Controllable Synthesis And Characterization Of Precious Metals (Au, Ag) Nanomaterials

Anisotropic noble metal (Au and Ag) nanoparticles are widely studied because their unique electronic, optical, and catalytic properties, which make them have many potential applications in defence science and technology, fine chemical, catalytic, medical science and so on. Due to the small size of the nanoparticles, slightly changing the reaction parameters, there is no doubt that will bring great changes on their structure and functions. Therefore, the exploration of the morphology, size, scale controllable synthesis of noble metal nanoparticles, and study of their microstructure and properties are very important for the development of the novel functional properties.In this dissertation, we develop simple and effective preparation methods for solution-phase synthesis of noble metal nanomaterials with controllable size and shape. We characterize and analyze the morphology, size, crystal composition and crystal structure, etc. of the nanomaterials by X-ray diffraction (XRD), UV-vis absorption spectrum (UV), scanning electron microscope (SEM), low-resolution and high-resolution transmission electron microscope (TEM), and Raman scattering spectroscopy, etc. We also explore the special properties of the obtained nanomaterials. Through exploring their growth mechanism, we reveal the growth rule the different morphology and size of nanoparticles, which make a contribution to research and development of noble metal nanomaterials. The main results and conclusions of the dissertation are as follows:(1) Single crystalline gold nanoplates with micrometer-scale sizes that are tens of nanometers in thickness were synthesized by one-pot heat-reduction of HAuCl4 with the disodium salt of ethylenediaminetetraacetic acid (Na2EDTA) in the presence of hexadecyltrimethylammonium bromide (CTAB) in aqueous solution. The morphology and structure were characterized and analyzed on SEM, XRD, TEM and HRTEM. The application of the as-prepared nanoplates in surface-enhanced Raman scattering (SERS) spectroscopy was investigated by using 4-aminothiophenol (PATP) as probe molecules with a source of the laser radiation of 785 nm. It was found that PATP can be oxidatively transformed into 4,4’-dimercaptoazobenzene on the surface of Au nanoplates during the SERS measurement.(2) The flower-like Ag microcrystal with nanoscale plate petals and hierarchical Ag microcrystal are synthesized by the ascorbic acid reduction method. The controllable synthesis of the two kinds of microcrystals is achieved by controlling the mole ratio of reactants in aqueous solution at room temperature. We characterized and analyzed the products by various analysis methods, and test the catalytic and SERS propertied of the two kinds of silver microcrystals. We further explore the morphology evolution of silver particles by changing the ratio of the reactants.(3) At room temperature, sodium citrate used as a stabilizer, the "branched" Au flowerlike nanocrystals was synthesized by reducing HAuCl4 with hydrogen peroxide. The shape-controlled "branched" Au nanocrystals were obtained by changing the experimental conditions. TEM and UV-vis absorption spectrum were mainly used to characterize and analyze their size, morphology, crystal structure, and composition. Also, the properties of catalytic and SERS of the as-prepared Au flowerlike nanocrystals were investigated.