Surface Chemistry of Metal Oxide Nanoparticles and Attachment of Metal Nanoclusters: Sensor, Optoelectronic and Photocatalytic Applications

摘要

Metal oxide nanoparticles are surprisingly reactive, and some undergo changes in color or in their photoluminescence (PL) spectra upon reaction. In the latter case, visible emission arises from electron decay from surface related states, and PL changes should be an indicator of chemisorption. A variety of surface science techniques, including X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), have been used to investigate adsorption of various molecules, including thiols, from the gas and solution phases, on metal oxide powders and films and to measure changes in the electronic structure of the surface due to adsorption. Examples of metal oxide nanopowders that have been studied include zinc oxide, zirconium oxide, gold oxide and tungsten oxide. In many cases it is shown that thiols reduce metal oxides to metals, with concomitant oxidation of the thiol to disulfide. Reactions with gases such as sulfur dioxide often lead to sulfite formation on the surface. Possibilities of using metal oxides for chemical sensing or optoelectronic device tuning are discussed. Dithiols can be used as chemical linkers to attach gold nanoparticles (AuNPs) to metal oxides, including zinc oxide nanorods. Various methods of sintering the nanocomposites to remove the ligands and place the AuNPs in physical contact with ZnO have been explored, and the effect of the AuNPs on the chemistry and optical properties of the ZnO have been investigated. It is demonstrated that the AuNPs enhance the photocatalytic oxidative properties of the nanorods, and possible applications for their use in the photocatalytic destruction of hazardous materials have been explored.