Photocatalytic degradation of anionic and cationic dyes over TiO2 P25, and Ti-pillared clays and Ag-doped Ti-pillared clays

Ti-pillared clay and a Ag doped Ti-PILC have been synthesised and characterised and their photocatalytic efficiency in the degradation of methylene blue and Remazol black dyes was compared with the efficiency of P25 titanium oxide. In the dark, the adsorption of methylene blue on Ti-clays is total and fast. Ag doping of the clay increases this kinetics of adsorption, but does not alter the amount adsorbed. In that case adsorption, by cation exchange, is the cause of the disappearance of the reactant from the solution and photocatalytic properties cannot be investigated. In contrast, for Remazol black, the amount adsorbed is small, and decreases upon Ag doping in agreement with its adsorption properties. The comparison of the different solids in the photocatalytic degradation of Remazol black shows that TiO2 remains the best catalyst. The Ti-pillared beidellite shows a low activity, which is decreased by addition of Ag but increases proportionally to the content of Ti. The effect of ultrasonic treatment of the reaction medium containing the Ti-PILC has also been investigated and discussed taking into account the release of semiconductor and the decrease of diffusion.