TiO2–SiO2–PDMS nanocomposite coating with self-cleaning effect for stone material: Finding the optimal amount of TiO2

Nano-sized TiO2 is widely used as photocatalysts for many applications; however, some aspects in the application in cultural heritage conservation are still unresolved. In particular, in this research, we focused our attention on nanostructured product composed by silica, polydimethylsiloxane (PDMS) and TiO2 nanoparticles. We explored the effect of variable amounts of nanoparticles on the features of coating, since this issue still has some unclear aspects. Several samples of limestone have been treated, and then, analysed. The chromatic variations induced by the treatments have been measured by colorimetric analysis, while the hydrophobic properties of coatings have been evaluated by contact angle measurements and capillary water absorption. The photocatalytic efficiency has been evaluated by methylene blue staining. In addition, two large facilities have been involved in this study, in order to obtain accurate results in a non-invasive way. On one side, middle-UV Raman spectroscopy measurements at IUVS beamline@Elettra (Trieste), by using UV synchrotron radiation (SR) source, revealed successful, with respect to conventional set-up, in order to quantify the amount of the anatase on the surface. On the other side, neutron radiography measurements at RAD Radiography Station@BNC (Budapest) permitted a sensitive monitoring of the water absorption dynamics on untreated and treated samples. © 2018 Elsevier Ltd