【作者】 陈静；

【导师】 王遵尧；

【作者基本信息】 南京大学 ， 环境科学与工程， 2018， 博士

【摘要】 近年来,卤代有机污染物在自然环境中不断检出,其在环境中的去除一直是水处理领域的研究热点。因此,研究其在典型水处理中的降解转化机制及中间产物的毒性变化,有助于开发安全有效的水处理技术。高锰酸钾(KMnO4)和高铁酸钾(K2FeO4,Fe(Ⅵ)是两种多功能强氧化剂和水处理剂,被广泛用于水处理中。本文以四种典型卤代有机物为研究对象,选取KMnO4和Fe(Ⅵ)为典型的绿色氧化剂,系统研究了四种典型卤代有机物的反应动力学、降解路径及机理,并评估了其在氧化过程中的毒性变化情况。具体从以下四个方面展开:(1)系统地研究了水处理中KMnO4氧化去除三氯生(TCS)的反应动力学、降解机理及毒性变化情况。考察了 pH值,氧化剂量,温度,无机离子(C1-SO42-和NO3-)及溶解性有机质(腐殖酸(HA)和富里酸(FA))等一系列环境因素对去除效率的影响。通过液相色谱-四极杆-飞行时间质谱仪(LC-Q-TOF-MS)共识别出11种中间产物,包括苯酚及其衍生物、苯醌、有机酸和醛类等,并提出两条主要的反应路径,分别是-C(8)-O(7)-键裂解和含氯较少的苯环开环。并根据前线电子云密度和总电荷分布的理论计算对上述提出的反应路径加以验证。此外,采用两种模式水生生物发光细菌和大型溞评估了 KMnO4氧化TCS过程中反应溶液的毒性变化情况,结果发现,初始浓度为20 mg/L的TCS在反应60 min后,其反应液对大型溞和发光菌的毒性分别降低了 95.2%和43.0%。另外,进一步考察发现氯化和氯胺消毒作用能够使主要的中间产物苯酚和1,4-苯醌形成低浓度的消毒副产物(Disinfection by-products,DBPs)。总之,KMnO4可作为一种有效的绿色氧化剂广泛的应用于废水中有机污染物的去除。(2)研究了溴代阻燃剂十溴二苯乙烷(DBDPE)在KMnO4/H2SO4氧化体系中的降解机理。结果表明,DBDPE在KMnO4/H2SO4反应体系中降解较完全,其去除率高达99.71%。将LC-Q-TOF-MS分析和气相色谱-电子电离-质谱(GC-EI-MS)分析相结合,对反应过程的中间产物进行分析,结果发现DBDPE首先被氧化生成1,2-双(过溴苯基)乙烷-1,2-二酮(P1)、五溴苯酚(P2)、2-(全溴苯基)乙醇(P3)和五溴苯甲酸(P28),这些产物进一步发生开环反应,生成相应的五元环和六元杂环产物。结合总电荷分布和Wiberg键级的计算,提出了两条主要的反应途径,包括乙基的C-C键的直接氧化和乙基碳与相邻碳之间的C-C键的裂解。此外,使用ECOSAR软件评估了 DBDPE及其降解产物的毒性,发现DBDPE能够对三种不同营养级的水生生物造成严重的损害,经过氧化转化之后的中间产物毒性均低于母体化合物。这表明KMnO4/H2SO4氧化体系可以高效去除溴代阻燃剂,这为环境中难降解的有机污染物库存的去除提供了新思路。(3)选取环境友好型氧化剂Fe(Ⅵ),系统的研究其对多氯代二苯硫醚(PCDPSs)的氧化反应的动力学和降解机理。首先测定了Fe(Ⅵ)在pH = 8.0时对17种PCDPSs(不同的氯原子数目(从2到7)和不同的氯原子位置)的二级反应速率常数(k,M-1s-1),结果发现k值随着氯原子数目和位置的变化而变化,另外还与PCDPSs的标准吉布斯自由能(△fG0)有关。此外,为阐明PCDPSs在Fe(Ⅵ)氧化作用下的降解机制,选取2,2’,3’,4,5-五氯二苯硫醚(PeCDPS)为目标化合物进行分析,结果表明Fe(Ⅵ)主要是通过攻击二价硫原子产生亚砜类产物,随后破坏C-S键形成含磺酸的三氯代化合物。另外苯环的羟基化以及羟基取代苯环上的氯原子反应也不容忽视,在反应过程中Fe(Ⅵ)的自身衰变产生的·OH为羟基取代反应提供了直接的证据。同时采用密度泛函理论(DFT)计算进一步确定了取代反应的可行性。毒性测试结果发现,PeCDPS经过氧化后,其产物毒性均有所降低。另外,在无机离子和腐殖酸等环境因子的存在下,Fe(Ⅵ)依旧能在几分钟内实现PeCDPS的去除。(4)系统地研究了常见的氯代抗菌剂苄氯酚(CP)在Fe(Ⅵ)氧化作用下的反应动力学、氧化产物和反应机理。实验结果表明,Fe(Ⅵ)能够在5 min内高效降解CP,并测得在pH 8.0时二级反应速率常数k为642.4 M-1 s-1。借助LC-Q-TOF-MS和离子色谱分析手段共鉴定了 22种氧化产物。质谱分析和理论计算表明,CP的酚羟基容易发生抽氢反应,形成活性的有机自由基(CP·),然后通过单电子耦合作用发生聚合反应,由此形成的耦合产物是无毒的并且易于从水中去除,这是Fe(Ⅵ)降解CP过程中最重要的路径。此外,反应过程中还会发生C(7)-C(8)键断裂、亲电取代、开环、羟基化和脱羰基等反应。研究结果表明,在真实水体中,Fe(Ⅵ)能够有效降解氯代抗菌剂CP,这为其实际废水处理提供了参考。更多还原

【Abstract】 Recently,there has been increasing concern about the widespread occurrence of halogenated organic compounds in the aquatic environment.The study of their degradation mechanisms in typical environmental processes and toxicity changes could be conducive to develop new strategies to deal with this concern.As two sorts of multifunctional oxidants and water treatment reagents,potassium permanganate(KMnO4)and ferrate(K2FeO4,Fe(Ⅵ))have been widely used in water treatment.Four typical halogenated organic compounds were chosen as the model halogenated organics and KMnO4/Fe(Ⅵ)as two typical oxidants in this study.Then the reactive kinetics,degradation products,pathways and toxicity changes in