Preparation, Regulation And Performance Characterization Of Gold And Alloy Nanocrystals

Nanomaterials have broad application prospects on national defense, electronics, chemical industry, metallurgy, light manufacturing, aviation, ceramics, nuclear technology, catalyst, medicine because they have excellent mechanical, electrical, magnetic, optical, chemical activity, catalytic and superconductivity properties due to their unique surface effect, quantum size effect and macroscopic quantum tunneling effect, and so on. Nanotechenology has been one of the most front and hot topics. Nobel metals such as gold, silver, and copper, which combined their chemical and physical properties with nanotechnology, have shown attracting potential applications because of their outstanding properties.Gold nanocrystals (Au NCs) have attracted much attention because of their potential applications in many fields such as optical materials, photocatalysis, microelectrode reactions, sizing agent, biological, medicine, catalyst and microelectronics. Au NCs which was called key factor of green nanotechnology has been the bright phearl of nanotechnology. The difficult, hot and front point of nanomaterials is the preparation of nanocrystals under control. It is expected to control the shape and size of nanocrystals. There are many methods to synthesis the Au NCs and great improvement have been achieved due to the investigation of dynamics. Proper means can be chosen depending on the environment, requirement and purpose. The morphology which has been reported of Au NCs includes spherical, triangle, hexagon, cubic and rod. Compared with uniform and monodisperse spherical nanocrystals, gold nanorods (Au NRs) is difficult to be synthesized with controlled morphology and size.We prepare Au NRs with seed-mediated methods, which reduce the gold ions. A series of factors on the morphology and size of Au NRs have been studied. It has been demonstrated that the concentration of CTAB has great effect on the Au NRs. It is difficult to prepare Au NRs under low concentration of CTAB and the yield could be reduced if the concentration of CTAB is excess. The concentration of silver ions is also quite important on the formation of Au NRs. The aspect ratio is small if the concentration of silver ions is too low and many spheres will be formed if the concentration of it is too high. The major function of AA to reduce gold ions and it has little effect on gold nanorods if only the amount is enough. The plasmon resonance could be tuned between 640nm and 833nm, and the aspect ratio could be tuned between 2.27 and 3.52 by controlling the concentration of gold ions. The morphology and plasmon resonance could be tuned between sphere and rod by controlling the iodide. Moreover, the amount of seeds and stirring time has little effect on Au NRs.Size, morphology, structure and component are key factors, which could affect the optics, electrics, magnetics and catalysis properties of Au NRs. We investigate the effect of iodide and silver ions on Au NRs during the overgrowth of it. It has been discovered that dumbbell-like Au NCs could be produced if there exists iodide in the growth solution and dogbone-like Au NCs will be gotten if silver ions exist. The mechanism has been explored by adsorbing of iodide and Under Potential Deposition (UPD) theory of silver.The morphology and plasmon resonance could be tuned between dumbbell-like and dogbone-like Au NCs by. controlling the concentration of iodide and silver ions when they exist simultaneously in the growth solution. It was discovered that small amount of iodide is benefit for the forming of dogbone-like nanocrystals. We have succeeded in tuning the third plasmon resonance by controlling the aspect ratio of dogbone-like Au NCs. When star-like Au NCs with four horns was formed, the intensity of the third peak could exceed the longitudinal plasmon resonance. The plasmon resonance of Au@Pt NCs could be tuned between 800nm and 955nm by controlling the amount of platinum.A series of NCs such as Au@Au-Pt,Au@Au-Pd and Au@Pt-Pd which have excellent catalysis properties have been prepared and the performance of them on oxidizing methanol have been explored by cyclic voltammograms (CVs).