Degree Type

Dissertation

Date of Award

2015

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Javier Vela

Abstract

Silica-based nanocomposites with core/shell configurations have diverse functionalities and applications. We present the preparation and characterization of Co3O4/porous-SiO2 nanocomposites with the examination of their catalytic activity in the dye sensitized water oxidation reaction; a generalized methodology to prepare metal chalcogenides/pnictides with one-pot and one-step manner; the synthesis of Au/Ag/SiO2 multishell nanorods and their application as imaging probes in single particle tracking experiments.

Silica supported Co3O4 nanocomposites have recently drawn much attention due to their high catalytic ability in the water oxidation reaction. We have synthesized several Co3O4/porous silica nanocomposites to study the synergetic effects of the catalyst microstructure and local environment on water oxidation catalytic activity. The catalytic activity study of Co3O4/porous SiO2 core/shell nanoparticles on oxygen evolution reaction reveals that the catalyst with a 19.8 ± 1.4 nm shell has superior activity than other catalysts due to two possible factors: the increased local concentration of Ru(bpy)32+ near the active Co3O4 and/or the reduced reorganization energy due to the lower dielectric constant. However, further increasing shell thicknesses resulted in the deterioration of catalytic activity possibly due to slower diffusion of reactants. In the Co3O4/SBA-15 system, the unmodified sample is more active than the modified ones. This is could be due to local surface permittivities of surface-modified composites (e.g., −SiPh and −SiMe3) being lower than those of the unmodified composites. Additionally, the loss of possible Ru(bpy)32+ binding sites and pore blocking after surface modification may cause the loss of reactivity.

Late transition metal chalcogenides and pnictides are popular materials for their unique physical properties and various applications, such as hydroprocessing and water electrolysis catalysts. We demonstrate a generalized route using trimethylsilyl reagents (TMSxE) to convert metal oxides into metal chalcogenides and pnictides through deoxysilylation reactions. The resulting nanocrystals are hollow (vesicle-like) and are surrounded by amorphous silica layer. The nonequivalent diffusion of ions induces the void formation inside the nanocrystals (nanoscale Kirkendall effect); simultaneous decomposition of the TMSxE produces silica layers that can serve as the protection layer preventing particle agglomeration and thus increasing both the robustness and thermal stability of the composites.

Plasmonic metal nanocrystals are a type of label/probe in optical applications, such as bioimaging labels, biochemical sensors, photothermal therapy, surface enhanced Raman spectroscopy and surface plasmon enhanced solar cells. Single particle orientation and rotational tracking (SPORT) is one of the techniques that can explicit the biophysics in biological systems. We present the fabrication of Au/Ag/SiO2 nanorods with well-controlled size, composition and shape for SPORT experiments. With the enhancement of the longitudinal dipolar LSPR due to the secondary silver coating, these multishell nanorods are able to provide sufficient sensitivity for detection at temporal resolution in millisecond range on both synthetic lipid bilayers and live cell membranes.

Copyright Owner

Chia-Cheng Lin

Language

en

File Format

application/pdf

File Size

112 pages

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