Fundamental research into gold nanocluster properties
Date
2021
Authors
Window, Phillip S., author
Ackerson, Christopher J., advisor
Neilson, James R., committee member
Kennan, Alan J., committee member
Peersen, Olve, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Gold materials are popular for research into many applications with their interesting properties, such as magnetism, bio-inactivity, and other size-dependent properties. As the size of the gold material decreases from a bulk material to the nanoscale, new properties are introduced moving through different size regimes. As the particle size reaches the 2-3 nm range and move into the quantum-confined particle range, the most interesting particle changes occur and gold nanomaterials have extremely interesting research potential. These materials exist between the bulk and molecular systems and have similar properties to both; however, they are different enough from both of these to have their own unique application possibilities. Some properties of gold nanoclusters can be attributed more to the core or more to the ligand layer of the nanocluster. Certain properties, like electronics and magnetism, are due to the superatomic electron count and electronic structure from the core and depend on the number of gold atoms in the nanocluster. Extensive research has been done on investigating and altering these properties in small nanoclusters, however, larger nanoclusters have hardly been studied as they can be more difficult to work with. Within this work is investigated the magnetism and thus electronic structure of Au102(SPh)44 and Au133(tBBT)52 in different oxidation states. Paramagnetism up to two unpaired electrons is observed with both these nanoclusters through solution phase magnetic studies. Through this, electronic structure information has been obtained to elucidate the behavior of unique superatomic 1G and 1H orbitals. Looking at the outside of a nanocluster structure, interactions of nanoclusters with other nanoclusters, molecules, surfaces, and solvents are all due to the ligand layer of the nanocluster. Investigations of the ligand layer have been performed extensively through many techniques. However, further studies are always helpful since controlling the ligand layer is essential for functionalization for potential applications. Within this work is investigated the interactions of Au25(SR)18 with other Au25 nanoclusters in both solution and solid phase, as well as ligand exchange reactions of Au133(tBBT)52. Studies on Au25(SR)18 within solution include investigations of a supramolecular assembly, or supercluster, formed solely of the nanocluster itself with control over its growth and size. Studies on Au25(SR)18 within the solid-phase include controlled crystallization techniques that result in different solid-phase structures with previously unseen properties. Ligand exchange studies have also been expanded from small nanocluster materials only in previously published studies to the large nanocluster, Au133(tBBT)52. Within this dissertation, some of the first empirical studies into the oxidation state- dependent properties of large gold nanoclusters, Au102(SPh)44 and Au133(tBBT)52, were performed. This betters the field's understanding of how many unpaired electron spins these large gold nanocluster can sustain at room temperature and further elucidates the behavior of superatomic electronic structure and behavior based on electron count. Furthermore, this dissertation presents the first investigations into the formation of supramolecular assemblies of gold nanocluster as recyclable materials, and more interactions of gold nanoclusters based on ligand layer interactions through polymorphism studies and ligand exchange studies. These investigations all help understand how to control the ligand layer for future applications of gold nanoclusters and nanoparticles, from molecular to bulk materials.