The Controlled Syntheses Of Au/ag Bimetallic Nanostructures And Their Surface-enhanced Raman Scattering Properties

Noble metal nanocrystals with two or more components have attracted increasing interest due to their multifunction and considerable potential applications in biotechnology,imaging,sensing,catalysis and surface-enhanced Raman spectroscopy(SERS).Their shape and size control is critical to the studies of applications.Therefore,shape and size control have received the greatest attention.Centering the controlled synthesis of Au-Ag bimetallic nanocrystals,our research mainly includes the following three sections:(1)Iodine ion-assisted controlled synthesis of Au nanoplates.Single-crystal Au nanoplates with triangular or hexagonal shape were prepared in Diethylene glycol(DEG)solution.The structures of the triangular Au nanoplates were investigated using scanning electron microscopy(SEM)and atomic force microscopy(AFM).It was found that the edge length of nanoplates ranging from 0.6 to 13?m can be tunned(Thickness is 20 nm).Results show that Iodine ion(I~-)plays important roles in the formation of Au nanoplates and the optimal molar ratio of I~-and HAuCl4 is 1:50.(2)The reconstruction of Ag-Au-Ag nanorods by hydrogen peroxide(H2O2).Short Ag-Au-Ag nanorods were synthesized by using Au decahedrons as seeds,and then Ag-Au-Ag nanobipyramids and nanocups were prepared through etching Ag-Au-Ag nanorods with H2O2.We demonstrated a rapid shape transformation from short Ag-Au-Ag nanorods to long Ag-Au-Ag nanorods and Au@Ag nanoplates with Au decahedron on one side under H2O2.Besides,we studied the influence of reaction conditions,such as seed size,the concentration of H2O2.Moreover,we designed experiments to explore its growth mechanism.Results show H2O2 has determining effect on the shape transformation.This new synthetic route can not only help to better understand the growth mechanism of Au and Ag bimetallic heterostructures but also promote the research in anisotropic noble metal nanostructures.(3)The preparations of bimetallic Au/Ag nanorods.Au-Ag nanorods and Ag-Au-Ag nanorods were prepared through using BDAC as capping agent and Au penta-fold twinned nanorods as seeds.We studied the influence of reaction conditions,such as,temperature,precursor concentration,the concentration of AA.It was found that slow rate of reduction of AgNO3 in the presence of low AA was critical in producing Au-Ag nanorods.By tuning the amount of the AgNO3,the length of the nanorods could be easily tailored.