Multifunctional TiO2-based hybrid coatings on limestone: Initial performances and durability over time

In the present work, the photocatalytic activity of different coatings containing titanium dioxide nanoparticles, both pure and in conjunction with metallic nanoparticles (silver and copper) to improve their photocatalysis and biocidal efficiency, was monitored over time. The nanoproducts were applied on travertine - a porous limestone - through spray-coating. An artificial accelerated ageing test - based on the prolonged exposure to ultraviolet light and the repeated application of stains - was used to simulate the extended use of the coatings on outdoor surfaces. Microscopical, aesthetical and physical macroscopic features, as well as self-cleaning and biocidal efficiencies of the coating-substrate system, were analysed assessing possible changes over time. The outcome of the research pointed out a good aesthetic compatibility with stone substrate (showing limited visual alteration) and high photocatalytic efficiency before ageing. Durability of self-cleaning and biocidal effects was also very clear while wettability of treated surfaces - especially without metallic nanoparticles - was the most altered characteristic of the coatings at the end of the ageing.