ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: chemical engineering
Description
The mitigation and conversion of carbon dioxide (CO2) to more useful carbon chemicals is a research topic that is at the forefront of current engineering and sustainability applications. Direct photocatalytic reduction of CO2 with water (H2O) vapor to C1-C4 hydrocarbons has significant potential in setting substantial groundwork for meeting the increasing energy demands with minimal environmental impact. Previous studies indicate that titanium dioxide (TiO2) containing materials serve as the best photocatalyst for CO2 and H2O conversion to higher-value products. An understanding of the CO2-H2O reaction mechanism over TiO2 materials allows one to increase the yield of certain products such as carbon monoxide (CO) and methane (CH4). The basis of the work discussed in this thesis, investigates the interaction of small molecules (CO, CH4,H2O) over the least studied TiO2 polymorph - brookite. Using the Gaussian03 computational chemistry software package, density functional theory (DFT) calculations were performed to investigate the adsorption behavior of CO, H2O, and CH4 gases on perfect and oxygen-deficient brookite TiO2 (210) and anatase TiO2 (101) surfaces. The most geometrically and energetically favorable configurations of these molecules on the TiO2 surfaces were computed using the B3LYP/6-31+G(2df,p) functional/basis set. Calculations from this theoretical study indicate all three molecules adsorb more favorably onto the brookite TiO2 (210) surface. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to investigate the adsorption and desorption behavior of H2O and CH4 on Evonik P25 TiO2. Results from the experimental studies and theoretical work will serve as a significant basis for reaction prediction on brookite TiO2 surfaces.
ContributorsRollins, Selisa F (Author) / Andino, Jean M (Thesis advisor) / Dai, Lenore L (Committee member) / Forzani, Erica S (Committee member) / Arizona State University (Publisher)
Created2012
Description
Environmentally responsive microgels have drawn significant attention due to their intrinsic ability to change volume in response to various external stimuli such as pH, temperature, osmotic pressure, or electric and magnetic fields. The extent of particle swelling is controlled by the nature of the polymer-solvent interaction. This thesis focuses on design and synthesis of environmentally responsive microgels and their composites, and encompasses methods of utilizing microgel systems in applications as vehicles for the adsorption, retention, and targeted delivery of chemical species. Furthermore, self-assembled microgel particles at ionic liquid (IL)-water interfaces demonstrate responsive colloidal lattice morphology. The thesis first reports on the fundamental aspects of synthesis, functionalization, and characteristic properties of multifunctional environmentally responsive microgels derived from poly(N-isopropylacrylamide) (PNIPAm) and other functional co-monomers. In particular, the uptake and release of active chemical species such as rheology modifiers into and from these ionic microgels is demonstrated. Moreover, a facile tunable method for the formation of organic-inorganic composites with Fe3O4 nanoparticles adsorbed and embedded within ionic microgel particles is explored. Additionally, the development of zwitterionic microgels (ZI-MG) is presented. These aqueous ZI-MG dispersions exhibit reversible parabolic swelling as a function of pH and display a minimum hydrodynamic diameter at a tunable isoelectric point (IEP). This study also elucidates the controlled uptake and release of surfactants from these particle systems. The extent of surfactant loading and the ensuing relative swelling/deswelling behaviors within the polymer networks are explained in terms of their binding interactions. The latter part of this thesis highlights the versatility of fluorescently labeled microgel particles as stabilizers for IL-water droplets. When the prepared particles form monolayers and equilibrate at the liquid-liquid interface, the colloidal lattice organization may re-order itself depending on the surface charge of these particles. Finally, it is shown that the spontaneously formed and densely packed layers of microgel particles can be employed for extraction applications, as the interface remains permeable to small active species.
ContributorsChen, Haobo (Author) / Dai, Lenore L (Committee member) / Chen, Kangping (Committee member) / Forzani, Erica (Committee member) / Lind, Mary Laura (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2015
Description
Polymer-gold composite particles are of tremendous research interests. Contributed by their unique structures, these particles demonstrate superior properties for optical, catalytic and electrical applications. Moreover, the incorporation of “smart” polymers into polymer-gold composite particles enables the composite particles synergistically respond to environment-stimuli like temperature, pH and light with promising applications in multiple areas.
A novel Pickering emulsion polymerization route is found for synthesis of core-shell structured polymer-gold composite particles. It is found that the surface coverage of gold nanoparticles (AuNP) on a polystyrene core is influenced by gold nanoparticle concentration and hydrophobicity. More importantly, the absorption wavelength of polystyrene-gold composite particles is tunable by adjusting AuNP interparticle distance. Further, core-shell structured polystyrene-gold composite particles demonstrate excellent catalyst recyclability.
