Synthesis And Characterization Of Metal Nanoparticles With Controllable Size And Shape

The unique properties and potential applications of metal nanoparticles are mainly determined by the size and shape. So far there have been many methods to prepare metal nanostructures, but spherical nanoparticles are usually the major products. It is therefore a great challenge to develop some simple and effect methods of synthesizing nanoparticles whose size and shape can be controlled at will.The main goal of the present work is to develop a simple and effect aqueous-phase method to synthesize gold and silver nanparticles with controllable size and shape. The synthesis was realized by the reduction of AgNO3 or HAuCl4 with Na3C6H5O7 respectively in the presence of SDSN as a capping agent. This non-template and non-seed method has its unique advantage that control the particle's shape and size by changing the reductant concentration. The role played by the capping agent is to assist the growth of good crystalline of nanoparticles. Their structure, size, shape, and optical and electronic properties were characterized systemically using TEM, HRTEM, SEM, AFM, XRD, SAED, ED, UV-Visible, and SERS. The major results of the thesis are outlined as follows:1. Silver nanoparticles with controllable diameter and aspect ratio were synthesized. The diameter (10-24 nm) of the nanorods or nanowires linearly depends on the reductant concentration; while the aspect ratio (8-150) of these nanoparticles shows logarithm-dependence.2. Gold nanoparticles with tadpole and necklace-shaped were prepared successfully. These nanoparticles possess novel three-dimensional structure, e.g. the size of the nanotadpoles can be controlled to be 12-31 nm (the head width), and the size of the nanonecklaces to be 20-35 nm. They show some novel optical and electronic properties.3. To explain concentration-dependent crystal growth mechanism of gold or silver nanoparticles with different size and shape respectively, we propose two preliminary models. The dramatically shape difference of gold and silver nanoparticles is largely attributed to the different reducing ability of the metal ions and coalescent ability with the capping agent.4. Spherical gold nanoparticles with uniform but controllable size (10-40 nm) were fabricated. AucorePtshell nanoparticles with well-dispersed and controllable size (8-150 nm) were also synthesized by using a seed-induced approach, and the SERS spectra of platinum nanoparticles were obtained.As a consequence, this novel synthetic method is expected to scale up, and will probably develop to a common method for synthesizing other metal nanoparticles with controllable size and shape.