Facile Synthesis and Structural Control of Multi-component Metallic Nanomaterials

Abstract

Noble metal nanoparticles exhibit unique physical and chemical properties that are highly dependent on their size, shape, and chemical composition. During the last few decades, intensive research has been focused on the development of various synthetic methods for producing uniform nanoparticles and the precise control of their size and shape. Recently, multi-component metallic nanomaterials have attracted much attention for their great potential application in catalysis, sensor, and biomedical application. These nanomaterials can have not only the individual characteristics of the different components, but also new and unexpected properties arising from the synergistic effect between them. In this dissertation, facile and structure-controllable synthesis of multi-component metallic nanomaterials were studied. Firstly, Ag-Cu core-shell and alloy bimetallic nanoparticles (NPs) were prepared by a solventless mix-bake-wash method. The simple one-step heating process was assisted by salt powder as a template, obtaining small bimetallic nanomaterials. The particle structure could be controlled by tuning the annealing temperature to generate hetero-structured core-shell NPs or homogeneous alloys. Whereas the as-synthesized Ag@Cu core-shell NPs consist of a core of face-centered cubic (fcc) polycrystalline Ag NPs and a shell of fcc Cu including trace amounts of copper oxides, the AgCu nanoalloy was found to comprise a single-phase NP with the same crystal structure as that of Ag, without the copper oxide species. Cyclic voltammetric measurements confirmed the chemical identification of the surface species and their stability to oxidation. Secondly, rattle-structured nanomaterials composed of a gold nanorod in a mesoporous silica nanocapsule (AuNR@mSiO2) were prepared by a novel solution-based consecutive process. Uniform-sized gold NRs were encapsulated inside a silver nanoshell, followed by SiO2 coating through the sol-gel technique. After selectively etching away the silver inner layer, a rattle-structured nanomaterial was obtained. The AuNR@mSiO2 rattle-shaped nanostructures were highly uniform in morphology, and the inner hollow space and the thickness of the mesoporous silica layer were easily controlled by adjusting the amount of each chemical agent. The drug-loading properties of the nanomaterial and the regrowth control of the core nanoparticles were also studied.