The photo-induced transformation of monuron (3-(4-chlorophenyl)-1,1 dimethylurea) was investigated in an aqueous solution containing nitrates and nitrites at 310 nm and 365 nm, respectively. In both NO(3)(-) and NO(2)(-) conditions, the degradation of monuron followed pseudo-first order kinetics. The intermediate products were identified by GC-MS, and the nitration, hydroxylation and coupling reactions were determined. In addition, the oxidation of the N-terminus group, the substitution of chlorine by ˙OH and the nitration by ˙NO(2) radical onto the phenyl ring were observed. The photo-induced transformation of monuron was studied under variable conditions of pH, inducer concentration, substrate concentration, humic acids, oxygen content and salts used as hydroxyl radical scavengers. The photodegradation rates were strongly influenced by all the above parameters. The degradation of monuron was also studied in the dark and in the presence of NO(2)(-) as well as in an aqueous solution with the addition of hydrogen peroxide.

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The photocatalytic degradation of isoproturon, a persistent toxic herbicide, was investigated in the presence of natural iron oxide and oxalic acid and under UV irradiation. The influence of the relevant parameters such as the pH and the iron oxide and oxalic acid concentrations has been studied. The presence of natural iron oxide and oxalic acid in the system effectively allow the degradation of isoproturon, whereas the presence of t-butyl alcohol adversely affects the phototransformation of the target pollutant, thus indicating that an OH radical initiated the degradation mechanism. The degradation mechanism of isoproturon was investigated by means of GC-MS analysis. Oxidation of both the terminal N-(CH) and isopropyl groups is the initial process leading to N-monodemethylated (NHCH), N-formyl (N(CH)CHO), and CHCHOH as the main intermediates. The substitution of the isopropyl group by an OH group is also observed as a side process.