Photoactive self-cleaning zinc oxychloride coatings

Abstract

Zinc oxychloride cement (ZOC) is considered a promising quick-drying material for fabricating photoactive coatings composed of three components: zinc oxide (ZnO), zinc chloride (ZnCl2), 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 (TiO2) nanoparticles to boost the photocatalytic performance. Two stoichiometries of ZnO:ZnCl:H2O (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 Zn5(OH)8Cl2·H2O 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 ZOC coatings were photoactive to decompose the pollutants from their surface. The addition of TiO2 nanoparticles into the coatings 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 TiO2 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.

Keywords

• Zinc oxychloride
• ZOC
• Self-cleaning
• Photocatalysis
• Photoactive surfaces