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Photo-generated conduction-band and shallow-trap electrons from UV irradiation on ethanol-adsorbed TiO2 and N-TiO2: an in situ infrared study

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Abstract

The dynamic behaviors of conduction-band electrons (\({\text{e}}_{CB}^{ - }\)) and shallow-trap electrons (\({\text{e}}_{ST}^{ - }\)) generated from UV irradiation on ethanol-adsorbed TiO2 and N-TiO2 have been studied by in situ Fourier transform infrared spectroscopy (FTIR) in a diffuse reflectance mode at 300 K and 0.1 MPa. UV irradiation on ethanol-adsorbed TiO2 resulted in the breaking of C–H bond of ethanol, the transfer of electrons from ethanol to the photo-generated holes on TiO2 and N-TiO2, the accumulation of \({\text{e}}_{CB}^{ - }\) and \({\text{e}}_{ST}^{ - }\), and the formation of acetate on TiO2 and the formation of acetate, formate, and formaldehyde on N-TiO2. Accumulated \({\text{e}}_{CB}^{ - }\) and \({\text{e}}_{ST}^{ - }\) are manifested by broad and featureless IR absorbance spectra, which can be fitted into two models for estimation of their relative concentrations. N-doping onto TiO2 produced a higher population of \({\text{e}}_{ST}^{ - }\) and generated \({\text{e}}_{ST}^{ - }\) and \({\text{e}}_{CB}^{ - }\) at a lower rate than TiO2. The average energy level of \({\text{e}}_{ST}^{ - }\) was determined to be 0.30 eV for TiO2 and 0.26 eV for N-TiO2 below the conduction band. Upon terminating UV irradiation, the IR intensity of accumulated \({\text{e}}_{CB}^{ - }\) and \({\text{e}}_{ST}^{ - }\) showed a gradual decay in a time scale of minutes. This study demonstrated that the recombination of photo-generated electrons and holes can be a slow process on TiO2 and N-TiO2 in the presence of adsorbed ethanol under ambient conditions.

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Acknowledgements

This work was supported by the University of Akron Polymer Science Faculty Initiation Fund. The authors thank Ms. Jie Yu and Mr. P. Patanapaniswa for valuable discussions.

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Authors and Affiliations

  1. Department of Polymer Science, The University of Akron, Akron, OH, 44325-3909, USA

    Jiawei Liu, Long Zhang, Xuesi Yao & Steven S. C. Chuang

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  1. Jiawei Liu
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  2. Long Zhang
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  3. Xuesi Yao
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  4. Steven S. C. Chuang
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Correspondence to Steven S. C. Chuang.

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Special Issue of the 1st International Symposium on Photocatalysis at Fuzhou University.

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Liu, J., Zhang, L., Yao, X. et al. Photo-generated conduction-band and shallow-trap electrons from UV irradiation on ethanol-adsorbed TiO2 and N-TiO2: an in situ infrared study. Res Chem Intermed 43, 5041–5054 (2017). https://doi.org/10.1007/s11164-017-3038-9

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  • DOI: https://doi.org/10.1007/s11164-017-3038-9

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