Development of visible light active self-cleaning clay roofing tiles as novel building materials: An investigation on the effects of a-Fe2O3 coating and firing temperature

In this study, in order to obtain visible light active self-cleaning property while maintaining physical stability, clay roofing-tiles were first prepared at several firing temperatures of the clay and coated with alpha-Fe2O3 films followed by a heat treatment. Pristine (uncoated) and coated samples then were compared in terms of i) physical properties as aesthetic appearance, stability against environmental conditions and ii) photocatalytic properties as self-cleaning characteristics under visible light by artificial pollutant, methylene blue (MB). Obtained results showed that clay roofing-tiles were improved in terms of both physical, and photocatalytic properties. Tiles with alpha-Fe2O3 coating showed higher photocatalytic activity, less water adsorption and less porosity compared to pristine tiles. Also, an appreciable surface wettability transition towards lower contact angles was achieved by light illumination. In terms of photocatalytic properties, the best results were obtained from the tile fired at 1025 ? and alpha-Fe2O3 coated samples having total removal efficiency of 86.1% and apparent reaction rate of 29.21 x 10(-2) h(-1). Although, in terms of physical properties, the tile fired at 1050 ? showed better performance with stability and aesthetic appearance, this sample showed lower values in both, total removal percentage of 83.7% and apparent reaction rate of 26.81 x 10(-2) h(-1). Thus, minor changes in firing temperature have a great impact on both, the photocatalytic properties, and the physical properties of the clay roofing tiles