Comparison of advanced oxidation processes and identification of monuron photodegradation products in aqueous solution

The photodegradation of monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in aqueous solutions under simulated solar irradiation has been conducted by different advanced oxidation processes (UV/H2O2, UV/H2O2/Fe2+, UV/H2O2/TiO2, UV/TiO2, dark H2O2/Fe3+). The degradation rates were always higher for the homogeneous catalysis in photo-Fenton reactions (UV/H2O2/Fe2+) compared to 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 to be 1 mM Fe(II) and 10 mM H2O2. Several intermediary products were identified using large volume injection micro-liquid chromatography with UV detection (μ-LC–UV), μ-LC–MS and GC–MS techniques and a degradation mechanism has been proposed.