Exploring the Unique Electrochemical Reactivity of Metallic Nanoparticles Less Than 4 nm in Diameter

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Francis P. Zamborini from the University of Louisville is supported by the Macromolecular, Supramolecular and Nanochemistry program to explore the unique electrochemical reactivity of metal nanoparticles, focusing on oxidation and galvanic displacement reactions for those with diameters below 4 nm. The team has shown that there is a negative shift in oxidation potential for Au nanoparticles with decreasing size from diameters of 250 nm to 4 nm. The shift increases significantly below 4 nm. A goal of the work is to characterize the specific shift in oxidation potential for Au nanoparticles ranging from 250 nm down to 1 nm in diameter. A combination of mass spectrometry and electrochemical methods is being used to correlate the exact nanoparticle/cluster size with the oxidation potential. This provides important fundamental information about the stability of metal nanoparticles against oxidation as a function of size and a new electrochemical method for characterizing the size of metal nanoparticles. They have discovered that the oxidation of small metal nanoparticles also depends on the electrode material, the method of attachment to the electrode, their aggregation state, and the ligands used to assist in their oxidation. They are exploring these parameters systematically in order to gain a full understanding of all of the factors affecting metal nanoparticle oxidation. Galvanic displacement is an electrochemical reaction involving the replacement of one metal with another metal, which has been used to form interesting alloys, but has not been fully studied as a function of size. This reaction is also being explored with nanoparticles of varied size and focusing on those below 4 nm. Since the oxidation behavior changes dramatically below 4 nm, it is expected that the galvanic displacement reaction will show unique reactivity in this size regime, allowing for nanoparticle transformations and alloy formation not possible with larger sizes. The exploration of the oxidation and galvanic displacement of very small metal nanoparticles will lead to the discovery of new chemistry, synthesis of unique metal nanomaterials, and development of a new method of metal nanoparticle characterization.This project has broad significance and importance in many ways. In terms of the impact on the scientific community, this research is relevant to the discovery of new chemistry involving small metal nanoparticles, a new method for characterizing the size of metal nanoparticles, and new methods of synthesizing unique metal alloy nanomaterials. It also provides important fundamental information about metal nanoparticle stability, which is crucial for the numerous potential applications in medicine, chemical analysis, and energy. It further provides significant, multidisciplinary training of students of all levels, including high school, undergraduate, graduate, and post-graduate students. The results of this research are being incorporated into the undergraduate chemistry curriculum to educate students about the important size-dependent properties of materials, which is at the heart of nanotechnology research. This information is being made available to other educational institutions for broader dissemination. A one-day symposium is being hosted dedicated to women in science, with an emphasis on biotechnology and nanotechnology research. This includes participation from middle school students up to science professionals, including poster and oral presentations and a keynote lecture from a prominent female scientist. The program is being publicized to broaden the impact.