A silver-based ink for assessing low activity photocatalytic films

A new type of photocatalytic activity indicator ink, paii, is described based on the photocatalysed reduction of Ag ions to the metal, rather than that of a dye, such as resazurin, Rz. UVA irradiation of an Ag ink film coating on a photocatalytic surface produces a brown colouration due to Ag nanoparticle formation. The Ag ink is easy to make and provides a simple method for the rapid assessment of photocatalytic films, with the added advantage of being particularly sensitive to low activity photocatalytic materials, such as commercial self-cleaning tiles for which no International Standards Organisation, ISO, test exists, including a Rz paii ISO. A felt-tipped pen applied Ag ink film is used to identify the presence of activity in a wide range of different materials, including examples of commercial self-cleaning glass, tile, paint and plastic awning materials. Unlike its well-established Rz paii counterpart, the Ag ink is effective on very hydrophobic and delicate, i.e. easily removed, photocatalytic films. A protocol is employed for the Ag ink to provide a quantitative measure of photocatalytic activity on both a low activity photocatalytic material, i.e. a Hytect™ tile, and a moderately active, reference photocatalytic material, Activ™ glass. The potential of the Ag ink to aid research and development into, and quality assurance of, low activity photocatalytic films, and also help in identifying activity in films previously considered inert, is discussed briefly.