Self-Cleaning and Antipolluting Properties of Tio2-Containing Cementitious Materials
M.V. Diamanti, M.F. Brunella, MP. Pedeferri, C. Pirotta, P. Manzocchi, S. Curtoni
Politecnico di Milano, IT
anatase, commercial mortars, photocatalysis, self-cleaning
ABSTRACT Nanocrystalline TiO2, in the form of anatase or rutile, is one of the most important and used photocatalysts because of the excellent efficiencies of conversion of chemical species, and its commercial availability . The work presented analyzes both the photocatalytic properties and the self-cleaning attitude displayed by TiO2-containing commercial cementitious materials used as insulating coverings for buildings: these materials could prove to be helpful in the contemporary challenge of finding sustainable materials for green buildings [2, 3]. Investigations were carried out on mortars obtained by adding anatase in different quantities and forms (as nanometric powder or aqueous solution added to the mix design, or as surface painting). The samples photocatalytic efficiency was first evaluated in VOC degradation; 2-propanol was used. The atmosphere of a cell containing the sample, irradiated with UV light, was saturated with the organic compound: the variation of atmosphere composition with irradiation time assessed the 2-propanol mineralization . Higher amounts of anatase in the material resulted in higher VOC conversions; moreover, materials containing anatase in form of aqueous solution show greater photoactivity comparing to materials containing anatase powders in the same percentages (figure 1). Finally, a surface painting containing anatase is more effective than the addition of anatase powders to cement, allowing higher photocatalytic efficiencies with lower anatase percentages. The obtained results were fully confirmed by further photocatalytic tests, consisting of an organic dye mineralization, performed by coloring a white surface with methyl-orange and irradiating it with UV light. Changes in surface color with irradiation time, measured through a spectrophotometer, quantified the mineralization degree (figure 2). Anatase-containing materials are defined as self-cleaning, since they maintain their original color in polluting environments thanks to an increased hydrophilicity. The self-cleaning properties were studied by exposing samples at the urban atmosphere for 3 months, and subsequently by moving them in a controlled chamber with low-intensity UV lamps. Color was monitored by using a spectrophotometer. Samples which most maintained the original color are those containing anatase in bulk, since anatase-containing paintings easily break and detach from samples surfaces. An interesting behavior was observed as samples were put into the chamber: the most photoactive ones were interested by a color shift towards yellow, ascribed to the formation of reaction products from the degradation of dust and contaminants adsorbed on the surfaces. After 30 days this shift was partially recovered, specially for efficient materials (figure 3). To conclude, the TiO2-containing commercial materials presented have proved to be efficient in degradating two different polluting compounds, as well as in limiting contaminants adhesion comparing to conventional materials surfaces; an improvement in photoactivity was observed by adding anatase in form of aqueous solution, while paintings showed adhesion drawbacks. REFERENCES  M.F. Brunella, M.V. Diamanti, M.P. Pedeferri, F. Di Fonzo, C.S. Casari, A. Li Bassi, Thin Solid Films (2006) doi:10.1016/j.tsf.2006.11.194.  O. Carp, C.L. Huisman, A. Reller, Prog. Solid State Chem. (2004) 32.  M. Lackhoff, X. Prieto, N. Nestle, F. Dehnb, R. Niessner, Appl. Catal. B: Environ. (2003) 43.  N.P. Mellott, C. Durucan, C.G. Pantano, M. Guglielmi, Thin Solid Films (2006) 502.
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