Photocatalytic self-cleaning properties of Mo:TiO2 loaded Zn–Al layered double hydroxide synthesised at optimised pH value for the application on mineral substrates

Abstract

Aiming to evaluate the dependence of the photocatalytic self-cleaning properties of layered double hydroxides (LDH) with intercalated active substances among their ultrathin nano-sheet layers on the synthesis parameters, particularly on the pH value, a series of ZnAl-LDH suspensions were synthesised using a modified low supersaturation co-precipitation method at various pH values between 7 and 10. The optimal pH value was found to be 8. The molybdenum doped TiO2 nanocomposite LDH suspensions (Mo:TiO2–ZnAl-LDH) were synthesised at the optimised pH value. The Mo/Ti mass ratio was systematically varied between 0 and 0.03 in order to cover the region below 0.03 which had been found to be optimal in our previous work [1] but it was at the limit of the investigation range (0.03–0.12). Systematic material characterisation study was performed. The photocatalytic self-cleaning properties of the optimally synthesised Mo:TiO2–ZnAl-LDH suspensions were characterised when applied on stone, brick and glass substrates and after having been illuminated only by using LED visible light. The best results were obtained when the newly developed suspension was applied on the stone substrate due to the combined influence of surface roughness, textural characteristics and pH value of the mineral substrate.