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

Mohammad Aldoasri,Nagib Elmarzugi,Sayed Ahmed,Mahmoud Adam,Sawsan Darwish

doi:10.3390/su9112002

Abstract

Stone surfaces and facades 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 facades 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, TiO2 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 TiO2 nanoparticles, to assess the feasibility of the use of TiO2 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 TiO2 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.

Highlights

The façades of historic buildings deteriorate with direct exposure to physical, chemical, and biological agents, which usually play an important role in the deterioration phenomenon [1,2]
The aim was to examine the feasibility of using nano-TiO2 based coating on historic marble stone surfaces in order to obtain a self-cleaning treatment, able to reduce deterioration effects
The TiO2 nanocoating enhanced the durability of the stone surface against an abrasion effect, and improved the mechanical properties of the marble stone surface

Summary

Introduction

The façades of historic buildings deteriorate with direct exposure to physical, chemical, and biological agents, which usually play an important role in the deterioration phenomenon [1,2]. There have been major developments in conservation science, colloids and interface science, together with materials science, which belong to the realm of popular nanosciences [8,9] The latter area has attracted the conservation experts, due to the increasing loss of efficacy of conventional methods to achieve higher self-cleaning, surface protection, and consolidation efficiencies [10]. In addition it may be used as an additive in lime binder and consolidation polymeric materials, to improve the durability of lime-based mortars and other consolidation materials [23,24], and seems to allow the realization of transparent coatings that could improve the cleaning ability of historical surfaces, without changing their appearance properties, acting in a preventive and less invasive way to preserve their original aspect [25] This may be due to the unique physical and chemical properties, size and the higher surface area of the nanoparticles

Methods

Results

Conclusion