【作者】 张晨曦；

【导师】 王文兴；

【作者基本信息】 山东大学 ， 环境科学， 2014， 博士

【摘要】 二嗯英是多氯代二苯并-对-二噫英(PCDDs)和多氯代二苯并呋喃(PCDFs)的总称,具有致癌、致畸和致突变的效应(三致效应),已被列入《斯德哥尔摩公约》持久性有机污染物(POPs)的黑名单中。PCDD/Fs的来源主要是垃圾焚烧、化工生产、金属冶炼及精炼过程和造纸工业等。受蒸汽压和温度的影响,进入大气的PCDD/Fs会以气相或者颗粒相的形式存在。常温状态下,低氯代的PCDD/Fs(低于六个氯原子)主要分布在气相中,高氯代的PCDD/Fs则主要分布在颗粒相中。在烟道气中,由于温度比较高,82%-93%的PCDD/Fs分布在气相中。PCDD/Fs在大气中的去除途径包括干湿沉降、光降解和大气氧化反应。颗粒相PCDD/Fs主要以干湿沉降的方式去除,而气相PCDD/Fs则主要通过与大气氧化剂发生反应而被去除。为了了解气相PCDD/Fs在大气中的化学行为,研究其与大气氧化剂的反应机理和速率常数是非常必要的。由于PCDD/Fs毒性高,蒸汽压低,通过实验研究反应机理和获得速率常数十分困难。量子化学计算作为研究分子与分子间相互作用的手段,被广泛应用于研究化学反应机理和获得速率常数。本论文针对前人研究中存在的问题,选取毒性较强、气相分配比占80%以上的2,3,7,8-TCDD和2,3,7,8-TCDF作为模型化合物,研究了二嗯英类物质的化学反应机理,得到了以下有意义的研究结果：1.2,3,7,8-TCDD/F与HOX、O3、NO3、Cl的反应机理研究在MP WB1K/MG3S//MPWB1K/6-31+G(d,p)水平下,研究了2,3,7,8-TCDD/F与大气中HOx自由基、03、N03自由基和C1原子的反应机理,采用小曲率隧道校正(SCT)的正则变分过渡态理论(CVT)计算了298.15K下的反应速率常数。研究表明,2,3,7,8-TCDD/F与OH自由基可以发生OH自由基加成反应和H原子抽提反应,其中OH自由基加成反应占主导地位。2,3,7,8-TCDD主要发生在与O相连的CA位点,而2,3,7,8-TCDF主要发生在C1和C4位点。298.15K时2,3,7,8-TCDD/F与OH自由基反应的总速率常数分别为7.75×10-12和9.78×10-13cm3molecule-1s-1;2,3,7,8-TCDD/F与HO2自由基只能发生加成反应,298.15K时的总速率常数分别为2.53×10-25和3.61×10-25cm3molecule-1s-1;2,3,7,8-TCDD/F与O3可以发生加成反应,298.15K时的总速率常数分别为3.17×10引和6.86×10-22cm3molecule-1s-1;2,3,7,8-TCDD/F与NO3自由基、C1原子可以发生加成反应和抽提反应,加成反应为主要反应方式。298.15K时2,3,7,8-TCDD/F与N03自由基反应的总速率常数为3.96×10-14和6.46×10-15cm3molecule-1s-1,与Cl原子反应的总速率常数分别为1.23×10-9和1.37×10-10cm3molecule-1s-1.通过计算大气寿命,得出2,3,7,8-TCDD/F与OH自由基的反应是其主要去除路径。特殊情况下,如夜间与N03自由基的反应比较重要,沿海地区黎明时与Cl原子的反应占主要地位。2.大气环境中OH自由基引发的2,3,7,8-TCDD的氧化降解机理在MPWB1K/MG3S//MPWB1K/6-31+G(d,p)水平下,研究了O2/NO/H2O存在的情况下,OH自由基引发的2,3,7,8-TCDD氧化降解机理,在热力学参数的基础上采用CVT/SCT的方法计算了相关的反应速率常数。研究表明,室温下2,3,7,8-TCDD与OH自由基的反应发生在丫位上占93%。γ位的TCDD-OH生成后,可以发生二嗯英环断裂反应和02加成反应。与NO的反应是TCDD-OH-O2过氧自由基的主要化学行为。含C-O’的自由基中间体可以抽提H2O中的H原子,得到二元醇和OH自由基。新产生的OH自由基可以引发新一轮的降解反应,这可以解释存在水蒸气时PCDD/Fs的降解效率会提高的实验现象。3.大气环境中OH自由基引发的23,7,8-TCDF的氧化降解机理在MPWB1K/MG3S//MPWB1K/6-31+G(d,p)水平下,研究了O2/NO/H2O存在的情况下,OH自由基引发的2,3,7,8-TCDF氧化降解机理,并计算相关的反应速率常数。不同加成位点的分支比随温度的变化而变化,C4-加成所占的比重随着温度的升高逐渐减小,C1-加成和CA-加成所占的比重明显增加。TCDF-OH的后续反应中,TCDF-OH(A)从动力学上比较倾向于断裂C-O键,而对TCDF-OH(B)来说,O2加成反应更为重要；TCDF-OH(1)和TCDF-OH(4)(?)匕较容易与02发生抽提反应,得到闭壳的羟基二苯并呋喃和H02自由基；TCDF-OH(2)和TCDF-OH(3)的主要反应路径为脱氯。在IM2d(t)-A的异构化降解的过程中会产生二嗯英环,这可以解释实验上关于PCDF转化为PCDD的假设。TCDF-OH-O2过氧自由基与NO的反应是无垒过程,相对于TCDF-OH-O2过氧自由基的自身异构化降解来说,这是其主要化学行为。4. PCDDs与OH自由基反应速率常数的QSAR研究计算了75种PCDDs与OH自由基加成反应的速率常数,应用定量构效关系(QSAR)方法研究了PCDDs氯原子取代数目和位置对反应速率常数的影响。研究发现,PCDDs与OH自由基发生加成反应的过程中,含Cl原子的反应位点的过渡态能量相对较高,这可能是受Cl原子空间位阻的影响。对于2,3,7,8-位氯取代的PCDDs来说,反应速率常数kα>kβ,而其它PCDDs的反应速率常数kα<kβ。α-位Cl原子的数目(Nα)对kα的影响很小,Cl原子的相对位置(主要是对位成对氯原子数目Np)要比c1原子的数目对kα的影响大；kβ随Nα和β-位cl原子的数目(Nβ)的增加而减小,邻位成对氯原子数目(Nο)的影响小于对位成对氯原子数目(Nm),cl原子的数目(N。和Np)要比cl原子的相对位置(No和Nm)对kβ的影响大；kγ受Cl原子取代数目和位置的影响很小；总速率常数KOH主要受Cl原子取代数目的影响,高氯代PCDDs (?)匕低氯代PCDDs的反应速率常数要小。更多还原

【Abstract】 Dioxins are the general term for polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs). Due to their properties of carcinogenesis, tetratogenesis and mutagenesis, and may enter human body through food chain and endanger the human health, PCDD/Fs have been enlisted in Stockholm Convention. The major sources of PCDD/Fs are waste incineration, chemical industry production, metal smelting and refining process, and paper manufacturing industry. The PCDD/Fs in the atmosphere are in the form of gas phase or particles, which are mainly influenced by saturated vapor pressure and temperature. At the ambient temperature, low chlorinated PCDD/Fs (mainly with six or less chlorine atoms) have high concentration in the gas phase, while