Photocatalytic degradation of imazaquin in an aqueous suspension of titanium dioxide

The photocatalytic degradation of imazaquin, a herbicide of the imidazolinone class, in an aqueous suspensions of titanium dioxide as catalyst was investigated. A pseudo-first-order kinetic model was used to describe the results. The effect of sonication time, catalyst loading, initial concentration of imazaquin, hydrogen peroxide and pH, temperature and radiation source were examined. The disappearance of imazaquin and the increase of nitrate ion content as a function of irradiation time were analyzed by HPLC. The ammonium ion formation was determined spectrophotometrically at 694 nm. A lower solution pH in the 3-11 range was found to be favorable to degradation. The addition of H2O2 up to 10(-3) mol l(-1) enhanced the degradation rate and decreased it at higher concentrations. The photocatalytic effect was more efficient in a suspension containing 2.0 g l(-1) TiO2 with I h sonication in the dark rather than with 20 min sonication before irradiation. Solar radiation decomposed the herbicide faster than an artificial source. The activation energy was estimated through the variation of temperature in the range 20-40 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.