Encapsulation of Magnetic Particles in Metallic Hollow Nanospheres
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Encapsulation of magnetic particles in metallic hollow nanospheres M. Toprak1, D. K. Kim1, M. Mikhailova1, Y. Zhang1, Y. K. Jeong2 and M. Muhammed1 1
Materials Chemistry Division, Royal Institute of Technology SE-100 44 Stockholm, Sweden KICET (Korea Institute of Ceramic Engineering and Technology) 233-5, Gasan-Dong, Geumcheon-Gu, Seoul 153-801, Korea
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ABSTRACT Novel metallic capsules containing magnetite with given size in the sub-micron range have been produced. These nanocapsules are prepared in several steps through a colloidal templating approach. The first step is the synthesis of size-selected SiO2 nanospheres. The second step is coating the SiO2 nanospheres by electroless deposition with gold, in order to form a porous gold shell around the silica. Electroless deposition is controlled by the concentration of gold in the coating solution. Subsequently, the core (SiO2) was removed to obtain gold capsules. The final step is the inclusion of magnetite nanoparticles inside these nanocapsules and recoating the capsules with gold in order to have continuous encapsulation. The nanocapsule and core-shell structure have been characterized by TEM and DSC INTRODUCTION There have been considerable efforts in the field of nanotechnology to design and control the fabrication of micro- and nano-sized capsules (or shells) that enable the encapsulation of various materials that are of scientific and technological interest. The interest in nanoscale materials stems from property dependence on size, composition, and structural order. In recent years, a great deal of attention has been drawn to the fabrication of composite microand nanoparticles that consist of either organic or inorganic cores coated with shells of different chemical composition. Colloidal particles represent very attractive building blocks to create ordered and complex materials. They can also be used as the core material for colloidal templating. The creation of core-shell particles is attracting a great deal of interest because they exhibit improved physical and chemical properties over their single-component counterparts, making them potentially useful in a broader range of applications. Particle characteristics can influence chemical properties, reactivity, selectivity, rate of dissolution, and bio-efficiency. These characteristics are primarily surface phenomena. Tailoring the surface properties of particles can be achieved by coating or encapsulating particles within a shell of preferred material [1,2]. Characteristics such as solubility, resonant optical properties, electrical and mechanical aspects of nano-particle constituent materials, and even agglomeration are influenced by chemical functionalization of nanoparticle surfaces [3-6]. For example, the shell can alter the charge, functionality, and reactivity of the surface. This can enhance the stability and dispersibility of the colloidal core. Magnetic, optical, or catalytic functions can be readily imparted to the dispersed colloidal matter depending on the properties of the coating [7]. Encaps
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