Suspended titanium dioxide (TiO2) nanoparticles produce hydroxyl radicals (•OH) that synergistically aid in disinfection when irradiated with UV light. To exploit the benefits of TiO2 photocatalysis without having to remove them, TiO2 was deposited onto 3M Company’s nanostructured thin film (NSTF). •OH production by suspended and TiO2-NSTF was determined by para-chlorobenzoic acid (pCBA), a •OH probe compound. Both techniques of introducing TiO2 to the samples produced equivalent •OH without forming bromate, a regulated byproduct in drinking water at all UV and TiO2 levels. Formation of bromate by ozone in brackish water and seawater were used to compare the disinfection byproduct (DBP) formation between the disinfection methods. Additionally, monitoring bromate, typically performed by ion chromatography, is complicated by chloride and other anions present in brackish water or seawater. Thus, a spectrophotometric method to measure bromate in saline systems is introduced.

abstract: There are increasing demands for gas sensors in air quality and human health monitoring applications. The qualifying sensor technology must be highly sensitive towards ppb level gases of interest, such as acetylene (C2H2), hydrogen sulfide (H2S), and volatile organic compounds. Among the commercially available sensor technologies, conductometric gas sensors with nanoparticles of oxide semiconductors as sensing materials hold significant advantages in cost, size, and cross-compatibility. However, semiconductor gas sensors must overcome some major challenges in thermal stability, sensitivity, humidity interference, and selectivity before potential widespread adoption in air quality and human health monitoring applications. The focus of this dissertation is to tackle these issues by optimizing the composition and the morphology of the nanoparticles, and by innovating the structure of the sensing film assembled with the nanoparticles. From the nanoparticles perspective, the thermal stability of tin oxide nanoparticles with different Al dopant concentrations was studied, and the results indicate that within certain range of doping concentration, the dopants segregated at the grain surface can improve the thermal stability by stabilizing the grain boundaries. From the sensing film perspective, a novel self-assembly approach was developed for copper oxide nanosheets and the sensor response towards H2S gas was revealed to decrease monotonically by more than 60% as the number of layers increase from 1 to 300 (thickness: 0.03-10 μm). Moreover, a sensing mechanism study on the humidity influence on H2S detection was performed to gain more understandings of the role of the hydroxyl group in the surface reaction, and humidity independent response was observed in the monolayer film at 325 ℃. With a more precise deposition tool (Langmuir-Blodgett trough), monolayer film of zinc oxide nanowires sensitized with gold catalyst was prepared, and highly sensitive and specific response to C2H2 in the ppb range was observed. Furthermore, the effect of surface topography of the monolayer film on stabilizing noble metal catalyst, and the sensitization mechanism of gold were investigated. Lastly, a semiconductor sensor array was developed to analyze the composition of gases dissolved in transformer oil to demonstrate the industrial application of this sensor technology. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

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Philosophiae Doctor - PhD / The depletion of fossil fuel resources such as coal and the concern of climatic change arising from the emission of greenhouse gases (GHG) and global warming [1] lead to the identification of the 'hydrogen economy' as one of the renewable energy sources and possible futuristic energy conversion solution. Sources of hydrogen as fuel such as water through electrolysis and liquid organic fuel (Hydrogen carriers) have been found as potential game-changers and received increased attention, due to its low-carbon emission.

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