【作者】 沈吉敏；

【导师】 陈忠林；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2007， 博士

【摘要】 水体日益严重得受到各种有机物的污染,对人体健康和水环境构成了严重威胁,必须采取适当的处理工艺将其从水环境中彻底去除或者将其浓度降低到安全水平。硝基苯、硝基氯苯等含芳环物质的种类在许多国家或组织列出的水体优先控制污染物的名单中都占到50%以上,利用常规的水处理工艺很难将这些芳香物质去除,O₃及以产生·OH为基础的高级氧化工艺（AOP）能有效地去除水中这些有机污染物。O₃和H₂O₂协同作用可以产生具有极强氧化作用的·OH。以硝基苯为目标物,对O₃/H₂O₂氧化体系去除水中有机物的效果和机理进行了研究,考察了pH值、H₂O₂剂量、自由基抑制剂或促进剂对硝基苯的去除效果的影响。当pH值≤7时,与单独臭氧化相比,H₂O₂促进臭氧化去除硝基苯的效果较为明显,H₂O₂投加量从1.0mg/L增加到4.0mg/L时,在氧化5min内,硝基苯的去除率有明显的增加,但当H₂O₂投加量由4.0mg/L提高到20mg/L时,硝基苯的去除率呈下降趋势;同时发现单独臭氧化硝基苯的过程能产生H₂O₂;几种有机物的加入,不同程度都降低了硝基苯的去除率。无论单独臭氧化还是催化臭氧化都不能使体系TOC大幅度降低,苯环上的硝基几乎以NO₃-形式脱出。LC-MS和GC-MS的测定结果表明,硝基苯臭氧化的主要产物为酚类和羧酸类物质。对O₃/H₂O₂体系中硝基苯反应的历程进行了推导,认为硝基苯的臭氧化降解过程分为两个阶段,首先是羟基自由基的作用,使苯环羟基化,然后是羟基化的芳环发生开裂,生成各种脂肪族化合物或进一步矿化。对硝基氯苯（pCNB）也是水体中常见的污染物质,测定pCNB与O₃反应速率常数为1.6L/（mol·s）;采用竞争动力学方法,以氯苯和硝基苯为参考化合物,测得pCNB与·OH的反应速率常数为2.6×109L/（mol·s）。pCNB臭氧化降解过程中,氯基和硝基主要以Cl-、NO₃-的形式存在,体系的TOC没有大幅度的降低。GC-MS、LC-MS的分析结果表明,pCNB臭氧化过程主要产物为对氯酚、对硝基酚、硝基氯酚等具芳环的酚类物质和乙二酸、丙二酸、马来酸、己二烯二酸等脂肪族化合物,根据这些产物对pCNB的臭氧化反应途经进行推测可知,pCNB的臭氧化降解机制与硝基苯臭氧化降解机制一致。通过量子化学计算,发现硝基氯苯的三种同分异构体—对硝基氯苯（pCNB）、间硝基氯苯（mCNB）和邻硝基氯苯（oCNB）的苯环上碳原子的电子云密度和自然轨道布居数（NOB）具有一定的差异。通过试验测得三种硝基氯苯（CNBs）与臭氧直接反应的二级速率常数分别为1.6、1.5、1.6L/（mol·s）,以硝基苯（NB）和氯苯（CB）为竞争物,利用竞争动力学测得三种物质与·OH的反应二级速率常数分别为2.6×109、2.8×109、3.2×109L/（mol·s）。对CNBs的臭氧化过程考察发现,氧化体系的pH呈减小的趋势,溶液颜色由无色突变到黄色然后迅速恢复到无色,氧化体系中的无机碳（IC）、Cl-、NO₃-逐渐升高,不同氧化阶段均有H₂O₂产生,当目标物pCNB浓度为50mg/L时,H₂O₂的最大浓度能达到1.8mg/L。整个臭氧化过程CNBs氧化去除达到99%时,而TOC去除率仅为45%左右。GC-MS和LC-MS的结果显示三种硝基氯苯的臭氧化产物都主要包括氯酚、硝基酚、氯硝基酚等酚类物质和草酸、丙二酸、顺丁烯二酸、己二烯二酸等羧酸类物质。pCNB在臭氧化过程中,氯基和硝基可以被·OH取代,生成硝基酚和氯酚,而oCNB和mCNB的氧化产物中,未检出硝基酚和氯酚,三种硝基氯苯苯环上的氢均可被·OH取代,生成硝基氯酚,LC-MS/GC-MS共检测出10种不同的硝基氯酚。CNBs苯环上的-Cl和-NO2的取代位不同,致使苯环上碳原子的电子云密度和NOB具有一定的差异,·OH与苯环上的H发生取代反应的几率与相应C的电子云密度和NOB具有一定的相关性,而与对应的键能关系不大,·OH氧化与硝基氯苯的反应可能类似于芳环的亲电取代反应。对硝基苯、硝基氯苯的O₃/H₂O₂氧化降解的机制的研究认为,降解的开始阶段是由于·OH的作用使得芳环羟基化,使得芳环电子云密度增大,芳环变得不稳定而裂解,不稳定的多羟基芳环在O₃作用下裂解。以含多羟芳环的大分子天然有机物单宁酸为目标物,对单宁酸O₃/H₂O₂氧化降解效果与机理进行了研究。发现H₂O₂的加入对臭氧氧化去除单宁酸没有明显地促进作用,从TOC去除率结果来看,O₃/H₂O₂氧化体系最终TOC要比单独的臭氧化低10%左右。用顺磁共振波谱（ESR）对O₃/H₂O₂氧化体系的·OH的相对强弱进行比较,发现单宁酸强猝灭体系的·OH。单宁酸的O₃/H₂O₂氧化副产物的主要有乙醛、乙二醛、甲基乙二醛等醛类物质,最终产物主要是乙二酸、丙酮二酸等羧酸类物质,以TOC计算,乙二酸、丙酮二酸这两种羧酸占有机物的1/3左右。更多还原

【Abstract】 Organic pollutions in water gradually become a serious threaten to human health and water environment. In order to keep water secure, proper treatment process should be innovated and adopted to eliminate or remove these pollutants. Aryls, such as NB and CNBs, occupies more than 50 percent of Priority Organic Compounds（POCs） listed in most countries. They are difficult to be eliminated with routine processes of water treatment. Ozonation and AOPs, which could produce·OH, perform powerfully in the removal of these aryls. The cooperation of O₃ and H₂O₂ can generated·OH which is a strong oxidatant.Selecting nitrobenzene （NB） as the model pollutant, the efficiency and mechanism of the degradation of NB in aqueous solution by