Fundamental Photoelectrochemical Properties of TIO₂/Water Interfaces : Relevance for Hazardous Waste Remediation

Citation

Kesselman, Janet M. (1997) Fundamental Photoelectrochemical Properties of TIO₂/Water Interfaces : Relevance for Hazardous Waste Remediation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5dmz-sa21. https://resolver.caltech.edu/CaltechTHESIS:07142025-223721756

Abstract

TiO₂ photocatalysis is a promising technology for the treatment of aqueous or gaseous systems contaminated by low levels of organic pollutants. The research described in this thesis explores fundamental mechanistic and kinetic questions for both TiO₂ photocatalytic and electrocatalytic degradation of aqueous organic contaminants. A recurring theme in this thesis is the use of TiO₂ electrodes to investigate kinetic and mechanistic aspects of the TiO₂ photocatalytic process. The use of electrodes provides additional experimental control of system parameters that is not possible in conventional TiO₂ slurry reactors.

The first study reports the kinetics of oxygen reduction at single-crystal, rutile TiO₂ electrodes as a function of applied potential. Platinum deposits are found to catalyze the reduction of oxygen at this surface. Application of a flux-matching condition to the independently measured reduction and photooxidation currents predicts significant recombination losses for TiO₂ particles operating under steady-state photocatalytic conditions.

In a second project, the contributions of direct and hydroxyl radical mediated oxidation pathways are determined at Nb-doped, polycrystalline TiO₂ electrodes. In addition to quantifying the branching ratio of these two mechanisms for a variety of organic substrates, the results suggest that surface interactions are important in determining the predominant reaction pathway in these systems.

Finally, the adsorption of 4-chlorocatechol at the TiO₂/H₂O interface is investigated as a function of pH and solution concentration. Quantitative measurements of the extent of adsorption are reported as well as spectroscopic evidence for the structure of the adsorbed complex. Further work correlates observed photocatalytic degradation rates with the extent of adsorption under various solution conditions.

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