Synthesis and characterization of quantum size metal oxide colloidal particles. Photocatalytic peroxide formation on ZnO and TiO2

Citation

Kormann, Claudius (1989) Synthesis and characterization of quantum size metal oxide colloidal particles. Photocatalytic peroxide formation on ZnO and TiO2. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05182007-110357

Abstract

The syntheses of transparent colloidal solutions of extremely small ZnO (d< 5nm) and Ti02 (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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