Assessing the effects of UVA photocatalysis on soot-coated TiO2-containing mortars

Abstract

The deposition of soot on building surfaces darkens their colour and leads to undesirable black crusts, which are one of the most serious problems on the conservation of built cultural heritage. As a preventive strategy, self-cleaning systems based on the use of titanium dioxide (TiO) coatings have been employed on building materials for degrading organic compounds deposited on building surfaces, improving their durability and performance. In this study, the self-cleaning effect of TiO-containing mortars coated with diesel soot has been appraised under laboratory conditions. The mortar samples were manufactured using lime putty and two different doses of TiO (2.5% and 5%). The lime mortars were then coated with diesel engine soot and irradiated with ultraviolet A (UVA) illumination for 30days. The photocatalytic efficiency was evaluated by visual inspection, field emission scanning electron microscopy (FESEM) and colour spectrophotometry. Changes in the chemical composition of the soot particles (including persistent organic pollutants) were assessed by analytical pyrolysis (Py-GC/MS) and solid state C NMR spectroscopy. The FESEM and colour spectrophotometry revealed that the soot-coated TiO-containing mortars promoted a self-cleaning effect after UVA irradiation. The combination of analytical pyrolysis and C solid state NMR showed that the UVA irradiation caused the cracking of polycyclic aromatic structures and n-alkyl compounds of the diesel soot and its transformation into methyl polymers. Our findings also revealed that the inclusion of TiO in the lime mortar formulations catalysed these transformations promoting the self-cleaning of the soot-stained mortars. The combined action of TiO and UVA irradiation is a promising proxy to clean lime mortars affected by soot deposition.

Radiological behaviour of pigments and water repellents in cement-based mortars

“…Most pigments used in these contexts comprise metal oxides. Pigments containing TiO 2 both whiten mortar and protect it from the deposition of organic compounds [9]. Synthetic [10] or natural [11] iron oxide-based pigments may be red (Fe 2 O 3 ) or black or grey (Fe 3 O 4 ) [12].…”

Low-Carbon Concrete Based on Binary Biomass Ash–Silica Fume Binder to Produce Eco-Friendly Paving Blocks

“…A property of great importance for new binders would be the ability to degrade organic matter, either to degrade organic dyes in wastewater or even to produce self-cleaning facades [132]. For the evaluation of the organic matter (pollutants) degradation potential, methylene blue (MB) compound was used [133].…”

TiO2-Based Mortars for Rendering Building Envelopes: A Review of the Surface Finishing for Sustainability

“…Therefore, many researchers, companies and practitioners have investigated the effect of TiO 2 -based mortars aiming to optimize the development of the coatings [1]. TiO 2 exists in three principal varieties of crystalline structures: anatase, rutile and brookite [8], which lead to differences in photocatalytic efficiency, with anatase being the most photoactive polymorph [9,10]. Anatase absorbs ultraviolet radiation (UV) with a wavelength lower than 380 nm [11] and then works through heterogeneous photocatalysis, an advanced oxidative process (AOP) associated with substantially reactive hydroxyl (OH•) radicals [12].…”

“…However, most of the research on photocatalytic TiO 2 -based mortars relates to white finishing substrates [55], even though colorful products are increasingly demanded [56] and may be attractive for design specifications. The interest in photocatalytic colored renders may be emphasized regarding the fact that biocolonization [57] and soot deposition [10] lead to changes in the surface color, which may be addressed by TiO 2 photoactivation.…”