Synthesis Of Shape Controllable Silver Nanoparticles And The Studies Of Their SERS Activity

In recent years, increasing researches have been focused on synthesizing nanomaterials with controllable size and shape. Noble metal nanoparticles, such as silver and gold nanoparticles, have been widely investigated, because their unique chemical and physical properties in the filed of optics, electronics, magnetism, and catalysis, which are strongly size and shape dependent. For the case of their optical properties, noble methal nanoparticles with different size and shape possess distict scattering and absorption properties, giving a variety of characteristic surface plasmon resonance (SPR) properties.According to the existing mechanism on SERS, SPR properties of the nanomaterials highly affect on their SERS activities. Thus, the control on size and shape of nanomaterials provides opportunities to investigate the correlations between SERS and SPR. This thesis is based on viewpoints mentioned above. We chose silver nanoparticles as the SERS substrates. First, synthesized several kinds of silver nanoparticles, in shape of trianglue, disk-like and hexagon with controllable size. The corresponding optical properties as well as the formation mechanisms are discussed and investigated. Secondly, we designed and optimized several types of SERS substrates, whose SPR properties were finely controllable by adjusting the size, shape, as well as the interparticle spacing. Furthermore, the correlation between the SPR properties of SERS substrates and their SERS activities is discussed, and the mechanism of SERS is presumed. There are mainly five aspects in this thesis listed as follow:1. Photoinduced synthesis of triangular silver nanoplates Triangluar silver nanoplates were synthesized by irradiating the growth solution, which contained silver nanoseeds, silver cations, and citrate anions. The sodium lamp was chosen as the light source. The citrate anions in the system acted as both reducing agents and stabilizers. The spectral evolution of the growth process was monitored by the UV-vis spectrometer, and the corresponding shape and size of the nanoparticles in details were investigated by transmission electron microscope (TEM). We also estimated the influences of the molar ration between silver cations and citrate anions on the final products. Furthermore, the provided method is economical, readily, and highly reproducible.2. Photoinduced synthesis of hexagonal silver nanoplates The hexagonal silver nanoplates were successfully prepared via a photochemical reaction, which is similar as described in synthsis of silver triangular plates. The spectral evolution of the growth process was monitored by the UV-vis spectrometer, and the corresponding shape and size of the nanoparticles in details were investigated by transmission electron microscope (TEM). The prepared hexagonal silver plates are symmetry in geometric structure, and monodispersed both in size and shape.A growth mechanism of hexagonal silver nanoparticles was discussed and outlined.3. Transformation of silver triangular nanoplates to silver nanodisk via a thermal process.The silver nanodisks were synthesized by a thermal etching method, in which the triangular nanoplates were used as theprecursors. This process occured under a certain molar ration between silver cations and citrate anions.Two types of silver nanodisks were obtained in the system, one type was small in diameter, and the other one was bigger. The shape transformation mechanism was discussed, which was different from the Ostwald ripening process. By separating the two types nanodisk, we obtained monodispersed nanoparticles both in size and shape.4. Transformation of silver triangular nanoplates to silver nanodisk via a chloride-ion-melting process.Silver nanodisks were obtained by a shape transformation process via a chloride ion etching of silver triangular nanoplates.The｛110｝facet of silver triangular nanoplates was selectively etched by the chloride ion. The UV-vis spectra was used to characterize the spectral evolution during the etching process, and the TEM images of silver nanoparticles were detected to investigate the etching process in details.A chloride ion etching mechanism was outlined. Moreover, the obtained silver nanodisks possess high SERS activity.5. Studies of the SERS activities of the silver triangular nanoplates and silver nanodisks self-assemble film.Silver triangular nanoparticle film was prepared via a self-assemble process. The silver nanodisk film was obtained by an in situ transformation process via the chloride ion etching of silver triangular nanoparticles. Both silver nanoparticle films were used as SERS substrates. Their SERS activities were estimated. By comparing their characteristic SPR absorption bands and SERS activities, the correlation between SPR and SERS was roughly outlined.