Determination of the photocatalytic efficiency of TiO 2 coatings on ceramic tiles by monitoring the photodegradation of organic dyes Vladimira Petrovic ˇ a , Vilma Ducman a , Srec ˇo D. S ˇ kapin b, * a Slovenian National Building and Civil Engineering Institute, Dimic ˇeva 12, 1000 Ljubljana, Slovenia 1 b Joz ˇef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 2 Received 27 July 2011; received in revised form 26 September 2011; accepted 27 September 2011 Available online 17 October 2011 Abstract A method for the evaluation of the photocatalytic effectiveness of nanotitania coatings on ceramic substrate was established. Decolourization of three organic dyes, including methylene blue (MB), rhodamine B (RB) and crystal violet (CV), was investigated under different experimental conditions. The results showed that the UV light spectrum and light intensity are important parameters when establishing this method. The effect of TiO 2 on the percentage degradation of the dyes was examined by varying its concentration in the suspensions between 0.1% and 4.5 wt%, which resulted in different thicknesses of the TiO 2 layers, and as expected higher percentages of nanotitania resulted in higher photocatalytic efficiencies. However higher amounts of titania lead to the formation of cracks on the surface, which might detrimentally affect adhesion and thus also long-term durability. The applicability of all the dyes used in the present study was proved, and there is good correlation between MB, RB and CV in the evaluation of self-cleaning efficiency. # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: D. TiO 2 ; Photocatalysis; UV/vis spectra; Organic dye decolourization 1. Introduction Industrial pollution is an important global problem, and has effects on the quality of urban and rural environments, including water, air and soil. The development of new materials that can be easily applied to facades, roofs, glass, tiles, pavements, textiles and similar surfaces with photocatalytic and self-cleaning, de-polluting properties would significantly contribute to a decrease in environmental pollution and its irreparable consequences. The use of materials with self- cleaning properties will not be just eco-friendly to the environment, but may also be able to prolong the life-time of buildings and a variety of exterior subjects. The initial aesthetics and mechanical properties of new buildings often deteriorate due to attack by environmental pollution (i.e. car fumes which coat building exteriors with grime or moss, fungi that stain roofs, etc.) [1–3]. In order to decrease environmental pollution, the photo- catalytic degradation of organic pollutants in the presence of TiO 2 as photo-catalysts appears to be a rapidly growing decontamination process. So far numerous experimental methods have been reported for the determination of the photo-catalytic activity of TiO 2 , as well as studies related to the use of semiconductors in the photo-mineralization of coloured organic substances. As model pollutants dyes are commonly used because their concentration can be easily monitored using a spectrometer. Among them, methylene blue (MB) has been widely studied due to its highly coloured nature, good chemical stability, and inexpensiveness. The method which employs MB dye dissolved in water in the presence of TiO 2 has been considered as a standard test for photo-catalytic surfaces by the International Organization for Standardization (ISO) [4,5]. A major advantage of using heterogeneous photo-catalysis, which are based on the generation of very reactive species such as hydroxyl radicals (OH) and others, is the total mineraliza- tion of organic dyes, which results in CO 2 , H 2 O and corresponding mineral acids. The semiconductor-sensitized photo-oxidative degradation of dye test reagents is considered www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 38 (2012) 1611–1616 * Corresponding author. Tel.: +386 1 477 3708; fax: +386 1 477 3875. E-mail address: sreco.skapin@ijs.si (S.D. S ˇ kapin). 1 http://www.zag.si. 2 http://www.ijs.si/. 0272-8842/$36.00 # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2011.09.050