Studies On The Synthesis And Application Of Magnetic Nanocomposites

At present, considerable effort has been devoted to tailor the surface properties of the nanoparticles in order to meet their application requirements, that is "Nanoengineering of particle surfaces". In addition, as one of the important nanomaterials, magnetic nanoparticle has the promising application due to their properties. Considering the above reasons, we focused our research on the synthesis and application of magnetic nanocomposites, and the dissertation consists of the following contents:In chapter 2, Pd/Fe₃O₄ and Pd/(SiO₂/Fe₃O₄) with core shell structure were prepared with the attention to solve the separation problem of nanocatalyst by the magnetic separation technique. And many merit results were obtained:1. Firstly, Pd/Fe₃O₄ and Pd/(SiO₂/Fe₃O₄) nanocomposites were prepared respectively by two procedures "In situ reduction of Pd²⁺ and "the assembly of Pd nanoparticle prepared beforehand". And then the catalytic behaviors of the obtained magnetic nanocomposites were measured by the Heck reaction of the cross-coupling of acrylic acid with iodobenzene. The results shown that those particles performed the good catalytic behavior and could be separated easily from the product mixture, which indicates that the magnetic support such as Fe₃O₄ and SiO₂/Fe₃O₄ has no obvious inhibition on the catalytic site Pd. For example, the TOF of Pd/(SiO₂/Fe₃O₄) catalyst in first run reached 3749 h^-1. Also it was found that the catalytic activity of Pd/Fe₃O₄ nanoparticle decrease with the increase of run times due to the conglomeration of particles. And Pd nanoparticle attached to SiO₂/Fe₃O₄ by the strong coordination of -NH₂ group with the palladium surface leached easily with the increase of run times. In spite of those problems, the above work laid the good foundation on the future research of nanocatalyst.2. During the preparation of Pd/(SiO₂/Fe₃O₄) nanoparticles, the author found the new method toprepare Pd nanoparticles with the size of 2-5 nm by mixing CNCH₂COOK and Na₂PdCl₄ (2:1) for 12h. Here CNCH₂COOK works as reducing agent instead of the conventional NaBH₄ and N₂H₄.H₂O to reduce Pd²⁺ besides the action to effectively stabilize palladium nanoparticles.