Asymmetric polystyrene-gold composite particles are successfully synthesized via seeded emulsion polymerization, where AuNPs serve as seeds, allowing the growth of styrene monomers/oligomers on them. These particles also demonstrate excellent catalyst recyclability. Further, monomers of “smart” polymers, poly (N-isopropylacrylamide) (PNIPAm), are successfully copolymerized into asymmetric composite particles, enabling these particles’ thermo-responsiveness with significant size variation around lower critical solution temperature (LCST) of 31°C. The significant size variation gives rise to switchable scattering intensity property, demonstrating potential applications in intensity-based optical sensing.
Multipetal and dumbbell structured gold-polystyrene composite particles are also successfully synthesized via seeded emulsion polymerization. It is intriguing to observe that by controlling reaction time and AuNP size, tetrapetal-structured, tripetal-structured and dumbbell-structured gold-polystyrene are obtained. Further, “smart” PNIPAm polymers are successfully copolymerized into dumbbell-shaped particles, showing significant size variation around LCST. Self-modulated catalytic activity around LCST is achieved for these particles. It is hypothesized that above LCST, the significant shrinkage of particles limits diffusion of reaction molecules to the surface of AuNPs, giving a reduced catalytic activity.
Finally, carbon black (CB) particles are successfully employed for synthesis of core- shell PNIPAm/polystyrene-CB particles. The thermo-responsive absorption characteristics of PNIPAm/polystyrene-CB particles enable them potentially suitable to serve as “smart” nanofluids with self-controlled temperature. Compared to AuNPs, CB particles provide desirable performance here, because they show no plasmon resonance in visible wavelength range, whereas AuNPs’ absorption in the visible wavelength range is undesirable.
A novel Pickering emulsion polymerization route is found for synthesis of core-shell structured polymer-gold composite particles. It is found that the surface coverage of gold nanoparticles (AuNP) on a polystyrene core is influenced by gold nanoparticle concentration and hydrophobicity. More importantly, the absorption wavelength of polystyrene-gold composite particles is tunable by adjusting AuNP interparticle distance. Further, core-shell structured polystyrene-gold composite particles demonstrate excellent catalyst recyclability.
Asymmetric polystyrene-gold composite particles are successfully synthesized via seeded emulsion polymerization, where AuNPs serve as seeds, allowing the growth of styrene monomers/oligomers on them. These particles also demonstrate excellent catalyst recyclability. Further, monomers of “smart” polymers, poly (N-isopropylacrylamide) (PNIPAm), are successfully copolymerized into asymmetric composite particles, enabling these particles’ thermo-responsiveness with significant size variation around lower critical solution temperature (LCST) of 31°C. The significant size variation gives rise to switchable scattering intensity property, demonstrating potential applications in intensity-based optical sensing.
Multipetal and dumbbell structured gold-polystyrene composite particles are also successfully synthesized via seeded emulsion polymerization. It is intriguing to observe that by controlling reaction time and AuNP size, tetrapetal-structured, tripetal-structured and dumbbell-structured gold-polystyrene are obtained. Further, “smart” PNIPAm polymers are successfully copolymerized into dumbbell-shaped particles, showing significant size variation around LCST. Self-modulated catalytic activity around LCST is achieved for these particles. It is hypothesized that above LCST, the significant shrinkage of particles limits diffusion of reaction molecules to the surface of AuNPs, giving a reduced catalytic activity.
Finally, carbon black (CB) particles are successfully employed for synthesis of core- shell PNIPAm/polystyrene-CB particles. The thermo-responsive absorption characteristics of PNIPAm/polystyrene-CB particles enable them potentially suitable to serve as “smart” nanofluids with self-controlled temperature. Compared to AuNPs, CB particles provide desirable performance here, because they show no plasmon resonance in visible wavelength range, whereas AuNPs’ absorption in the visible wavelength range is undesirable.
ContributorsZhang, Mingmeng (Author) / Dai, Lenore L (Committee member) / Phelan, Patrick E (Committee member) / Otanicar, Todd P (Committee member) / Lin, Jerry (Committee member) / He, Ximin (Committee member) / Arizona State University (Publisher)
Created2015
Description
A low temperature amorphous oxide thin film transistor (TFT) and amorphous silicon PIN diode backplane technology for large area flexible digital x-ray detectors has been developed to create 7.9-in. diagonal backplanes. The critical steps in the evolution of the backplane process include the qualification and optimization of the low temperature (200 °C) metal oxide TFT and a-Si PIN photodiode process, the stability of the devices under forward and reverse bias stress, the transfer of the process to flexible plastic substrates, and the fabrication and assembly of the flexible detectors.
