Supersensitive test of photocatalytic activity based on ISO 22197-1:2016 for the removal of NO

Andrew Mills*, Rachel Andrews, Ri Han, Christopher O'Rourke, Stephanie Hodgen

*Corresponding author for this work

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1 Citation (Scopus)
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A supersensitive test (SST) for photocatalytic activity is described, based on ISO 22197-1:2016 for the removal of NO, i.e. the standard NO removal ISO. The key reaction is the photocatalysed oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) by oxygen, which, for most materials, is the dominant reaction at the end of the 5 h irradiation period employed in the standard ISO. The SST uses the same photoreactor as the standard NO ISO, but with 3 (instead of 1) sample pieces and a flow rate of 0.25 L min−1 (instead of 3 L min−1) and, as a consequence, is 36 x's more sensitive than the standard ISO. The SST is used to assess the activities of materials that show little if any activity when tested using the standard ISO, such as commercial self-cleaning samples (such as glass (Activ™), paint and plastic), as well as bank notes. An expression is derived, and verified using films of P25 powder, which relates rate, and so photocatalytic activity, directly to the average %NO removed, measured under either standard ISO or SST conditions, in the last 15 min of irradiation, i.e. %NOrem, where the latter value is directly related to the photocatalytic area, A, and the reciprocal of the flow rate, 1/f. This relationship allows all %NOrem values < 25 %, measured using either standard ISO or SST conditions, to be combined to create a universal scale of photocatalytic activity. The universal scale of activity is illustrated using the calculated %NOrem values for high, medium and low activity materials which spans over 3 orders of magnitude of activity. The possible uses of this scale are discussed briefly.

Original languageEnglish
Article number112734
JournalJournal of Photochemistry and Photobiology A: Chemistry
Early online date28 Jun 2020
Publication statusPublished - 01 Sep 2020


  • ISO
  • Low activity
  • Nitric oxide
  • Photocatalysis
  • Titanium dioxide

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Physics and Astronomy(all)


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