure Co and Ni silicate hydroxides were also studied. The aerogel samples containing iron and cobalt or iron and nickel present two separate phases, one containing iron in the form of ferrihydrite and the other either Co or Ni silicate hydroxides. The silicate hydroxides are present in the aerogels in form of nanoparticles with a one-dimensional appearance in electron microscopy images, which are therefore anisotropic nanostructures, such as nanoneedles or nanosheets. The study of the magnetic properties indicates that the coercivity is greatly modified by size and shape of the particles going from pure Co or Ni silicate hydroxides to the aerogel samples containing only nickel or only cobalt. Finally, in the samples also containing iron, the total magnetic behavior is influenced both by the presence of ferrihydrite and by the possible diffusion of iron in the nanostructures of cobalt or nickel silicate hydroxide.