Degradation of thiacloprid in aqueous solution by UV and UV/H2O2 treatments

Although some studies concerning flash photolysis and photocatalytic ozonation of thiacloprid have already been published, no complete investigation and explanation of the effects of thiacloprid photodegradation under the conditions of UV and UV/H2O2 (high-pressure mercury lamp and H2O2) have been reported yet. The photochemical degradation of thiacloprid (0.32 mM) was studied under a variety of solution conditions, by varying the initial concentrations of H2O2 from 0 to 162 mM and the pH from 2.8 to 9. In the UV/H2O2 system, thiacloprid reacted rapidly, the maximum first-order rate constant (2.7 × 10−2 min−1, r = 0.9996) being observed at the H2O2/thiacloprid molar ratio of 220 and pH 2.8. Under these conditions, 97% of the thiacloprid was removed in about 120 min. The thiacloprid degradation is accompanied by the formation of a number of ionic byproducts (Cl−, acetate, formate, SO42-, and NH4+) and organic intermediates, so that after 35 h of irradiation, 17% of organic carbon remained non-degraded. The application of UV radiation, or H2O2 alone, yielded no significant thiacloprid degradation. The study of the rate of removal of thiacloprid from natural water showed that it is dominantly influenced by the presence of HCO3-.