A water-dispersed titanium dioxide/poly(carbonate urethane) nanocomposite for protecting cultural heritage: Eco-sustainable treatments on Neapolitan Yellow Tuff

With the aim of improving the preventive conservation and maintenance solutions of outdoor stone heritage, in the present work, water dispersions of the TiO2 /poly(carbonate urethane) nanocomposite material were applied to Neapolitan Yellow Tuff samples. The good film-forming properties of the nanocomposite were exploited; after water casting at room temperature, the TiO2 nanoparticles remained uniformly trapped in a thin PU film. Moreover, untreated and treated tuff samples were weathered at a site selected to appropriately represent a typical urban pollution background. In the recent past, building materials in urban areas, such as stone and mortar, have shown evidence of increasing rates and levels of damage. The morphology of the tuff surfaces before and after treatments was analysed by ESEM, and their aesthetical compatibility was assessed using colorimetric measurements. Reflectance measurements were conducted to evaluate the soiling undergone by tuff samples after rain exposure, whereas the biocide ability was investigated by appraising the ATP content through the bioluminescent reaction between cellular ATP and the enzymatic complex luciferin-luciferase. Finally, water-absorption tests were performed to check the water-repellency of the treatment.