Synthesis and characterization of photocatalytic hydrophobic hybrid TiO2 -SiO2 coatings for building applications

Building materials undergo degradation caused by pollutant agents. Different solutions are proposed for the preservation of building façades: one of them is to modify their surface in order to confer self-cleaning properties, that are obtained by superhydrophobic treatments or by use of photocatalytic materials. This work describes the synthesis of three different TiO2 and SiO2 hybrid sols and their deposition as coatings on ordinary solid gray bricks used for building construction. The dried sols were characterized by TEM (STEM-EDX), Raman and XRD analyses, confirming their anatase nanocrystalline structure with a little amount of brookite. The coated surfaces of the bricks have been characterized by functional tests and show both hydrophobic and photocatalytic properties. Before irradiation all coatings display high water contact angle (WCA) > 145° and Methylene Blue (MB) stains were photodegraded in a few hours under the irradiation of a solar lamp. The contact angles are reduced by long irradiation times but the hydrophobic properties are recovered keeping the samples in the dark.