3.3. Photodegradation experiments
3.3.1. Comparison of degradation kinetics for OPP and monuron
Fig. 5 shows the evolution of OPP and monuron adsorbed on clays with time under irradiation.
OPP is rapidly degraded in the presence of light, the OPP absorption of UV enters in the ranges of sunlight emission spectra, indicating that direct photolysis of the compound is occurring. The disappearance of monuron was done on a scale of time much more important, half-life time was 21 hours. In aqueous medium Hill et al. (1955) showed that the disappearance of 83% of monuron in aqueous solution exposed to the sun during 48 days. Curves followed first order kinetics and half lives are given in Table 3. The different rates observed for the two pesticides suggest that the difference in chemical structure can give rise a different photochemical behaviour.