Photocatalyzed N-de-methylation and degradation of crystal violet in titania dispersions under UV irradiation

TiO2-mediated photocatalytic process has been successfully applied to degrade dye pollutants. In order to obtain a better understanding on the mechanistic details of the TiO2-assisted photodegradation of crystal violet (CV, N,N,N′,N′,N″,N″-hexamethylpararosaniline) dye with UV irradiation, 17 intermediates of the process were separated, identified and characterized by HPLC–ESI-MS techniques in this study. The results indicated that the N-de-methylation degradation of CV dye took place in a stepwise manner to yield mono-, di-, tri-, tetra-, penta-, and hexa-N-de-methylated CV species with N-hydroxymethylated intermediates, which were found for the first time, generated during the processes. Several probable photodegradation pathways were proposed and discussed. The reaction mechanisms of TiO2/UV proposed in this study would be useful for future application of this technology for decoloration of dyes.