Field study in an urban environment of simultaneous self-cleaning and hydrophobic nanosized TiO2-based coatings on stone for the protection of building surface

D Colangiuli; M Lettieri; M Masieri; A Calia

doi:10.1016/j.scitotenv.2018.10.044

Field study in an urban environment of simultaneous self-cleaning and hydrophobic nanosized TiO₂-based coatings on stone for the protection of building surface

Sci Total Environ. 2019 Feb 10;650(Pt 2):2919-2930. doi: 10.1016/j.scitotenv.2018.10.044. Epub 2018 Oct 4.

Authors

D Colangiuli¹, M Lettieri², M Masieri³, A Calia⁴

Affiliations

¹ IBAM-CNR (Institute of Archaeological and Monumental Heritage), University Campus, Prov.le Lecce-Monteroni, 73100 Lecce, Italy.
² IBAM-CNR (Institute of Archaeological and Monumental Heritage), University Campus, Prov.le Lecce-Monteroni, 73100 Lecce, Italy. Electronic address: mariateresa.lettieri@cnr.it.
³ IBAM-CNR (Institute of Archaeological and Monumental Heritage), University Campus, Prov.le Lecce-Monteroni, 73100 Lecce, Italy. Electronic address: m.masieri@ibam.cnr.it.
⁴ IBAM-CNR (Institute of Archaeological and Monumental Heritage), University Campus, Prov.le Lecce-Monteroni, 73100 Lecce, Italy. Electronic address: a.calia@ibam.cnr.it.

PMID: 30373068
DOI: 10.1016/j.scitotenv.2018.10.044

Abstract

Titanium dioxide based nanocomposites for stone coating have been found to be promising in laboratory conditions to obtain manifold protective actions against pollution and weathering affecting the outdoor built heritage. Lasting performances in real conditions of these multifunctional coatings have been scarcely examined, although this is a key issue in evaluating their potential for applications in a real building context and their optimization. This paper illustrates a field study aimed at investigating simultaneous hydrophobic and self-cleaning effectiveness, on the medium-long run, of TiO₂ NPs/fluoropolymer coatings applied on a limestone. The samples coated with the nanocomposites were exposed for one year in an urban environment and their surface was monitored. Hydrophobic properties were checked through contact angle measurements and a capillary water absorption test, while self-cleaning efficiency was evaluated by a photodegradation test of Rhodamine B. Optical microscopy observations and colour measurements were also performed. In addition, the contents of Ti and water-soluble ions on the sample surfaces were determined by X-ray Fluorescence and ion chromatography, respectively. The overall findings showed that TiO₂ NPs did not affect the ability of the polymer to protect the stone surface against water penetration. The coatings were able to preserve the surfaces from dirt. However, photocatalytic efficiency progressively decreased, due to the loss of the photocatalyst from the coating surface, which may be attributed to a polymer modification by ageing. The embedding of nanosized titania within the polymer limited the adsorption and accumulation of soluble salt ions on the coated surface, which may increase the stone damage risk. The study supports that TiO₂ NPs embedded in a fluoropolymer host matrix to appropriate amounts may be a suitable option to obtain stone coatings with both barrier effects against water penetration into the stone and photocatalytic ability, and provides useful knowledge for the improvement of these nanocomposites.

Keywords: Lasting performance; Natural ageing; Perfluoropolymer; Photocatalytic TiO(2) nanoparticles; Self-cleaning/hydrophobic stone coating; Soluble salt loads.