O₃/H₂O₂ system were investigated. Effects of pH, H₂O₂ dose and the inhibitor or accelerant of·OH on the removal rate of NB were studied. H₂O₂ could obviously improve the ozonation of NB below pH 7. H₂O₂ dose was increased from 1.0mg/L to 4.0mg/L, within the time of 5-min reacting, the removal rate of NB was enhanced. However, as H₂O₂ dose increased from 4.0mg/L to 20mg/L, the removal efficiency of NB decreased. Different quantities of H₂O₂ were yielded in different reaction phases of single ozonation system. The addition of some organisms could make the removal of NB decreased with different degrees. Both systems of single ozonation and H₂O₂-catalysed ozonation could not reduce TOC observably. During the NB degradation process, organonitrogen was almost completely converted to nitrate and the pH value reduced significantly. Results of LC-MS and GC-MS show that main intermediate products were phenolic compounds and carbonyl compounds. Finally, a possible reaction pathway of the catalytic ozonation of NB was proposed. It had been found that the catalytic ozonation of NB can be divided into two steps. First, hydroxyl radical attacked phenyl ring, then the ring opened, forming into various aliphatic compounds or being mineralizd to inorganic compounds.pCNB is another stubborn organic pollutant in water. The kinetics and mechanism of ozonation of p-nitrochlorobenzene （pCNB） were investigated. The reaction rate constants of pCNB with O₃ was 1.6L/（mol·s） by direct measuration. With nitrobenzene and chlorobenzene as the reference compounds, the reaction rate constants of pCNB with·OH, measured by means of a competition kinetics, was 2.6×109L/（mol·s） During the ozonation of pCNB, organic nitrogen and organic chlorine were almost completely converted to nitrate and chloride, TOC could not be obviously reduced. Results of LC-MS and GC-MS show that main intermediate products were aromatic substances such as p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol, etc., and nonaromatic substances such as oxalic acid, malonic acid, maleic acid, muconic acid, etc. A possible reaction pathway of ozonation of pCNB , proposed according to these products, was found to be in accord with that of NB. Due to the dissimilar place of either nitryl or chlorine, nitrochlorobenzene has three isomers as p-nitrochlorobenzene（pCNB）, m-nitrochlorobenzene（mCNB） and o-nitrochlorobenzene（oCNB）. Basing on the quantum chemistry, electron cloud density of carbon atom on phenyl and NOB were calculated to be different of these three isomers. The secondary rate constants of these three CNBs reacting directly with O₃ were 1.6, 1.5, 1.6L/（mol·s）, respectively. Taking nitrobenzene and chlorbenzene as reference compounds, measured with competition kinetics method, the secondary rate constants of three CNBs reacting with·OH were 2.6×109, 2.8×109, 