Birnessite-induced mechanochemical degradation of 2,4-dichlorophenol

DCP (2,4-dichlorophenol) is the key-intermediate in the synthesis of some widely used pesticides and is an EPA priority pollutant. The mechanochemical breakdown of DCP loaded on birnessite (δ-MnO2), montmorillonite saturated with Na(+) or Cu(2+) and hematite was investigated. Mechanical force was applied by grinding of mixtures of DCP and the minerals, using mortar and pestle. Grinding of DCP for 5 min with the montmorillonites or with hematite resulted in negligible degradation during grinding, while grinding with birnessite induced the immediate degradation of 90% of the loaded DCP. Incubation for 24h after grinding did result in up to 30% degradation of the DCP loaded on the other minerals tested. HPLC and LC-MS analysis revealed that the transformation of DCP yielded oligomerization products as well as partial dechlorination. DCP degradation on birnessite was accompanied with a substantial increase in the extractability of manganese from the mineral into an acidic aqueous solution, indicating that Mn(IV) in the mineral transformed into Mn(II) and that birnessite served as an electron acceptor in the transformation. The oligomerization and partial dechlorination brought about by grinding, suggest a reduction in bioavailability and toxicity.