Photocatalytic activity indicator inks for probing a wide range of surfaces

Abstract

Three photocatalyst inks based on the redox dyes, Resazurin (Rz), Basic Blue 66 (BB66) and Acid Violet 7 (AV7, are used to assess the photocatalytic activities of a variety of different materials, such as commercial paint, tiles and glass and laboratory made samples of sol-gel coated glass and paint, which collectively exhibit a wide range of activities that cannot currently be probed by any one of the existing ISO tests. Unlike the ISO tests, the ink tests are fast (typically < 10 min), simple to employ and inexpensive. Previous work indicates that the Rz ink test at least correlates linearly with other photocatalytic tests such as the photomineralisation of stearic acid. The average time to bleach 90% of the key RGB colour component of the ink (red for Rz and BB66 inks) and green for AV7 ink) is determined, ca. 11% and ca 21%, respectively, which compare well with those reported for the current ISO tests. Additional work on commercial self-cleaning glass using an Rz ink showed that the change in the red component of the RGB image of the ink correlated linearly with that of the change of absorbance (at 608 nm) (as measured using UV/Vis spectroscopy) and the change in the a* component of the Lab colour analysis of the ink, as measured using diffuse reflectance spectroscopy. As a consequence, all three methods generate the same ttb(90).The advantages of the RGB digital image analysis method are discussed briefly.

Kinetics of reduction of a resazurin-based photocatalytic activity ink

“…These inks have been used to create a recently-proposed, quick and simple quantitative activity test for such materials [15] and the Rz ink, in particular, has been used for measuring the photocatalytic activities of indoor and outdoor self-cleaning glass, using just a mobile camera and app [16].…”

“…To date, much of the focus of paii research has been with regard to finding the best ones for probing the different activities exhibited by the various diverse, popular commercial photocatalytic products, such as glass, tiles, paint, fabric and concrete [13,15]. Interestingly, in most cases, it has been noted that, under normal operating conditions, the kinetics of dye reduction is zero-order with respect to the concentration of the dye in the film [13].…”

Assessment of activity of ‘transparent and clear’ and ‘opaque and highly coloured’ photocatalytic samples using a fluorescent photocatalytic activity indicator ink, FPaii

“…The method used to prepare the Rz ink has been described in detail elsewhere [10]. However, briefly, 0.15 g of hydroxyethyl cellulose, HEC, (CAS No.…”

“…Recent work within the group has shown that by coating the photocatalyst film with a photocatalyst activity indicator ink (paii), and irradiating the combination with UVA light, a striking colour change is effected, usually within minutes, (when UV irradiance = 2 mW cm -2 ), and at a rate which provides a measure of the photocatalytic activity of the underlying photocatalyst film [10]. The basic components of a typical paii are: a redox dye, such as blue-coloured, Resazurin, Rz, which is readily and irreversibly reduced by the photogenerated electrons on the TiO2, i.e.…”

“…However, this apparent 'limitation' to the applicability of paii technology presumes that the assessment of the concentration of the redox dye in the paii, as a function of irradiation time, t, requires the accurate measurement of the colour of the indicator film, via either UV/Vis absorbance measurements (which is only appropriate for clear samples) or diffuse reflectance/RGB analysis (usually appropriate for opaque samples) [10,20]. Note that the latter techniques are only appropriate for use with opaque, but NOT highly coloured samples.…”