Photodegradation of crystal violet in TiO(2) suspensions using UV-vis irradiation from two microwave-powered electrodeless discharge lamps (EDL(-2)): products, mechanism and feasibility.

Aqueous crystal violet (CV) solutions containing P25-TiO(2) photocatalyst were irradiated with ultraviolet-visible (UV-vis) light from two microwave-powered electrodeless discharge lamps (EDL(-2)). The results demonstrated that approximately 94.4% of CV was effectively removed after 3 min of irradiation, with a pseudo-first order kinetic constant of 0.838 min(-1). According to 32 kinds of products, a five-step degradation pathway of CV was proposed. Further investigations showed that (1) three kinds of N-demethylated products and 4-dimethylaminobenzophenone (DLBP) were the main intermediates; (2) malachite green (MG) and leuco-crystal violet could not be generated by N-demethylation and phototransformation reactions, respectively; (3) bis(4-(dimethylamino)phenyl)methanone preferentially generated via decomposition of the conjugated structure of CV could be further N-demethylated into DLBP. Moreover, the unique degradation pathways of CV and MG were ascribed to the different substituents on the conjugated structures. Additionally, the cost and kinetic constant of different processes was also evaluated, and the results indicated the feasibility of this method for treatment of CV in field situations.