The formmation and optics of nanomaterials: The synthesis and assembly of cadmium selenide nanorods and catalytic study of gold-doped nano ceria

This thesis includes two aspects of research on nanocrystals. The first is a study of the effect of ligands on the synthesis, solubility, and assembly of colloidal CdSe nanorods (NRs); the second is the structure and kinetics of the surface of metal-doped nano-sized ceria catalysts in various gaseous media by situ Raman spectroscopy.;CdSe NRs are chosen as a model system to study the role of ligands in the growth kinetics and morphology of one-dimensional nanostructures. The effect of ligand length on the dimensions, shape and occurrence of branching of the resulting NRs is explored. The shorter the ligand, the more elongated and branched are the resulting NRs. The organic capping shell on the resulting NRs is investigated. Hydrogen bonding interactions between the hydrophilic endgroups of the phosphonic acid molecules play a critical role in the self-assembly of CdSe NRs with added ligands. A "trapped ligand" model of the capping structure of the colloidal NRs can explain conditions of strong NR aggregation in solution and in dry-cast films. The tight parallel alignment of the NRs strongly indicates inter-rod attractions through the hydrophilic endgroups of phosphonic acid ligands, and this may prove to be important in applications of one-dimensional colloidal nanostructures. Also, we have synthesized, for the first time, well-dispersed CdSe NRs using akylphosphonates as ligands.;In situ Raman scattering shows that peroxide species can be generated by the interaction of a reducing gas (CO/He) with the Au-ceria nanocatalyst surface. Strong peroxide bands are seen only for Au-CeO2 but not for the undoped CeO2 samples. This is consistent with published calculations of the interaction of CO with CeO2 and Au-CeO 2. The doping Au species weaken the bond between the oxide and surface oxygen atoms near the Au species, making the oxygen atoms on ceria more mobile and active. Our experiments also show that peroxide species at various vacancy defects can be distinguished both by varying temperature and the CO/He gas flow rate. The Raman scattering study of Au-CeO2 for CO oxidation and water-gas-shift (WGS) reaction conditions indicates that both reactions on the Au-CeO2 surface are consistent with the Mars-van Krevelen mechanism and that the peroxide species could be a possible intermediate for both reactions on the Au-CeO2 surface. Moreover, in situ Raman spectra combined with catalytic efficiency data suggest that in situ Raman scattering could provide a general way to monitor the mobility/activity of surface oxygen atoms and to possibly predict the catalytic performances of various Au-CeO2 catalysts.