Comparison of the oxidation of halogenated phenols in UV/PDS and UV/H(2)O(2) advanced oxidation processes.
Comparison of the oxidation of halogenated phenols in UV/PDS and UV/H(2)O(2) advanced oxidation processes.
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UV/PDS和UV/H2O2高级氧化工艺中卤代酚的氧化比较
作者：
紫外光/过二硫酸盐(PDS)和紫外光/过氧化氢(H_2O_2)能有效地降解卤代酚(HPS，如2，4-溴苯酚和2，4，6-三氯苯酚)；同时，关于这两个过程的相关降解动力学和机理的信息有限。为了了解这一点，对两种典型的羟基苯酚(即溴代酚和氯代苯酚)在UV/PDS和UV/H_2O_2过程中的降解进行了研究和比较。结果表明，不同取代位置的HPS在UV/PDS工艺中的降解速率顺序为：对位取代HPS(4-BP和4-CP)>；邻位取代HPS(2-BP和2-CP)>；间位取代HPS(3-BP和3-CP)；而在UV/H_2O_2工艺中，降解速率顺序为对位取代HPS>；间位取代HPS>；邻位取代HPS。这些差异归因于SO4·−和HO·与HPS反应活性的不同，这是基于竞争方法计算的。进一步的密度泛函理论计算表明，SO4·−比HO·更容易通过电子转移与HPS发生反应。在水基质(如Cl-−、HCO3-−和天然有机物(NOM))存在下，2-BP在UV/PDS和UV/H_2O_2处理过程中的降解都受到抑制，这是由于这些背景物质对自由基的清除作用。降解产物和途径进一步证实，SO4·−是一种强单电子氧化剂，主要通过电子转移方式与羟基磷灰石反应，而HO·主要通过电子转移和羟基加成作用与羟基磷灰石反应。
UV/peroxydisulfate (PDS) and UV/hydrogen peroxide (H2O2) can effectively degrade halophenols (HPs, e.g., 2,4-bromophenol and 2,4,6-trichlorophenol); meanwhile, information about the discrepancies in the related degradation kinetics and mechanisms of these two processes is limited. To gain this knowledge, the degradation of two typical HPs (i.e., bromophenols and chlorophenols) in UV/PDS and UV/H2O2 processes were investigated and compared. The results showed that the degradation rates of HPs with different substitution positions in the UV/PDS process were in the order of para-substituted HPs (i.e., 4-BP and 4-CP) > ortho-substituted HPs (i.e., 2-BP and 2-CP) > meta-substituted HPs (i.e., 3-BP and 3-CP), while in the UV/H2O2 process, these rates were in the order of para-substituted HPs > meta-substituted HPs > ortho-substituted HPs. These discrepancies were ascribed to the different reaction activities of SO4˙− and HO˙ with HPs, which were calculated based on the competition method. Further density functional theory (DFT) calculations suggested that SO4˙− reacts more readily with HPs via electron transfer than HO˙. In the presence of water matrices (such as Cl−, HCO3− and natural organic matter (NOM)), the degradation of 2-BP in both UV/PDS and UV/H2O2 treatment processes was inhibited due to the scavenging of free radicals by these background substances. The degradation products and pathways further confirmed that SO4˙− is a strong one-electron oxidant that reacts with HPs mainly via electron transfer, while HO˙ reacts with HPs via electron transfer and hydroxyl addition.
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