Synthesis and Characterization of Quantum Size Metal Oxide Colloidal Particles. Photocatalytic Peroxide Formation on ZnO and TiO₂

Author: Kormann, Claudius

Year: 1989

Degree: Dissertation (Ph.D.)

Advisors: Hoffmann, Michael R.; Gray, Harry B.

Committee Members: Weinberg, William Henry; Hoffmann, Michael R.; Gray, Harry B.; Morgan, James J.; Lewis, Nathan Saul; Anson, Fred C.

Option: Chemistry

DOI: 10.7907/bya7-6g55

Abstract

The syntheses of transparent colloidal solutions of extremely small ZnO (d < 5nm) and TiO₂ (d < 3 nm) particles in water, alcohol, and acetonitrile are presented. Quantum size effects are observed during particle growth and at final stages of synthesis. They are qualitatively and quantitatively (TiO₂) interpreted by using a simple molecular orbital (MO) picture and a quantum mechanical model developed by Brus. The optical absorption and fluorescence properties as well as the surface acid-base properties are characterized in detail. The two materials are shown to be active photocatalysts in the formation and degradation of H₂O₂ and organic peroxides and in the degradation of chlorinated hydrocarbons. Quantum yields and steady state concentrations are given as function of various reaction parameters such as the oxygen concentration, the nature and concentration of electron donor, pH, and charge of the electron donor. Rates of reaction are correlated with surface speciation as calculated by the SURFEQL computer code. Transparent colloidal solutions of Fe₂O₃ (hematite) have also been prepared, however only negligible photocatalytic activity is found when compared to ZnO and TiO₂. Evidence is presented for OH• radical activity when aqueous TiO₂ suspensions are illuminated at high pH.

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