Fundamental studies of the influence of ligands on the molecular structure of noble metal nanoclusters

Dr. Heriberto Hernández,¹ Professor

Co-PI: Dr. Grant E. Johnson,² Scientist, Team Lead

¹Grinnell College, Grinnell, IA 50112

²Pacific Northwest National Laboratory, Richland, WA 99354

Ultra-small nanoclusters are aggregates of two or more metal atoms bonded in specific geometric structures. These materials are at the forefront of chemical research because of their applications in technologies that increase the energy efficiency and selectivity of large-scale industrial chemical reactions and enable solar energy generation. To put the unique size of these materials in perspective, the period at the end of the previous sentence is around one hundred thousand nanometers in diameter. In comparison, nanoclusters are typically one nanometer or smaller. At this molecular scale, nanoclusters exhibit unique size-dependent properties that do not evolve predictably to the bulk phase. Achieving the scalable synthesis of size-focused clusters with predetermined properties is one of the grand scientific challenges in this field. To address this challenge, this project will build capacity at Grinnell College, an emerging research institution, to enable a predictive understanding of how different organic ligand molecules influence the structure and properties of ultrasmall noble metal nanoclusters. This objective will be achieved through the acquisition of new mass spectrometry capabilities that will be used to recruit and train a diverse group of undergraduate students. Understanding the influence of ligands on cluster synthesis and properties requires closely integrated experimental and computational research, which provides an ideal training environment for undergraduates. Students will learn how to use mass spectrometry to characterize the size, charge, and composition of solution-phase synthesis products. Students will also learn how to deposit nanoclusters onto solid supports using the specialized ion soft-landing technique developed at Pacific Northwest National Laboratory. Soft landing allows the preparation of size-selected clusters on surfaces without the solvents, counterions, and contaminants that often confound characterization and theoretical modeling. After deposition, students will learn how to analyze the supported clusters using vibrational spectroscopy and electrochemical characterization techniques. By comparing the experimental results with computational modeling, students will gain insight into the size-dependent molecular-level structures of clusters. This approach will train students in molecular modeling using quantum chemistry calculations. The fundamental knowledge obtained from this project will address knowledge gaps inhibiting the scalable synthesis of size-selected noble metal nanoclusters with tailored properties for a broad range of energy-related applications and build the research capacity at Grinnell College to train a new generation of scientists in cutting-edge experimental and molecular modeling techniques.