臭氧氧化降解吡虫啉的动力学研究

Kinetics study of imidacloprid degradation by ozonation

研究臭氧氧化工艺降解吡虫啉的动力学特性以及臭氧分子和羟基自由基分别与吡虫啉反应的动力学特性。采用竞争动力学法,以对氯苯甲酸（pCBA）为竞争参照物测定吡虫啉与羟基自由基的二级反应速率常数（k·OH-Imid）。研究结果表明：臭氧可以有效降解水中的吡虫啉;在臭氧平均质量浓度为1.15 mg/L时,随着pH由6.0增至8.6,准一级动力学常数由0.079 min^-1增至0.326 min^-1;在pH为7.0条件下,臭氧平均质量浓度为1.41 mg/L,当碱度（以CaCO3计）由0 mg/L增至250 mg/L时,吡虫啉降解的准一级动力学常数由0.121 min^-1降至0.034 min^-1。在pH为2.0及50 mmol/L叔丁醇存在的条件下,臭氧分子与吡虫啉反应的二级动力学常数为（10.92±0.12）（mol/L）^-1·s^-1;当pH为7.0时,吡虫啉与羟基自由基反应的二级动力学常数为2.92×10^9（mol/L）^-1·s^-1;当pH在6.0-8.6范围内变化时,此二级反应动力学常数在2.65×10^9-3.79×10^9（mol/L）^-1·s^-1范围内波动。

Kinetics tests in ozonation of imidacloprid in water were performed. The kinetics for reactions between imidacloprid with molecular ozone and hydroxyl radicals were investigated. An indirect competition method was used to determine the second-orderrate constant for hydroxyl radicaloxidationof imidacloprid（k·OH-Imid） in the presence of p-chlorobenzoic acid（pCBA） as the reference compound. The results demonstrate that the ozonation is an effective method to remove imidacloprid from water. The pseudo first-order rate constants of imidacloprid degradation increases from 0.079 min^-1 to 0.326 min^-1 with the increase of pH from 6.0 to 8.7 at an average ozone dose of 1.15 mg/L. When the alkalinity（CaCO3） increases from 0 mg/L to 250 mg/L at pH 7.0 and an average ozone dose of 1.41 mg/L, the pseudo first order rate constant decreases from 0.121 to 0.034 min^-1. The second-order rate constant（（10.92±0.12）（mol/L）^-1·s^-1for the reaction of imidacloprid and molecular ozone is determined at pH 2.0 and in the presence of 50 mmol/L tert-butyl alcohol. The rate constant is 2.92×10^9（mol/L）^-1·s^-1 at pH 7.0. The rate constants are estimated to range at2.65×10^9-3.79×10^9（mol/L）^-1·s^-1 at pH 6.0-8.6.