Study On The Morphology-Controlled Synthesis Of Metal Nanomaterials

Metal nanomaterials have unique physical and chemical properties different from their bulk materials, and have widely potential applications in optics, electronics, magnetics, catalyst, sensing, biomedicine, etc. These peculiar and fascinating properties of nanomaterials strongly depend on the size and the shape of the nanoparticles, thereby morphology-controlled preparation of nanomaterials is very important and significative. Nowadays a great variety of methods have been used to obtain metal nanostructures, and it has been proved that polyol process is the best way. Up to now, people have prepared lots of uniform metal nanostructures with various morphologies by using the polyol process, such as nanowires, nanocubes, triangular nanoplates, nanobipyramids, and so on. However, polyol process is rigorous with the experimental conditions and the experimental temperature is high(¹60°C).We studied the shape-controlled synthesis process of nanomaterials in aqueous solution at ambient temperature, in order to find a facile and energy-efficient approach to prepare metal nanomaterials. On the basis of the recent research, we mainly studied one-step crystal growth method and three-step crystal growth method to synthesize silver nanomaterials in the assistance of the crystal seed. We also studied shape-controlled synthesis of copper nanomaterials. Different experimental conditions were performed to study their influence on the morphology of the product, and the possible reaction mechanism accounting for the anisotropic growth of crystal was studied too.The first part of this dissertation is about the synthesis of silver nanomaterials through a one-step crystal growth process in the assistance of the crystal seed. In this process, we found that the characteristics of the products such as the shape, yield and size were influenced by the different reacting conditions: The main product with branched structure, width about 2um, length about 7um, was obtained by adding seed solution 10ml, as well as NaOH 1ml; numerous branched nanostructured materials coexistent with a spot of nanoparticles were obtained when the concentration of CTAB was comparatively large.The second part of this dissertation is about the synthesis of silver nanomaterials through a three-step crystal growth process in the assistance of the crystal seed. In this process, we obtained triangle silver nanoplates in the presence of cetyltrimethylammonium bromide (CTAB) and silver seeds. The product was purified by centrifugation and characterized by transmission electron microscopy (TEM) and scanning electron microscopic (SEM). Triangle silver nanoplates with a diameter of 150 nm and an average thickness of 30 nm were synthesized when the seed solution added to the reaction system was 0.5ml. The formation mechanism of triangle silver nanoplates was studied by simple varying the concentrations of different reaction components or substituting them with other counterparts. It was found that the shape of the resultant silver nanomaterials have close relationship with the amount of the crystal seed and that the CTAB molecules' absorption on the surface of the (111) basal plane of these single-crystal nanoplates was an important reason to form the silver nanoplates.The last part of this dissertation is about the shape-controlled synthesis of copper nanomaterials. Copper nanowires and hexagon copper nanoplates were prepared by reducing CUNO₃ with N₂H₄·H₂O in the presence of EDA and in aquous solution at ambient temperature. Small copper nanoparticles formed first in the reaction. Due to the direct action of ethylenediamine, these small copper nanoparticles grow up to nanowires or hexagon nanoplates at different experimental conditions. The products were purified by centrifugation and characterized by transmission electron microscopy (TEM). The well-defined copper nanowires had the diameter about 85 nm, the length tens of micron, and the diameter of the hexagon nanoplates was about 300nm. It was found that the shapes of the resultant copper nanomaterials were highly depended on the reaction temperature and the adding amount of EDA.