Photoactive Cu–TiO2 Coatings with Hierarchical Texture: Effect of Anatase and Rutile on Wetting and Copper Release Kinetics in Saline

Abstract New-generation antibacterial surfaces must not only inhibit microbial growth, but also maintain their functionality when used as “touch surfaces” and self-clean under the influence of light. This paper proposes a simple approach to the formation of Cu–TiO2 composite coatings on copper foil, with the approach combining laser micro/nanotexturing and subsequent deposition of TiO2 nanodispersions of controlled polymorphic forms (anatase/rutile). It is shown that the coating retains its initial hierarchical roughness and a significant titania content after sonication in water. Photocatalytically induced self-cleaning of the coating under irradiation with wavelengths corresponding to the blue region of the visible light spectrum is more pronounced for anatase-containing composites. Moreover, the photocatalytic activity of the anatase-containing composite shifts toward the visible region relative to the initial anatase particles. This widening of the photoactivity region of the composites is due to the fact that copper oxide functions as a sensitizer, which absorbs visible light, thus leading to injecting electrons from copper oxide to the conduction band of anatase in the presence of a heterojunction. Irradiation has different effects on composites with different polymorphic modifications when they are exposed to saline: e.g., anatase enhances the accumulation of dissolved copper, while rutile reduces its concentration relative to unirradiated conditions. Thus, in the method proposed for preparing the composites, polymorphic forms of TiO2 enable one to control the self-cleaning and the ionic response of copper, i.e., the key parameters of photoactive coatings intended for antibacterial applications.