high chlorinated PCDD/Fs (primarily hepta-and octa-chlorinated homologues) mainly distributed in the particle phase. In the flue gas,82%～93%of PCDD/Fs are distributed in the gas phase due to high temperature. The atmospheric fate for PCDD/Fs is removed from the atmosphere via the dry or wet deposition, photolysis and the reactions with the atmospheric oxidants (including OH radical, HO2radical, O3, NO3radical, and Cl atom). Particle-phase PCDD/Fs are removed from the atmosphere via the dry or wet deposition, while gas-phase PCDD/Fs are depleted via photolysis and degradation reactions. It is critical to know the reaction mechanism and accurate rate coefficients of PCDD/Fs with various oxidants in order to assess their dominant atmospheric fate.Due to their toxicities and the rather low vapor pressure, the reaction mechanism and direct kinetic measurements of the reactions are difficult to obtain by experimental study. Theoretical study can provide accurate predictions for the reaction mechanism by calculating the energies and can generate kinetic data of key elementary reaction steps. In this paper, the writer has done the following works:1. Mechanism of2,3,7,8-TCDD/F with HOx、O3、NO3、Cl2,3,7,8-tetrachlorinated dibenzo-p-dioxins and2,3,7,8-tetrachlorinated dibenzofuran (2,3,7,8-TCDD/F) were chosen to research the initiation reactions with OH radical, HO2radical, O3, NO3radical, and Cl atom at the level of MPWB1K /MG3S//MPWB1K/6-31+G(d,p) due to the highest toxicities and80%in the gas phase. Based on the quantum chemical information, rate constants were calculated using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) in order to assess the relative importance of the reactions initiated by various oxidation agents.The results show that2,3,7,8-TCDD/F and OH radical have two possible reaction patterns, i.e., OH radical addition and H atom abstraction, and OH radical addition is the main way. The oxygen-bonded Ca is the most favorable site for OH radical addition of2,3,7,8-TCDD, and the C1and C4are the most favorable sites for OH radical addition of2,3,7,8-TCDF. The rate constants obtained from the reactions of the TCDD/F with the OH radical are7.75×10-12and9.78×10-13cm3molecule-1s-1, respectively.2,3,7,8-TCDD/F can only react with HO2radical by H atom abstraction reaction, the rate constants at298.15K are2.53×10-25and3.61×10-25cm3molecule-1s-1, respectively.2,3,7,8-TCDD/F can react with O3radical by OH radical addition reaction, the rate constants at298.15K are3.17×10-21and6.86×10-22cm3molecule-1s"1, respectively.2,3,7,8-TCDD/F can react with NO3radical and Cl atom by OH radical addition and H atom abstraction, the OH radical addition is the main reaction way, the rate constants with NO3radical and Cl atom at298.15K are3.96×10-14/6.46×10-15and1.23×10-9/1.37×10-10cm3molecule-1s-1, respectively. The atmospheric lifetime τ of the2,3,7,8-TCDD/F with respect to OH radicals, O3, NO3radicals, and Cl atoms are estimated, and the study show that2,3,7,8-TCDD/F will be mainly scavenged by OH radical, while NO3radical is the primary oxidant at night and Cl atom dominates after sunrise in coastal and marine areas.I. Mechanism for OH-initiated Degradation of2,3,7,8-TCDD in AtmosphereThe OH-initiated atmospheric degradation reaction of2,3,7,8-TCDD was investigated using DFT calculation in order to find out favorable reaction pathways and reaction sites in the presence of O2and NO/H2O. Based on the quantum chemical