Preparation, Assembly And Application Of Imidazolium Ionic Liquids Stabilized Gold Nanoparticles

Due to their peculiar and fascinating properties, precious metal, especially gold nanoparticles, have many potential applications in the areas of catalysis, sensors, electronics, optics, biology and so on. Therefore, gold nanoparticles are always one of the research hotspot. The characteristics of gold nanoparticles are closely related to their size and shape, so shape control is a primarily direction in gold nanoparticles research. Ionic liquid, always known as "molten salt", is a class of organic salt with melting point lower than 100℃. Ionic liquids are used as green solvent for high expectations since its discovery and provide a new opportunity for nanoparticles preparation. But compared with the traditional methods, nanoparticle preparation using ionic liquid systems still need further investigation. In this thesis, we studied the preparation of gold nanostructures with various shapes using imidazolium ionic liquids as the capping agents. We also investigated the patterns of spherical gold nanoparticles formed at the air/water interface. The SERS enhancements activities of these nanoparticles were also investigated. The thesis is divided into six sections, which are summarized as following:PartⅠ, a brief introduction of the research background. It is mainly about the progress of gold nanoparticles which containing their preparations and applications. And then, a brief introduction about ionic liquids is presented. Finally, the use of ionic liquids in the preparation of nanoparticles is summarized.PartⅡ, the properties of the Langmuir monolayers formed of a long chain ionic liquid, [C16mim]Br, was first investigated. These Lanumuir monolayers were very stable and can be used as a shape-control template to prepare nanoparticles. Through a simple Langmuir monolayer route, gold nanoplates with diameters in micro-scale were obtained. The obtained nanoplates were characterized by using TEM, HRTEM, SAED, SEM and UV/vis spectra. Base on these results, a connection-fusion mechanism was proposed. The role of the molecular structure of the membrane material and the surface pressure was also investigated. PartⅢ, uniform gold nanorods were prepared via a three-step seed-mediated growth method using a long-chain ionic liquid, C12mimBr, as a capping agent. The aspect ratio of the nanorods was controlled by using different additives. Based on the literatures and the HRTEM results, the structures of these nanorods were defined. The catalytic experiments showed that the short gold nanorods had excellent catalytic efficiency for the reduction of nitro compounds. The interaction energies between the individual surfactants and different gold crystalline planes were calculated using a molecular dynamics simulation. This calculation result was used to explain the experimental results.PartⅣ, a functionalized ionic liquids, [camphorC2mim]Cl, was synthesized, and then, two-dimensional dendritic gold nanostructures were prepared at the air/water interface with the assistance of this ionic liquid. The role of the ionic liquids and the effects of the molar ratio of HAuCl4/[camphorC2mim]Cl and the concentration on the morphology were discussed. The obtained gold dendrites can be used as a substrate for Raman scattering, and they exhibit much higher surface enhancement than those of the widely used electrochemically roughed gold substrate.PartⅤ, hierarchical, three-fold symmetrical, single-crystalline gold dendrites were synthesized via a galvanic replacement method in the mixture of ethanol and water with the assist of an ionic liquid. The metal substrate, the volume ratio of ethanol and water, the gold precursor and the additives have demonstrated a significant effect on the dendrite morphologies. Structural characterizations by using HRTEM and SAED suggested the growth direction of the obtained gold dendrites. The obtained gold dendrites were found to yield large SERS enhancement factors.PartⅥ, chiral ionic liquid monolayer-stabilized gold nanoparticles were synthesized in a two-phase liquid-liquid system. These gold nanoparticles were found to self-assemble into some unusual structures at the air/water interface. Control experiments revealed that the molecular structure of the capping agents significantly affects the formation of these patterns. These gold nanoparticles can be used to fabricate SERS substrate and the enhancement activity can be greatly improved through the assembly.