溶液初始pH值对2,4-D臭氧直接反应动力学的影响

引言 目前,农药被大量研制及施用,由此带来的农药污染越来越受到人们的重视.含氯苯氧梭酸类除草剂2,4-D(2,4-二氯苯氧乙酸)是一种使用较广、应用较早的除草剂.2,4-D自然降解较慢,由于具有非挥发性和可溶性,易导致地下水或地表水污染,水体中已经可以检测到2,4-D的存在.

Effect of initial pH value in aqueous solution on direct reaction kinetics of 2,4-D with ozone

In order to understand the kinetics of direct oxidation between ozone molecule and 2,4-dichlorophenoxyacetic acid(2,4-D), the ozone oxidation of 2,4-D using sufficient tert butyl alcohol as free radical inhibiting agent was studied in a bubbling reactor.The effect of initial pH on 2,4-D direct oxidation process was discussed.The results show that direct oxidation of 2,4-D and transfer of O3 are affected by initial pH.When the value of initial pH is lower than 3.3, the solution pH value maintains approximately constant during the process.When it is larger than 3.3, the solution pH value drops abruptly and reaches a steady value in a short period, while concentration of ozone increases rapidly and does a steady concentration.With the increasing of initial pH the steady ozone concentration and pseudo first order rate constant increase, and the time required to reach this steady value decreases.Hatta numbers are lower than 0.03 for different pH values.The 2,4-D degradation process by ozone molecule follows the slow rate kinetics.It shows that the direct reaction of 2,4-D and ozone molecule is a control step of whole kinetics process.