Assessing the Effects of UVA Photocatalysis on Soot-Coated TiO2-containing Mortars

11 páginas.-- 7 figuras.-- 4 tablas.-- 56referenciasThe 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 2) 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 2-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 (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 13C NMR spectroscopy. The FESEM and colour spectrophotometry revealed that the soot-coated TiO 2-containing mortars promoted a self-cleaning effect after UVA irradiation. The combination of analytical pyrolysis and 13C 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 2 in the lime mortar formulations catalysed these transformations promoting the self-cleaning of the soot-stained mortars. The combined action of TiO 2 and UVA irradiation is a promising proxy to clean lime mortars affected by soot depositionJ.M. de la Rosa and A.Z. Miller thank The Spanish Ministry of Economy and Competitiveness (MINECO) for the “Ramón y Cajal” and Juan de la Cierva postdoctoral contracts, respectively. J.S. Pozo-Antonio was supported by a postdoctoral contract within the framework of the 2011–2015 Galician Plan for Research, Innovation and Growth (Plan I2C) for 2014. This work was also co-funded by the Strategic project FCT - UID/ECI/04028/2013.Peer reviewe