Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 120-132). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 120-132). Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Photoelectrochemical cells (PEC) and microbial fuel cells (MFC) are two promising environmental technologies with the purposes of energy production and pollutant degradation. In this study, p-type Cu2O thin film electrodes were synthesized by electrodeposition on the ITO glass. The influences of various electrodeposition conditions, including the deposition potential, temperature, electrolyte pH, substrates and deposition duration on the morphology and the photoelectrochemical properties of the Cu2O films were investigated. The so-called p-type micro-crystal Cu2O thin film photocathodes were synthesized at -0.4 V, 70 °C and pH 10. An innovative composite Cu2O/TiO2 photoelectrode was developed by dip-coating TiO2 on the surface of the Cu2O film. The outer TiO2 layer would help reduce the electron-hole recombination and hence improve the catalyst stability. The photocatalyst was shown to be capable of photocatalytic degradation of model pollutants. Under simulated solar irradiation, methylene blue, acridine orange, and bromocresso brilliant blue G were effectively degraded in the Cu2O-based PEC. The composite Cu2O/TiO2 photoelectrode could further enhance the photodegradation of the dyes. For the study on MFC with the saline wastewater-inoculated MFCs, an electricity output of 581 mW/m2 could be achieved at a NaCl concentration of 200 mM. Based on the characterization of the bioande using the electrochemical impedance spectroscopy (EIS) technique, the R(QR)(QR) model, instead of the conventional R(QR) model, was found to fit well with the EIS data of the carbon cloth bioanode. The results support the two-interface-based physical model for the description of the bioanode, including an interface on the flat electrode and the other for the porous biofilm matrix. The new model was employed to monitor the biofilm formation and development on the carbon clothe anode during the MFC start-up. In addition, photocatalytic MFC was developed by using the Cu2O film as the photocathode for the MFC. With the simulated solar light illumination, the PMFC open circuit voltage could be increased by 200 mV comparing to the MFC test. Moreover, the cathode material (Cu2O) is much less expensive than Pt used by common MFCs. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material. In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations. / published_or_final_version / Physics / Master / Master of Philosophy

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There is significant interest in understanding and exploiting the extraordinary property enhancements of polymers, enabled by adding small concentrations of nanoparticles to polymer hosts to create polymer nanocomposites (PNCs). Thin film PNCs hold potential for novel technological applications in areas such as optoelectronics or photovoltaic devices. One of the key challenges that limits the potential of PNC-based technologies is the control of nanofiller dispersion throughout the matrix. This requires a fundamental understanding of the energetic interactions that affect dispersion. Thin film PNCs pose a greater challenge than bulk PNCs, largely because interfacial interactions become increasingly important as the material is confined. It is equally important to find effective processing schemes that promote nanofiller dispersion in a manner that can be readily scalable for industrial operations. Accordingly, the last few years have seen an upsurge in processing schemes involving supercritical solvents, due in part to their tunable solvent strength. To this end, our research is aimed at gaining control of nanoparticle dispersion within thin film hosts using supercritical CO₂ (scCO₂) as a processing aid. This research examined a series of related problems. For the first project, we investigated the effects of scCO₂ sorption on the structural stability and kinetics of destabilization of homopolymer films. We showed that the films are metastable under these conditions, and the barrier to nucleation is larger than that encountered in air/vaccum. We also examined the issue of nanofiller dispersion within homopolymer thin films. In a model athermal mixture, polystyrene-coated gold nanoparticles in polystyrene hosts, interfacial segregation was generally observed, and was shown to be a function of the wetting characteristics of the brush-matrix interface and the ratio of the size of the particles to the unperturbed dimensions of the host chains. In a separate system, we show how scCO₂ can serve to prevent coarsening, which is ubiquitous in air/vacuum environments at elevated temperatures, for these nanofillers. Finally, we made nanocomposite micellar structures from block copolymers, with a fluorinated block. Gold nanoparticles were sequestered within the discontinuous domain. We then showed how scCO₂ could be used to invert the structure, placing the nanoparticles in the continuous phase.