Study On The Morphology-Controlled Synthesis Of Silver Nanomaterials And Their Applications

The nanomaterials with nanometer sizes in one, two or three dimensions have the unique physical, chemical and mechanical properties that are neither those of bulk materials nor those of molecular compounds. And they have been exploited for the extensive potential applications in optics, electronics, magnetics, catalyst, sensing, biomedicine, microreactor, etc. These peculiar and fascinating properties of nanomaterials strongly depend on the particle size, the shape and the interparticle distance of the nanoparticles, thereby morphology-controlled preparation of nanomaterials is very important and significative. Silver nanostructures is one of such most important nanomaterials studied in this recent decade, because the bulk silver exhibits the highest electrical and thermal conductivities among all metals and the silver nanostructure displays the excellent surface plasmon resonance property. Nowadays a great variety of effective chemical methods have been demonstrated to be able to prepare silver nanostructures. Though no simple method has yet been found to fabricate silver nanostructures with arbitrary shapes, polyol process supplies the best way. Until now, polyol process has been succeed in preparing uniform silver nanostructures with various morphologies, such as wires, belts, cubes, spheres, triangular plates and bipyramids. However there are still many mysteries in the actual formation mechanism of silver nanostructures, which bring puzzles in mass production and still need more fundamental studies. Based on the newest international researches, the studies on the morphology-controlled synthesis of silver nanostructures, size-depended properties, and their application in materials chemistry and analysis are the chief aims in this these.The normal two-step polyol process including the introduction of preformed seeds (Pt) and the inducement of poly(vinyl pyrrolidone) (PVP) has been developed as a powerful approach to synthesis silver nanowires. Here, the silver nanowires without other metal elements as impurities were synthesized through two-step polyol process under shielding gas atmosphere. It is demonstrated that the first seeding step is critical to obtain silver nanowires as principal product, and it is found that the shielding gas atmosphere not only improves the repeatability of experiments but also affects the morphology of final product, for example: nanocubes could be prepared with the shielding of hydrogen gas, which would hardly appear with the shielding of argon or air. This work supplies some new evidences to explain the actual grow mechanism of silver nanowires.Uniform silver nanorods have been synthesized through a nanowire-seeding, multistep polyol process in high concentration reaction system, successfully. In this developed three-step polyol process, the silver nanowires are used as seeds in step 3 to radial grow into nanorods with larger diameter and similar length in high concentration reaction system. It is presumed that desorptionof PVP from the surface of silver is the critical factor to cause the dominant regrowth of wirelike seeds towards radial direction but not axial direction. More details of the radial growth mechanism have been discussed. This synthesis strategy will be significant in the large scaled preparation of nanomaterials.A novel one-step polyol process by using control agents is reported. These control agents could be classified into three types: molecule, metal cations, and inorganic anions. It is presumed that the control agents herein could influence the initial nucleation and therefore the morphologies of final products through forming silver salt colloids or varying reduction rate of silver ions. In these studies, a novel, effective strategy named "seed catalysis" has been discovered here to synthesize silver nanostructures with controllable morphology by using Na2S as control agent. The formed Ag2S colloids in the initial reaction could act as both seeds and catalysts, and thereby, the morphology of products is well controlled by the concentration of Na2S added, and the growth of silver crystal is accelerated by catalysis of Ag2S. The evolution of silver nanowires is also investigated by electron microscopes and UV-vis adsorption spectra, and then it is suggested a reasonable mechanism to explain the role of Ag2S seeds.Finally, this thesis investigates the structure, optical, and corrosion properties of silver nanostructures with different morphologies, and studies their applications in preparing hollow platinum nanostructures and electrical conductive composites, and researches on the surface enhance Raman scattering.