The influence of FeCl3 on the photocatalytic degradation of dissolved azo dyes in aqueous TiO2 suspensions

The study concerned decolouration of solutions of azo, anionic (Acid Orange 7, Reactive Red 45, Acid Yellow 23) and cationic (Basic Blue 41 and Basic Orange 66) dyes during illumination with UV (λmax 366 nm) irradiation in the presence of TiO2 and FeCl3. The process of decolouration during illumination of the solutions studied containing FeCl3 underwent significant intensification in the case of anionic dyes and unfavourable inhibition in case of cationic dyes. It was also observed that FeCl3 had a diverse influence on the adsorption of the dyes studied on TiO2. The adsorption of anionic dyes and decolouration of solutions before the illumination was observed only in the presence of FeCl3. In case of cationic dyes the addition of FeCl3 caused elimination of these phenomena. An additional cause of decolouration of anionic dyes solutions before illumination was the precipitation of their poorly soluble compounds from Fe3+.