Photocatalytic Discoloration of Organic Compounds on Outdoor Building Cement Panels Modified by Photoactive Coatings

Cement based Eternit plates modified by TiO2/SiO2 surface layers acquired self-cleaning properties. The TiO2/SiO2 coating was transparent indicating that the small TiO2 (rutile) crystals cause no significant scattering. The parameters related to the composition of the TiO2/SiO2 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 TiO2/SiO2/Eternit plates was observed showing the stable performance of the TiO2/SiO2 coating. FTIR spectroscopy shows the stability of the acrylic and cellulose components on the TiO2/SiO2/Eternit plates after repetitive self-cleaning cycles. A self-cleaning mechanism is suggested in agreement with the experimental findings. The SiO2 layers seem to avoid the radical attack on the acrylic topmost layers of the Eternit plates due to the TiO2 (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 TiO2/SiO2 layers leading to the formation of rutile from the Ti-colloids at temperatures as low as similar to 80 degrees C. (C) 2007 Elsevier B.V. All rights reserved.