Construction,Mechanism And Performance Studies Of Anisotrotic Noble Metal Nanostructures

In the past few decades,researchers synthesized noble metal nanostructure with various morphologies using different methods.Meanwhile,they also investigated their functions and applications in catalysis,bological markers,medical imaging,and surface enhanced Raman spectroscopy（SERS）.By controlling the morphology,size and other geometric parameters of noble metal nanostructures,people could adjust their physical and chemical properties,and optimize catalytic and optical properties.In this dissertation,we prepared hollow Pt/Au nanostructure,triangular silver nanoplates and Au-Ag nanopyramid based on the anisotropic growth and selective etching.Moreover,their growth mechanism,catalytic and SERS properties were also investigated.Our research mainly includes the following three sections:（1）The preparations of hollow Pt/Au nanostructure.We report a facile method which can be used to synthesize hollow Pt/Au nanostructures with a high density of Pt nanorods.This strategy involves using water-soluble polymer as reducing agent and protective agent,KI as shape-modifier and growth-induced agent,and Au nanoparticles as seeds.Mechanistic study demonstrated that the formation of such nanostructures involved three main steps: the shape transformation of Au seeds from small sized nanopartiles to nanoplates;the selective growth of Pt on {110} of nanoplates;the selective etching on {111} of Au nanoplates.Through adjusting the reaction conditions,spherical Pt nanoparticles with dendrite structure could be prepared.Electrocatalytic oxidization of methanol was used to investigate their catalyticperformance and they exhibited shape-dependent catalytic ability.（2）The controlled synthesis of triangular silver nanoplates via seeded growth.The advantage of this method is that the product can be adjusted through controlling reaction conditions.The coordinating effect of acetonitrile to Ag+ plays important roles.This coordination suppresses self-nucleation of Ag during the growth.Besides,the selective absorption of sodium citrate on {111} facets of the Ag nanoplate seeds facilitates the anisotropic growth of the Ag nanoplates.By tuning the amount of the AgNO₃ and seeds,the size of the triangular Ag nanoplates could be easily tailored.（3）The selective etching of Au-Ag nanorods.We prepared various bimetallic Au-Ag nanorods with different lengths through using seeded growth.Further,we selectively etched the Au-Ag nanorods with propylene diamine and oxygen in air as etching agent,resulting in the formation of Au-Ag or Ag-Au-Ag nail-shaped nanostructure.The effect of temperature,etching agent and other reaction parameters were systematically investigated for figuring out a reasonable mechanism.The surface enhanced Raman spectroscopy（SERS）of the products was tested.Results show that etched products had improved SERS performance.