The Study Of The Chemical Synthesis Of Au And Ag Nanosized Structures And Their Optical Properties

Noble metal nanostructures take on surface plasmon resonance (SPR) absorption under irradiation of incident light, thus show various potential applications in the fields of embellishment, biomedical sciences, sensing detection, Surface Enhanced Raman Scattering (SERS) substrates, laser induced inertial confinement fusion and so on. In this thesis, we have prepared the Au and Ag nanoparticles, and we have studied these properties such as optical, electrical and eatalytic properties. Some important results obtained are deseribed as follows:1. We describe a green protocol using tannic acid, a polyphenolic plant extract, as both the reducing and stabilizing agent. In this seedless process, the silver nanoplates have been prepared via the reduction of AgNO3by Tannic acid (TA) at room-temperature. This synthesis was a seedless process, without any other surfactant or capping agent to direct the anisotropic growth of the nanoparticles. The shape of the silver particles and the optical in-plane dipole plasmon resonance bands of these nanoplates could be controlled by varying the experimental parameters such as TA concentration and the pH of solution. Furthermore, this "green" method utilized in this thesis can be extended to fabricate other2D metal nanostructures. The double reduction system consisted of NaBH4and hydrogen peroxide which was used to prepare triangular silver nanoplates, and the as-prepared nanoplates were made to keep on growing through multi-stage growth of Ag ions by trisodium citrate. The UV-vis spectrum of the triangular silver nanoparticle self-assembled film (TSNF) is markedly different from that of the colloid of silver nanoparticles. It was found that the SERS enhancement ability of the TSNF is remarkable, and slightly lower than that of the spherical silver nanoparticle film (SSNF). Both electromagnetic mechanism (EM) and chemical mechanism (CM) were attributed as the reason for the difference in the SERS enhancement ability between the TSNF and the SSNF. 2. We describe a green protocol using glucose, as both the reducing and stabilizing agent. On the basis of the alkaline pH (10) of the glucose solution under solvothermal conditions, we can first synthesize stable silver NPs and then induce their linear welding into the nanowires leading to self-supporting3D silver spongelike networks. As we know, we have not been aware of reports on silver spongelike networks structured used such method. The advantages of the method are:(a) it is a simple route with just one step,(b) it is a seedless process, and does not need any other surfactant or capping agent to direct the growth of the silver spongelike frameworks,(c) this "green" method utilized in this thesis can be extended to fabricate other3D noble metals spongelike frameworks architectures. The electric field enhancement of the silver spongelike networks has been described to be a systematic investigation by using three-dimensional finite-difference time-domain (3D-FDTD) simulation. Surface enhanced Raman scattering (SERS) measurements have indicated that the junction regions, the hollow nanostructured and the sharp nanotips of the broken ligaments in the silver spongelike networks act as electromagnetic "hot-spots". The3D-FDTD calculations have indicated that the silver spongelike networks may exhibit a high quality SERS characteristic because of the Ag chain length, chain diameters, chains gap, chains angle and sharp nanotips. A maximum enhancement factor of3.5×1012can be obtained with the silver spongelike networks. As potential nanoantennas, silver spongelike networks can offer an effective method to optimize plasmon coupling for synthesizing devices.3. We provide a convenient and low cost way for the large-area self-organized synthesis of Ag nanorings through heat treatment of Ag+/PVA/PVP composite film on quartz glass. Because of templates and sophisticated apparatus are not necessary, the way provided here can be an important complement to existing methods for the fabrication of rings. In addition, the as-prepared special structural features with nanoparticle-attached Ag nanorings have been applied in SERS properties with Rhodamine6G (R6G) as the probe molecules. Using the3D-FDTD simulation, the theoretical examination of the local EM properties lets us to evaluate the contributions of nanoring and nanoparticle-attached Ag nanorings to the experimentally obtained SERS intensities. Via simulations, we provide that the weak enhancement can be remarkably improved through nanoparticle-attached Ag nanorings and availably utilizing transversely polarized light. In addition to we provide strong lateral coupling induced at the adjacent site between small Ag nanoparticles and nanoring.4. We report a facile silica colloidal templating method to synthesize Au/Ag bimetallic hollow nanospheres with fine monodispersity and controllable atom ratio of Ag and Au. As we know, we have not been aware of reports on Au/Ag bimetallic hollow nanospheres structured for SERS applications. The application of these Au/Ag bimetallic hollow nanospheres bimetallic structured films as SERS substrates is first investigated by using R6G as a probe molecule. We show that the as-prepared Au/Ag bimetallic hollow nanospheres structured films are extremely efficient SERS substrates in terms of high Raman intensity enhancement, excellent stability, and reproducibility. We report the preparation of Ag-Pd bimetallic dendrites by employing multi-stage galvanic replacement reaction (MGRR), which is a simple yet effective and versatile tool. Compared to one-stage reaction approach, multi-stage reaction is more favorable for compositional and modality control. We propose that these charged surface layers control galvanic charge transfer by controlling the stage of galvanic replacement reaction and reaction temperature at the deposition front. These bimetallic dendrites films exhibit high SERS activity and may have potential applications in investigation of "in situ" Pd catalytic reactions using SERS. This difference in the behaviors of the SERS activity is consistent with a strong influence of the changing morphology of the structures. The resulting nanostructures can be engineered to possess tailored, hierarchical morphologies and compositions that present new opportunities for systematically studying the optical catalytic properties of bimetallic NPs.5. We report a facile seed-assisted hydrothermal to synthesize ZnO nanorod arrays on quartz glass through changing the hydrothermal temperature, pH and initial concentration of Zn source in precursor solution. The large-scale arrays of vertically aligned ZnO-NRs decorated with Au-NPs were synthesized using ZnO nanorod arrays. This hybrid substrate manifests high SERS sensitivity to melamine and a detection limit as low as1.0×10-1010M (1.26?g L-1). A maximum enhancement factor of1.0×109can be obtained with the ZnO NF-Au film. The ZnO@Ag core-shell nanorods arrays were synthesized through physical sputtering method. We have studied the SERS enhancement effect of the ZnO@Ag core-shell nanorods array using PATP organic molecules as probe molecule. The result demonstrates for the first time that directional charge transfer between nanoscale metal and semiconductor tunneling through the interconnecting molecules may be examined by SERS.