UV/H2O2降解三氯生动力学及反应机理

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，H2O2的投加量小于1 mmol/L时，三氯生的降解速率随H2O2浓度的增加而增加，而当H2O2的投加量大于1 mmol/L时，由于H2O2对HO ·的捕获作用增强，三氯生的降解速率随H2O2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/H2O2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/H2O2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 H2O2. 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 H2O2. 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/H2O2. A tentative pathway was proposed, where dechlorination and hydroxylation reaction were involved.