Photocatalytic activity and stability of TiO 2 /ZnAl layered double hydroxide based coatings on mortar substrates T. Vulic a,⇑ , O. Rudic a , S. Vucetic a , D. Lazar b , J. Ranogajec a a University of Novi Sad, Faculty of Technology, Bul. Cara Lazara 1, 21000 Novi Sad, Serbia b University of Novi Sad, Faculty of Science, Trg Dositeja Obradovica 3, 21000 Novi Sad, Serbia article info Article history: Received 26 July 2013 Received in revised form 24 December 2014 Accepted 30 December 2014 Available online 7 February 2015 Keywords: Cement mortar Pozzolanic mortar Surface properties Photo-induced hydrophilicity Self-cleaning Durability abstract The surface properties and photocatalytic activity of the cement and pozzolanic mortar samples coated with TiO 2 /ZnAl layered double hydroxides were studied with the intention to design suitable protective, hydrophilic coatings. In order to underline the existing correlation between the water uptake character- istics and the surface features, the coated mortars were subjected to water absorption test by capillarity, to photo-induced surface water absorption test and to photo-induced hydrophilicity test by contact angle measurements. The self-cleaning behavior of the mortar systems was evaluated by monitoring the photocatalytic rhodamine B removal efficiency in correlation with the development of photo-induced surface hydrophilicity. The coating durability was assessed towards the weathering effect of rain (essential for the coating self-cleaning properties). The positive result of the coating deposition was the improvement of photocatalytic activity, photo-induced hydrophilicity and the decrease of mortar systems surface roughness. The study revealed that the developed coating promotes self-cleaning effect. Ó 2015 Published by Elsevier Ltd. 1. Introduction The surfaces of building materials are constantly exposed to the actions of environmental factors, pollutants of inorganic and organic origin as well as to the actions of microorganisms, which are significantly contributing to deterioration phenomena. The deterioration of building materials presents irreversible changes of some properties which decrease their length of exploitation. It involves chemical, physical and biological processes and always starts at the surface penetrating gradually into the material. Mortars, as constructive elements, provide links between other materials (fundamentally rocks or bricks) on the one hand, and cover the surfaces of columns, walls, facades on the other hand. They are, at a certain extent, ‘‘the skin‘‘ of buildings. Some char- acteristics of the mortars (heterogeneous mineral phase composi- tion and high porosity) can affect their durability, making them susceptible to external agents and contributing to the physical and mechanical instability of the contact between mortars and sub layering materials (bricks, stones and constructive building elements) [1]. This stimulates the entrance of polluting agents as the initiators of the deterioration of the materials that mortars are protecting or binding. A significant amount of damage could be avoided if the building materials were adequately protected. The application of the protective coatings could decrease the neg- ative action of the pollutants minimizing their direct contact with the substrate. Since the degradation processes start on the mate- rial surface, the deposition of suitable protective coating can change and improve the surface properties, resulting in a moder- ation of the building materials deterioration and prolongation of the material exploitation. Different types of coatings with addi- tional functions have been developed [2–9]. The interest for this area of research is enormous, but there are still areas that have not been scientifically covered. One of the most convenient and environmental friendly solution is the development of multifunc- tional self-cleaning materials and their application on large exposed surfaces of the building materials. Self-cleaning effect is a photo-induced phenomenon which comprises two different processes: photocatalytic degradation reactions of different pollu- tants and improvement of surface hydrophilicity by decreasing water contact angle and creating a uniform water film on the coated surfaces [10]. Beside light irradiation, the presence of water is also necessary for the development of both mentioned self-cleaning processes. The pollutants attached onto the self- cleaning surfaces are decomposed (partially or totally) due to the photocatalytic action and the dirt residue is removed during the first rain shower due to the surface hydrophilicity. http://dx.doi.org/10.1016/j.cemconcomp.2014.12.015 0958-9465/Ó 2015 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail addresses: tvulic@uns.ac.rs (T. Vulic), ognjenrudic@tf.uns.ac.rs (O. Rudic), snezanap@uns.ac.rs (S. Vucetic), dlazar@df.uns.ac.rs (D. Lazar), janjar@uns.ac.rs (J. Ranogajec). Cement & Concrete Composites 58 (2015) 50–58 Contents lists available at ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp