Metal and alloy nanoparticles: Synthesis, properties and applications

The development of effective strategies for the synthesis of metal and alloy nanoparticles with controllable size, shape, and composition is essential for the exploitation of the novel spectroscopic properties of the nanoparticles in analytical/bioanalytical detections and the catalytic properties of the nanoscale materials in fuel cell reactions. This dissertation focuses on developing the ability to control the size, shape and composition of metal and alloy nanoparticles. The understanding of how the formation of metal nanoparticles is influenced by the presence of pre-synthesized nanoparticles and how the precise control over size, shape, and composition of nanoparticles is manipulated by synthetic strategies are some of the important areas of our synthesis work. Several effective strategies have been demonstrated for the synthesis of gold, platinum, and their alloy nanoparticles with controlled size, shape, and composition. One important insight of the study involves the reductive mediation by the surface Pt-H species for the formation of metal or core-shell nanoparticles. Another significant insight involves the establishment of the correlation between the particle size and the surface plasmon resonance optical and the surface-enhanced Raman scattering spectroscopic properties. To gain fundamental insights into the synergistic catalytic activities of the bimetallic alloy nanoparticle catalysts in fuel cell reactions, we employed an array of analytical techniques to characterize the structures and properties of the nanoparticles, including size, composition, surface structures and electrochemical properties. The results have shown that the electrocatalytic properties of the nanocatalysts depend on the bimetallic composition and the thermal treatment condition. The discovery of a maximum mass activity in the bimetallic composition region (60-80%Au) indicates a qualitative concurrence with both theoretical and experimental findings in terms of the participation of Au sites in the adsorption of carbon monoxide or oxygenated species. The mechanistic understanding of the electrocatalytic oxidation of methanol and reduction of oxygen has implications to the design of active catalysts in fuel cells such as DMFCs and PEMFCs.