Electrochemical Synthesis And Property Of Noble Metal Nanostructures

1. Controllable Electrochemical Synthesis of Silver Dendritic Nanostructures and Their SERS PropertiesAg dendritic nanostructures have been fabricated on FTO covered glass substrates by the electrodepositon method and have been used as SERS substrates which exhibit extremely high SERS activity. An advantage of the prepared method reported here is that the size, shape, and branch density of the silver dendrites can be varied by the applied potential, the surfactants and the concentration of AgN03. The general trends in the formation of the structures have been also identified. The dendrite surfaces can therefore be precisely tailored to tune the interparticle spacings and surface plasmon modes to match the requirements of the SERS experiment. The Ag dendrites prepared in PVP solution with diameter of 60-100 nm and many sub-10 nm interparticle spacings exhibit much better surface enhanced Raman scattering than those dendrites with diameter of 20-50 nm and interparticle spacings larger than 10 nm prepared in mixed PVP/citrate solution, which was able to clearly detect rhodamine 6G concentrations up to 10-10 M. Alloy or composite dendrites for further applications could also be prepared by this easy controlled electrodeposition method.3-D flower-like microstructure deposited at low driving force follows diffusion controlled growth and deposition occurs by an instantaneous mechanism. Once all of the nucleation sites are occupied, further increasing the deposition time would only increase the size of the nanocrystals and not their number density because no new nucleation sites are created. Individual flowerlike Ag particles were investigated by optical microscopy. Both sensitivity and reproducibility can be found at the same time.2. Electrodeposition Pd/Cu Bimetallic Nanotubes and Their Application in Nitrate Electroreduction.We have synthesized Pd/Cu bimetallic nanotubes and nanorods in AAO membranes by a one-step coelectrodeposition. Whether nanotubes or nanorods would be finally formed is determined by the applied potential. Fast deposition induced by a higher negative potential can deplete metal ions near the end of a tube in a channel of the membrane, thus the deposition is dominated by ions diffusing to the growth sites, which results in formation of nanotubes. Contrarily, the alloy nanorods are formed in a deposition-dominated process at a lower negative potential. The Pd/Cu nanotubes are formed by Pd and Cu nanoparticles. Electrochemical measurment demonstrated that the Pd/Cu bimetallic nanotube electrode is less sensitive to hydrogen poisoning compared to Pd/Cu films though the catalysis of films was better at the low potential. The Pd/Cu bimetallic nanotubes were oxidized to uniform PdxCu1-xO nanotubes after the bimetallic nanotubes exposed to air for six months.3. Synthesis of sub-10 nm Cu2O Nanowires by Poly(vinyl yrrolidone)-Assisted ElectrodepositionOrdered sub-10nm cuprous oxide nanowires were synthesized by electrodeposition in anodic aluminum oxide (AAO) membranes assisted with poly(vinyl pyrrolidone) (PVP) as soft templates. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy demonstrate that a nanowire has a core of Cu2O and a thin shell of CuO. The formation of the copper oxide was attributed to the oxidized process of Cu nanowires.The formation of ultrathin nanowires is attributed to the arrangement of the PVP in the channels of AAO membranes under an electric field. The diameter and the length of the nanowires depend on the applied potential in the electrodeposition. PVP is the key of the formation of ultrathin nanowires. The growth of the ultrathin nanowires also depends on the concentration of CuCl2·2H2O, and the confinement of the channels in the AAO membrane. UV-vis absorption spectroscopy shows the quantum confinement effect of the Cu2O nanowires.