these processes were investigated.Detailed studies consist of the following four aspects:(1)The potential applicability of potassium permanganate for removal of triclosan(TCS)in water treatment was systematically investigated.A series of kinetic experiments were carried out to study the influence of various factors,including the pH,oxidant doses,temperature,and presence of typical anions(Cl-,SO42-,NO3-),humic acid(HA)and fulvic acid(FA)on triclosan removal.A total of eleven products were detected by liquid chromatography-quadrupole-time-of-flight-mass spectrometry(LC-Q-TOF-MS)analysis,including phenol and derivatives thereof,benzoquinone,an organic acid,and aldehyde.Two main reaction pathways involving C-0 bond cleavage(-C(8)-O(7)-)and benzene ring opening(in the less chlorinated benzene ring)were proposed,and were further confirmed based on frontier electron density calculations and point charges.Furthermore,the changes in the toxicity of the reaction solution during TCS oxidation by KMnO4 were evaluated by using both the luminescent bacteria Photobacterium phosphoreum and the water flea Daphnia magna.The toxicity of triclosan to D.magna and P.phosphoreum after 60 min at an initial concentration of 20 mg/L was reduced by 95.2%and 43.0%,respectively.Phenol and 1,4-benzoquinone,the two representative degradation products formed during permanganate oxidation,would yield low concentrations of disinfection by-products(DBPs)after chlorination and chloramination.Overall,KMnO4 can be used as an effective oxidizing agent for TCS removal in water and wastewater treatment.(2)The KMnO4 degradation of decabromodiphenyl ethane(DBDPE),an additive in brominated flame retardants(BFRs),was investigated in a sulfuric acid system.The degradation tests showed that DBDPE reacted completely with KMnO4 in sulfuric acid,and a removal rate of 99.71%seems realistic.Many products were detected by liquid chromatography-quadrupole-time-of-flight-mass spectrometry(LC-Q-TOF-MS)analysis and gas chromatography-electron ionization-mass spectrometry(GC-EI-MS)analysis.The degradation initially forms 1,2-bis(perbromophenyl)ethane-1,2-dione(Pi),pentabromophenol(P2),2-(perbromophenyl)ethanol(P3)and pentabromobenzoic acid(P28),and the subsequent transformation of these primary intermediates generates ring-opening,five-membered ring and six-membered heterocycle products over time.Two main reaction pathways involving the direct oxidation of the C-C bond of the ethyl group and the cleavage of the C-C bond between ethyl carbon and the adjacent carbon were proposed,and were further confirmed by point charges analyses and Wiberg bond order calculations.Furthermore,the toxicity of DBDPE and its degradation products were evaluated using the ECOSAR program.DBDPE was found to be a toxic substance that could cause great damage to three kinds of organisms in different trophic levels,while all the transformation products were less toxic than parent compound.This study is the first to report the degradation of DBDPE by KMn04 in acid and the obtained results can provide valuable guidance on the treatment of DBDPE leakage from point sources like storage tanks.