Date of Award

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemical Engineering

Advisor

Kitchens, Christopher L

Committee Member

Bruce , David

Committee Member

Hirt , Douglas

Committee Member

Mefford , Thompson

Abstract

Global carbon dioxide (CO2) emissions have steadily risen over the last 50 years, with 34 billion tons of CO2 released in 2009 alone. Its potential as a greenhouse gas has negatively affected of our lives and environment by the resulting ocean acidification and climate change. To mitigate atmospheric CO2, various strategies have been implemented for CO2 separation, capture, storage and use as a chemical feedstock. The use of CO2 in various chemical industries is attractive as its non-flammable, non-toxic, and relatively inert properties have made it an inherently safer alternative to traditional organic solvents, as well as, a greener carbon feedstock. Also, the accessible critical properties, appreciable critical density, high diffusivity and tunable thermophysical properties make liquid and supercritical CO2 an attractive solvent for industrial applications.
In recent years, significant progress has been made in the field of tunable solvent media by employing the reversible reaction of CO2 with amines to produce carbamates. This class of compounds possesses ionic properties that are significantly different from their amines resulting in a non-ionic to ionic switching mechanism that provides for switchable solvent properties, reversible surfactants, low molecular weight organogelators and stimuli responsive materials. The focus of this dissertation is therefore the implementation of the reversible CO2 - amine reaction for the formation of smart surfaces, greener amine protection mechanisms, and cationic metallic nanoparticle synthesis. Chapter 2 of this dissertation demonstrates the reversible reaction of CO2 with amine-containing self-assembled monolayers to yield 'smart' surfaces that undergo a reversible change in structure, charge, and wettability upon reaction with CO2. The formation carbamate esters are also a widely implemented mechanism for amine protection during organic synthesis. However, traditional methods of protection incur increased solvent use and energy consumption due to a separate deprotection reaction. To solve this dilemma, the reversible protection of amines using CO2 induced carbamates was demonstrated in chapter 3; by reducing n-alkyl benzophenone imine and n-phenyl, nalkylurea yields by up to 67% compared to non-protected amines. The applicability of this chemistry to these classes of nucleophilic substitution reactions and has significant potential to alter the way we approach amine protection in organic synthesis. Another research area that has grown popularity over the last decade is the development of metallic nanoparticles, specifically gold nanoparticles (GNPs), due to their size and shape dependent optical and catalytic properties. Chapter 4 of this dissertation demonstrates the successful application of polyethylene imine (PEI) in the synthesis of cationic GNPs, which are of significant interest for biomedical applications. In this work, we investigated the effect of pH, PEI concentration and reduction method on the size and stability of amine-stabilized gold and silver nanoparticles. Furthermore the potential of carbon dioxide as a stabilizing aid through reversible carbamate formation was explored, leading to a decrease in particle size at ambient temperature along with an increase in stability. In summary, this work has demonstrated the great potential of employing the reversible reaction of carbon dioxide with primary and secondary amines as an effective and greener alternative to conventional methods in a diversity of fields that include 'smart' materials, organic chemistry, and functional nanomaterials.

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