Photocatalytic Nanocomposites for the Protection of European Architectural Heritage

Abstract

In the field of stone protection, the introduction of inorganic nanoparticles, such as TiO2, ZnO, and Ag in polymeric blends can enhance the protective action of pristine treatments, as well as confer additional properties (photocatalytic, antifouling, and antibacterial). In the framework of the “Nano-Cathedral” European project, nanostructured photocatalytic protective treatments were formulated by using different TiO2 nanoparticles, solvents, and silane/siloxane systems in the blends. The results about the characterization and application of two promising nano-TiO2 based products applied on Apuan marble and Ajarte limestone are here reported, aiming at investigating the complex system “treatment/stone-substrate”. The nanocomposites show better performances when compared to a commercial reference siloxane based protective treatment, resulting in different performances once applied on different carbonatic substrates, with very low and high open porosity, confirming the necessity of correlating precisely the characteristics of the stone material to those of the protective formulations. In particular, the TiO2 photocatalytic behavior is strictly linked to the amount of available nanoparticles and to the active surface area. The alkyl silane oligomers of the water-based formulation have a good penetration into the microstructure of Ajarte limestone, whereas the solvent-based and small size monomeric formulation shows better results for Apuan marble, granting a good coverage of the pores. The encouraging results obtained so far in lab will be confirmed by monitoring tests aiming at assessing the effectiveness of the treatments applied in pilot sites of historical Gothic Cathedrals.

Superhydrophobic Coatings Based on Siloxane Resin and Calcium Hydroxide Nanoparticles for Marble Protection

“…Using Equation (3) and the values of Table 1, it is calculated that ∆E* = 0.36 ± 0.04 for the marble specimen that was coated with siloxane and ∆E* = 3.76 ± 0.03 for the marble specimen that was coated with siloxane+Ca(OH) 2 . According to the literature, color variations which correspond to ∆E* < 3 are insignificant as they are not perceived by human eye [28][29][30]; the accepted level for conservation purposes is ∆E* < 5 [28]. Consequently, the results, which are reported in Table 1, suggest that the siloxane material (∆E* = 0.36) has a negligible effect on the color of the marble.…”

Inspecting adhesion and cohesion of protectives and consolidants in sandstones of architectural heritage by X-ray microscopy methods

“…A characterization of these products, including FTIR spectroscopy, rheology and DLS measurements, was reported in previous studies [27,30]. To the purpose of this research, it is important to emphasize that they are marked by a different aggregation of the silane units and a different nanoparticle size.…”

“…In the framework of the EU-funded Nano-Cathedral Project (grant agreement No 646178), aimed at synthesizing and testing innovative nano-structured products [26,27] for the preservation of historical architecture [28], the evaluation of the suitability of the products was carried out by integrating different methodologies and laboratory tests [26,27,[29][30][31][32]. The new nanomaterials, that is, protectives and consolidants formulated by companies involved in the project, were previously tested by laboratory routines in order to evaluate their effectiveness over time.…”

Electrokinetic Characterization of Natural Stones Coated with Nanocomposites for the Protection of Cultural Heritage

“…Particle size was measured on a 90 Plus Dynamic Laser Light Scattering instrument (Brookhaven Instruments Corporation, Holtsville, NY, USA) equipped with a 35-mW laser and an Avalanche photodiode detector collecting the scattered light at 90 • . The protective effectiveness and the general properties of these products have already been assessed in previous studies [29,30]. The alkyl groups provide the coatings with hydrophobic properties, while TiO 2 nanoparticles at low concentration are introduced to impart photocatalytic and self-cleaning properties.…”