Shape-controlled Synthesis And Growth Mechanism Of Au, Pt Nanostructures

Due to their unique physical and chemical properties, noble metals, such as gold, silver and platinum have been regarded as crucial meaterials in economy, national defence and the development of society. The noble metal materials in nano scales show remarkable quantum size, surface and intersurface effects, thus the colligation of these effects will greatly extend the application of these noble materials in other fields.The properties of noble metal nanomaterials are size and shape dependent, thus the size and shape controlled synthesis of noble metal nanomaterials is one of the most focused subjects in the field of nanomaterials research. In the case of our research, we demonstrated the synthetic methods for the synthesis of gold, platinum and platinum/lead nanoparticles with different size and shape by using UV-irradiation and thermochemistry reduction method in water and organic system.The effects of solution pH on the growth of gold nanoparticles during the UV irradiation were investigated. The results showed that in the solution with lower pH values, the initial formed nanoclusters directly grow to nanopartilces with polydispersed size and shape. When the solution pH values were increased to around neutral condition, the growth of particles experienced a process of nucleation-aggregation-disintegration-growth and accompanied with the transformation of particle sizes and shape, which can be characterized by SPR spectra. At high pH values, the growth of particles still obeyed the rule of nucleation-growth process. The growth mechanism of the gold nanoparticles under different solution pH conditions was further discussed.When the irradiation was performed with a continuous method, the gold nanoparticles with diameter about 2 nm and nanoplate could be synthesized in the presence of both PVP and citric acid or only citric acid with a high concentration. At a lower citric acid concentration, the nanoparticles grow from spherical to 3-D coralloid structures and then transform to networkes. After a long time irradiation, the as-formed networkes grow to perfect nanoplates. A novel self-repaire mechanism for the growth of gold nanoplates was presented.The thermochemical reduction metal precursors in organic media were one of the effective synthetic methods for metal nanoparticles with special structures. By changing the experimental parameters, such as reaction temperature, reaction time, capping reagent and reducer, the Pt nanoparticles with different surface types was obtained. Under an optimized reaction condition, the 3-D multipod Pt nanoparticles were synthesized. This kind of nanoparticles could self-assemble to form porous netlike Pt nanostructures which can be used as fuel cell catalysts.In the case of fuel cell, one of the effective methods to improve its performance was using the Pt based alloy nanoparticles as catalysts. The Pt/Pb nanorods with cubic and hexagonal phase were synthesized with thermochemistry reduction method in organic solution. The results showed that the initial formed nanorod was Pt riched cubic phase, and then they transformed to hexagonal phase with the increase of reaction time and temperature. A mechanism based on the competing factors for the formation of either kinetically or thermodynamically stable PtPb nanorods was discussed.