Self-cleaning materials on Architectural Heritage: Compatibility of photo-induced hydrophilicity of TiO₂ coatings on stone surfaces - 22/01/13

Doi : 10.1016/j.culher.2012.02.006

Enrico Quagliarini ^a,^⁎ , Federica Bondioli ^b,^{^{1
Tel.: +39 0592056242; fax: +39 0592056243.}}, Giovanni Battista Goffredo ^a,^{^{2
Tel.: +39 0712204248; fax: +39 0712204378.}}, Antonio Licciulli ^c,^{^{3
Tel.: +39 08321835725; fax: +39 08321830130.}}, Placido Munafò ^a,^{^{2
Tel.: +39 0712204248; fax: +39 0712204378.}}
^a Department of Architecture, Constructions and Structures, Polytechnic University of Marche, via Brecce Bianche, 60131 Ancona, Italy
^b Department of Materials and Environmental Engineering, University of Modena and Reggio Emilia, via Vignolese 905, 41100 Modena, Italy
^c Salentecsrl, via dell’Esercito 8, 73020 Cavallino (LE), Italy

Corresponding author. Tel.: +39 07 12 20 42 48; fax: +39 07 12 20 43 78.

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Abstract

Titanium dioxide (TiO₂) can be used to realize transparent self-cleaning coatings on stone surfaces as an active and preventive protection system, limiting cleaning and maintenance actions, reducing their costs in Architectural Heritage. This self-cleaning ability is due to photo-induced hydrophilicity on treated surfaces. The aim of this investigation is to analyze this effect, since it could bring to a greater water absorption, a potential source of damage for stone surfaces. Titania sol, obtained by sol-gel and hydrothermal processes, was deposited on travertine by spray coating, in two different ways. Water absorption by capillarity, static contact angle and a specific surface water absorption analysis were assessed before and after the TiO₂ treatments. The effects of deposited amount of titania on the characteristics of treated surfaces were evaluated. It was shown that there were no evident changes in the substrate reactivity without ultraviolet (UV) light exposure, while it seems that hydrophilicity due to UV light does not lead to higher water absorption, thus encouraging the use of TiO₂ coatings in the field of Architectural Heritage. However, before widely applying this conservative treatment, some further researches are recommended in order to better assess its durability and sustainability.

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Keywords : Water absorption, TiO₂, Architectural Heritage, Contact angle, Stone surfaces, Self-cleaning surfaces