Synthesis Of Gold Nanomaterials With The Assistance Of Surfactants

Among many kinds of nanomaterials, gold nanomaterials have attracted wide attention and have been studied extensively. This is mainly due to their unique physical, chemical, and biocompatible properties, besides the common properties for the nanomaterials. Furthermore, the properties and applications of gold nanocrystals largely depend on their sizes and shapes.Over the past decade, there has been tremendous progress in the shape-controlled synthesis of gold nanocrystals. In particular, a variety of colloidal chemical methods have been developed to fabricate gold nanocrystals, and there is a growing emphasis on these methods. In the synthesis of gold nanocrystals by colloidal chemical methods, various surfactants have been widely employed as capping agents to exert exquisite control over the nucleation and growth of gold nanocrystals. In addition to the role of capping agents, surfactants which undergo strong interactions with gold, and can even form coordination complexes. All in all, a variety of surfactants with different headgroups, hydrophobic chains, counterions, and molecular architectures, have been used for the shape-controlled synthesis of gold nanocrystals. Meanwhile, there are also many key points which are needed further investigation. In this thesis, we studied the preparation of gold nanostructures with various shapes using surfactants as the capping agents. The thesis is divided into three sections, which are summarized as following:Section Ⅰ, Control synthesis and assembly of gold nanoparticles using the typical nonionic surfactants:Siloxane surfactant induced self-assembly of gold nanoparticles and their application to SERS; The high yield synthesis and characterization of gold nanoparticles with superior stability and their catalytic activity. The work can be divided into two parts:1. A siloxane surfactant was used for the mild synthesis and simultaneous1D assembly of gold nanoparticles. The lengths of the gold nanochains could be tuned by facile adjustment of the surfactant concentration. The multiple interactions between the siloxane surfactant and gold nanoparticles made the nonuniform spatial distribution of stabilizers at the nanoparticle surfaces and then led to the1D assembly. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was introduced to interpret the relationship between the capping mechanism and the excellent stability of the nanoparticles. These gold nanochains were shown to yield a large SERS enhancement for Rhodamine6G.2. The typical nonionic biosurfactant ethoxylated sterol (BPS-30) is used to the facile, green, and high yield approach for the synthesis and stabilization of relatively monodispersed gold nanoparticles. The obtained gold nanoparticles capped by BPS-30not only showed remarkable stability after several months of storage under ambient conditions, but also exhibited exciting stability in the high concentrations of electrolyte aqueous solutions. The UV-vis absorption spectrum was used to determine the yield of the gold nanoparticle. Moreover, the catalytic efficiency of the gold nanoparticles was evaluated by using the reduction of4-nitroaniline by potassium borohydride in aqueous solutions.Section Ⅱ, Control synthesis and assembly of gold nanoparticles using imidazolium ionic liquid surfactants at the air/water surface:One-step synthesis and assembly of gold nanochains using Langmuir monolayer of long-chain ionic liquid and their applications to SERS; Novel two-step synthesis of various gold nanostructures using Langmuir monolayers. The work can be divided into two parts:1. gold nanochains were prepared at the air/water interface under the Langmuir monolayer of a long-chain ionic liquid1-hexadecyl-3-methylimidazolium bromide (C16mimBr) through the reduction of AuCl4-ions by UV-light irradiation. It is revealed that these nanochains are self-assembled from gold nanoparticles about an average diameter of15nm. The synthesis and assembly of the Au nanoparticles can be achieved in one step. Both the π-π interactions and the steric hindrance play important roles in the formations of the nanochains.2. Ribbon-like, wedge-shaped, and spherical gold nanostructures were prepared via a novel two-step growth method. Various gold nanostructures were first pre-formed in aqueous solution by using β-cyclodextrin (β-CD) as both reducing and capping agent. Due to the continuous growth of the pre-formed gold nanostructures at the air/water interface with the help of the Langmuir monolayers of1-hexadecyl-3-methylimidazolium bromide (C16mimBr), morphology changes can be observed obviously. A possible mechanism based on the interaction between β-CD and the pre-formed gold nanostructures is proposed.Section Ⅲ, The benzyl-n-hexadecyl dimethylammonium chloride-stabilized gold nanoparticles were found to self-assemble into ringlike structures at low temperature and honeycomb-shaped patterns at high temperature. The π-π stacking interactions between the BHDC molecules contribute to the ordered arrangement of the capping agents at the surface of gold nanoparticles. Then the similar core/shell hybrid nanomaterials are obtained and the organic shell plays a key role in the formation of the unique patterns. These varied structures are suggested to be a result of Marangoni-Benard convection in evaporating droplets and π-π stacking interactions of the nanoparticle suspension. Other four surfactants are also used to further verify the mechanism from the molecule interactions level between capping agents.