Photo-induced properties of TiO2/ZnAl layered double hydroxide coating onto porous mineral substrates

Due to the actions of many environmental aspects, such as inorganic and organic pollutants as well as microorganisms, porous building materials are constantly damaged and deteriorated. Deposition of photocatalytic coating on the surface of building material is one of the most effective procedures for the protection of the material from both environmental and economic point of view. Three types of porous brick substrates and one stone material were chosen and investigated regarding chemical and mineralogical composition, textural and surface (roughness and microhardness) properties. In order to improve the porous building material surface properties the newly designed TiO2–ZnAl layer double hydroxide (TiO2–ZnAl LDH) coatings were prepared, applied and investigated. New experimental technique based on the Fourier Transform Infra-Red spectrometry in diffuse reflectance (DRIFT) modality was established and compared to existing methods (contact angle measurements without addition of water, surface water absorption and contact angle assessment after spraying with water as the function of UV/Vis irradiation time) in order to assess the photo-induced hydrophilicity of the coated materials. The DRIFT analysis confirmed the existence of the photo-induced hydrophilicity by assessing the surface OH− groups׳ quantity during UV/Vis irradiation necessary for the development of the surfaces hydrophilicity. The obtained results indicate a strong influence of the reference building material surface characteristics on the photo-induced hydrophilicity, photocatalytic and self-cleaning properties of the newly designed TiO2–ZnAl LDH coatings.