Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: Kinetics, products, and pathways
Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: Kinetics, products, and pathways
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DOI：
10.1016/j.watres.2016.03.039
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发表时间：
2016-06-01
期刊：
影响因子：
12.8
通讯作者：
Wu, Daoji
中科院分区：
文献类型：
--
作者：
Luo, Congwei;Jiang, Jin;Wu, Daoji
首次研究了254 nm波长下过硫酸盐对恶臭化合物2，4，6-三氯茴香醚（TCA）的转化效率和产物。水基质的影响（即，天然有机物（NOM）、pH、碳酸盐/碳酸氢盐（HCO 3-/CO 3-）和氯离子（Cl-））。测定了TCA与硫酸根（SO 4-中心点）反应的二级速率常数为（3.72 +/- 0.10）× 10（9）M-1 s（-1）。随着过硫酸盐投加量的增加，TCA降解的准一级速率常数k（obs）增大，且SO 4-中心点对TCA降解的贡献远大于HO中心点。在pH = 4.0 ~ 9.0范围内，TCA的降解率随pH的升高而降低，这可能是由于在酸性条件下（pH < 6），磷酸二氢盐对自由基的清除能力低于磷酸氢盐。NOM通过清除自由基和吸收紫外线的作用显著降低kobs值，其中清除自由基的作用占主导地位。在UV/过硫酸盐工艺中，随着CO 3-/HCO 3-浓度从0.5 mM增加到10 mM，kobs从2.32 x 10（-3）s（-1）降低到0.92 x 10（-3）s（-1），而k（obs）则从不存在Cl-时的2.54 × 10（-3）s（-1）略微下降到存在10 mM Cl-时的2.10 × 10（-3）s（-1）。这些动力学结果大多可以用稳态动力学模型来描述。此外，液相色谱/电喷雾离子化-三重四极杆质谱法在强大的前体离子扫描方法被用来选择性地检测TCA的氧化产物。发现2，4，6-三氯苯酚（TCP）是主要的氧化产物（即，TCP的初始产率在90%以上。TCP与SO 4-中心点之间的二级速率常数估计为（4.16 +/- 0.20）× 10（9）M-1 s（-1）。此外，三种产品（即，在TCP与SO 4-中心点的反应中检测到了2，6-二氯-1，4-苯醌和两种芳环开环产物），在UV/过硫酸盐过程中TCA的氧化反应中也出现了这两种产物。提出了一个初步的途径，其中TCA的初始单电子氧化SO 4-中心点和进一步的反应（例如，异羟基化和芳环断裂）形成的阳离子中间体TCA中心点。(C)2016由Elsevier Ltd.出版
The transformation efficiency and products of an odorous compound 2,4,6-trichloroanisole (TCA) at the wavelength of 254 nm in the presence of persulfate were investigated for the first time. The effects of water matrix (i.e., natural organic matter (NOM), pH, carbonate/bicarbonate (HCO3-/CO3-), and chloride ions (Cl-)) were evaluated. The second order rate constant of TCA reacting with sulfate radical (SO4-center dot) was determined to be (3.72 +/- 0.10) x 10(9) M-1 s(-1). Increasing dosage of persulfate increased the observed pseudo-first-order rate constant for TCA degradation (k(obs)), and the contribution of SO4-center dot to TCA degradation was much higher than that of HO center dot at each experimental condition. Degradation rate of TCA decreased with pH increasing from 4.0 to 9.0, which could be explained by the lower radical scavenging effect of dihydrogen phosphate than hydrogen phosphate in acidic condition (pH < 6). NOM significantly decreased kobs due to the effects of radical scavenging and UV absorption with the former one being dominant. kobs decreased from 2.32 x 10(-3) s(-1) to 0.92 x 10(-3) s(-1) with the CO3-/HCO3- concentration increased from 0.5 mM to 10 mM in the UV/persulfate process, while k(obs) slightly decreased from 2.54 x 10(-3) s(-1) in the absence of Cl- to 2.10 x 10(-3) s(-1) in the presence of 10 mM Cl-. Most of these kinetic results could be described by a steady-state kinetic model. Furthermore, liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry at powerful precursor ion scan approach was used to selectively detect oxidation products of TCA. It was found that 2,4,6-trichorophenol (TCP) was the major oxidation product (i.e., the initial yield of TCP was above 90%). The second order rate constant between TCP and SO4-center dot was estimated to be (4.16 +/- 0.20) x 10(9) M-1 s(-1). In addition, three products (i.e., 2,6-dichloro-1,4-benzoquinone and two aromatic ring-opening products) were detected in the reaction of TCP with SO4-center dot, which also appeared in the oxidation of TCA in the UV/persulfate process. A tentative pathway was proposed, where the initial one-electron oxidation of TCA by SO4-center dot and further reactions (e.g., ipso-hydroxylation and aromatic ring-cleavage) of the formed cation intermediate TCA center dot were involved. (C) 2016 Published by Elsevier Ltd.