Controlling Gold Nanoclusters with Atomic Precision for Catalytic Applications

2019-10-30T17:47:37Z (GMT) by Anindita Das
The major goal of this thesis is synthesis and structure determination of stable, ligand-protected, gold nanoclusters in the ~ 1 nm size regime. These structurally well-characterized clusters are then tested as catalysts in probe
chemical reactions to gain an atomic-level understanding of size- and/or structure-dependent catalytic pathways.
Chapter 2 describes the synthesis and structure determination of a new mixed phosphine/thiolate-protected [Au24(PPh3)10(SC2H4Ph)5X2]+ (where, X= Cl/Br) nanocluster. This cluster, which differs by a single Au atom, shows drastic differences in properties from the previously reported biicosahedral [Au25(PPh3)10(SC2H4Ph)5X2]2+ nanocluster protected by the same type and number of phosphine and thiolate ligands. Chapter 3 describes the synthesis and atomic structures of some of the smallest members of the crystallographically characterized thiolate-protected Aun(SR)m clusters, where n and m represent the number of metal atoms and thiolate ligands respectively. These ultra-small nanoclusters lie at the interface between organo-gold complexes and plasmonic gold nanoparticles, i.e. the origin of the first metallic bonds and the nucleation of clusters from organometallic precursors occur in this domain. Total structure determination of thiolateprotected
small Au24, Au23 and Au18 clusters has revealed new types of Au core packing structures and surface ligand binding motifs, which offer mechanistic insights into nucleation and size evolution of gold clusters. Chapter 4 discusses the role of protecting ligands in dictating the size and structure of gold clusters. Here, the electronic and steric effects of ligands on the structure and properties of a nanocluster are illustrated, through the case study of a Au36(SR)24 nanocluster. These insights are expected to offer some new standpoints in terms of structural and size control in nanoclusters, as well as the factors dictating the stability of nanoclusters. In chapter 5, the newly synthesized Au nanoclusters mentioned above have been tested as catalysts in the model catalytic reaction involving reduction of 4-nitrophenol by NaBH4. Preliminary results suggest that the detailed atomic structures, rather than the nominal size (n) in AunLm clusters, dictate their catalytic properties. Finally, chapter 6 summarizes the major achievements of this thesis and some future directions in this field.