Study On The Chemical Solution Synthesis Of Ni Nanocrystals And Ni-Au Hybrid Nanocrystals

Research on synthesis of Ni nanocrystal is of great importance due to their potential applications in catalysis,magnetics,and information storage.At present,the morphologies of successfully prepared Ni nanocrystals reported in the literature are mostly spherical,The preparation of non-spherical Ni nanocrystals is more difficult and so that the related reports are very limited.In addition,the combination of Ni nanocrystals with specific shapes and noble metals with surface plasmon resonance properties is an attractive system.In this thesis,Ni nanorods with five-fold twinned structure and Ni nanocubes were prepared by organic liquid-phase method.Ni-Au hybrid nanocrystals with dumbbell-like structure were synthesized by thermal injection method that used Ni nanocrystal seeds which were prepared in the first step.The factors affecting the formation,magnetic properties and formation mechanism of Ni nanocrystals and Ni-Au hybrid nanocrystals were discussed in details.After analyzing the experimental results,the following conclusions were obtained:(1)Using Ni acetylacetonate as a precursor,oleylamine as a solvent and reducing agent,and tungsten hexacarbonyl as a nucleation inducer,two types of nanocrystalline Ni nanocrystals were synthesized:five-fold twinned nanorods and nanocubes.The results show that the introduction of trace amounts of tungsten hexacarbonyl can reduce the reaction temperature of Ni acetylacetonate in oleylamine system,and finally will reduced the reaction rate.When the hexacarbonyl tungsten is changed from a high concentration to a low concentration,the morphology of the product will change from sheets to nanorods or nanocubes.By controlling the reaction time and concentration of tungsten hexacarbonyl,nanocrystals mainly with cubic and rod-like morphologies can be obtained.Considering the role of tungsten hexacarbonyl,the formation mechanism of Ni nanocrystals with two main morphologies was presented.(2)Based on the preparation of Ni nanorods in the first step,Ni-Au hybrid nanocrystals with dumbbell-like structure were synthesized by thermal injection method using[(C6H5)3P]AuCl complex as Au precursor.Ni-Au hybrid nanocrystals have Ni in the stem part and Au in both ends.By changing the type of Au precursor,the concentration of[(C6H5)3P]AuCl complex,the injection temperature,and the quenching process after injecting[(C6H5)3P]AuCl complex,it was found that the dumbbell-shaped Ni-Au hybrid nanocrystals could be synthesized only when the appropriate concentration of[(C6H5)3P]AuCl was used in a quenching process.(3)The results of magnetic measurement show that the five-fold twinned nanorods and nanocubes are ferromagnetic at room temperature.Both nanorods and nanocubes have greater coercivity than commonly spherical Ni nanocrystals.Meanwhile the saturation magnetization of nanorods is larger than that of nanocubes.Ni-Au hybrid nanocrystals also exhibit typical ferromagnetic properties.Comparing with pure Au nanoparticles,UV-vis absorption spectra analysis of Ni-Au hybrid nanocrystals revealed that the surface plasmon resonance peak of Ni-Au hybrid nanocrystals was red-shifted and broadened.