Abstract
Synthesis of Pd Nanorods and Branched Particles by a Seeding Growth Approach In this thesis work, we observed the effects of oxidative etching on the Pd seeds. Two synthetic methods of Pd seed solution were demonstrated to block the oxidative influence: the CTAB-capped seeds were prepared under nitrogen and the TSC-capped seed solution was generated by substituting the capping agent to trisodium citrate (TSC). Both the approaches can successfully extend the lifetime of Pd seeds from initially fifteen minutes to several days. Via the following seeding growth in the presence of Cu(OAc)2, we obtained Pd nanorods by using the CTAB-capped seeds. From the TEM characterization, we conclude that the uniform Pd nanorods have an average length of 130 nm and exhibit a penta-twinned structure. The introducing of Cu2+ cations has also been found the key factor for increasing the nanorod yield and this could be referred to the underpotential deposition (UPD). In addition, when the TSC-capped seeds were applied to the seeding growth, a rarely seen Pd branched particles with an average size of 30 nm were obtained. The formation of these unusual Pd nanostructures may be attributed to the strong binding of TSC on the surface of the Pd seeds. Seed-Mediated Synthesis of Controllable Ultrahigh Aspect Ratio Gold Nanorods The three-step seed-mediated growth method has been widely used for growing gold nanorods with high aspect ratios, however few reports are available for tailoring the nanorod length to micrometer scale. In this study, gold nanorods can be extended to 1 μm in length by growing the seeds in a growth solution containing nitric acid. By increasing the concentrations of nitric acid, gold nanorods with different aspect ratios of 23, 35, 38, 49 can be generated. The addition of nitric acid could apparently retard the reaction, especially in concentrated ones, and possibly allows a better control in early stage of the growth. In the presence of the worm-like micelle of CTAB created by using nitrate anions as counter ions, the gold seeds grow into long nanorods. Another possible factor for the growth of high aspect ratio nanorods may be contributed by the chloride－enhanced oxidizing strength of nitric acid. Because the particles may serve as primary structure for oxidative etching due to the twinned defects, as a result, they may re-dissolve into the solution. That’s why we observed that main byproducts converted from initially spherical particles to gold nanoplates for the nanorods prepared in concentrated nitric acid.