Research On Gold Nanoparticles Synthesized By Tryptophan Reduction In Aqueous Solution And Their Characterization

Gold nanoparticles (GNPs) become the frontiers of nanotechnology research fortheir unique physical and chemical properties and broad application in industrialcatalyses, microelectronics, optical materials, biological sensors, medicine deliveryand molecular diagnoses, et al. The size, shape and composition of GNPs highly affecttheir properties and applications. Therefore, realizing the controlled synthesis,improving the particles’ stability, dispersion and increasing the purity and yield ofGNPs become a challenging research subject. Based on the biosorption-reductionsynthesis of GNPs, according to the green chemistry and morphology-controlledrequirements, eco-friendly biological molecules of tryptophan are utilized tosynthesize GNPs by directly reducing gold salt precursor in this thesis. With the aid ofcharacterization methods including Ultraviolet-visible(UV-Vis), transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction(XRD),X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy(FTIR), the influences of reaction parameters (temperature, pH and concentration oftryptophan) and exogenous substances(surfactants, metal ions) on the morphology ofGNPs are investigated, and the reduction process and morphology evolution are alsopreliminary explored.Firstly, reaction temperature has a certain effect on the size of GNPs, but not theshape: the higher the temperature, the smaller the gold nanospheres. pH play animportant role in the reduction process: overly acidic or alkali that is unfavorable forthe reaction process or make the reaction not happen at all, which further affect thesize and shape of particles. The concentration of tryptophan influences not only on thesize but also the shape of formed GNPs. Under the lower concentration of tryptophanirregular GNPs are generated, and with the increasing of concentration, goldnanospheres with good monodispersity and smaller size were obtained.Besides, surfactants have important influence on the morphology of GNPs.Especially in the existent of cationic surfactant cetyltrimethyl ammonium bromide(CTAB), lots of triangular, truncated triangular and hexagonal particles synthesized.Foreign metal ions Ag(I) promoted the reduction of Au(III), and induced thegeneration of small amount of irregular gold-silver alloy nanoparticles. Finally, FTIR analyses and a simple control experiment confirmed that the indolegroup is the dominating reducing segment involved in the reduction of Au(III). Andpreliminary explorations of morphology evolution found that snowflake GNPsexperienced the anisotropic growth of nuclear to thorny particles, and then formed bytheir aggregation. While, due to the surfactants induced directional growth, GNPs ofrod-like, flake (triangular, truncated triangular and hexagonal) formed.