Abstract
The photodegradation of parathion in the direct photolysis, UV/TiO 2 , UV/H 2 O 2 and UV/TiO 2 /H 2 O 2 systems was investigated at 25°C. The effect of light intensity was also examined to clarify the relationship between the photo flux and decomposition rate of parathion. Results of the study demonstrated that no obvious degradation of parathion in dark reaction occurred within 24 hours. However, the addition of TiO 2 and/or H 2 O 2 promotes the degradation efficiency of parathion. Adding H 2 O 2 was more effective in the photocatalytic oxidation of parathion than TiO 2 . Also, hydrogen peroxide was found as an intermediate with the maximum concentration of 55 μM in UV/TiO 2 system during the photodegradation of parathion. A higher intensity of lamp could increase the degradation rate of parathion. However, the quantum efficiency for degradation of parathion decreased from 0.053 to 0.006 when light intensity increased from 100 W to 450 W. Photodecomposition followed a pseudo-first-order reaction. The rate constants of parathion ranged from 0.003 min -1 for direct photolysis to 0.023 min -1 for UV/TiO 2 /H 2 O 2 system. This study indicated that photocatalytic degradation is a highly promising technology for detoxifying parathion.