Surface properties and de-polluting performance of a photocatalytic coating incorporating novel core@shell nanospheres for cementitious substrate

The surface of long-term exposed building materials usually shows serious deterioration under continuous environmental erosion, which can greatly shorten the service life of building structures. The application prospect of multifunctional photocatalytic materials in civil engineering is promising but the engineering application is still limited due to the inherent defects of traditional photocatalytic materials. In this paper, the ordinary Portland cement (OPC) and alkali activated slag (AAS) mortar samples were prepared with a photocatalytic coating incorporating novel core@shell nanospheres which feature with TiO2 core and CoAl-layered double hydroxide shell (TiO2@CoAl-LDH). The surface roughness, microhardness, contact angle and capillary water absorption of coated and uncoated mortars were analyzed and characterized to explore the effect of photocatalytic coating on surface properties. The photocatalytic activity and photo-induced hydrophilicity of the coated mortar were investigated by degrading methylene blue and contact angle tests. A simulated rainwater washing test was designed to evaluate the long-term stability of photocatalytic coatings on mortar substrate. The results show that compared with unwashed coated mortar, the coated mortar after rainwater washing can still maintain a higher photocatalytic activity, whereby the surface hydrophilicity was increased with the decrease of the surface roughness and capillary water absorption. As a newly developed protective coating material, TiO2@CoAl-LDH is expected to confer multifunctional properties to the cementitious materials.