Self-cleaning and de-polluting stone surfaces: TiO2 nanoparticles for limestone

To evaluate the self-cleaning and de-polluting properties of a transparent titania coating, in this investigation a titanium dioxide based suspension was deposited by spray coating on travertine, a porous limestone largely used as building material. To assess compatibility with stone substrates, microstructure analysis, color and gloss measurements, static contact angle analysis and two different water absorption tests were carried out. Self-cleaning and de-polluting activities were assessed by the use of rhodamine B decoloration and NOx degradation tests. The results showed good compatibility with stone surfaces and evident efficiency, allowing the use of titania coatings for real outdoor applications.