Photocatalytic nanostructured TiO2 for protection of porous and compact stone

The enhanced photocatalytic activity for degradation of a wide range of pollutants makes nanostructured TiO2 an ideal candidate for self-cleaning coatings. The deposition of different types of TiO2 nanocrystalline coatings on stone has been investigated in order to test the surface protection and self-cleaning abilities of the nanostructured materials. TiO2 nanocrystals with controlled size, shape and surface chemistry have been prepared by using two distinct synthetic approaches, namely colloidal synthesis by hot injection and hydrothermal nanophase crystallisation. Two different types of stones, possessing different porosity, namely porous calcarenite and a compact limestone have been selected, being both widely used in South Italian monuments and building relevant for cultural heritage. The physical properties of coated and uncoated stone surfaces, respectively, have been investigated, and colour, wettability and stability of the coatings have been checked. The self-cleaning properties of the nanostructured TiO2 coated surfaces under solar irradiation have been tested by monitoring the degradation of a model organic molecule, namely an organic dye. The obtained results have confirmed that the nanocrystalline TiO2 coatings are promising candidate for environmental protection upon appliance on either porous and compact stone. Moreover, the nanostructured TiO2 obtained colloidal synthesis by hot injection has demonstrated to provide hydrophobic treated surfaces.