Photodegradation of Diuron Induced by Iron(III) in the Aquatic Environment

The degradation of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) photoinduced by iron(III) in aqueous solution has been investigated with different iron(III) species (monomeric species Fe(OH)2+ and water soluble oligomeric species), in homogeneous phase under monochromatic excitation at 365 nm and under sunlight. The degradation of diuron was also studied in heterogeneous phase with a hydrated iron(III) oxide: αFeOOH (goethite). In homogeneous phase, the rate of degradation depends on the concentration in Fe(OH)2+, the most reactive species in terms of OH radicals formation. The major photoproduct is 3-(3,4-dichlorophenyl)-1-formyl-1-methylurea which represents more than 60% of diuron disappearance. The mechanism only involves the attack by OH radicals arising from iron(III) excited species. The half lives of diuron when submitted to such a process in the environment were estimated to be 1–2 hours and a few days according to the concentration of Fe(OH)2+ (respectively 70% and <10% of total iron(III) concentration). In heterogeneous phase, the degradation of diuron is slower and the major photoproduct is 3-(3,4-dichlorophenyl)-1-methylurea.