Monuron photodegradation products in aqueous solution [articol]

Abstract

The photodegradation of monuron (3-(4-chlorophenyl)-1, 1-dimethylurea) in aqueous solutions under simulated solar irradiation has been conducted in this study by different advanced oxidation processes (UV/H2O2, UV/H2O2/Fe2+,UV/H2O2/TiO2, UV/TiO2). The degradation rates were always higher for the homogenous catalysis in photo-Fenton reactions (UV/H2O2/Fe2+) when compared with the heterogeneous photocatalytic systems (TiO2/UV and UV/H2O2/TiO2).Optimal concentrations of Fe2+ and H2O2 for the abatement of the herbicide in the photo-Fenton system were found.Several intermediary products were identified using large volume injection micro-liquid chromatography with UVdetection, LC-MS and GC-MS techniques and from the analytical data, a degradation mechanism was proposed. The degradation mechanism of monuron is initiated by the attack of hydroxyl radicals at the N-terminal group and consists of two sequential N-dealkylations followed by hydrolysis to an aniline derivate (4-chloroaniline). Further oxidations leads to ring opening and smaller organic molecules, easier to oxidize.