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Preparation and characterization of quantum-size titanium dioxide

Kormann, Claudius and Bahnemann, Detlef W. and Hoffmann, Michael R. (1988) Preparation and characterization of quantum-size titanium dioxide. Journal of Physical Chemistry, 92 (18). pp. 5196-5201. ISSN 0022-3654 . http://resolver.caltech.edu/CaltechAUTHORS:20150814-140635561

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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 TiO_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_2 particles appear to form with rutile structure. Excess 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^(3+) species, which has a characteristic visible absorption spectrum. As much as 10% of the available Ti^(4+) ions can be reduced photochemically in the solid with a quantum yield of 3%. Molecular oxygen reoxidizes the Ti^(3+) centers, leading to detectable amounts of surface-bound peroxides. The pH of zero point of charge (pH_(zpc)) 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 E_a = 58 ± 4 kJ/mol has been measured for this reaction. The photocatalytic activity of the small TiO_2 particles is demonstrated.


Item Type:Article
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http://dx.doi.org/10.1021/j100329a027DOIArticle
http://pubs.acs.org/doi/abs/10.1021/j100329a027PublisherArticle
ORCID:
AuthorORCID
Hoffmann, Michael R.0000-0002-0432-6564
Additional Information:© 1988 American Chemical Society. Received: December 15, 1987; In Final Form: February 25, 1988. We are grateful for the assistance of M. Weller (HMI), Carol Garland (CIT), and K. Weiss (Fritz-Haber-Institut, Berlin) during the electron microscopic studies. D.W.B. thanks Prof. A. Henglein (HMI) and the Hahn-Meitner Institut for granting him a leave of absence. We extend our appreciation to G. Mills for helpful discussions and useful criticism. Financial support was provided by the US. EPA (R81162-01-0).
Funders:
Funding AgencyGrant Number
Environmental Protection Agency (EPA)R81162-01-0
Record Number:CaltechAUTHORS:20150814-140635561
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150814-140635561
Official Citation:Preparation and characterization of quantum-size titanium dioxide Claudius Kormann, Detlef W. Bahnemann, and Michael R. Hoffmann The Journal of Physical Chemistry 1988 92 (18), 5196-5201 DOI: 10.1021/j100329a027
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59548
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:17 Aug 2015 18:41
Last Modified:17 Aug 2015 18:41

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