Date of Graduation

5-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

Ryan Tian

Committee Member

Neil Allison

Second Committee Member

Dan Davis

Third Committee Member

Bill Durham

Keywords

Pure sciences; Applied sciences; Aging; Fuel cells; Humidity sensor; Lattice intercalation; Nanobelts; Titanate

Abstract

Titanate nanobelts (NBs) have structural characteristics beyond that of clays. Due to a negatively charged lattice matrix of edge-shared TiO6-octahedra, the location of intercalated cations within the interlayer space may dictate the charge-conductions. This environment may in turn govern the lattice-framework's stability and surface properties, based upon our preliminary

data.

On that basis, these nanomaterials have been found in our lab to possess superb biological compatibility that is closely related to the types of the intercalated cations. In addition, a prolonged agitation was proven to enable us to manipulate the titanate NBs' length. In a parallel study, a ripening was observed in the post-synthesis aging process at room temperature (RT). This process implied, for the first time, a new way of changing the NBs' aspect ratio in nanosynthesis.

This novel post-synthesis manipulation of aspect ratio has enabled us to successfully improve our yield of the NB-membrane by four folds, which is significant in scale-up fabrication of the NB-entangled membranes, which have shown interest as a proton exchange membrane (PEM) in fuel cells (PEMFC) and gas sensing capabilities. PEMFCs provide the highest power density in comparison with all other fuel cell types currently available. In order to improve the fuel cells efficiency, further advancements into enhancing the thermal stability while maintaining adequate hydration levels of the PEM

membrane is continually sought after. Unfortunately, the polymer structure of Nafion© membranes structural stability and water retention falls short at elevated temperatures. However, based on our preliminary data, intercalated titanate NBs/Nafion© composites may hold the key to overcoming these technological drawbacks.

Lastly, aging and surface modification of titanate materials has been used to attain the high selectivity and sensitivity in electrochemical sensing when applied to an electrode surface. Our initial findings suggest that the intercalated titanate NBs is ideal for use on an interdigitated electrode surface for direct sensing of relative humidity at different percentages.

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