Photoactive self-cleaning zinc oxychloride coatings

Zinc oxychloride cement (ZOC) is considered a promising quick-drying material for fabricating photoactive coatings composed of three components: zinc oxide (ZnO), zinc chloride (ZnCl 2 ), and water. However, its massive application has not been implemented due to the lack of research about its stability and mechanical performance. Thus, this article aims to provide insights about the self-cleaning photoactivity of ZOC coatings incorporated with titanium dioxide (TiO 2 ) nanoparticles to boost the photocatalytic performance. Two stoichiometries of ZnO:ZnCl:H 2 O (112 and 415) were studied to investigate the influence of the molar ratio of the components on the physical and chemical properties. According to these results, no significant differences were observed in the physical and chemical properties between the two stoichiometries studied; however, the mechanical properties were affected. The coatings crystallized as simonkolleite Zn 5 (OH) 8 Cl 2 ·H 2 O with a laminar hexagonal morphology, show high surface area, and absorbs light in the UVA region. The self-cleaning activity was evaluated using four model pollutants: Rhodamine B, Methylene blue, Orange G, and Carbon under accelerated weathering conditions. All the coatings were photoactive to decompose the pollutants from their surface and the addition of TiO 2 nanoparticles did not significantly enhance the self-cleaning efficiency, but it improves the mechanical performance of the coatings. These results could be associated with the fact that TiO 2 works as filler for voids in the coatings without affecting its settings. The stability of the coatings was confirmed after the exposure to accelerated weathering at high humidity conditions, which places them as an attractive, low-cost, and easy to apply self-cleaning material. • The photocatalytic activity of zinc chloride cement (ZOC) was explored by first time. • The incorporation of 1% of TiO 2 favored mechanical performance of ZOC. • All the pastes were photoactive to decompose the pollutants from their surface. • The zinc oxychloride cement was stable under humid environments.