Photocatalyst activity indicating adhesive labels for use in the field

The preparation and characterisation of a resazurin-based photocatalyst activity indicator label is described. The label is applied to a number of different TiO2-based, photocatalytic materials, including self-cleaning: glass, tile, paint and awning materials, as well as a thin, sol-gel film, produced in-house. In all cases, the label exhibited a blue to pink colour transition upon irradiation with UV light. In most cases, the time taken to bleach 90% of the red component of the digital image of the ink, ttb(90), was twice that for a traditional Rz ink, produced by the drawdown method, since the former was twice as thick. Although not as fast as a drawdown Rz ink, by a factor of ca. Two, it still only takes minutes to change and the Rz label is much more easily used, stored and does not need the sample to be: very smooth, horizontal or flat. As such it appears ideal for testing samples, both quantitatively and qualitatively in situ, i.e. in the field.