Research On Chemical Synthesis Of NiAu Bimetallic Nanoparticles And Thermal Stability

Bimetallic nanomaterials perform much more attractive characteristics such as fascinating selectivity, optical, catalytic activity and magnetic properties in comparison with monometallic nanomaterials. Therefore, they own more extensive applied potentials in various fields including energy, chemical industry, biomedicine. More research efforts have been focused on bimetallic materials because of the distinct nanostructures and properties. With the continuous progress and breakthrough in the research of bimetallic nanomaterials, more and more bimetallic nanomaterials with different component, structures and morphologies have been successfully prepared. Based on the existing synthetic methods and technologies, we devoted ourselves to researching on NiAu bimetallic nanoparticles, including synthesis process, microstructural characterization and thermal stability.1. In this thesis, the Au@Ni nanospindles were synthesized in a mild chemical solution reflux system using oleylamine as both solvent and reductant. Reactant ratio(Ni(acac)3:H[AuCl4]?4H2O) should be adjusted appropriately and added in order of the synthesis system. During the preparation of NiAu nannospindles, various influencing factors such as reactant ratio, reaction temperature, heating rate and surfactants would be thoroughly explored with comparative experiments and the regulation of dynamic parameters. It turned out to make a great difference on dispersion and uniformity of the final sample.2. The structure evolution characteristics of Au@Ni nanoparticles in vacuum and oxidizing circumstances were investigated through in-situ scanning transmission electron microscopy. With an oxidizing-driving multilayer reconstruction mechanism, the spindles structure would translate into Ni@Au@NiO multi-shell structure in the oxidizing condition. However, under the vacuum condition, the Au@Ni nanoparticles transform following four difference stages: polyhedron recrystallisation of Ni substrate; crytal plane-selective segregation of Au atoms; single crystallisation of Ni substrate; surrounding dispersion of Au atoms. The exploration above offers an inspiration for the perspective application in structure thermal stability of Au@Ni bimetallic catalysts by heating processes.3. The structural evolution and reconstruction dynamics of Au@Ni bimetallic nanospindles in three distinct continuous atmospheres are studied by in-situ STEM and DFT simulations. In the oxidization atmosphere, the Au component facilitates separation of oxygen, and induces Ni matrix oxidation, which concurrently promotes the transmigration of Au atoms, thus emerging multi-shell structures which are signified by Ni@Au@NiO. The following hydrogen reduction makes surface reconstruct, yielding fcc-NiAu clusters. More intriguingly in catalyzing cycles, the exothermic excitations released from CO oxidization drive the inverse Au segregation and Ni recrystallization on the particle surface.