Synthesis and Characterization of Transition Metal and Metal Oxide Nanoparticles Using Dendritic Complexes

Abstract

The research in this dissertation focuses on the synthesis and characterization of metal/metal oxide nanoparticles in solution and on surfaces with a high degree of control over size and size dispersity; such well-defined nanoparticles were made using metal ion-dendrimer complexes and silica-supported organometallic dendrimers. The metal oxide-based materials can be used as laboratory surrogates for combustion-generated nanoparticles to assess their role in mediating pollutant formation. Nickel nanoparticles with low size dispersity were prepared by a dendrimer-ligand-based method employing five generations amine-terminated poly(propylene imine) dendrimer, DAB-Amn. After coordination, borohydride reduction of Ni(II) ion-dendrimer complexes yielded Ni(0) nanoparticles, as determined by X-ray photoelectron spectroscopy (XPS). The diameter of the Ni nanoparticles (l.85–2.70 nm) was found to be inversely proportional to dendrimer generation and the NH2:Ni(II) ratio. Silica-supported iron oxide nanoparticles were prepared by impregnation of silica with ferrocenoyl dendrimers, DAB-(NHCOFc)n, followed by thermal treatment. XPS and thermogravimetric analysis indicated that thermal decomposition at 450 °C in the presence of air results in formation of silica-supported Fe2O3 nanoparticles and successful removal of organic materials from the silica surface. Control over nanoparticle diameter (2.50–3.31 nm) was shown to be possible by manipulating the dendrimer generation, calcination temperature, and the metal loading on the silica support. Fe2O3/SiO2 nanoparticles were used as laboratory surrogates in mediating monochlorobenzene decomposition and conversion to byproducts. Surface-mediated reactions of monochlorobenzene with Fe2O3/SiO2 were studied under pyrolytic and oxidative conditions between 300–550 °C. Fe2O3/SiO2 prepared by incipient wetness of silica support with iron(III) nitrate was also studied. The results obtained under pyrolysis conditions indicate that the Fe2O3 nanoparticles promote furans formation and other chlorinated byproducts. Fe2O3 nanoparticles obtained from ferrocenoyl dendrimers were found to have higher activity in the production of furans than those catalysts obtained from iron nitrate precursors, with the smallest nanoparticle being the most active. Fe2O3 nanoparticles had different properties under pyrolytic and oxidative conditions. Under oxidative conditions iron oxide-mediated monochlorobenzene destruction, rather than the formation of furans and chlorinated byproducts was observed. From a general synthesis point-of-view, my work has significance for and impact on the field of nanoparticle formation and the environment.