The Synthesis And Characterization Of Metal Nanorings

Metal nanomaterials have many special properties as compared to their bulk counterparts.These unique properties are closely correlated to their size, morphology, chemical composition and crystalline phase. A variety morphologies of metal nanostructures have been successfully prepared to date such as metallic nanorod, nanosphere, nanowire. However, there has little research on ring-like shapedmetal nanostructures, which may give rise to special shape dependent properties and promote the device performance. Therefore, it is very interesting to fabricate various metal nanoring and investigate their properties.In this thesis, novel Fe@SiO2nanocomposites, Cu andAg nanorings were prepared using hydrothermal method which is one of the most popularmethod for nanopartiles’ synthesis. By using the different synthetic strategies such as different surfactants, temperature etc., we are able to prepare different metal nanorings. We investigated the growth mechanism of these nanorings and further characterized their crystalline structure, morphologies and chemical composition. These nanorings are expected to provide unique shape dependent properties, which have great potential in a wide range of applications. The main research work in this thesis is as follows:(1) The dispersed a-Fe2O3@SiO2composite structure was synthsized through coating SiO2onto a-Fe2O3nanoring using sol-gel method. We successfully achieved the controllable synthesis of α-Fe203@Si02composite nanostructures. By investigating the influences of the reaction conditions on the growth of core-shell hybrid structures, and the optimal synthetic conditions have been obtained. Fe@SiO2nanostructures are then prepared by H2reduction of Fe2O3@SiO2composite structure. After that, the alkalis (NaOH) with different concentrations were used to treat aggregated Fe@SiO2nanoparticle and resulted in free-standing Fe@SiO2nanoparticles. The results indicate that the outer diameter, inner diameter and thickness of α-Fe nanoring is80nm,10-12nm and40nm, respectively.(2) Cu nanorings were prepared by hydrothermal method. The high productivity (more than30%-50%) of the fabrication of Cu nanorings was achieved through screening the dominant factor of growth process and finding out the optimal condition. Meanwhile, the formation mechanism of the Cu nanorings and nanosprings was also proposed as following "three steps" growth:1. the formation of Cu nanoparticles,2. the bending of nanowires and3. eventually the fusion of two free ends of the nanowires together. Particularly, inorganic NaBr plays a critical role in the high yield of Cu nanoring/spring,(3) The Ag nanorings were successfully high-yield synthesized by hydrothermal method. The possible growth mechamismwas studied and the crystalline structure and morphology are characterized by of XRD,SEM.