Two competitive primary processes in the photodegradation of cationic triarylmethane dyes under visible irradiation in TiO2 dispersions

The photocatalytic degradation of two cationic triarylmethane dyes, crystal violet (CV) and fuchsin basic (FB), was examined in aqueous TiO2 suspensions under visible light irradiation. The techniques of (HNMR)-H-1, UV-Vis and EPR have been used to identify the photodecomposed products and intermediates and to demonstrate the photocatalytic mechanism of the dye on the semiconductor surface. The degradation undergoes a competitive primary process between demethylation and decomposition of the whole conjugated structure.