Molybdenum doped TiO2 nanocomposite coatings: Visible light driven photocatalytic self-cleaning of mineral substrates

The molybdenum doped TiO2 nanocomposite layer double hydroxide (LDH) suspensions, Mo:TiO2-LDHs, were synthesized by a wet impregnation method in order to enhance the pure TiO2 (water suspension) photocatalytic activity and consequently its self-cleaning efficiency under exposure to visible light. The aim was to produce nanocomposites by a simple, energy saving and cost beneficial synthesis. The mass ratio Mo/Ti was systematically varied (0.03, 0.06, 0.09, 0.12). The obtained nanocomposite Mo:TiO2-LDH suspensions were first characterized by UV-vis spectroscopy (band-gap energies), Zeta-sizer (particle size distribution and stability) and X-ray diffraction (XRD) (structure) and then applied onto the model mineral substrates, brick and stone. The photocatalytic activity of the obtained coating was determined based on the degradation kinetics of the Rhodamine B (RhB) under artificial visible light irradiation (white LED). The obtained results were compared to the ones of the unmodified TiO2-LDH suspension. The obtained results also showed that all prepared nanocomposites have good photocatalytic activity, particularly the suspension Mo:TiO2-LDH with the Mo/Ti 0.03 mass ratio which possesses the best value. In addition, as regards the visible light driven self-cleaning effect, this suspension has proven to be a good protective functional coating for porous mineral substrates (bricks and stones).