Degradation efficiencies and mechanisms of the ZnO-mediated photocatalytic degradation of Basic Blue 11 under visible light irradiation

A ZnO-mediated photocatalysis process was used to successfully degrade Basic Blue 11 (BB-11) under visible light irradiation. The effects of influential factors like initial dye concentration, catalyst dosage, and initial pH were studied. To obtain a better understanding the mechanistic details of ZnO-assisted photodegradation of the BB-11 dye with low watt visible light irradiation, a large number of the intermediates resulting from the photodegradation were separated, identified, and characterized by high-performance liquid chromatography-photodiode array-mass spectrometry (HPLC-PDA-MS) techniques. The results indicated that the N-de-alkylation and oxidative degradation of BB-11 dye took place and that N-hydroxyalkylated intermediates were generated during the process. From the same identified intermediates we got under UV or visible light irradiation, it is proposed that the major oxidant under visible light irradiation was {radical dot}OH radical, not O₂^-{radical dot}. HPLC-PDA-MS analysis verified the identity of intermediates, and a reaction mechanism based on them was proposed.