IIN Frontiers in Nanotechnology Seminar Series – Jillian Dempsey
Department of Chemistry
University of North Carolina at Chapel Hill
Growing Model Catalysts through the Tailored Design of Shaped Bimetallic Nanoparticles
As-synthesized colloidal semiconductor nanocrystals are capped by surface-coordinating ligands that act to passivate surface sites and suspend the colloidal particles in solution. Displacement of these ligands from the nanocrystal surface can be promoted by reaction with other ligands, chelating small molecules, or addition of charge carriers. By monitoring the ligand displacement reactions using UV-Vis absorption, 1H NMR, and FTIR spectroscopies, insight to the nanocrystal electronic structure and native surface composition can be gleaned. For instance, upon thermochemical doping of CdSe with chemical reductants, we find that a portion of the native anionic ligands are liberated from the nanocrystal surfaces and observe that added electrons reduce surface-based Cd and Se ions before filling the conduction band. These data reveal a new mechanism for charge balance in thermochemical doping reactions wherein anionic oleate ligands are liberated from the surface as free carriers are trapped in a subpopulation of cadmium-based localized surface states. Separately, the addition of chelating diamine ligands to PbS strips native Z-type lead oleate ligands. Quantifying the binding isotherms of these displacement reactions allows us to map the relative subpopulations of Z-type ligands and thereby elucidating the native surface topology. These indirect imaging studies support computational predictions that PbS nanocrystals have a size dependent shape, transitioning from an octahedron to cuboctahedron.
Jillian L. Dempsey is an associate professor at the University of North Carolina. She received her S.B. in 2005 from the Massachusetts Institute of Technology, where she worked in the laboratory of Prof. Daniel G. Nocera. As an NSF Graduate Research Fellow, she carried out research with Prof. Harry B. Gray and Dr. Jay R. Winkler at the California Institute of Technology, receiving her PhD in 2011. From 2011 to 2012, she was an NSF ACC Postdoctoral Fellow with Daniel R. Gamelin at the University of Washington. In 2012, she joined the faculty at the University of North Carolina at Chapel Hill. She has received numerous awards, including the Harry B. Gray Award for Creative Work in Inorganic Chemistry by a Young Investigator (2019), the J. Carlyle Sitterson Award for Teaching First-Year Students (2017), a Sloan Research Fellowship (2016), and a Packard Fellowship for Science and Engineering (2015). Jillian’s research group explores charge transfer processes associated with solar fuel production, including proton-coupled electron transfer reactions and electron transfer across interfaces. Their research bridges molecular and materials chemistry and relies heavily on methods of physical inorganic chemistry, including transient absorption spectroscopy and electrochemistry. Outside of the lab, Jillian enjoys running, cooking, yoga, and watching her two-year-old Orin play basketball.