Photocatalytic discoloration of organic compounds on outdoor building cement panels modified by photoactive coatings

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2007-05, Vol.188 (2), p.334-341
• Main Authors: Yuranova, T., Sarria, V., Jardim, W., Rengifo, J., Pulgarin, C., Trabesinger, G., Kiwi, J.
• Format: Article
• Language: English
• Subjects: Cement panels/plates; Daylight radiation; Self-cleaning; SiO 2/TiO 2 colloids
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2006.12.032

Cement based Eternit plates modified by TiO 2/SiO 2 surface layers acquired self-cleaning properties. The TiO 2/SiO 2 coating was transparent indicating that the small TiO 2 (rutile) crystals cause no significant scattering. The parameters related to the composition of the TiO 2/SiO 2 coating were investigated in relation to concentration and ratio of the components and the time and temperature necessary for the colloid networking to produce the self-cleaning effect. The repetitive discoloration of natural pigments on the TiO 2/SiO 2/Eternit plates was observed showing the stable performance of the TiO 2/SiO 2coating. FTIR spectroscopy shows the stability of the acrylic and cellulose components on the TiO 2/SiO 2/Eternit plates after repetitive self-cleaning cycles. A self-cleaning mechanism is suggested in agreement with the experimental findings. The SiO 2 layers seem to avoid the radical attack on the acrylic topmost layers of the Eternit plates due to the TiO 2 (h + vb) generated under solar simulated radiation. The profile and thickness of the coating was estimated by confocal microscopy. X-ray diffraction showed that the Eternit plates had a structure forming function on the TiO 2/SiO 2 layers leading to the formation of rutile from the Ti-colloids at temperatures as low as ∼80 °C.