Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor(s)

Dr. Mita Ray / Dr. Paul Charpentier

Abstract

This thesis explores the synthesis of metal oxide 1-D nanowires using a sol-gel method in supercritical carbon dioxide (sc-CO2), as an environmental friendly enabling solvent. Porous nanowires were synthesized and their performance was tested in dye sensitized solar cell and sacrifical hydrogen production. Titanium isopropoxide (TIP) was used as a precursor for titania synthesis while copper, bismuth and indium were examined as dopants, respectively. The sol-gel reactions were catalyzed by acetic acid in CO2 at a temperature of 60 °C and pressure of 5000 psi. It was observed that acetic acid/monomer ratio > 4 produced nanowires while a lower ratio led to the formation of various morphologies, depending on reaction conditions. The synthesized undoped and doped nanowires were characterized by electron microscopy (SEM and TEM), N2 physisorption, FTIR, XRD, XPS, thermal analysis. These results showed high aspect ratio nanowires as observed by SEM (15-25) with surface areas ranging from 40 to 126 m2/g. These surface areas are comparable and sometimes exceeded the surface area of Degussa P25 (i.e. 50 m2/g).

Copper doped nanowires were examined as sacrificial photocatalytic catalysts in ‎Chapter 3. It was found that the modified sol-gel synthesis approach in supercritical CO2 produced primarily a single oxidation state (Cu (I)) of active Cu2O/TiO2, which was confirmed by XPS and XANES analyses. Wt % of copper and initial concentration of sacrificial agent were optimized to enhance hydrogen production with the results compared to undoped titanium nanowires and Degussa P25. The Cu2O/TiO2 nanowires showed improved hydrogen production at 1 % Cu (I) loading which produced about 10 times more hydrogen than Degussa P25 and 47 times more than undoped nanowires, respectively.

‎Chapter 4 discusses the synthesis and application of Indium (In) doped titania for DSSCs and sacrificial hydrogen production. Indium has high conductivity, transparency for visible light, and good electron mobility, making it an attractive dopant for such applications.

In ‎Chapter 5, sacrificial hydrogen production by bismuth titanate nanowires using formaldehyde as the sacrificial agent is examined. Bismuth titanate was previously shown theoretically to have all the requirements to be an effective photocatalyst to produce hydrogen when doped with transition metals. However, little experimental work has been reported on the performance of bismuth titanate nanowires. Bismuth titanate nanowires were synthesized using a sol-gel methodology in supercritical CO2 with different levels of bismuth loading (1, 1.4, and 2 mol % bismuth). These nanowires were investigated for their sacrificial photocatalytic hydrogen production, which was compared to that of undoped titanium nanowires and P25.

‎Chapter 6 deals with the experimental results of bismuth titanate, which is known as an active visible light photocatalyst, with most of its applications focused on remediation of water and wastewater. However, very limited applications of bismuth titanate in DSSCs have been reported in the literature. The effect of Bi loading on TiO2 nanowires for DSSCs was investigated by testing the J-V curves of the solar cells. The influence of Bi on the internal processes of electron transport was also evaluated by electrochemical impedance spectroscopy.

In order to integrate these nanowires into polymeric systems for easy processability and application, the synthesis of polysulfone polymers was examined in ‎Chapter 7. These polymers were designed to contain carboxylic functional groups to enable coordination with titanium and titanium doped photocatalyst. The goal was to produce an organic-inorganic membrane for photocatalytic membrane reactor that can reduce fouling by degradation of pollutants. The membrane was also examined to be cast as nanotubes using an anodic aluminum oxide (AAO) template method.