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Time-resolved Microwave Conductivity. Part 2.-Quantum-sized TiO_2 and the Effect of Adsorbates and Light Intensity on Charge-carrier Dynamics

Martin, Scot T. and Herrmann, Hartmut and Hoffmann, Michael R. (1994) Time-resolved Microwave Conductivity. Part 2.-Quantum-sized TiO_2 and the Effect of Adsorbates and Light Intensity on Charge-carrier Dynamics. Journal of the Chemical Society. Faraday Transactions, 90 (21). pp. 3323-3330. ISSN 0956-5000. http://resolver.caltech.edu/CaltechAUTHORS:20120307-094831811

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Abstract

Charge-carrier recombination dynamics after a pulsed laser excitation are investigated by time-resolved microwave conductivity (TRMC) for quantum-sized (Q-) TiO_2 and P25, a bulk-phase TiO_2. Adsorbed scavengers such as HNO_3, HC, HCIO_4, isopropyl alcohol, trans-decalin, tetranitromethane, and methyl viologen dichloride result in different charge-carrier recombination dynamics for Q-TiO_2 and P25. The differences include a current doubling with isopropyl alcohol for which electron injection into Q-TiO_2 is much slower than into P25 and relaxation of the selection rules of an indirect-bandgap semiconductor due to size quantization. However, the faster interfacial charge transfer predicted for Q-TiO_2 due to a 0. 2 eV gain in redox overpotentials is not observed. The effect of light intensity is also investigated. Above a critical injection level, fast recombination channels are opened, which may be a major factor resulting in the dependence of the steady-state photolysis quantum yields on l^(–1/2). The fast recombination channels are opened at lower injection levels for P25 than for Q-TiO_2, and a model incorporating the heterogeneity of surface-hole traps is presented.


Item Type:Article
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http://dx.doi.org/10.1039/FT9949003323DOIUNSPECIFIED
http://pubs.rsc.org/en/content/articlelanding/1994/ft/ft9949003323PublisherUNSPECIFIED
Additional Information:© 1994 The Royal Society of Chemistry. Paper 4/02297A; Received 18th April, 1994. We are indebted to Prof. Nathan S. Lewis for the loan of microwave components and to Prof. Geoffrey A. Blake for the use of the excimer laser. We are grateful to ARPA and ONR {NAV 5 HFMN N0001492J1901} for financial support. S.M. is supported by a National Defence Science and Engineering Graduate Fellowship. H.H. wishes to thank NATO/DAAD for financing a research visit at the California Institute of Technology. Wonyong Choi, Dr. Amy Hoffman, Nicole Peill and Dr. Andreas Termin provided valuable support and stimulating discussion.
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ARPA ONRN0001492J1901
National Defense Science and Engineering Graduate FellowshipUNSPECIFIED
NATO/DAAD UNSPECIFIED
Record Number:CaltechAUTHORS:20120307-094831811
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120307-094831811
Official Citation:Time-resolved microwave conductivity. Part 2.—Quantum-sized TiO2 and the effect of adsorbates and light intensity on charge-carrier dynamics Scot T. Martin, Hartmut Herrmann and Michael R. Hoffmann J. Chem. Soc., Faraday Trans., 1994, 90, 3323-3330 DOI: 10.1039/FT9949003323
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29614
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:13 Mar 2012 16:39
Last Modified:26 Dec 2012 14:55

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