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Issue 21, 1994
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Time-resolved microwave conductivity. Part 2.—Quantum-sized TiO2 and the effect of adsorbates and light intensity on charge-carrier dynamics

Abstract

Charge-carrier recombination dynamics after a pulsed laser excitation are investigated by time-resolved microwave conductivity (TRMC) for quantum-sized (Q-) TiO2 and P25, a bulk-phase TiO2. Adsorbed scavengers such as HNO3, HCl, HClO4, isopropyl alcohol, trans-decalin, tetranitromethane, and methyl viologen dichloride result in different charge-carrier recombination dynamics for Q-TiO2 and P25. The differences include a current doubling with isopropyl alcohol for which electron injection into Q-TiO2 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-TiO2 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-TiO2, and a model incorporating the heterogeneity of surface-hole traps is presented.

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Article type: Paper
DOI: 10.1039/FT9949003323
Citation: J. Chem. Soc., Faraday Trans., 1994,90, 3323-3330
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    Time-resolved microwave conductivity. Part 2.—Quantum-sized TiO2 and the effect of adsorbates and light intensity on charge-carrier dynamics

    S. T. Martin, H. Herrmann and M. R. Hoffmann, J. Chem. Soc., Faraday Trans., 1994, 90, 3323
    DOI: 10.1039/FT9949003323

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