Photocatalytic oxidation kinetics and mechanisms of meta-substituted phenols by TiO₂/UV : a molecular structure-reactivity study

Document Type



Master of Science (MS)


Environmental Engineering

First Advisor's Name

Walter Z. Tang

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

William J. Cooper

Third Advisor's Name

Kevin E. O'Shea

Fourth Advisor's Name

Hector R. Fuentes


Phenols, Photocatalysis

Date of Defense



The oxidation kinetics of m-substituted phenols by TiO2/UV were investigated. An attempt was made to correlate Swain-Lupton parameters (R) for aromatic substituents with the oxidation kinetic constants, based upon molecular structure and reactivity theory. Irradiation experiments were carried out with suspended aqueous TiO 2 powder and substrate mixture in a Rayonet Photochemical Reactor. Langmuir-Hinshelwood model was applied to obtain apparent kinetic rate constants. A linear correlation is observed between Langmuir-Hinshelwood kinetic parameters and Hammett constants for m-chloro, m-bromo and m-fluoro phenols. The changes in p values of Hammett plots at pH 3 suggest that the main degradation pathway may involve a positively charged intermediate, such as a radical cation formed by direct electron transfer to the positive holes at low pH. At high pH levels, however, substrate speciation, surface charge of the semiconductor, and bandgap shift appear to lead to a change in the degradation mechanism.



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