Self-cleaning and antifouling nanocomposites for stone protection: Properties and performances of stone-nanomaterial systems

The development of nanocomposites combining photocatalytic, antifouling and protective features has provided interesting and promising results in the last years. However, few data about the behaviour of the nanomaterials applied on stone surfaces are available in the literature. In the framework of the EU-Horizon 2020 project "Nano-Cathedral", nanostructured protective treatments have been designed with different nanoparticles (TiO2, Ag, ZnO), solvents and silane/siloxane-based polymeric matrices. The innovative formulations have been applied on 6 lithotypes, selected among the stones used in five medieval cathedrals (Vitoria-Gasteiz, Ghent, Cologne, Vienna and Pisa) and a contemporary theatre (Oslo Opera House), which are emblematic of different European geological and environmental areas. The treated stone specimens have been fully characterized to evaluate the surface optical and morphological compatibility, the reduction of water absorption by capillarity, the change in wettability and water vapour permeability properties. The selected treatments fulfil all these requirements and exhibit good photocatalytic and antifouling properties once applied on stone specimens. Different accelerated ageing procedures have also been performed in order to evaluate the stability of the polymeric matrices in the presence of photoactive TiO2.