UV／H2 O2降解三氯生动力学及反应机理

摘要

为考察紫外催化过氧化氢工艺降解三氯生的降解效能，利用动力学模型对三氯生的表观降解速率进行模拟。考察氧化剂投加量、三氯生浓度、NOM质量浓度和pH对三氯生降解速率的影响。结果表明，H2 O2的投加量小于1 mmol／L时，三氯生的降解速率随H2 O2浓度的增加而增加，而当H2 O2的投加量大于1 mmol／L时，由于H2 O2对HO·的捕获作用增强，三氯生的降解速率随H2 O2投加量的增加而降低。当三氯生的初始浓度增加时，体系中HO·的稳态浓度随之降低，导致三氯生降解的表观速率降低。体系中存在NOM时，三氯生的降解速率显著降低，主要是由于NOM能够与三氯生竞争光子和HO·。三氯生去质子化后更快地被UV／H2 O2降解，其去质子化形态的摩尔吸光系数变大，而且其与HO·的二级反应速率更快。通过LC／MS－MS检测UV／H2 O2氧化TCS得到6种产物，推测TCS的降解途径主要是通过脱氯反应和羟基化反应。%The aim of this work is to investigate the transformation efficiency of triclosan ( TCS) at the wavelength of 254 nm in the presence of H2 O2 . The effects of oxidant dosage, TCS concentration, NOM, and pH were evaluated. Most of these kinetic results could be described by a steady⁃state kinetic model. Increasing dosage of H2O2 increased the observed pseudo⁃first⁃order rate constant for TCS degradation (kobs) when H2O2<1 mmol/L. However, when H2O2>1 mmol/L, kobs decreased with H2O2 dosage increased due to the effects of radical scavenging by H2 O2 . Increasing concentration of TCS decreased the steady⁃state concentration of HO·. The presence of NOM significantly decreased kobs due to the effects of UV absorption and radical scavenging. When pH=9, kobs was higher than that when pH=5-7. This could be attributed that the deprotonated TCS was more reactive than protonated TCS. Six products were detected in TCS treated by UV/H2 O2 . A tentative pathway was proposed, where dechlorination and hydroxylation reaction were involved.