Assistance of Magnesium Cations on Degradation of Refractory Organic Pollutant by Ozone: Nitrobenzene as Model Compound

Abstract

Selecting nitrobenzene as a model compound, the assistance of magnesium cations on ozon ation of refractory organic pollutant was investigated in pure water background. It is interesting to find that the presence of magnesium cations with a level of tens of millimoles per liter can obviously increase the degradation and mineralization efficiency of nitrobenzene compared with the case of ozonation alone. At lower pH condition, the magnesium cations still effectively assisted the ozonation of nitrobenzene. Ozone decomposition was accelerated by the presence of magnesium cations. It was confirmed that the presence of magnesium cations promoted the generation of hydroxyl radicals. It was speculated that the formation of hydroxyl group by the deprotonation of the hexaqueous magnesium cations complex Mg[H₂O]₆ ²⁺ promoted the hydroxyl radical formation. However, the promotion was found to be unremarkable and should not be the sole reason for the assistance of magnesium cations on ozonation. The complexation reaction between the hexaqueous magnesium cations complex and carboxylic group may be part of the reason for the magnesium cation- assisted ozonation of organic pollutants. This finding will provide fundamental support for the applications of ozone to treat the concentrated water from membrane filtration which contains both high concentration of magnesium cations and organic pollutants.

Keywords:

• Ozone
• Magnesium cation
• Catalysis
• Refractory organic pollutant
• Hydroxyl radical
• Membrane concentrate

ACKNOWLEDGMENTS

Funding for this work was provided by the Natural Science Foundation of China (Grant 50708067), Shanghai Rising-Star Program and SNSF (Grant 08QA14067, 07ZR14116), the Foundation for the Author of the National Excellent Doctoral Dissertation of China (Grant 2007B48) and the Foundation of The State Key Laboratory of Pollution Control and Resource Reuse of China (Grant PCRRY08013). We appreciate the critical comments of the anonymous reviewers.