The protection of marble surfaces: the challenge to develop suitable nanostructured treatments

Marbles have been extensively used in historical architecture owing to their good mineralogical and microstructural properties, durability, and aesthetic quality. Nevertheless, the protection of historical marbles in outdoor conditions is a difficult task, mainly because of their low open porosity. An overview of nanostructured protective treatments based on the use of SiO2, TiO2, ZnO, and Ag nanoparticles to confer superhydrophobic, self-cleaning, and antifouling properties to the surface is proposed. Particular attention is devoted to the development of photocatalytic nano-TiO2-based treatments. In this regard, advantages, drawbacks, and critical issues in the use of nanocomposites are covered. Recent advances using modified innovative TiO2 nanoparticles, in dispersion and as nanocomposites, are reported. Nanocomposites based on suitable TiO2 nanoparticles seem very promising, and a comparison of the results obtained in controlled lab conditions and on real deteriorated surfaces is also presented