Protecting of Marble Stone Facades of Historic Buildings Using Multifunctional TiO2 Nanocoatings

Abstract

Stone surfaces and façades of historic buildings, due to their predominately outdoor location, suffer from many deterioration factors, including air pollution, soluble salts, relative humidity (RH)/temperature, and biodeterioration, which are the main causes of decay. In particular, the façades of the buildings deteriorate with direct exposure to these factors; deformation and disfiguration of superficial decoration and formation of black crusts are often observed on the stones. The development and application of self-cleaning and protection treatments on historical and architectural stone surfaces could be a significant improvement in the conservation, protection and maintenance of Cultural Heritage. A titanium dioxide nanoparticle has become a promising photocatalytic material, owing to its ability to catalyze the complete degradation of many organic contaminants and environmental factors. In this study, TiO 2 nanoparticles, dispersed in an aqueous colloidal suspension, were applied directly to historic marble stone surfaces, by spray-coating, in order to obtain a nanometric film over the stone surface. The study started with an investigation of some properties of TiO 2 nanoparticles, to assess the feasibility of the use of TiO 2 on historic stone and architectural surfaces. Scanning electron microscopy (SEM) was, coupled with energy dispersive X-ray (EDX) microanalysis, (SEM-EDX), in order to obtain information on coating homogeneity and surface morphology, before and after artificial aging; the activity of the coated surface was evaluated through UV-light exposure, to evaluate photo-induced effects. The changes of molecular structure occurring in treated samples were spectroscopically studied by attenuated total reflection infrared spectroscopy (ATR-FTIR); activity of the hydrophobic property of the coated surface was evaluated by Sterio microscopy, model Zeiss 2010 from Munich, Germany, equipped with photo camera S23 under 80X magnification. The efficacy of the treatments was evaluated through capillary water absorption, and colorimetric measurements, performed to evaluate the optical appearance. Results showed that TiO 2 nanoparticles are good candidates for coating applications on historic stone surfaces, where self-cleaning photo-induced effects are well evident; they enhanced the durability of stone surfaces toward UV aging, improved resistance to relative humidity (RH)/temperature and abrasion affect, reduced accumulation of dirt on stone surfaces when left in open air for 6 months, and did not alter the original features.

Development of Multifunctional Coatings for Protecting Stones and Lime Mortars of the Architectural Heritage

“…Moreover, a hydrophobic environment could protect the photocatalyst from washing away owing to the rain action (Shajari-Ghasemkheili and Sarraf-Mamoory 2019). In support of this approach, the scientific literature provides some works dealing with photocatalytic-hydrophobic coatings (Kamegawa, Shimizu and Yamashita 2012;La Russa et al 2012;Kapridaki and Maravelaki-Kalaitzaki 2013;Kapridaki et al 2014;Gobakis et al 2015;Kamegawa, Irikawa and Yamashita 2015;Kapridaki and Maravelaki 2016;Aldoasri et al 2017;Colangiuli et al 2019;Lanka et al 2019; Shajari-Ghasemkheili and Sarraf-Mamoory 2019. However, the coatings so far reported for Built Heritage are based on TiO 2 and organic water repellent agents.…”

Preliminary Evaluation of Coating Hydrophobization of Natural Stone from Repedea - Iasi area (Romania)

“…Nevertheless, some authors specialized in the assessment of consolidated, impregnated or coated lithic surfaces actually use the ΔE*ab Scale in Stone Materials Conservation which provides the following interpretation of the total color change [25] Considering the data in the paragraphs above and analyzing the values in table 5, we may conclude that after chemical hydrophobicization treatment samples P1, P2, P3, P6 and P8 "underwent" a ΔE*ab color change greater than 5 units, which means that the S1 -LTP Mattstone H2O solution causes a noticeable difference (ΔE*ab = 5.28) and the products S2, S3, S6 and S8 show major color differences, as follows:…”

“…S8 -Tenax Ager (ΔE*ab = 9.42). After coating, the rest of the solutions (S4, S5 and S7) cause small perceptible differences, a desirable aspect especially in the case of the Science of Heritage Immovable Property Conservation [25].…”

Recent Advances in Protective Coatings for Cultural Heritage–An Overview

“…The interest on the application of nanocomposites for CH protective coating is shown in the present literature, which counted hundreds of papers per year in the last decade [110], as well as by the recent Horizon 2020 project, titled "Nano-Cathedral" [111], dedicated to innovative solutions based on nanocomposites for protecting European historical buildings. Because of the large amount of literature on these kinds of materials, we report here some of the results, which allow an in-depth discussion on these applications, whereas additional details can be found in cited references and reviews [112][113][114][115][116][117].…”