Limestones coated with photocatalytic TiO 2 to enhance building surface with self-cleaning and depolluting abilities (original) (raw)
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Photocatalytic TiO2 coatings on limestone
Journal of Sol-Gel Science and Technology, 2011
The application of photocatalytic coatings on stone has been investigated for providing surface protection and self-cleaning properties. Sol-Gel and hydrothermal processes were used to synthesise TiO 2 colloidal suspensions and coatings with enhanced photocatalytic activity without any thermal curing of the coated stone. The stone was a porous limestone (apulian sedimentary carbonatic, calcite stone). Films and powders prepared from TiO 2 sols were studied using X-ray diffraction to evaluate the microstructure and identify rutile and anatase phases. A morphological and physical characterisation was carried out on coated and uncoated stone to establish the changes of appearance, colour, water absorption by capillarity and water vapour permeability. The photocatalytic activity of the coated surface was evaluated under UV irradiation through NO x and organics degradation tests. The performances of the synthesised TiO 2 sols were compared with commercial TiO 2 suspension. Since the coating doesn't need temperature treatments for activating the photocatalytic properties, the nano-crystalline hydrothermal TiO 2 sols seem good candidate for coating applications on stone that cannot be annealed after the coating application.
Building and Environment, 2019
Over the last few years, photocatalytic titanium dioxide coatings have been explored in laboratory conditions to create building materials with self-cleaning and depolluting abilities. Assessing the performances of the photocatalytic surfaces under real conditions may provide basic knowledge to evaluate the potential of real applications of TiO 2 coatings in buildings. In this study, the performance of photocatalytic limestone surfaces obtained through coating with waterdispersed TiO 2 nanoparticles were investigated in an urban environment. Coated and uncoated samples were exposed to an urban site for one year. Before the exposure and periodically afterwards, optical microscopy observations, colour and contact angle measurements were performed on the sample surface. At the end of the exposure period, samples underwent a capillary water absorption test and self-cleaning efficiency was evaluated by a Rhodamine B photodegradation test. Ti and soluble fraction amounts on the sample surfaces were determined by X-ray Fluorescence (XRF) and ion chromatography, respectively. The overall results showed the TiO 2 coating was better able to preserve the surface colour properties early after exposure. After eight months, this effect was lost and the self-cleaning efficiency was reduced to negligible final rates. No clear wettability results and no meaningful capillary behaviour were recorded. A decrease of the photocatalytic activity was due to both partial titania loss and deactivation phenomena. The role of soluble salt ions either adsorbed from the environment or produced by the photocatalytic abatement of pollutants was recognized in the deactivation of the photocatalysts and their accumulation deserves attention for possible stone damage risk implications.
Self-cleaning and de-polluting stone surfaces: TiO 2 nanoparticles for limestone
h i g h l i g h t s " Limestone is a building material largely used for urban architectural surfaces. " A TiO 2 -nanoparticle coating was tested on it. " Compatibility, self-cleaning and de-polluting effects were assessed. " Results showed good compatibility with limestone surface. " Evident photocatalytic efficiency was also demonstrated.
Photocatalytic nanostructured TiO2 for protection of porous and compact stone
The enhanced photocatalytic activity for degradation of a wide range of pollutants makes nanostructured TiO2 an ideal candidate for self-cleaning coatings. The deposition of different types of TiO2 nanocrystalline coatings on stone has been investigated in order to test the surface protection and self-cleaning abilities of the nanostructured materials. TiO2 nanocrystals with controlled size, shape and surface chemistry have been prepared by using two distinct synthetic approaches, namely colloidal synthesis by hot injection and hydrothermal nanophase crystallisation. Two different types of stones, possessing different porosity, namely porous calcarenite and a compact limestone have been selected, being both widely used in South Italian monuments and building relevant for cultural heritage. The physical properties of coated and uncoated stone surfaces, respectively, have been investigated, and colour, wettability and stability of the coatings have been checked. The self-cleaning prop...
Building and Environment, 2016
Coating with nanostructured Titanium dioxide is able to enhance natural stone surface with self-cleaning and depolluting abilities; nonetheless, the durability of the coatings is a crucial issue to be assessed in relation to their potential for use in the context of the building heritage. In this paper, the resistance of coatings applied on a compact and a soft limestone, which differ in roughness, porosity and cohesion features, has been investigated. A peeling and a water impact test were performed and their effect on the coated surface was evaluated as film loss by qualitative/quantitative ESEM-EDS analyses. Self-cleaning effectiveness was assessed by performing a photodegradation test of Rhodamine B. Crack-free and conformable films showed a good anchorage to both limestones; after the durability tests the coated surfaces exhibited almost unchanged Ti/Ca ratios and self-cleaning efficiencies. Large adhesion failures and decreased Ti amounts were recorded where coatings were fissured; they especially occurred on the surface of the compact limestone, along with a reduced self-cleaning ability. High surface roughness accounted for a better adhesion of both crack-free and fissured films to the soft limestone, but some erosion of the coated surface, which affected this friable stone under the water impact, compromised their preservation. Nonetheless, good self-cleaning performances were still provided due to the retention of nanoparticles under the surface. The overall results support that preservation of nanostructured TiO 2 coatings on the stone surface depends on the inherent characteristics of both films and supports; durability of the stone itself can play an important role.
