【作者】 郭耀广；

【导师】 柳建设； 王兆慧；

【作者基本信息】 东华大学 ， 环境科学与工程， 2014， 博士

【摘要】 近年来,具有“三致”效应和遗传毒性的溴代阻燃剂及氯酚类防腐剂在生产、使用及废弃处理过程中导致的水环境污染问题日益加剧,严重威胁了人类的生活和健康。因此,开发新型、绿色、高效的处理技术去除水环境中典型卤代污染物的研究具有重要意义。本文以典型溴代阻燃剂四溴双酚A(TBBPA)和氯代防腐剂2,4,6-三氯酚(2,4,6-TCP)为研究对象,利用基于光化学的高级氧化技术开展其降解研究,主要开展了以下几个方面的工作：(1)为了克服TBBPA水中难溶性问题导致的向传统高级氧化体系加入甲醇等有机溶剂增溶,产生二次污染及自由基湮灭降低反应效率等缺陷。利用TBBPA在强碱性水溶液可溶及persulfate (PS)可同时被碱及紫外光激活生成硫酸根自由基的双重特性,开展了碱性UV/PS体系降解TBBPA的研究,考察pH、TBBPA和PS初始浓度、溴离子对于TBBPA降解动力学的影响。结果表明,TBBPA的降解动力学符合准一级动力学模型；TBBPA的降解速率随着溶液的初始pH和PS初始浓度升高而增大,随着TBBPA初始浓度的升高而下降；外加Br-与否对TBBPA的降解和多溴代有机物的生成几乎没有影响；TBBPA的矿化率随着反应时间而增大,但4h的总矿化率只有25%左右；TBBPA在降解过程中,生成大部分的中间产物是单苯环溴代有机物,脱溴产物较少；通过对降解中间产物的分析,对TBBPA在碱性UV/PS体系中的降解途径进行了推测,提出了TBBPA中异丙基和苯环之间化学键的断裂为主导反应的反应机理。(2)因还原脱溴是提高TBBPA矿化反应的限速步骤,为进一步提高TBBPA的降解效率,采用环境友好、兼具还原和氧化能力的Ti02光催化体系开展降解TBBPA的研究。考察了通气环境、底物初始浓度、溶液pH、常见氢供体及电子受体对Ti02光催化技术降解TBBPA动力学的影响,通过反应产物分析,提出了改变通气环境引导的还原-氧化分段式光催化技术降解TBBPA的反应机理。结果表明,TBBPA初始浓度对其自身还原降解和脱溴速率均呈现先上升后下降双重影响；在强碱性条件下,TBBPA的还原降解与脱溴速率随着溶液初始pH的升高而增大；甲醇作为氢供体作用于TBBPA还原降解和脱溴的效果更佳; NO3-、SO42-等常见电子受体会抑制TBBPA还原降解和脱溴；体系在通氮气条件下,光生电子对TBBPA的还原脱溴是主导反应,通氮气后接着通空气或自始至终通空气,光生空穴或羟基自由基对TBBPA的氧化反应是主导反应。本研究为利用UV/TiO2体系通过改变通气条件实现含TBBPA污水的“还原脱溴-氧化分解”分段式过程预处理提供了一定的理论依据。(3)为避免传统高级氧化技术降解氯酚类有机污染物的氧化剂投入成本高、催化剂二次污染等局限性,采用铁-硫光化学循环原理耦合高级氧化技术,提出了新型photo-sulfite体系,并以2,4,6-TCP为模型污染物,开展其降解机制研究。考察了pH、紫外光、S(Ⅳ)剂量、铁(Ⅲ/Ⅱ)配体等因素2,4,6-TCP降解的影响；同时,考察了反应过程中铁的物种形态变化及S(Ⅳ)和pH的变化情况；通过特定醇类自由基捕获实验初步揭示了photo-sulfite的反应机制。结果表明,photo-sulfite体系对2,4,6-TCP等有机污染物具有很高的降解效果；pH3-4利于photo-sulfite反应的进行；铁配体的影响依赖于Fe(Ⅲ)配合物的光化学行为及中间产物的性质；紫外光在反应体系中促进起着Fe(Ⅲ)/Fe(Ⅱ)循环的作用,即(a)当S(Ⅳ)足量的初始反应阶段,FeSO3+是主要活性物种,经光解生成Fe2+和SO3·-,接着进一步被生成SO5·-和S04·-,氧化降解有机物；(b)随着S(Ⅳ)的消耗和pH下降,铁的光活性物种由FeSO3+自发地换为FeOH2+,光解生成·OH,继续降解有机物。同时,水中S02无机污染物被氧化去除。通过中间产物和降解产物分析,初步提出了2,4,6-TCP在photo-sulfite高级氧化体系中降解反应机理：首先2,4,6-TCP在硫酸根自由基作用下逐级脱氯；随后,脱下的氯离子会在硫酸根自由或羟基自由基的氧化作用下继续参与到2,4,6-TCP的转化反应中,生成毒性更强多氯代酚类有机化合物。此外,脱氯产物苯酚等也可能会在抽氢作用下生成二苯并呋喃等毒性更强的有机物。Photo-sulfite体系成功实现了水中无机二氧化硫与氯代酚等无机／有机卤代酚类污染物同时转化。本研究比较适合无机亚硫酸盐和持久性有机污染物共污染水体的修复,同时也可用于工业脱硫废水与其他有机废水混合废水的治理,但反应过程中毒性副产物的生成问题在实际工程中需予以重视。更多还原

