Synthesis and Characterization of Multi-Pod-Shaped Gold/Silver Nanostructures

We describe here a novel method which shows that related large molecules, tannic acid, can control the morphology of silver/gold nanoparticles, resulting in the formation of multi-pod-shaped nanostructures. In this work, multi-pod-shaped gold/silver nanostructures have been synthesized using tannic acid as a reducing as well as a capping agent. The multi-pod-shaped Au/Ag nanostructures have been confirmed by transmission electron microscopy. The growth process of gold/silver nanostructures has been studied by UV/vis spectroscopy and extended X-ray absorption fine structure analysis. On the basis of these results, we propose a model explaining the role of tannic acid in the growth of gold/silver nanostructures. The reducing and capping properties of tannic acid favor the formation of unisotropic crystal growth. The growth of gold/silver nanostructures occurs as a consequence of the galvanic replacement reaction between Au³⁺ and Ag⁰ and subsequent reduction of both metal ions by tannic acid. Furthermore, it was found that not only the amount of gold ions but also the galvanic replacement reaction between silver and chloroauric acid plays an important role in the morphology control of the multi-pod-shaped nanostructures.