Assembly Nanostructures Of Magnetic Metals Of Nickel And Cobalt: Controlled Synthesis And Properties Study

The work in this dissertation could be divided into two parts.In the first part, solution-based routes assisted by complexants were developed to realize the chemical synthesis and simultaneous assembly of isolated nanoparticles into hierarchical nanostructures. We established a new route for the synthesis of magnetic assembly nanostructures without any surfactants or external magnetic field, which was successfully used in the fabrication of metallic nickel and cobalt hierarchical nanostructures. In the one-step solution chemical reduction method, nickel and cobalt assembly nanostructures with different-shapes were created by controlling the crystal growth with various complexants, together based on the magnetic interactions of magnetic particles. In the hydrogen reduction route, metallic nanoarchitectures were fabricated by hydrogen reduction of the hydroxides precursors, which were prepared first with the assistance of different complexant agents. The details are summarized as follows.1. Prickly nickel microwires assembled by nanothorns were fabricated from the anisotropic growth of metallic nickel nanocrystals and their simultaneous assembly assisted by citrate. By adjusting the reagent concentrations and temperature, microstructures of the nickel wires were modulated. Formation of the assembly nanostructures could be ascribed to the kinetic control of the reaction process and the inherent magnetic interactions between the magnetic particles. Such a complexant-assisted method could be extended to the other complexing systems, which was proved as a general route for the synthesis of nickel microwires. As-prepared nickel assembly nanostructures showed microstructure-dependent magnetic properties and catalysis for the growth of carbon nanotubes in pyrolyzing acetone. Using the nickel wires as in-situ reductant, prickly Ag_shell-Ni_core wires were obtained through a simple transmetallation reaction. The surface modification with silver showed little influence on the morphology and magnetic properties of the nickel wires, while greatly improved their oxidation-resistance and blocked their catalysis for the growth of carbon nanotubes in pyrolyzing acetone.