SURFACE ENGINEERING ON NATURAL STONE THROUGH TiO2 PHOTOCATALYTIC COATINGS
2011
The application of semiconductor photocatalytic films on natural stone has been investigated for surface protection and selfcleaning. Sol Gel and hydrothermal processes were used to synthesize TiO2 sols with enhanced photocatalytic activity and without the need of thermal curing of the coated surface. The stone was a local (apulian) carbonatic sedimentary and porous stone. Films and powders prepared from the TiO2 sols were studied using x-ray diffraction to evaluate the microstructural evolution and identify rutile and anatase phases. A morphological and physical characterization was carried on the coated stone to establish the coating adhesion and the changes of aspect, colour and hydric behaviour. The photocatalytic activity was evaluated by dye degradation rate under UV irradiation measuring the color change with a colorimeter. The hydrothermal process proved to be effective for obtaining photocatalytic surfaces with selfcleaning and antipollution properties. With no need of high...
TiO2 nanocoatings for architectural heritage: Self-cleaning treatments on historical stone surfaces
Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems, 2013
The development and application of nano-engineered surface treatments on stones could become a useful tool for the realization of smart systems to better preserve and maintain architectural surfaces. Titanium dioxide nanoparticles can be used to realize transparent self-cleaning coatings applicable directly on preexisting surfaces, limiting cleaning actions and conservation processes, thus reducing their costs. The aim of this investigation is to evaluate the potential use of TiO 2 on stone surfaces, especially in the field of architectural heritage. An aqueous colloidal dispersion based on titanium dioxide, obtained by sol-gel and hydrothermal processes, was applied by spray coating on travertine, a limestone largely used in buildings, both historical and modern. The maintenance in the original appearance of treated substrates was evaluated monitoring both colour and gloss changes produced by the treatments. Physical changes induced to stone by titanium dioxide were studied by wettability analyses. The efficiency of TiO 2 photocatalysis was assessed by depolluting and soiling removal tests under ultraviolet light. The effects of deposited amount of titania on treated surfaces were also evaluated. Obtained results seem to allow the use of selected TiO 2 treatments on the selected substrate, travertine, without altering in an evident and harmful way the original properties of limestone. Photoinduced effects (hydrophilicity, degradation of pollutants and decolourization of soiling) are very evident, and the combination of these properties may lead to an actual self-cleaning effect.
TiO2-based nanocoatings for preserving architectural stone surfaces: An overview
Construction and Building Materials
Titanium dioxide has been recently used in its nanometric form to develop smart products and coatings on several building components so as to better preserve their visual aspect, mainly by way of its very efficient photocatalytic function. The integration of further nanostructured materials with titanium dioxide may enhance its features or add new properties to these products. The aim of this review is to provide a report on the latest developments in a specific area of the maintenance of architectural surfaces: the use of multifunctional (self-cleaning, de-polluting, biocidal) nanocoatings based on titanium dioxide on architectural stone surfaces. The results of several studies concerning different products containing TiO2 nanoparticles, potentially added with other nanometric elements, have been summarised and compared from several points of view focused on their compatibility with treated substrates and their effectiveness against diverse degrading agents (soil, pollution and mic...
Applied Surface Science, 2013
A self-cleaning photocatalytic coating for limestone materials, based on TiO 2 nanoparticles obtained by the sol-gel process has been studied. TiO 2 sol was applied directly to the surface or after a SiO 2 intermediate layer. The selected test materials are the Modica and the Comiso calcarenites, limestones of Ragusa Formation outcropping in the south eastern Sicily (Italy). SEM-EDS, XRD and Raman investigations were carried out to characterize the TiO 2 nanoparticles and coating. Nanocrystalline anatase and, to a lesser extent, brookite forms are obtained. To evaluate the harmlessness of the treatment, colorimetric tests, water absorption by capillarity and crystallization of salts measurements were performed. Photocatalytic activity of the TiO 2 colloidal suspension and of the coatings (TiO 2 and SiO 2 /TiO 2) was assessed under UV irradiation through methyl orange dye degradation tests. The results show good photodegradation activity and satisfactory compatibility between the sol and the surface of the investigated limestones.