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Time-resolved Microwave Conductivity. Part 1.—TiO_2 Photoreactivity and Size Quantization

Martin, Scot T. and Herrmann, Hartmut and Choi, Wonyong and Hoffmann, Michael R. (1994) Time-resolved Microwave Conductivity. Part 1.—TiO_2 Photoreactivity and Size Quantization. Journal of the Chemical Society. Faraday Transactions, 90 (21). pp. 3315-3322. ISSN 0956-5000. http://resolver.caltech.edu/CaltechAUTHORS:20120302-072504258

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Abstract

Charge-carrier recombination dynamics after laser excitation are investigated by time-resolved microwave conductivity (TRMC) measurements of quantum-sized (Q-) TiO_2, Fe^(III)-doped Q-TiO_2, ZnO and CdS, and several commercial bulk-sized TiO2 samples. After pulsed laser excitation of charge carriers, holes that escape recombination react with sorbed trans-decalin within ns while the measured conductivity signal is due to conduction-band electrons remaining in the semiconductor lattice. The charge-carrier recombination lifetime and the interfacial electron-transfer rate constant that are derived from the TRMC measurements correlate with the CW photo-oxidation quantum efficiency obtained for aqueous chloroform in the presence of TiO_2. The quantum efficiencies are 0. 4 % for Q-TiO_2, 1. 6 % for Degussa P25, and 2. 0 % for Fe^(III)-doped Q-TiO_2. The lower quantum efficiencies for Q-TiO_2 are consistent with the relative interfacial electron-transfer rates observed by TRMC for Q-TiO_2 and Degussa P25. The increased quantum efficiencies of Fe^(III)-doped Q-TiO_2 and the observed TRMC decays are consistent with a mechanism involving fast trapping of valence-band holes as Fe^(IV) and inhibition of charge-order recombination.


Item Type:Article
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http://dx.doi.org/10.1039/FT9949003315 DOIUNSPECIFIED
http://pubs.rsc.org/en/content/articlelanding/1994/ft/ft9949003315PublisherUNSPECIFIED
Additional Information:© 1994 Royal Society of Chemistry. Paper 4/02296C; Received 18th April, 1994. We are indebted to Prof. Nathan S. Lewis for the loan of microwave components, to Prof. Geoffrey A. Blake for the use of the excimer laser and to Dr. Detlef W. Bahnemann for providing the Sachtleben Chemie samples. We are grateful to ARPA and ONR {NAV 5 HFMN N0001492J1901) for financial support. S.M. is supported by a National Defense Science and Engineering Graduate Fellowship. H.H. wishes to thank NATO/DAAD for financing a research vist at the California Institute of Technology. Nicole Peill, Dr. Amy Hoffman and Dr. Andreas Termin provided valuable support and stimulating discussion.
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Funding AgencyGrant Number
ARPAUNSPECIFIED
Office of Naval Research (ONR)N0001492J1901
National Defense Science and Engineering Graduate FellowshipUNSPECIFIED
NATO/DAAD UNSPECIFIED
Record Number:CaltechAUTHORS:20120302-072504258
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120302-072504258
Official Citation:Time-resolved microwave conductivity. Part 1.—TiO2 photoreactivity and size quantization Scot T. Martin, Hartmut Herrmann, Wonyong Choi and Michael R. Hoffmann J. Chem. Soc., Faraday Trans., 1994, 90, 3315-3322 DOI: 10.1039/FT9949003315
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29552
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:02 Mar 2012 16:02
Last Modified:26 Dec 2012 14:54

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