Unique Electrochemistry and Optical Properties of Metal Nanoparticle Assemblies

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In this project funded by the Macromolecular, Supramolecular, and Nanochemistry program of the Division of Chemistry, Professor Francis P. Zamborini of the University of Louisville and his team study the oxidation of small gold nanoparticles using a combination of chemical characterization techniques. Nanoparticles are tiny particles that contain thousands of atoms. While they are much larger than chemical molecules, which contain only a few atoms, they are still much smaller than solid materials that are large enough to see with the naked eye, containing trillions of atoms. Nanoscale materials are unique because they have sizes intermediate between molecules and solids, but sometimes have properties not easily predicted by averaging the two size extremes. The aim of the research is to understand the unusual electrochemical reactivity of metal nanoparticles smaller than 2 nm and of alloy nanostructure composition, arrangement, and reactivity. The aim is to develop new analytical tools for metal nanostructures, and also uncover unique properties, reactivity, and applications. The project impacts the education of students at all levels through research training and wider incorporation of nanotechnology into the undergraduate curriculum. A yearly one-day symposium highlights research by women of all ages from middle school up to academic and industrial professionals. The goal of this symposium is to inspire more young female students to pursue a long term career in science. These activities impact the education and economy in Kentucky and beyond through broad dissemination. This project aims to correlate the specific size with the oxidation potential for nanospheres below 2 nm, which show unusual electrochemical reactivity that change dramatically as a function of size. The project also addresses the atomic arrangement of metals in two-component alloy nanospheres by determining electrochemical oxidation behavior. This method allows the sensitive detection of transformations that occur during heating or catalytic reactions. Another focus of the project is the size-selective electrochemical deposition of negatively-charged gold nanospheres onto electrodes. This process has potential for the design of highly active supported electrocatalysts. The research team also uses gold nanoplate-nanosphere dimer structures as a platform for sensitive molecular detection by surface enhanced Raman spectroscopy (SERS). Images of the structures are directly correlated to the SERS signal. A unique trimer structure is used to study catalytic reactions on non-SERS active metals. The well-controlled nanoplate-nanosphere dimer and trimer assemblies aid in better understanding and controlling SERS detection for the study of reactions at the single molecule level.