Photocatalytic degradation of ethyl violet in aqueous solution mediated by TiO2 suspensions

The photodegradation of dye pollutants under visible light irradiation in TiO2 dispersions continues to draw considerable attention because of the improving effective utilization of cost free solar energy and its potential application in treating wastewater from textile and photographic industries. To get a better understanding of the mechanistic details of this TiO2-assisted photodegradation of the ethyl violet dye (EV, N,N,N′,N′,N″,N″-hexaethylpararosaniline) with visible light irradiation, the intermediates of the process were identified and examined by the HPLC-ESI-MS technique in this research. The analytical results indicated that seventeen intermediates were separated and identified. The experimental results indicated that the N-de-ethylation degradation of EV dye took place in a stepwise manner to yield mono-, di-, tri-, tetra-, penta-, hexa-N-de-ethylated EV species and, most of all, to yield N-hydroxyethylated intermediates, which were found for the first time in TiO2-mediated photocatalysis process. The possible degradation pathways were proposed and discussed in this research. The reaction mechanisms of TiO2/Vis proposed in this research would be useful for future application in the decoloration of dyes.