Shape Control Synthesis and Microstructure Studies of Metal Nanoparticles

Sammanfattning: Metal nanoparticles have been extensively studied in recent years due to their unique chemical, biological and physical properties. Gold (Au) and palladium (Pd) nanoparticles are two of the most popular materials because Au nanoparticles have a strong localized surface plasmon resonance effect and Pd nanoparticles have high hydrogen adsorption and chemical catalytic capacities. In the colloidal-chemical synthesis of gold (Au) and palladium (Pd) nanoparticles, capping agents are widely used to control the shape and size of nanoparticles. Capping agents are usually surfactants, polymers, organic ligands and dendrimers. In this work, an anionic surfactant, sodium oleate (NaOL) was mixed with common capping agents such as hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC) and polyvinylpyrrolidone (PVP) in order to tune the shapes of nanoparticles. Three mixtures of capping agent: CTAB-NaOL, CTAC-NaOL, and PVP-NaOL were applied to the synthesis of Pd nanoparticles, resulting in the formation of Pd nanodendrites under proper circumstances including temperature, pH value and ratio between the capping agents. The large surface area makes Pd nanodendrites advantageous in catalytic applications. However, the application of CTAB-NaOL mixture in the growth of Au nanorods plays a remarkably different role. It increased the rod-shape yield and narrowed the aspect ratio of Au nanorods. A growth-induced strain was discovered in the Au nanorods, leading to slight bending in a large percentage (≈ 47%) of the Au nanorods. A variety of techniques were used to investigate the microstructure and properties of Au and Pd nanoparticles. Transmission electron microscopy including selected area electron diffraction and Kikuchi pattern methods, energy dispersive X-ray spectroscopy, and scanning transmission electron microscopy were employed to study microstructure and elemental composition. Ultraviolet-visible spectroscopy, dynamic light scattering and conductivity measurements were used to characterize the growth kinetics of metal nanoparticles. Through these techniques, the effects of the capping agent ratio, pH value and precursor types on the growth of Pd nanodendrites were investigated. Additionally, the growth-induced strain in Au nanorods was studied as well. Investigations of the shapes and microstructure of metal nanoparticles have the potential to expand their applications in the fields of surface plasmonic sensing and catalysis.