Mixed oxide semiconductor TFTs on flexible plastic substrates suffer from performance and stability issues related to the maximum processing temperature limitation of the polymer. A novel device architecture based upon a dual active layer improves both the performance and stability. Devices are directly fabricated below 200 ºC on a polyethylene naphthalate (PEN) substrate using mixed metal oxides of either zinc indium oxide (ZIO) or indium gallium zinc oxide (IGZO) as the active semiconductor. The dual active layer architecture allows for adjustment to the saturation mobility and threshold voltage stability without the requirement of high temperature annealing, which is not compatible with flexible plastic substrates like PEN. The device performance and stability is strongly dependent upon the composition of the mixed metal oxide; this dependency provides a simple route to improving the threshold voltage stability and drive performance. By switching from a single to a dual active layer, the saturation mobility increases from 1.2 cm2/V-s to 18.0 cm2/V-s, while the rate of the threshold voltage shift decreases by an order of magnitude. This approach could assist in enabling the production of devices on flexible substrates using amorphous oxide semiconductors.
Low temperature (200°C) processed amorphous silicon photodiodes were developed successfully by balancing the tradeoffs between low temperature and low stress (less than -70 MPa compressive) and device performance. Devices with a dark current of less than 1.0 pA/mm2 and a quantum efficiency of 68% have been demonstrated. Alternative processing techniques, such as pixelating the PIN diode and using organic photodiodes have also been explored for applications where extreme flexibility is desired.
Mixed oxide semiconductor TFTs on flexible plastic substrates suffer from performance and stability issues related to the maximum processing temperature limitation of the polymer. A novel device architecture based upon a dual active layer improves both the performance and stability. Devices are directly fabricated below 200 ºC on a polyethylene naphthalate (PEN) substrate using mixed metal oxides of either zinc indium oxide (ZIO) or indium gallium zinc oxide (IGZO) as the active semiconductor. The dual active layer architecture allows for adjustment to the saturation mobility and threshold voltage stability without the requirement of high temperature annealing, which is not compatible with flexible plastic substrates like PEN. The device performance and stability is strongly dependent upon the composition of the mixed metal oxide; this dependency provides a simple route to improving the threshold voltage stability and drive performance. By switching from a single to a dual active layer, the saturation mobility increases from 1.2 cm2/V-s to 18.0 cm2/V-s, while the rate of the threshold voltage shift decreases by an order of magnitude. This approach could assist in enabling the production of devices on flexible substrates using amorphous oxide semiconductors.
Low temperature (200°C) processed amorphous silicon photodiodes were developed successfully by balancing the tradeoffs between low temperature and low stress (less than -70 MPa compressive) and device performance. Devices with a dark current of less than 1.0 pA/mm2 and a quantum efficiency of 68% have been demonstrated. Alternative processing techniques, such as pixelating the PIN diode and using organic photodiodes have also been explored for applications where extreme flexibility is desired.
ContributorsMarrs, Michael (Author) / Raupp, Gregory B (Thesis advisor) / Allee, David R. (Committee member) / Dai, Lenore L (Committee member) / Forzani, Erica S (Committee member) / Bawolek, Edward J (Committee member) / Arizona State University (Publisher)
Created2016
Description
The horizontal desalination units belonging to the humidification-dehumidification family purify water using air as a carrier gas. The temperature required for separation can vary from ambient to 99 °C so waste heat, fuel combustion, or solar collectors can drive the process. A unit in which air flows horizontally affords several advantages over similar vertical “Dewvaporation” towers (as an example), including ease of construction and potentially increased efficiency. The objective was to build and test horizontal units and identify areas of potential efficiency improvements. The desalination units consisted of: 1.) A series of aligned, corrugated, polypropylene sheets covered on the outside with absorbent, water-wettable cloth. 2.) A basin that caught saline water flowing downward from the absorbent cloth. 3.) Ten pumps to cycle the basin water back onto the cloth. 4.) An air blower on the front of the unit that drove air horizontally across the cloth, increasing the humidity of the air. 5.) A steam generator on the back of the unit producing steam that mixed with the incoming air to increase the temperature and humidity. 6) A steam box that caused the air to mix with the steam and return to flow inside the corrugations in the plastic sheets, creating a countercurrent heat exchanger as the exiting air transferred its heat to the incoming air and causing purified water to condense from the cooling, oversaturated air. The tested unit produced distillate at a rate of 0.87 gallons per hour with 13 parts per million total dissolved solids and an energy reuse factor of 2.5. Recommendations include the implementation of a continuous longitudinal pump design, a modification of the basin to accommodate top and bottom unit center dividers, increase in insulation coverage, and optimization of air flow rate.
ContributorsJackson, Skyler (Author) / Beckman, James R. (Thesis advisor) / Krause, Stephen J (Committee member) / Dai, Lenore L (Committee member) / Arizona State University (Publisher)
Created2015