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Investigation on Preparation and Properties of Core-Shell Structural Magnetic Nanocomposites Based on Layered Double Hydroxides

Author: ZhangGuoYan
Tutor: ZhangHui
School: Beijing University of Chemical Technology
Course: Chemical Engineering and Technology
Keywords: core-shell structure LDH Fe3O4@CuMgAl-LDH phenol hydroxylation quantum dots Fe3O4-SiO2-QDs-SiO2@IBU-LDH
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 44
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Abstract


With increasing development of the national economy, the versatility of magnetic nanocomposites has aroused wide interest owing to their their special physical and chemical properties. Recently, researchers have prepared a variety of magnetic nanocomposites with specific features, and among the magnetic nanocomposites, the core-shell structured magnetic ones are attracted more interests. In this paper, the core-shell structured magnetic nanocomposites have been successfully prepared involving a Fe3O4 core and a layered double hydroxide shell. We discuss the relationship between the structure and the properties and provide a new vision and new ideas for studying the core-shell structure magnetic nanocomposites. The main contents and innovations are as follows:(1) The magnetic Fe3O4 nanoparticles with different diameters (ca. 200 nm and 500 nm) were prepared by a solvothermal reaction via modulating the initial concentration of [Fe3+] and characterized by XRD, SEM and VSM techniques. The obtained magnetic nanoparticles present spherical and nearly uniform morphology with strong saturation magnetization.(2) A well-defined core-shell structured magnetic nanocatalyst of Fe3O4@CuMgAl-LDH was fabricated via optimizing preparation method and conditions. The prepared nanocomposites presents well-defined core-shell structure involving CuMgAl-LDH coating of ca.50 nm onto the 500 nm Fe3O4core and strong magnetism as 53.69 emu/g. The low temperature N2 adsorption-desorption curve shows an obvious hysteresis loop, indicating that the nanocomposite material has a rich pore structure.The obtained Fe3O4@CuMgAl-LDH nanocomposites was employed in phenol hydroxylation by H2O2 and exhibits high catalytic activity compared with other related catalysts. Under optimal reaction condition the phenol conversion and the efficiency of H2O2 reaches 47.2% and 45.3% over Fe3O4@CuMgAl-LDH, respectively. Moreover after separrtion with a external magnetic field, the activity of the recycled catalyst nearly preserves its initial activity and the basic structure of it unchanged. The mechnism of the phenol hydroxylation and relationship between the core and the shell are discussed base on the H2-TPR and XPS. We proposed that the Fe3O4 core and the CuMgAl-LDH shell are linked via the bond of Cu-O-Fe and Mg-o-Fe. Fe3O4@CMAO at diffierent calcined temperature are obtained by calcined the Fe3O4@CuMgAl-LDH at different temperatures.(3) The magentic fluorescent nanocomposites Fe3O4-SiO2-QDs-SiO2 @IBU-LDH are succsessfully synthesised by coprecipitation method. The obtained nanocomposites presents well-defined core-shell structure involving IBU-LDH coating of ca.10 nm onto the 230 nm Fe3O4 core modified by silica and quantum dots with a silica intermediate layer thickness about 20 nm and strong magnetism as 4.43 emu/g. These results show that the LDH-based core-shell fluorescent magnetic nanoparticles in magnetic targeting drug-loaded drug delivery system has potential applications.

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