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Ultrafast Electron Injection and Recombination Dynamics of Coumarin 343-Sensitized Cerium Oxide Nanoparticles

  • Jennifer M. Empey
    Jennifer M. Empey
    Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18thAvenue, Columbus, Ohio 43210, United States
  • Christopher Grieco
    Christopher Grieco
    Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18thAvenue, Columbus, Ohio 43210, United States
  • Natasha W. Pettinger
    Natasha W. Pettinger
    Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18thAvenue, Columbus, Ohio 43210, United States
  • , and 
  • Bern Kohler*
    Bern Kohler
    Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18thAvenue, Columbus, Ohio 43210, United States
    *Email: [email protected]
    More by Bern Kohler
Cite this: J. Phys. Chem. C 2021, 125, 27, 14827–14835
Publication Date (Web):July 5, 2021
https://doi.org/10.1021/acs.jpcc.1c03904
Copyright © 2021 American Chemical Society
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Abstract

Dye-sensitized electron injection into cerium oxide (CeO2) nanoparticles is studied using femtosecond transient absorption spectroscopy. Following the 430 nm photoexcitation of coumarin 343 molecules adsorbed on CeO2 nanoparticles, mid-infrared (mid-IR) transient absorption signals appear within 500 fs. Mid-IR signals are assigned to electrons injected into broadly distributed trap or defect states found roughly midway between the Ce 5d conduction band edge and the bottom of the empty band of Ce 4f states. These states are proposed to have Ce 5d character. In contrast, mid-IR signals are not observed when electrons in bare CeO2 nanoparticles are promoted from the valence band to the band built from Ce 4f orbitals by UV excitation. Transient absorption signals from the oxidized dye rise within 300 fs and decay somewhat more slowly than the mid-IR signals, suggesting that electron relaxation occurs within CeO2 in competition with back-electron transfer to the oxidized dye. These results reveal elementary events important for understanding photocatalysis using CeO2 nanoparticles.

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.1c03904.

  • Band alignment of C-343/TiO2; additional steady-state and transient absorption spectra and decay traces; and description of fitting parameters used for various transient decay traces (PDF)

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