Visible- and solar-active photocatalytic ceramic coatings

The photocatalytic ceramic coatings have potential applications in advanced wastewater treatment, targeting their reuse. However, the limited number of large-scale applications is mainly related to the type of radiation required to activate the photocatalyst as most of the catalysts investigated in the beginning were UV-active ceramic materials. To extend the application field, during the past few years, research has focused on the development of visible (Vis)- or solar-active photocatalytic ceramic coatings. This chapter outlines the results recorded in the development of diode- or tandem-type Vis-active photocatalytic structures, such as: (a) Multilayered composites based on a wide band gap n-type semiconductor (e.g., titanium dioxide (TiO2)) and on a narrow band gap p-type semiconductor (CuxS, CuInS2, or Cu2ZnSnS4). (b) 3D composites with a wide band gap ceramic semiconductor matrix (TiO2) and graphene oxide reduced graphene oxide, or graphitic carbon nitride as filler. The most important factors that influence the photocatalytic degradation efficiency of the standard pollutant (methylene blue) are outlined for each group of composite structures, considering the filler type and content, the surface roughness and the surface charge, the pH, and the irradiance value in static and continuous flow operating conditions.