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.
Highlights
Natural stone materials used in historical architecture, being open porous systems that are exposed to the environment, are subject to different deterioration processes
As it is well known, the main responsible actors of this decay are phenomena of natural and anthropogenic origin, i.e., contact with liquid and vapour water, with its deriving effects, including salt crystallization and freezing-thawing cycles, with gaseous pollutants, like CO, CO2, NOX, SO2, O3, atmospheric aerosols like fine and ultra-fine particulate matter, biological contaminants, and microorganisms [1,2]. Given this combination of deteriorating factors, strategies for stone protection have become increasingly concerned with pursuing a multi-functional approach, which is aimed at reducing water penetration on one side and soiling and corrosion from air-borne pollutants, on the other
In the case of ANC, the presence of a wide band probably indicates that a certain cross-linking has occurred, as it can be expected from a reactive starting material
Summary
Natural stone materials used in historical architecture, being open porous systems that are exposed to the environment, are subject to different deterioration processes As it is well known, the main responsible actors of this decay are phenomena of natural and anthropogenic origin, i.e., contact with liquid and vapour water, with its deriving effects, including salt crystallization and freezing-thawing cycles, with gaseous pollutants, like CO, CO2 , NOX , SO2 , O3 , atmospheric aerosols like fine and ultra-fine particulate matter, biological contaminants, and microorganisms [1,2]. In the field of natural stone conservation, photocatalytic treatments have been set up as an effective strategy to reduce the accumulation of pollutants, biofilm, and particulate matter on architectural surfaces with a decrease of the aesthetical and chemical decay during the years [6]
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