Mechanochemical degradation of 2,4-D adsorbed on synthetic birnessite

Mechanochemical degradation of 2,4-D (2,4-dichlorophenoxyacetic acid) adsorbed on synthetic birnessite (δ-MnO2) was investigated using heat conduction calorimetry. The overall transformation kinetics of 2,4-D on birnessite after light grinding were approximately first-order, with an apparent activation energy of approximately 37 kJ mol−1 for the range of temperatures 10–50°C. The two decomposition products detected under mechanochemical degradation and incubation were 2,4-dichlorophenol and CO2, but no consumption of gaseous oxygen was detected. A positive correlation was found between Mn(II) produced and CO2 evolved, suggesting that the decomposition of 2,4-dichlorophenol involves the oxide substrate as a source of oxygen and yields Mn(II).