Involvements of chloride ion in decolorization of Acid Orange 7 by activated peroxydisulfate or peroxymonosulfate oxidation

The effects of chloride anion (Cl-) (up to 1.0 mol/L) on the decolorization of a model compound, azo dye Acid Orange 7 (AO7), by sulfate radical (SO4-center dot) based-peroxydisulfate (PS) or peroxymonosulfate (PMS) oxidation under various activated conditions (UV254 (nn)/PS, Thermal (70 degrees C/PS, UV254 (nm)/PMS, Co2+/PMS) were investigated. Methanol and NH4+ were used as quenching reagents to determine the contributions of active chlorine species (dichloride radical (Cl-2(-center dot)) and hypochlorous acid (HClO)). The results indicated that the effects of Cl- on the reaction mechanism were different under various activated conditions. For UV/PS and Thermal/PS, the inhibition tendency became more clear as the Cl(-)concentration increased, probably due to the reaction between Cl- and SO4-center dot and the generation of Cl-2(-center dot) or HClO. For UV/PMS, Cl- did not exhibit inhibition when the concentration was below 0.1 mol/L. As Cl- concentration reached to 1.0 mol/L, the decolorization rate of AO7 was, however, accelerated, possibly because PMS directly reacts with Cl- to form HClO. For Co2+/PMS, Cl- exhibited a significant inhibiting effect even at low concentration (<= 0.01 mol/L). When Cl- concentration exceeded 0.1 mol/L, the activation of PMS by Co2+ was almost completely inhibited. Under this condition, HClO maybe played a major role in decolorization of AO7. The results implicated that chloride ion is an important factor in SO4-center dot-based degradation of organic contamination in chloride-containing water.