Controllable Synthesis Of Metallic Nanostructures And Their Properties

As the development of technology and science, in many areas such as biological technology, information, environment, energy, advanced manufacturing technology and even national defense all need more contribution of traditional metal nanostructures. Among the metals, great efforts have been devoted to Ag, Co and Pt due to their unique properties. Meanwhile, many reports indicated that mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. In this paper, we studied the controllable growth of Ag dendrites and its Roman scattering (SERS) activity towards rhodamine B; and we studied the Co/Pt bimetallic nanostructures and its catalytic properties; also, we studied the growth of Ag nanowires with controllable size. As following:Large-area, homogeneously distributed lying dendritic silver nanostructures were prepared on a Pt film substrate using a square-wave electrodeposition technique without any additive. Individual dendrites were found to lie on the substrate and have a three-dimensional structure. The number density increases with electrolyte concentration (C) and loose films composed of overlapping dendrites were obtained at high C. The square-wave potential and its frequency determine the formation of the dendritic structure. The Ag dendrites exhibit high surface-enhanced Raman scattering (SERS) activity towards rhodamine B. The SERS activity of the dendrites is comparable to that of Ag films consisting of overlapping dendrites. It is much higher than that of Ag nanoparticles (NPs), and even higher than that of NPs’aggregates.Platinum-cobalt bimetallic structures have been synthesized in high yield via a galvanic replacement of Co dendrites in an aqueous K2PtCl6solution at room temperature. Increasing the K2PtCl6concentration results in different surface morphologies. Starting from furry coatings, a higher Pt/Co ratio leads to very rough surfaces built with upright standing nanoflakes, and finally a relatively smooth, cauliflower-like cover is obtained. The growth is discussed as the interplay of several mechanisms like the concentration driven nucleation, consumption of Co substrate, stoichiometry of the replacement reaction, and the electron transfer through the growing flakes. While the mono metallic structures are catalytically inactive towards the reduction of4-nitrophenol by sodium borohydride, the catalytic activity of the bimetallic structures is quite high and optimized by a Pt atomic percentage of27%. This indicates a catalytic role of the bimetallic interfaces.Silver nanowires with adjustable diameters were rapid synthesized via a microwave-assistant method by adding Na2S·9H2O into the solution. The formation of Ag2S colloids helped to reduce the concentration of free Ag+at the initial step, and subsequently release Ag+into the solution as the Ag+reduced to Ag0atoms. The superheating solvent and the hot surfaces by microwave heating also accelerated the reduction of silver precursors and the nucleation of the silver cluster, leading to uniform silver nanowires. By adjusting the concentration of Na2S·`9H2O, silver nanowires with controllable size can be obtained. Then Pd nanotubes were synthesized and exhibited good catalytic activities in the degradation of azo dyes and the reduction of4-NP by NaBH4, due to the nanostructures and rough surface.