One-Step Synthesis Of Gold Nanostructures By Polysaccharides

The unique properties and potential applications of gold nanoparticles are mainly determined by the size and shape. So far there have been many methods to prepare gold nanoparticles; however, most of them are either complicate or difficult to control the shape and size. In addition, most of the synthetic methods reported to date relied heavily on the use of chemical reducing agents. All of these chemicals are highly reactive and pose potential environmental and biological risks. The cost of production is relatively high materially and environmentally. The aim of this dissertation is to develop some simple, economical and effective solution-phase methods to synthesize gold nanoparticles with controllable size and shape, using the abounding existence of the naturally-occurring polysaccharides. Their morphology, size, structure and optical properties were characterized systemically by TEM, HRTEM, SEM, XRD, SAED, EDS and Uv-vis spectrophotometer. The growth mechanism of two-dimensional gold nanoplates was primarily investigated. The main contents and results of the thesis are outlined as follows:1. Single-crystal gold nanoplates with high-yield, large size, regular triangular, hexagonal or truncated triangular shapes, several micrometers in size and tens of nanometers in thickness have been successfully synthesized by a simple, one-step method at 70℃using chitosan as reducing/capping agents. The concentrations of precursors (chitosan, HAuCl₄), the concentration of acetic acid, the molecular weight of chitosan and stirring speed are crucial to the morphologies and sizes of the final product.2. A possible formation mechanism of the gold nanoplates has been proposed, Formation of such large size single-crystal nanoplates is related to the preferential adsorption of chitosan molecules. In addition, the preferential (thermal-induced fusion) growth of small triangular gold nanoplates is another way to the formation of gold nanoplates with large size.3. A green method for the preparation of gold nanoparticles has been developed by using natural polysaccharides (sodium alginate and chitosan) as reducing agents. Gold nanoparticles with tadpole, coherent-rice, and rice in shape and gold nanosponges have been successfully prepared through one-step hydrothermal synthesis at 120℃～150℃.As a consequence, these simple, convenient, economical, effective synthetic methods are expected to make these processes amenable to large-scale industrial production, and will be probably developed as common methods for synthesizing other metal nanostructures with controllable size and shape.