TiO2-based nanocoatings for preserving architectural stone surfaces: An overview

• Nanocoatings formed by titanium dioxide can be applied on architectural stones.
• Physical properties and photocatalysis of TiO2 on stones have been investigated.
• TiO2 nanoparticles can efficiently improve stone conservation and aspect over time.
• Treated stones can lead to environmental benefits and reduce maintenance costs.
• This review aims to provide a report on the current state of the art in this field.

Titanium dioxide has been recently used in its nanometric form to develop smart products and coatings on several building components so as to better preserve their visual aspect, mainly by way of its very efficient photocatalytic function. The integration of further nanostructured materials with titanium dioxide may enhance its features or add new properties to these products. The aim of this review is to provide a report on the latest developments in a specific area of the maintenance of architectural surfaces: the use of multifunctional (self-cleaning, de-polluting, biocidal) nanocoatings based on titanium dioxide on architectural stone surfaces. The results of several studies concerning different products containing TiO2 nanoparticles, potentially added with other nanometric elements, have been summarised and compared from several points of view focused on their compatibility with treated substrates and their effectiveness against diverse degrading agents (soil, pollution and microorganisms). From the discussed works, the application of TiO2-based products on several architectural stones seems to be feasible and valuable; however several features are in need of deeper analyses before real large-scale use. In addition, possible future developments by scientific research may provide further increased performances and additional features and functions to these treatments.