Layered Nano‐TiO₂ Based Treatments for the Maintenance of Natural Stones in Historical Architecture

Layered treatments of natural stones based on dispersions of experimental nano‐TiO 2 and commercial TEOS showing photocatalytic and self‐cleaning properties were set up and tested. To enhance nano‐TiO 2 efficacy, a surface pre‐treatment with tetraethyl orthosilicate was proposed to avoid the penetration of NPs into the crystalline porous substrates and to improve their adhesion to the stone. Two treatment applications (wet‐on‐wet and wet‐on‐dry) were compared, showing different results. A strong interaction Si−O−Ti was the key factor for the successful treatment, leaving the band gap and relevant properties of nano‐TiO 2 unaltered. The layered treatments were tested on a porous calcarenite (Noto stone) and a very compact marble (Carrara marble). The combined SiO 2 ‐nano‐TiO 2 treatments can find application in suitable cases where a surface consolidation is needed, ensuring a depolluting and self‐cleaning durable activity.