Photogenerated Charge Carriers and Paramagnetic Species in (W,N)-Codoped TiO2 Photocatalysts under Visible-Light Irradiation: An EPR Study

Andrea Folli, Jonathan Z. Bloh, Eva-Panduleni Beukes, Russell Francis Howe, Donald E Macphee

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

(W,N)-codoped TiO2 has recently attracted interest due to substantial band gap narrowing in conjunction with good visible-light photocatalytic activities. A complete picture of the fundamental mechanism at the origin of their photoactivity is, however, far from being understood. We present an EPR study on (W,N)-codoped titanias by recording spectra in the dark and under 550 nm visible-light irradiation to identify the major species involved in the formation and migration of photogenerated charge carriers. Interstitial N-lattice O (formally NO2-) paramagnetic groups with and without a specific close range coupling interaction with a neighboring W, that is, [NiO](w)(center dot) and [NiO](center dot), respectively, are observed when visible light excites electrons from diamagnetic intraband gap states located at similar to 2.30 V versus RHE (formally NO3-) to the conductance band at around -0.05 V versus RHE. The [NiO](w)(center dot) EPR signal, reported here for the first time, is characterized by a much stronger hyperfine interaction between the unpaired electron and the N-14 nucleus than ordinary [NiO](center dot) found in N-doped TiO2, leading to a much higher spin density on the N center. The overall signal also contains superhyperfine coupling of the unpaired electron with the W-183 nuclide (natural abundance 14.31%), the only naturally occurring nuclide of W with a nonzero nuclear spin.

Original languageEnglish
Pages (from-to)22149-22155
Number of pages7
JournalThe Journal of Physical Chemistry C
Volume117
Issue number42
Early online date18 Sep 2013
DOIs
Publication statusPublished - 24 Oct 2013

Keywords

  • N-DOPED TIO2
  • TITANIUM-DIOXIDE
  • PHOTOACTIVITY
  • PARAMETERS
  • RESONANCE
  • MECHANISM
  • POWDERS
  • ORIGIN
  • FILMS

Cite this

Photogenerated Charge Carriers and Paramagnetic Species in (W,N)-Codoped TiO2 Photocatalysts under Visible-Light Irradiation : An EPR Study. / Folli, Andrea; Bloh, Jonathan Z.; Beukes, Eva-Panduleni; Howe, Russell Francis; Macphee, Donald E.

In: The Journal of Physical Chemistry C, Vol. 117, No. 42, 24.10.2013, p. 22149-22155.

Research output: Contribution to journalArticle

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AB - (W,N)-codoped TiO2 has recently attracted interest due to substantial band gap narrowing in conjunction with good visible-light photocatalytic activities. A complete picture of the fundamental mechanism at the origin of their photoactivity is, however, far from being understood. We present an EPR study on (W,N)-codoped titanias by recording spectra in the dark and under 550 nm visible-light irradiation to identify the major species involved in the formation and migration of photogenerated charge carriers. Interstitial N-lattice O (formally NO2-) paramagnetic groups with and without a specific close range coupling interaction with a neighboring W, that is, [NiO](w)(center dot) and [NiO](center dot), respectively, are observed when visible light excites electrons from diamagnetic intraband gap states located at similar to 2.30 V versus RHE (formally NO3-) to the conductance band at around -0.05 V versus RHE. The [NiO](w)(center dot) EPR signal, reported here for the first time, is characterized by a much stronger hyperfine interaction between the unpaired electron and the N-14 nucleus than ordinary [NiO](center dot) found in N-doped TiO2, leading to a much higher spin density on the N center. The overall signal also contains superhyperfine coupling of the unpaired electron with the W-183 nuclide (natural abundance 14.31%), the only naturally occurring nuclide of W with a nonzero nuclear spin.

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