Photocatalyzed N-de-ethylation and degradation of Brilliant Green in TiO2 dispersions under UV irradiation

The photocatalytic degradation of Brilliant Green (BG, Bis(4-diethylaminophenyl)phenylmethylium chloride), a cationic dye, was investigated in an irradiated TiO2 aqueous dispersion. In this study, in order to obtain a better understanding on the mechanistic details of this TiO2-assisted photodegradation of the BG dye with UV irradiation, four intermediates of the process were separated, identified, and characterized by HPLC-PDA-ESI-MS technique. The results indicated that the N-de-ethylation degradation of BG dye took place in a stepwise manner to yield mono-, di-, tri-, and tetra-N-de-ethylated BG species generated during the processes. The photodegradation of the BG dye featured competitive reactions between N-de-ethylation and cleavage of the BG chromophore ring structure at different pH values. However, most of all, the higher degradation rate at acid pH was observed for the cationic dyes of triphenylmethane of TiO2-mediated experiments for the first time. These results should be useful for future applications of the treatment technology to dye pollution.