Abstract
CHAPTER 1 One−Pot Synthesis of Silver Nanocubes and Their Morphological Transformation We have used one-pot reaction to synthesize cubic silver nanoparticles with average sizes of 62 to 80 nm in aqueous solution at 50 ºC for 6 hours. The reagents used here are AgNO3, cetyltrimethylammonium chloride (CTAC), ascorbic acid, and NaOH. In this method, silver nanoparticles are obtained by using ascorbic acid as reducing agent to reduce AgCl(s) in the presence of CTAC. NaOH is added to increase the reducing ability of ascorbic acid. Silver nanocubes with sizes varying from 62 to 80 nm are obtained by increasing the amount of AgNO3. Different amounts of NaOH also influence the morphology of silver nanoparticles. By increasing the amount of NaOH, the formation of {111} facets is enhanced and the shapes of silver nanoparticles change from cubes to truncated cubes and cuboctahedra due to the increased reaction rate. In addition, reaction rate is also increased when CTA+NO3─ serve as the surfactant. Furthermore, silver cuboctahedra are obtained and evolve into truncated octahedra by increasing the reaction temperature. CHAPTER 2 Synthesis and Plasmonic Properties of Au−Pd Core−Shell Heterostructures with Variable Shapes and Shell Thickness In this work, we report the investigation of plasmonic properties of Au−Pd core−shell heterostructures with different shapes, including cubes, cuboctahedra, truncated octahedra, and octahedra. Here, we have used a seed-mediated growth method to synthesize Au−Pd core−shell heterostructures with 35, 45, and 74 nm gold octahedra as cores. Au−Pd core−shell heterostructures with various shapes and sizes are prepared by mixing cetyltrimethylammonium bromide (CTAB), octahedral gold cores, H2PdCl4, and ascorbic acid at 50 ºC in less than 2 hours. The uniform shape of these nanocrystals and the ability to tune the shell thickness allow us to investigate their localized surface plasmon resonance (LSPR) properties. When the shell thickness become thin enough, blue shift of Au LSPR absorption band of Au−Pd core−shell heterostructures is observed. The Au LSPR absorption band red-shifts and become more obvious when the shape of core−shell nanostructures transforms from cubes to octahedra due to the shell thickness variation induced by change in the mole ratios of Pd : Au in a nanoparticle. Comparing to previous studies, this is the first time the plasmonic properties of bimetallic core−shell heterostructures with various shapes and tunable sizes is investigated. For Au−Pd core−shell octahedra, their Au LSPR absorption band is more pronounced and they may have the potential to be applied for plasmonic sensing such as hydrogen sensing.