3.2×109L/（mol·s）, respectively. It suggested that the free radical reaction is the primary reaction in the ozonation process of CNBs. It was found that pH value of the solution decreased during the process, the color of the solution turned yellow suddenly, then came back to colorlessness rapidly, and the concentration of IC,Cl- and NO₃- in the system increased gradually. H₂O₂ was generated in each different phase of the process, when the concentration of the pCNB is 50mg/L, the concentration of H₂O₂ could reach maximally to 1.8mg/L. The degradation efficiency of CNBs was 99%, but the removal rate of TOC was only 45%. Intermediate products were analyzed by GC-MS/LC-MS. The products of these three CNBs mainly contain phenolic matters such as chlorophenol, nitrophenol, nitrochlorophenol, and carboxylic matters such as oxalic acid, malonic acid, maleic acid,muconic acid. In the ozonation process of pCNB, -Cl and -NO2 could be replaced by·OH, chlorophenol and nitrophenol were formed meanwhile. But in the ozonation process of oCNB and mCNB, neither nitrophenol nor chlorophenol was detected. The hydrogen on the phenyl of all these three CNBs could be replaced by·OH, thus nitrochlorophenol was produced, and ten different nitrochlorophenols were detected by GC-MS/LC-MS. The difference of the substitutional place of -Cl or -NO₂ on the phenyl could lead to the difference of the electron cloud density of carbon and the natural bond orbital （NBO） population. The probability of the reaction between·OH and the hydrogen on the phenyl has some relationship with electron cloud density of carbon and NOB, but little relationship with bond energy. The reaction between·OH and CNBs is probably similar to the electrophilic substitution reactions of aryl.In the degradation of NB and CNBs by O₃-O₃/H₂O₂, aryl ring was hydroxylated by·OH first, electron cloud density on the aryl increased, then the instable aryl was cracked by ozone. Tannic acid, being polyhydroxyl, is one of macromolecule nature oganic matters, the efficiency and mechanism of tannic acid degradation by O₃ and O₃/H₂O₂ were studied. Results show that the addition of H₂O₂ has no obvious promotion on the ozonation efficiency of tannic acid. But the system of O₃/H₂O₂ performs 10 percent more than solo ozonation in the removal of TOC. The relative generating intensity of·OH in the O₃/H₂O₂ system was detected by Electronic Spin Resonance（ESR）. It was found that tannic acid consumingly restrained the generation of·OH, it mainly attributes to the polyhydroxyl structure of tannic acid. In addition, ozone reacts speedily with tannic acid. Ozonation of tannic acid are mainly aldehydes such as acetaldehyde, glyoxal, methyl glyoxal. Analysis of Ion Chromatogram show that final products of tannic acid are oxalic acid, ketomalonic acid, they occupies 30 percent of TOC in both systems.更多还原