Preparation and characterization of quantum-size titanium dioxide
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 TiO/sub 2/ 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 TiO/sub 2/ 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 Ti/sup 3 +/ species, which has a characteristic visible absorption spectrum. As much as 10% of the available Ti/sup 4 +/ ions can be reduced photochemically in the solid with a quantum yield of 3%. Molecular oxygen reoxidizes the Ti/sup 3 +/ center, leading to detectable amounts of surface-bound peroxides. The pH of zero point of charge (pH/sub zpc/) of the aqueous colloidal suspension has been determined to be 5.1 /plus minus/ 0.2. The acid-catalyzed dissolution of the aqueous colloid yielding Ti(IV) oligomers has been studied, and an activation energy E/sub a/ = 58 /plus minus/ 4 kJ/mol has been measured for this reaction. The photocatalytic activity of the small TiO/sub 2/ particles is demonstrated.
- Research Organization:
- California Institute of Technology, Pasadena (USA)
- OSTI ID:
- 6187727
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 92:18
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
14 SOLAR ENERGY
IODIDES
OXIDATION
TITANIUM OXIDES
STRUCTURAL CHEMICAL ANALYSIS
ACETONITRILE
CHEMICAL PREPARATION
COLLOIDS
ETHANOL
EXPERIMENTAL DATA
MATHEMATICAL MODELS
PARTICLES
PHOTOCHEMICAL REACTIONS
PROPANOLS
QUANTUM MECHANICS
SEMICONDUCTOR MATERIALS
WATER
ALCOHOLS
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
DISPERSIONS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
IODINE COMPOUNDS
MATERIALS
MECHANICS
NITRILES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
SYNTHESIS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
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