Efficient self-cleaning treatments for built heritage based on highly photo-active and well-dispersible TiO2 nanocrystals

Abstract The present study reports on the preparation and characterization of innovative “self-cleaning” nano-TiO 2 treatments to be used in cultural heritage, based on dispersion of solar-light activated TiO 2 nanocrystals. The semiconductor has been prepared by an easy and low-cost non-aqueous procedure, providing anatase (NA_TiO 2 ) nanoparticles photo-active not only under UV-light but also under solar irradiation. NA_TiO 2 allows obtaining very stable dispersions either in water or in ethylene glycol used to produce homogeneous nano-TiO 2 treatments on Noto stone and Carrara marble, which display excellent aesthetic compatibility, do not remarkably affect the capillary water absorption of the stones and slightly increase their wettability. The new treatment exhibits higher photocatalytic activity compared to that based on commercial TiO 2 (P25_TiO 2 ). This behavior has been attributed not only to the morphological properties of the treatments and of the stones, but also to the presence of residual benzyl alcohol molecules anchored on the anatase NP surfaces. This provides solar light absorption and partially improves the charge trapping, thus increasing the photoefficiency. The overall results suggest that the positive combination of high dispersion, solar-light absorption and reduced recombination effects in NPs plays a key role in the development of efficient photocatalytic treatments for stone restoration.