Preparation, Properties And Applications Of Noble Metal Nanoparticles

Interest in noble metal nanoparticles stems mainly from their size and morphology dependent physicochemical properties, making them potential candidates for a wide variety of applications in electrics, mechanics, sensor, magnetics, optics and catalyzer. The shape and size are key parameters of metal nanoparticles because of their close relation to the chemical and physical properties. Many scientists'ultimate goal is to pursue readily-operationalized methods to synthesize high-yield and morphology-controlled noble metal nanoparticles at low-cost and mild conditions. The purpose of this dissertation is to study the preparation of sliver and gold nanoparticles by chemical techniques. With TEM, XRD, SEM, SERS and UV-vis, the growth mechanism, influencing factors and related physicochemical properties of obtained noble metal nanoparticles have been studied.A facile method to prepare novel gold nanoplates with concave centers in hexagonal liquid crystal systems at mild temperature has been established. The bubbles existing in this system after stirring and centrifugation provide sufficient O2 to couple with the Cl- dissolved in water domains to form the O2/Cl- pair. O2 possesses high electrochemical potential, which is sufficient to oxidize Au0 to Au+ or Au3+ ions. The oxidative etching process is proposed to explain the formation of the novel nanostructures, and the glycine is the key factor in the reaction. Such novel nanoplates with concave centers of regular shapes exhibit better electro-catalytic activity and could find potential applications in electronics and catalysis.Multi-branched gold nanostructures have been synthesized through a simple one-step method in TBAB aqueous solution. This method requires simple operation and mild temperature. Most of obtained particles have more than six sharp branches and the distance from the center to the branch tip is (100±30) nm. The growth mechanism is based on the relative weak adsorption capacity of TBAB, which leads to the incompletely covered gold surface. There follows the growing process of gold nanoparticles on the uncovered gold surface and branches appear. In addition, positively charged TBAB layer prevents the branches from aggregating with each other, and is favorable for the branch growth. Raman measurements show that they are active SERS substrates for probing PATP and probably other analytes. The multi-branched nanostructures will provide new structural diversity for the applications in biological tagging, optoelectronics, SERS and catalysis. In SDS-TBAB system, with the help of TBAB, micelles are formed at much lower concentration of SDS (0.4 mmol/L), and short branched gold nanoparticles are the main products.Multi-branched gold nanostructures have been synthesized readily with a high yield by using low-cost melamine as the capping agent. UV-vis analysis indicates a broad absorption in the range of 500-800 nm due to the non-uniform morphology of gold nanoparticles.Silver tangled nanowires and dendritic structures are readily synthesized by reducing silver nitrate with different concentrations of ascorbic acid in a polyacrylamide aqueous solution at mild conditions. Polyacrylamide provides a soft template for the growth of tangled silver nanowires. During the initial stage, silver nuclei are formed quickly and simultaneously adsorbed by polyacrylamide with a tangled structure. As the time is prolonged, the nanoparticles contact with each other and grow along the polymer chain, leading to the formation of tangled silver nanowires. The tangled nanowires will provide a new structure for the application in surface enhanced Raman scattering.