<p> In this dissertation, as a monitoring technology for cyanotoxins, a multiwalled carbon nanotube (MWCNT)-based electrochemical biosensor was developed to determine microcystin-LR (MC-LR), a potent cyanobacterial toxin, in sources of drinking water supplies. The performance of the MWCNT array biosensor is evaluated using micro-Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron-transfer resistance on the MC-LR concentration is observed in the range of 0.05 to 20 µg L<sup>-1</sup>, which enables cyanotoxin monitoring well below the World Health Organization provisional concentration limit of 1 µg L<sup>-1</sup> for MC-LR in drinking water. </p><p> In addition to the development of monitoring tools for cyanotoxins, visible light-activated (VLA) TiO<sub>2</sub> and monodisperse TiO<sub>2</sub> were developed and evaluated for treatment of water contaminants of emerging concern. These materials were synthesized using modified sol-gel methods (i.e., wet chemistry-based methods) such as self-assembly-based and ionic strength-assisted techniques. For this study, first, VLA-sulfur-doped TiO<sub>2</sub> (S-TiO<sub> 2</sub>) nanocrystalline films were synthesized by a self-assembly-based sol-gel method using nonionic surfactant to control nanostructure and an inorganic sulfur source for decomposing MC-LR under visible light illumination. Second, the effects of solvent on the synthesis of VLA-S-TiO<sub>2</sub> films were scrutinized. Four different polar, protic solvents, isopropanol, 1-butanol, ethanol, and methanol, were chosen as the solvent in four titania sol-gel preparations. Third, monodisperse anatase titania nanoparticles with controllable sizes (typically 10-300 nm) were synthesized using an efficient and straightforward protocol via fine tuning of the ionic strength in the devised sol-gel methodology. Finally, noble metal Ag-decorated, monodisperse TiO<sub>2</sub> (TiO<sub> 2</sub>-Ag) aggregates were successfully synthesized by an ionic strength-assisted, simple sol-gel method and were used for the photocatalytic degradation of the pharmaceutical oxytetracycline (OTC) under both UV and visible light irradiation. With a self-assembly-based sol-gel method, nanostructured anatase S-TiO<sub> 2</sub> with high surface area (> 100 m<sup>2</sup> g<sup>-1</sup>) and porosity (> 30 %) was synthesized and the sample calcined at 350 <sup> o</sup>C demonstrated the highest visible light absorption and visible light-induced photocatalytic activity in the decomposition of MC-LR. The structural and morphological properties of S-TiO<sub>2</sub> could be also tailor-designed using different solvents in the sol-gel synthesis, while inducing negligible effects on the sulfur doping and the visible light activation of TiO<sub> 2</sub>. Thus, it can be concluded that the enhancement of photocatalytic activity of S-TiO<sub>2</sub> films can be achieved by judicious choice of the main solvent for the sol-gel method. With an ionic strength-assisted sol-gel method, monodisperse spherical anatase TiO<sub>2</sub> (10-300 nm in diameter) as well as monodisperse TiO<sub>2</sub>-Ag aggregates with 350 nm of diameter were synthesized. For TiO<sub>2</sub>-Ag, its visible light absorption increased due to the presence of Ag on the surface of monodisperse TiO<sub>2</sub>, which resulted in the enhancement of the photocatalytic degradation of OTC under both UV-visible light and visible light irradiation compared to pure TiO<sub>2</sub>. There was an optimal Ag content to obtain the highest photocatalytic degradation of OTC. These newly developed materials demonstrated the efficient decomposition of water contaminants of emerging concern, especially MC-LR and OTC, under UV-visible light and visible light illumination.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3622058 |
| Date | 19 July 2014 |
| Creators | Han, Changseok |
| Publisher | University of Cincinnati |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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