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HERO ID
90582
Reference Type
Journal Article
Title
Preparation and characterization of quantum-size titanium dioxide
Author(s)
Kormann, C; Bahnemann, DW; Hoffman, MR
Year
1988
Is Peer Reviewed?
Yes
Journal
Journal of Physical Chemistry B
ISSN:
1520-6106
EISSN:
1520-5207
Volume
92
Issue
18
Page Numbers
5196-5201
DOI
10.1021/j100329a027
Abstract
The syntheses of transparent colloidal solutions of extremely small titanium dioxide particles (d < 3 nm) in water, ethanol, 2-propanol, and acetonitrile are presented. Quantum-size effects are observed during particle growth and at the final stages of synthesis. They are quantitatively interpreted by using a quantum mechanical model developed by Brus. The particles prepared in aqueous solution possess the anatase structure and consist of about 200 TiO2 molecules at their final growth stage. The colloidal particles can be isolated from solution as white powders that are soluble in water and ethanol with no apparent change in their properties. In organic solvents the quantum-size TiO2 particles appear to form with rutiel structure. Excessive negative charge on the particles resulting either from deprotonated surface hydroxyl groups or from photogenerated or externally injected charge carriers causes a blue shift in the electronic absorption spectrum, which is explained by an electrostatic model. Electrons can be trapped in the solid as a Ti3 +/ species, which has a characteristic visible absorption spectrum. As much as 10% of the available Ti4 +/ ions can be reduced photochemically in the solid with a quantum yield of 3%. Molecular oxygen reoxidizes the Ti3 +/ center, leading to detectable amounts of surface-bound peroxides. The pH of zero point of charge (pHzpc) of the aqueous colloidal suspension has been determined to be 5.1 +/- 0.2. The acid-catalyzed dissolution of the aqueous colloid yielding Ti(IV) oligomers has been studied, and an activation energy Ea = 58 +/- 4 kJ/mol has been measured for this reaction. The photocatalytic activity of the small TiO2 particles is demonstrated.
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