Photocatalytic Degradation of a Systemic Herbicide Picloram from Aqueous Solution Using Titanium Oxide (TiO2) under Sunlight

摘要

The photocatalytic degradation of picloram (4-amino-3,5,6-trichloro-2-pyridincarboxylicacid), which is one of popular acidic herbicide, was investigated with the existence of titanium oxide(TiO 2 )undersunlight. Thetotalphotocatalyticdegradationof20ppmofpicloramwasoccurredwithin30 min irradiation with TiO 2 , while a negligible degradation was found without TiO 2 under sunlight.The influence of various parameters, like TiO 2 dosage, solution initial pH, intensity of light, reactiontemperature and irradiation time, was found during the photocatalytic degradation of picloram.The mineralization of picloram was proved by the deterioration of total organic carbon (TOC) of thephotocatalytic process. The pseudo–first order kinetics of photocatalytic degradation was obtainedaccording to the Langmuir–Hinshelwood model, and the reaction rate constant was 17.6 × 10 ?2 min ?1 .Chloride ion, ammonium ion, nitrate ion and CO 2 were erected as the final products after completingthe photocatalytic degradation of picloram. The intermediate products could not be determinedby the GC–MS during the degradation of picloram. Therefore, the degradation mechanism of thepicloram was proposed based on the frontier electron density and the point charge at each atom ofthe picloram molecule. The photocatalytic degradation method, using sunlight, may develop into asa pragmatic technique to purify picloram contaminated wastewater.