Shape Selective Oxidative Etching and Growth of Single-Twin Plate-Like and Multiple-Twin Decahedral and Icosahedral Gold Nanocrystals in the Presence of Au Seeds under Microwave Heating

摘要

Shape-and size-controlled synthesis of gold nanocrystals was studied by using a microwave-polyol method in the presence of Au seeds and poly(vinylpyrrolidone) (PVP) as a polymer surfactant.Mixtures of spherical,triangular,hexagonal,octahedral,and decahedaral particles were prepared as Au seeds by reducing Au~(3+) in AuCLt-in ethylene glycol (EG).When Au nanoparticles were prepared from AuCl_4~-/Cl~-/PVP/EG solutions by using these Au seeds,significant changes in shapes and sizes of the Au seeds occurred.Such changes depended strongly on the concentrations of AuCl_4~-and CI~-.Large single-twin plate-like particles and multiple-twin decahedral particles were the major products at high concentrations of AuCLt-,whereas icosahedral particles were preferentially produced at high Cl~-concentrations.It should be noted that the octahedral and spherical particles involved in the Au seeds were completely dissolved at high AuCLt~-and Cl~-concentrations.The significant changes in shapes and sizes of Au nanoparticles could be explained by the oxidative etching of the Au seeds by AuCl_4~-+Cl~-anions in the range of 60-160 °C and crystal growth of specific shapes of Au nanocrystals in the range of 160-198 °C on the basis of changes in color and UV-vis-NIR spectra of solutions and TEM images of products during etching.