Preservation of Historical Stone Surfaces by TiO2 Nanocoatings

Giovanni Goffredo,Placido Munafò

doi:10.3390/coatings5020222

Abstract

We proposed the application of titanium dioxide (TiO2) for the preservation of historical (architectural, monumental, archaeological) stone surfaces. Solar light can activate the photocatalytic effect of TiO2 nanoparticles: heterogeneous photocatalysis is the key factor for the development of self-cleaning, depolluting and biocidal treatments able to photochemically degrade external damaging materials and prolong the durability of treated substrates, maintaining their original aspect and limiting ordinary cleaning activities. In this study, TiO2 nanoparticles dispersed in an aqueous colloidal suspension were applied directly on travertine, a light-colored limestone, by spray-coating in order to obtain a nanometric film on stone samples. To assess the feasibility of use of TiO2, we studied the characteristics of the nanocoating-stone system by monitoring the microscopic features of the coatings, the aesthetical changes induced to coated surfaces and the self-cleaning efficiency. We also monitored the self-cleaning ability over time during an accelerated ageing process to evaluate the durability of TiO2-based treatments. We confirmed both compatibility and effectiveness of TiO2 coating in the short term, anyway its efficiency decreased after artificial ageing. Further studies are necessary to better evaluate and eventually improve the stability of self-cleaning efficiency over prolonged time for outdoor stone surfaces.

Highlights

The use of nanotechnological solution to better preserve historical and artistic items as well as architectural, monumental and archaeological elements is greatly increasing nowadays
TiO2 nanoparticles dispersed in an aqueous colloidal suspension have been applied directly on travertine, a porous limestone, by spray-coating in order to obtain a nanometric film over the stone surface
The presence of TiO2 nanoparticles over stone surface were clearly confirmed by SEM/EDX analysis (Figure 2)

Summary

Introduction

The use of nanotechnological solution to better preserve historical and artistic items as well as architectural, monumental and archaeological elements is greatly increasing nowadays. Titanium dioxide (TiO2) nanoparticles activated by solar light may be potentially applied even on pre-existing surfaces—a requisite for their potential use in the field of restoration—to longer maintain the original characteristics of treated substrates [13,17,18,19,20,21]. TiO2 nanoparticles dispersed in an aqueous colloidal suspension have been applied directly on travertine, a porous limestone, by spray-coating in order to obtain a nanometric film over the stone surface. To assess the feasibility of use of TiO2 on stone architectural surfaces, we studied the characteristics of the nanocoating/substrate system by monitoring the microscopic features of the coating, the aesthetical changes caused to coated surfaces and the photoactivity of TiO2 thin film. Photocatalytic activity of the coating was assessed by self-cleaning test. The work we present here is the synthesis of our investigations on this topic

Application of TiO2 Nanoparticles

Microanalysis of the Coating

Compatibility between TiO2 Nanocoating and Travertine

Preservative Effect of TiO2 Nanocoating

Self-Cleaning Ability of TiO2 over Time

Conclusions