Dissertation Defenses

Doctoral Dissertation Announcement

---

Candidate: Wen Guo

Degree of: Doctor of Philosophy

Department: Chemistry

Title: Designing Molecular and Nanoscale Materials for Environmental Chemistry Processes

Committee:
Dr. Sherin Obare, Chair
Dr. Ekkehard Sinn
Dr. Kathleen Baker
Dr. Yirong Mo

Date: Monday, March 15, 2010 9:30 a.m. - 11:30 a.m.
2734 Wood Hall

Abstract:
This dissertation focuses on fundamental studies to identify materials that detect and degrade common organic environmental pollutants. Two widespread ground water contaminants, organohalides and organophosphorus compounds, are investigated. Due to continuous usage of these compounds as well as their toxicity, reliable and sensitive methods for their detection and degradation are urgently needed. 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 part per million (ppm) range. Furthermore, we have developed catalysts consisting of flavin mononucleotide (FMN) for degradation of the chlorinated ethylenes: cis-1,2-dichloroethylene (cis-DCE), trichloroethylene (TCE) and tetrachloroethylene (PCE). Reduced FMN in the form of 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•. However, when FMN was anchored to nanocrystalline titanium dioxide (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. Furthermore, the FMN/TiO2 hybrid catalyst was effective toward the reduction of three organophosphorus compounds: fenthion, ethion and diethyl chlorophosphate. The reactivity of the catalyst with the organophosphorus compounds occurred at mild conditions in both aqueous solutions and in organic solvents.