Degree Type

Dissertation

Date of Award

2004

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

William S. Jenks

Abstract

This dissertation concerns the elucidation of degradation mechanisms of organic contaminants in aqueous suspension of TiO2, and extending understanding of photo catalysis condition to optimize degradation efficiency.;The degradation mechanism of maleic acid, an important intermediate from the photocatalytic degradation of aromatic contaminants, was investigated via product distribution study and control experiments. The understanding of the mechanism of degradation of these compounds can assist us for the ascertaining of the better conditions to perform the mineralization of recalcitrant organic compounds.;The challenge to degrade a cyanyric acid, a recalcitrant species, by modifying TiO2 suspension was carried out. The addition of fluoride to aqueous suspensions of TiO2 has proved to be an important mechanistic tool in unraveling a long-standing conundrum in photocatalytic degradation. By using this method in parallel with other methods for producing homogeneous hydroxyl-type reagents, it is shown that cyanuric acid is susceptible to degradation under easily accessible conditions.;There are isotope studies of photocatalysis of dimethyl phenyl phosphonate, a simple and safe form of organic phosphonate. Exposure of DMMP and related simple phosphonates to TiO2-mediated photocatalytic conditions results first in the loss of one of the methyl esters. An important unsettled mechanistic point is the mechanism by which the methyl is removed. Through the isotope studies of TiO2-mediated photocatalytic degradation of phosphonates, now we can understand removal of the alkyl ester portion of the compounds to produce phosphonic acid monoesters among the primary steps. The retention of 18O in the formation of MMPP clearly demonstrates that the dealkylation mechanism involves degradation of the methyl group exclusively, and neither attack at phosphorus by HO·ads or a related species, nor photoinduced hydrolysis.;With an attempt to activate the modified TiO2 photo catalysts by the visible light and decrease the rapid recombination of excited electrons/holes during photoreaction, WOx-TiO2 powder was prepared by a sol-gel method. The WOx-TiO2 catalysts were characterized by XRD, XPS, and SEM-EDX. The degradation of 4-methoxyresorcinol by using WOx-TiO2 under visible light irradiation was observed.

DOI

https://doi.org/10.31274/rtd-180813-10983

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Youn-Chul Oh

Language

en

Proquest ID

AAI3145675

File Format

application/pdf

File Size

173 pages

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