Photoinduced transformations of Acid Violet 7 and Acid Green 25 in the presence of TiO2 suspension

An azo dye (Acid Violet 7) and an anthraquinone dye (Acid Green 25) were degraded in aqueous solution using titanium dioxide as photocatalyst. Their fate was studied through dyes decomposition, identification of the main and secondary transformation products and assessment of mineralization. Carbon complete mineralization was achieved in both cases together with the total conversion of the sulphonic groups into sulphate ions; nitrogen was recovered as nitrate and ammonium ions. ansformation intermediate products were identified by means of HPLC/MS and GC/MS techniques. Acid Violet 7 transformation involved the detachment of sulphonic group, hydroxylation, and detachment of the amino acetic moiety, with the formation of hydroxyl naphthalene. Conversely, Acid Green 25 transformation proceeded through the formation of 19 initial compounds and involved the detachment of one (or two) sulphonic groups and/or hydroxylation, followed by the detachment of the benzenic ring.