|Title||Designing molecular and nanoscale materials for environmental chemistry processes|
This dissertation focuses on fundamental studies to identify materials that detect and degrade common organic environmental pollutants Chapter 1 represents the overview of two widespread ground water contaminants: organohalides and organophosphorus compounds. Due to continuous usage of these compounds as well as their toxicity, reliable and sensitive methods for their detection and degradation are urgently needed. In Chapter 2 a description of molecular sensors designed with high sensitivity and selectivity to detect and distinguish between three organophosphorus (OP) pesticides are described. These sensors provide dual optical and electrochemical signals for detection, which minimizes false-positives. The signal transduction occurs in real time with detection limits in the ppm range Chapter 3 reports an organic molecule 9,11,20,22-tetraaza-tetrapyridopentacene (TATPP), capable of storing and shuttling multiple electrons, which are desirable for potential applications including remediation of environmental pollutants. We demonstrate the ability to photochemically modulate the reduction of TATPP and we investigate its reactivity. Chapter 4 describes the degradation of the chlorinated ethylenes: cis-1,2-dichloroethylene (cis-DCE), trichloroethylene (TCE) and tetrachloroethylene (PCE). Flavin mononucleotide (FMN) was used as a catalyst to aid in the degradation process. FMNH2 was produced in methanol solvent by the photoreduction of FMN. In aqueous solution, FMN was not fully reduced to FMNH2 but instead yielded the semiquinone radical FMNH&bullï¼›. However, when FMN was anchored to nanocrystalline TiO2, band gap irradiation resulted in electron transfer from the TiO2 conduction band to FMN, thus yielding FMNH2. The FMNH2 generated in aqueous solution on the TiO2 surface was a stronger reductant toward chlorinated ethylenes, relative to FMNH2 in solution. By combining the reactivity of the TiO2 conduction band electrons (TiO2(e -CB)) with FMNH2, the reduction rate constants for the chlorinated ethylenes increased by two orders of magnitude relative to FMNH2 alone. In Chapter 5, we report that the FMN/TiO2 hybrid catalyst is effective toward the reduction of three organophosphorus compounds: fenthion, ethion and diethyl chlorophosphate. The reactivity of the catalyst with the organophosphorus compounds occurs at mild conditions in both aqueous solutions and in organic solvents.
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