Photo-oxidation of NO using an exterior paint--screening of various commercial titania in powder pressed and paint films.

The present work aims to evaluate the photocatalytic activity of photo-TiO(2) from various producers (Evonik, Kemira, Kronos, Millennium, Sachtleben and Tayca), in the form of powder pressed films and upon incorporation in a water-based paint, for outdoor NO abatement. The photocatalytic activity of the different samples was evaluated in terms of NO conversion and selectivity towards nitrite and nitrate ions following approximately the ISO 22197-1:2007(E) standard. The highest yields obtained for powder pressed films were achieved with VLP7000 (0.70), followed by VLP7101 (0.55) and UVLP7500 (0.55), all from Kronos. On the other hand, when incorporated in paint films, the highest yields were obtained with PC500 and PC105 from Millennium and UV100 from Sachtleben (ca. 0.15). The paint matrix plays an important role on the photocatalytic activity. In particular, the time for steady state is one or two orders of magnitude higher when the photocatalysts are incorporated in paint films in relation to the powder pressed films. The paint films were activated following the procedure recommended by the above-mentioned standard. However, the photocatalytic activity of films incorporating P25 (Evonik) was displayed only when higher power radiation and higher humidity conditions were used. This allowed for similar levels of photocatalytic activity as the other paint films.