information, rate constants were calculated using CVT/SCT over a suitable temperature range of250-400K. The results show that more than93%of the OH radical addition reaction for2,3,7,8-TCDD occurs on Cy. In the ensuing reactions of TCDD-OH, the bond cleavage of dioxin ring and O2addition are both important. The reaction with NO in atmosphere is the main removal way of the peroxy radical isomers TCDD-OH-O2. The carbonyl free radicals can abstract H atom from H2O to reach a stable state and the OH radical will be regenerated simultaneously, which can interprete the significantly increasing destruction efficiency of PCDD/Fs in the presence of water vapor.3. Mechanism for OH-initiated Degradation of2,3,7,8-TCDF in AtmosphereThe OH-initiated atmospheric chemical reaction mechanism and kinetics of2,3,7,8-TCDF was investigated using the DFT and CVT/SCT in the presence of O2and NO/H2O. The reaction mechanism of2,3,7,8-TCDF with OH radical and ensuing reactions including bond cleavage of furan ring, O2addition or abstraction, dechlorination process, bimolecular reaction of TCDF-OH-O2peroxy radical with NO and reaction of carbonyl free radicals TCDF-OH-O with H2O are researched. The results show that the branching ratios R of C4-addition will decrease as the temperature rises, while the branching ratios R of CA-addition and C\-addition increase noticeably and the branching ratios R of other addition reactions are elevated slightly. In the subsequent reactions of TCDF-OH, TCDF-OH(A) is kinetically favored to open up the C-O bond, while oxygen addition is more important for TCDF-OH(B), TCDF-OH(1) and TCDF-OH(4) are more likely to produce the closed shell dibenzofuranol structures and HO2radical, The dechlorinate processes of TCDF-OH(2) and TCDF-OH(3) are the dominant pathway. In the isomerization of M2d(t)-A, the furan ring of2,3,7,8-TeCDF can be turned into dioxin ring, which may explain the experimental hypothesis that PCDFs can be transformed to PCDDs. The reaction with NO in atmosphere is the main removal way of the peroxy radical isomers TCDF-OH-O2.4. QSAR Study on the Rate Constants of Polychlorinated Dibenzo-p-dioxins with OH RadicalThe rate constants of75PCDDs with OH radical at298.15K are obtained, the rate constants (kα,&β，kγ, and KOHh) are further quantified by the studies on quantitative structure-activity relationships (QSAR). According to the QSAR models, the relations of these rate constants with the numbers and positions of Cl atoms were discussed. The results show that the barrier of OH radical addition on carbon that connecting with Cl atom are higher than others, which may be due to the steric hindrance of the Cl atom. The rate constants of PCDDs that Cl atoms substitution occur on the2,3,7,8-site have the following order:kα>kβ, while others are the opposite. For the kα, Nα had limited effects on kα, and the effect of the number of relative position for these Cl atoms (mainly Np) is more than the number of Cl atoms. For the kp, it is negatively associated with Nα and kβ. The effects of relative positions of these Cl atoms are different, with the following order:N0<Nm. The effect of the number of Cl atoms (mainly Nα and Nβ) is more than the number of relative position (No and Nm) for these Cl atoms. κγ, is immune to the numbers and positions of Cl atoms. For the kOH is mainly effected by the number of Cl atoms, the kOH of high chlorinated PCDDs is less than the koH of low chlorinated PCDD/Fs.更多还原