Photooxidation contribution study on the decomposition of azo dyes in aqueous solutions by VUV-based AOPs

The effects of pH value, VUV intensity, initial dye concentration, initial H₂O₂ concentration, and TiO₂ loading dose on the degradation of three azo dyes: acid Orange 8, acid Blue 29, and acid Blue 113 were studied to explore and compare the treatment efficiencies among the adopted AOPs. It was found that pH played an important role in the degradation of dyes using VUV irradiation. For VUV/H₂O₂, VUV/TiO ₂, and VUV/TiO₂/H₂O₂ processes, the decoloration rates of the three azo dyes were more efficient under acidic conditions relative to alkaline conditions. The degradation rates of dyes increased with increasing concentrations of H₂O₂, but reaction rates were retarded at high concentrations of H₂O ₂ because the H₂O₂ compound acted as a scavenger of the hydroxyl radical. In this paper, three azo dyes were decomposed efficiently by VUV irradiation only demonstrating the effectiveness of VUV direct photolysis.