Synthesis And Performance In SERS Of Ultrafine Gold Nanowires

Since Haruta discovered that gold nanopaticles had catalytic activity in the low temperature CO oxidation in 1987,intensive research efforts have been devoted to the subject of Au catalysis.It has been found that the size of Au nanoparticle is one of key factors influencing the catalytic activity of gold.Up to date,the study of the synthesis and catalysis of Au mainly focuses on zero-dimensional gold nanoparticles.The ultrafine nanowires(less than 3 nm)with large aspect ratio may be the bridge to connect the macro-catalyst and nanostructure.The diameter of the nanowires is nanoscale,so they can keep the small size effect just like nanoparticles and have high catalytic activity.Meanwhile the length of nanowires is micrometer scale,which can be easily separated from reactions just like bulky materials.Nanowire may be a kind of novel catalyst materials with the high catalytic activity of nanostructure and the easy separation of macro-catalyst.However,there are a few reports about the synthesis and related properties of Au nanowire,which may be due to the problems including poor reproducibility,low yield,poor morphology,and long reaction time etc.in synthesis.In this thesis,we studied the synthesis and growth mechanism of Au nanowires,as well as their performance in Surface-Enhanced Raman Scattering(SERS)and the catalytic application.The main results are described as follows:(1)Synthesis and growth mechanism of Au nanowires:Ultrafine gold nanowires and Au-Ag bimetallic nanowires with diameter size of 2 nm and length of 0.1-10 μm have been synthesized by using oleylamine as the template.This facile method is easy to prepare the ultrafine gold nanowires in a large scale with good reproducibility.By tracking the reaction process,the possible growth mechanism of ultrathin nanowires was proposed,which can be explained by oriented attachment theory.Moreover,we demonstrate a first simple strategy without involving any organic templates to obtain ultrafine Au nanowires with diameter about 2 nm and 200 μm in length on the C-coated Cu grid.For the template-free method,the reaction mechanism may be related to the evaporation of the solvent.The filter paper under the Cu grid substrate absorbed the solvent of the mother liquor along a certain direction,which induces the as-reduced Au nanoparticles line up along the certain direction.When the following HAuCl4 between the Au nanoparticles was reduced,the new-produced Au nanoparticles would adhere to each other and the present nanoparticles to form nanowires.(2)Study on the SERS Performance of obtained Au ultrafine nanowires:A strong Raman enhancement was found with Rhodamine 6G as probe molecule and the Au ultrafine nanowires as substrates.There are obvious peaks appeared even at a low concentration of 2×10-6 M Rhodamine 6G solution,suggesting the potential application of the Au ultrafine nano wires in SERS.