| dc.description.abstract | Nanoparticles have received much attention due to their unique structure and physical and chemical properties compared to their bulk material counterparts, which allow them to be used in a variety of applications, such as imaging, medical applications, and catalysis. As such, close examination of the structure and electronic properties of various nanoparticles is of incredibly high interest.
In this work, X-ray absorption spectroscopy (XAS), supported by other characterization techniques, was used to study the structure and bonding properties of a number of different nanoparticle catalysts. First, a series of W-doped TiO2 nanoparticles was examined, in order to determine the changes in atomic structure that allowed for the W-TiO2 4% doping to exhibit greater photothermalcatalytic activity than the other samples. Extended X-ray Absorption Fine Structure (EXAFS) fittings results showed that the dopant W atoms replaced Ti atoms within the lattice, creating Ti vacancies. As the W doping concentration increased to 4%, the Ti vacancies also increased, as did the number of dangling oxygen and oxygen vacancies, which could act as catalytic sites. Formation of WO3 outside of the lattice at 10% doping was also seen in the fitting results, showing why the 4% sample exhibited greater catalytic activity.
Next, a series of manganese cobalt oxides supported on carbon nanotubes were studied, with XAS results allowing for a clearer picture of the phase transition from a cubic structure to a tetragonal structure as the amount of manganese in the samples increased and the amount of cobalt decreased. Mn1.5Co1.5O4, which contains an equal ratio of Co and Mn, was found to have a dual-phase structure, based on both EXAFS fitting results and linear combination X-ray absorption near-edge structure (LC XANES) fitting. This was unlike the other samples studied, which were either completely cubic phase or tetragonal phase structures, and further understanding of the dual-phase structure would potentially allow for better fine-tuning of the structure of the sample, and as such, its catalytic applications.
Finally, a number of ruthenium nanoparticle samples, both monometallic and bimetallic, were synthesized and supported on three different zeolite supports (Y, beta, and mordenite) with varying concentrations of the ruthenium ion precursor to determine the effect of concentration and support on the local structure and bonding properties. It was found that bimetallic samples of Ru and Pd displayed strong indications of metal core formation, whereas Ru and Co bimetallic samples showed little metal core formation, as seen in the EXAFS fitting results for all samples.
This work highlights the importance of the relationship between the structure of nanoparticles and their properties. X-ray absorption spectroscopy gives a deep understanding of the structure and bonding properties of representative sites of nanoparticles, and by using the information obtained from such studies, a clearer picture of the nanoparticle structure can be formed. These results could lead to further development into tailoring the structure of certain nanoparticles in order to optimize their performance in relevant applications. | en_US |
