Evaluation of self-cleaning photocatalytic paints: are they effective under actual indoor lighting systems?

The aim of the paper is to assess the photocatalytic performance of self-cleaning paints - available in the market - designed for applications in indoor environment. Three self-cleaning photocatalytic paints were deeply characterised by means of complementary analytical techniques (X-Ray Diffraction, Thermogravimetry, Fourier Transform Infrared Spectroscopy in reflection mode and Absorption UV-Vis Spectroscopy). In addition, the photocatalytic properties of the paints were tested accordingly to ISO 10678 and ISO 2197-1 standards and in ad-hoc planned tests to evaluate their ability in methyl red and methylene blue bleaching under UVC, Xenon (with and without UV-400 filter), fluorescent and LED lamps exposure. To the best of our knowledge, this is the first paper dealing with the photocatalytic activity tests of indoor commercial self-cleaning paints under actual indoor light. Although restricted to the three investigated paints, the outcomes suggest that all samples are scarcely active under visible light and the pollutant probes are selectively bleached thanks to their sensitising effect. Consequently, the pollutants ability in injecting electrons in the TiO2 conduction band deeply affects their removal. The paper highlights the requirement for an improved photocatalytic paint formulation with visible light active photocatalysts as well as the need of adequate ISO standards for visible light driven activity tests.