Incorporation of functionalized Ag-TiO2NPs to ormosil-based coatings as multifunctional biocide, superhydrophobic and photocatalytic surface treatments for porous ceramic materials

Abstract Microbial fouling on the surface and water retention are common problems affecting porous ceramic materials (stone, concrete…) that can alter their properties, shorten their service life and even pose a health risk. Though proper maintenance (disinfection, drainage…) can mitigate these issues, it is a time and resource intensive process and preventive measurements are desired, such as hydrophobic or anti-fouling coatings. In this work, we report a simple sol-gel route to obtain a multifunctional coating combining superhydrophobic, biocide and photoactive properties, by incorporating TiO2 nanoparticles (NPs), functionalized with –SH or –NH terminated alkoxysilanes, and AgNPs into an organically modified silica matrix (ormosil). The low surface energy of the ormosil, combined with the nano-roughness created by the accumulation of Ag-TiO2NPs on the surface promotes a Cassie-Baxter wetting state, leading to water repellence and a lower bioreceptivity of the coatings due to a decreased cell attachment. The influence of this factor was evidenced by the comparatively higher cell attachment on the smoother surface of xerogels samples prepared from the ormosils, where TiO2 surface charge plays a major role. The incorporation of AgNPs increases the photocatalytic effectiveness of the TiO2 and effectively inhibits the growth of the tested microorganisms (Escherichia coli and Saccharomyces cerevisiae), even in the absence of light. Surface functionalization of the TiO2NPs affects the distribution, size and stability of the AgNPs, and thus, the biocide and photocatalytic effectiveness of the treatments.