【Abstract】 Recently, the production, use and disposal of brominated flame retardants and chlorophenols preservatives with teratogenicity, carcinogenicity, mutagenicity and genetoxicity have caused more and more serious water pollution problems, which threaten the human life and health. Therefore, it is very important to explore novel, green, and efficient techniques to remove the typical halogenated organic pollutants from water environment. In the present studies, the degradation of tetrabromobisphenol A (TBBPA), one of typical brominated flame retardants, and2,4,6-trichlorophenol (2,4,6-TCP), one of typical chlorinated preservatives, selected as model pollutants, are investigated by the photochemical advanced oxidation processes (AOPs). The main studies are as followed:(1) TBBPA with limited water solubility can only dissolve in alkaline aqueous solution and the available AOPs for TBBPA degradation almost performed in acidic or neutral conditions. As such, some common organic solvents were employed to be added into water to increase the solubility of TBBPA, which can lead to both secondary pollution problems and lower degradation caused by quenched radicals with organic solvent, such as methanol. In order to overcome the abovementioned problems, the degradation of TBBPA by alkaline UV/PS system was carried out owing that both base and ultraviolet irradiation can simultaneously activate persulfate (PS) to generate sulfate radicals. The effects of pH, initial concentrations of TBBPA and PS, and the bromide ion on degradation kinetics of TBBPA were examined. The results showed that the degradation of TBBPA was fitted for the pseudo-first-order kinetic model, and the degradation efficiency was significantly enhanced with the initial pH and initial concentration of PS increase, decreased with the increase of initial concentration of TBBPA instead. There were no significant influences of addition of Br-on the degradation of TBBPA and polybrominated organics production. The mineralization of TBBPA increased as the reaction time prolonged, but the total mineralization of4h was only about25%, and most of the intermediate products of TBBPA were single benzene ring-brominated organic compounds, and less debromination products. Ultimately, the pathway of cleavage between the isopropyl group and one of the benzene rings of TBBPA was regarded as the main step for the degradation of TBBPA in the alkaline UV/PS system.(2) C-Br bond cleavage is considered as a key step to reduce their toxicities and increase degradation rates for TBBPA. To further improve the degradation efficiency of TBBPA, photocatalytic degradation of TBBPA by the environment-friendly UV/TiO2system, with both reduction and oxidation capacities was investigated. The influences of atmospheres, initial concentration of TBBPA, pH, common hydrogen donors and electron acceptors on the degradation kinetics of TBBPA were examined. Moreover, the major reaction products were identified and a possible pathway of sequential reduction-oxidation for photocatalytic degradation of TBBPA by changing atmospheres was proposed. The results indicated that the degradation and debromination of TBBPA were declined with decreasing or increasing the initial concentrations of TBBPA; and that methanol, a hydrogen donor, had a better performance for the reductive degradation and debromination of TBBPA. Furthermore, the common electron acceptors, such as NO3-, SO42-, inhibited the degradation and debromination of TBBPA. Reductive debromination for TBBPA was the dominant reaction with N2-saturated and photo-induced holes or hydroxyl radicals involving the oxidation reaction played a significant role as soon as air saturated into the reaction system. This study provided some fundamentals for the pretreatment of TBBPA-contaminated wastewater by a two-stage reductive debromination/subsequent oxidative decomposition process in the UV-TiO2system by changing the reaction atmospheres.(3)To avoid the limitations of high input costs of oxidants and secondary pollution caused by catalysts from traditional AOPs for the degradation of chlorophenols organics, a novel photo-sulfite system based on the photochemical cycle theory of iron-sulfur coupled with AOPs, was proposed to examine the mechanism from the degradation of2,4,6-TCP selected as a model pollutant. This study examined the photo-sulfite system and its capacity to degrade aqueous organic contaminants. The changes in concentrations of Fe(II), sulfite, model pollutant molecule and proton were measured over reaction time, with different dosages of Fe(III) and sulfite. As such, the dynamic speciation profiles for Fe(III/II) species were established by MEDUSA software to give insights into the photochemistry of iron species. The experiments of pH effect, additions of iron ligands and radicals scavenging were used to probe the underlying reaction mechanism. It was evident that the photo-sulfite system had good performances for the decomposition of2,4,6-TCP and other organic pollutants, and pH3～4was favorable for the photo-sulfite reaction. Under UV irradiation, the effects of the ligands depended on the photochemistry of their Fe(III) complexes and nature of degradation byproducts. And UV irradiation enables to activate two Fe3+/Fe2+cycle-relevant reactions:(a) initially, FeSO3+is the dominant Fe(III) species as sulfite is sufficient, and the photolysis of FeSO3+to produce Fe2+and SO3·-subsequently promotes the generation of reactive SO5·-and SO4·-;(b) photochemically active species spontaneously switch from FeSO3+to FeOH2+, with the depletion of sulfite and the decrease in solution pH. FeOH2+is photolyzed to produce highly reactive oxidant-·OH, which continues to degrade organic pollutants. S(Ⅳ), acting as a iron ligand and inorganic pollutant, is simultaneously oxidized with the degradation of organic contaminants.The degradation mechanism of2,4,6-TCP in photo-sulfite system was proposed based on the identification of intermediates. Initially, phenol was formed via the dechlorination of2,4,6-TCP step by step due to the oxidation of sulfate radicals; and then, the freedom chloride ions taken off from2,4,6-TCP would continue to be involved2,4,6-TCP conversion reaction to generate more toxic polychlorinated phenols compounds by the oxidation of sulfate or hydroxyl radicals. In addition, more toxic dibenzofuran could be formed by hydrogen abstraction of sulfate or hydroxyl radicals from dechlorination products, such as phenol. The proposed photo-sulfite process should be ideally suited for sulfite contaminated wastewaters with recalcitrant organic compounds or the mixed industrial wastewaters from desulfurization wastewater and other organic wastewaters. However, the generation of toxic byproducts must be attached importance in practical engineering.更多还原