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The Role of Metal Ion Dopants in Quantum-Sized TiO_2: Correlation between Photoreactivity and Charge Carrier Recombination Dynamics

Choi, Wonyong and Termin, Andreas and Hoffmann, Michael R. (1994) The Role of Metal Ion Dopants in Quantum-Sized TiO_2: Correlation between Photoreactivity and Charge Carrier Recombination Dynamics. Journal of Physical Chemistry, 98 (51). pp. 13669-13679. ISSN 0022-3654.

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A systematic study of metal ion doping in quantum (Q)-sized (2-4 nm) TiO_2 colloids is performed by measuring their photoreactivities and the transient charge carrier recombination dynamics. The presence of metal ion dopants in the TiO_2 crystalline matrix significantly influences photoreactivity, charge carrier recombination rates, and interfacial electron-transfer rates. The photoreactivities of 21 metal ion-doped colloids are quantified in terms of both the conduction band electron reduction of an electron acceptor (CCl_4 dechlorination) and the valence band hole oxidation of an electron donor (CHCl_3 degradation). Doping with Fe^(3+), Mo^(5+), Ru^(3+), Os^(3+), Re^(5+), V^(4+), and Rh^(3+) at 0.1-0.5 at.% significantly increases the photoreactivity for both oxidation and reduction while Co^(3+) and Al^(3+) doping decreases the photoreactivity. The transient absorption signals upon laser flash photolysis (λ_(ex) = 355 nm) at λ = 600 nm are extended up to 50 ms for Fe^(3+)-, V^(4+)-, Mo^(5+)-, and Ru^(3+)-doped TiO_2 while the undoped Q-sized TiO_2 shows a complete "blue electron" signal decay within 200 μs. Co^(3+)- and Al^(3+)-doped TiO_2 are characterized by rapid signal decays with a complete loss of absorption signals within 5 μs. The quantum yields obtained during CW photolyses are quantitatively correlated with the measured transient absorption signals of the charge carriers. Photoreactivities are shown to increase with the relative concentration of trapped charge carriers. The photoreactivity of doped TiO_2 appears to be a complex function of the dopant concentration, the energy level of dopants within the TiO_2 lattice, their d electronic configuration, the distribution of dopants, the electron donor concentration, and the light intensity.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1994 American Chemical Society. Received: July 15, 1994; In Final Form: October 12, 1994. We are grateful to ARPA and ONR {N0014-92-J-1901} for financial support. We thank the Beckman Institute of Caltech for allowing us to use its laser resource center. Dean Willberg, Jay Winkler, Scot Martin, and Nicole Peill were critical to the success of this project.
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Advanced Research Projects Agency (ARPA)UNSPECIFIED
Office of Naval Research (ONR)N0014-92-J-1901
Issue or Number:51
Record Number:CaltechAUTHORS:20150810-083412806
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Official Citation:The Role of Metal Ion Dopants in Quantum-Sized TiO2: Correlation between Photoreactivity and Charge Carrier Recombination Dynamics Wonyong Choi, Andreas Termin, and Michael R. Hoffmann The Journal of Physical Chemistry 1994 98 (51), 13669-13679 DOI: 10.1021/j100102a038
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59337
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 17:19
Last Modified:03 Mar 2020 13:01

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