The Photocatalytic Degradation Of Trichlorfon And Chlorpyrifos By TiO₂ And ZnO

Trichlorfon and chlorpyrifos have been widely used to protect crops from damaging insect pests, however, tow organphosphorus pesticides pollute the soil environment seriously. In this work, the photocatalytic degradation of trichlorfon and chlorpyrifos by TiO2 and ZnO were analyzed. The influence of different degradation parameters and the best degradation conditions were discussed. This subject provides theoretical basis for the photocatalytic degradation of organophosphorus pesticides using semiconductor nano-material.The TiO2 and ZnO photocatalyst was prepared by the method of sol-gel and hydrothermal synthesis. The product was characterized by UV-vis, X-ray diffraction, SEM and FT-IR. The effects of initial concentration of pesticides, pH, photocatalyst amount, irradiation time and light source on the photocatalytic efficiency were discussed by GC-MS. The results showed that:(1) The various degradation parameters such as the initial concentration of pesticides, pH, photocatalyst amount, irradiation time and light source have obvious influence on the photocatalytic degradation. When initial concentration of pesticides increased, the degradation of trichlorfon decreased. And the degradation rate increased and later became flat with the prolonging time of photolysis. Alkaline condition and mercury lamp favored this reaction. The concentration 100-150mg/L TiO2 or ZnO was the optimum, however, the degradation rate of the concentration 0-100mg/L ZnO increased more significantly than the concentration 100-200mg/L.(2) The various degradation parameters such as the initial concentration of pesticides, pH, photocatalyst amount, irradiation time and light source have obvious influence on the photocatalytic degradation. There was a significant positive correlation between lower concentrations of chlorpyrifos and degradation rate, while negative correlation with higher concentrations. The concentration 20mg/L was the optimum. And the degradation rate increased and later became flat with the prolonging time of photolysis. Alkaline condition and mercury lamp favored this reaction. The best condition for degradation of 50-100mg/L TiO2 was determined. As the concentration of the photocatalyst increases from 10 to 150mg/L, the photodegradation efficiency of chlorpyrifos increases rapidly, then the efficiency increases slowly when the amount of ZnO is above 150mg/L.(3) The photocatalytic degradation activity of TiO2 is lower than ZnO under the same conditions, in the process of degradation of trichlorfon. The acid-base property and agglomeration of the photocatalysts are the possible reasons. But in the process of degradation of chlorpyrifos, the photocatalytic degradation activity of TiO2 is higher than ZnO under the same conditions. The possible reasons are the photocorrosion and the different surface charges. The structure difference between trichlorfon and chlorpyrifos is the main cause of the different photocatalytic degradation activity.