UV-enhanced Fe2+/PDS system for degradation of acid orange 7: Kinetics, degradation mechanism and toxicity assessment

Based on the deficiency of the Fe²⁺ catalyzed persulfate (PDS) process, ultraviolet (UV) synergistic Fe²⁺ activated PDS system was introduced in this study for the degradation of acid orange 7 (AO7) dye. The effects of different initial pH, PDS dosage, Fe²⁺ dosage, and different UV intensities on the degradation rate of AO7 were investigated, and a kinetic model for the apparent reaction rate was determined. The results showed that the UV/Fe²⁺/PDS system was effective in degrading AO7 in a wide pH range. Under optimal conditions, 96 % removal of AO7 was achieved in 10 min. The effects of different inorganic anions on AO7 were discussed; Cl⁻ had little effect on the degradation effect, and SO₄²⁻, NO₃⁻ and HCO₃⁻ inhibited the degradation of AO7 by the system to varying degrees. The presence of reactive radicals (SO₄^·− and·OH) in the reaction was determined by quenching experiments and EPR capture and their degradation contribution was further investigated. Nine intermediates of AO7 were detected by LC-MS/MS, and the degradation pathway of AO7 was inferred by combining with UV-Vis spectra. Finally, the ecotoxicity and tritogenic effects of AO7 intermediates were assessed by Toxtree and T.E.S.T toxicity prediction models, which showed that the final degradation product toxicity was non-mutagenic, non-teratogenic, and devoid of hereditary and non-hereditary carcinogenicity.