Mechanochemical degradation of atrazine adsorbed on four synthetic manganese oxides

Atrazine is an important contaminant of world water systems with effects on aquatic life and humans. Thus, its reactivity with soil minerals is an important issue. We have studied the mechanochemical degradation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) adsorbed on synthetic pyrolusite (β-MnO2), birnessite (δ-MnO2), and cryptomelane types I and II (α-MnO2, α-MnO2) using differential scanning calorimetry (DSC) and spectroscopy. The overall transformation kinetics of atrazine on cryptomelane type II after light grinding does not appear to follow first order kinetics. However, first order kinetics seems to apply to birnessite at 30°C. The three decomposition products detected under mechanochemical degradation and incubation were DEA, DIA, and DDA, Mn(II) and CO2, but no consumption of gaseous oxygen was detected. A positive correlation was found between Mn(II) produced and CO2 evolved only for cryptomelane II, suggesting that the decomposition of atrazine on this mineral surface involves the oxide substrate as a source of oxygen and yields Mn(II).