(3)The oxidation of polychlorinated diphenyl sulfides(PCDPSs),dioxin-like compounds,by Fe(Ⅵ)was investigated.Kinetics of the reactions of Fe(Ⅵ)with seventeen PCDPSs,differ in number and positions of chlorine atoms(from 2 to 7),were investigated at pH 8.0.The second-order rate constants(k,M-1 s-1)of the reactions varied with the numbers and positions of chlorine atoms and appeared to be related with standard Gibbs free energy of formation(△fG0)of PCDPSs.Mechanism of the reaction was investigated by identifying oxidized products(OPs)of the reaction between Fe(VI)and 2,2’,3’,4,5-pentachlorodiphenyl sulfide(PeCDPS)at pH 8.0.Mechanism of oxidation involved major pathway of attack on sulfur(Ⅱ)by Fe(Ⅴ)in steps to yield sulfoxide type products,and subsequent breakage of C-S bond with the formation of sulfonic acid-containing trichloro compound.Minor pathways were hydroxylation of benzene ring and substitution of chlorine atom with hydroxyl group.A substitution step was carried out by ·OH,generated from self-decay of Fe(Ⅵ).The feasibility of the substitution reaction was supported by density functional theory(DFT)calculations.Oxidation of PeCDPS resulted in OPs of decreased toxicity.Removal experiments in the presence of ions and humic acid demonstrated degradation of PeCDPS by Fe(Ⅵ)in minutes.(4)The reaction kinetics,products,and mechanisms of the antimicrobial agent chlorophene(CP)by ferrate oxidation were investigated in aqueous solutions.Chlorophene is very readily degraded by Fe(Ⅵ),with the apparent second-order rate constant,k,being 642.4 M-1 s-1 at pH 8.0.A total of twenty-two oxidation products were identified using a liquid chromatography-quadrupole-time-of flight-mass spectrometry(LC-Q-TOF-MS)and ion chromatography,and their structures were further elucidated using MS/MS spectra.According to the extracted peak areas in mass spectrum,the coupling products(dimers,trimers,and tetramers)formed via single-electron coupling mechanism was the main reaction products of CP.Theoretical calculations demonstrated that hydrogen abstraction should easily occur at the hydroxyl group to produce reactive CP· radicals for subsequent polymerization.Cleavage of the C-C bridge bond,electrophilic substitution,hydroxylation,ring opening,and decarboxylation were also observed during Fe(Ⅵ)oxidation process.In addition,the degradation of CP by Fe(Ⅵ)was also effective in real waters,which provide a basis for potential application.更多还原