In order to better understand the photodegradation mechanism of azo dye, this study chose acid orange 7 (AO7) as a target, and used liquid chromatography–mass spectrometry (LC/MS) analysis to identify the degradation products of AO7 from TiO2 photocatalysis. The condition effects of irradiation wavelengths (UV and Vis), oxidant types (K2Cr2O7 and KMnO4) and dissolved oxygen (DO) levels were investigated to observe the difference in degradation products. Our results showed AO7 degradation process was slower and produced more intermediate under Vis irradiation. Our results showed AO7 degradation process was slower and produced more intermediate under Vis irradiation. The addition of oxidants extended the degradation process of AO7 due to their oxidation capability and their cooperation with TiO2 in generating hydroxyl radicals (●OH). In the absence of DO, the degradation of AO7 was reduced because of the multiple roles of oxygen involving in the formation of reactive oxygen species, mineralization and direct photocatalytic reactions, etc. According to the identifications of products varied with different conditions, the possible pathways of AO7 degradation in above photocatalytic systems were proposed. There were four degradation mechanisms to be summarized, including azo bond (N=N) cleavage, hydroxylated products generation, naphthalene ring oxidation, and the cleavage of C–N bond linked to the benzene ring, etc. In addition, the reactive efficiency of ●OH was calculated for the amount of ●OH reacting with AO7 or its intermediates based on the quantification data of ●OH formation as previously reported. Through those calculations, the stoichiometry and the roles of ●OH in the serial reactions of degradation mechanisms could be estimated and studied.

Stoichiometry of hydroxyl radicals for photodegradation mechanism of azo dye AO7

256th National Meeting (2018)

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