题名 | 多元铁基复合金属氧化物材料的制备与多氯联苯的降解研究 |
作者 | 黄林艳 |
学位类别 | 博士 |
答辩日期 | 2015-05 |
授予单位 | 中国科学院研究生院 |
授予地点 | 北京 |
导师 | 郑明辉 ; 苏贵金 |
关键词 | 多氯联苯,氯代芳烃,铁基复合氧化物,催化降解,纳米材料,Polychlorinated biphenyls, Chlorinated aromatic hydrocarbons, Iron-based composite oxide, Catalytic degadation, Nano-material |
其他题名 | Preparation of iron-based composite oxides and their applications in degradation of polychlorinated biphenyls |
学位专业 | 环境科学 |
中文摘要 | 多氯联苯(PCBs)为一类持久性有机污染物,虽然目前已禁止生产和使用,然而仍然有大量的 PCBs赋存于封闭工业设备容器中或已逸散到周围环境中,这些 PCBs将会对人类健康和生态环境造成极大的潜在危害。由于受经济、技术、社会舆论等的影响,目前 PCBs的各处理处置方法在实际应用中都受到一定的限制。因此,迫切需要开发能耗低、经济、绿色高效的处理新方法。利用新型多元复合金属氧化物材料对 PCBs进行降解为这类物质的处置提供了新的思路。 本论文分别利用共沉淀法、多元醇介导法和水热法合成了系列二元和三元铁基复合金属氧化物材料,研究了合成的材料对选定的 PCBs模型化合物的催化降解活性,并初步探讨了降解反应机制。本论文的主要研究成果有: 1.采用共沉淀法合成了一系列NiFe复合氧化物材料,并对材料进行了物化性质表征。同时考察了不同灼烧温度得到的材料对十氯联苯( CB-209)的降解活性,并与多元醇介导法合成的 Fe3O4进行比较。结果表明,灼烧温度为400°C得到的NiFe2O4材料具有最高的表面活性氧量和比表面积。材料对CB-209降解活性评价结果表明,制备的NiFe2O4对CB-209降解表现出最高的反应活性,Fe3O4次之,这可能与 NiFe2O4丰富的表面活性氧及Ni-Fe间存在协同作用有关。 2.通过检测分析 NiFe2O4催化降解 CB-209过程中的中间产物和超氧自由基,并结合理论计算探讨了 CB-209热催化降解反应路径,且与 Fe3O4反应体系进行比较。结果显示,在 NiFe2O4和 Fe3O4降解 CB-209两种反应体系中均有低氯代联苯、氯苯、羟基化合物和有机酸中间产物的生成,说明 CB-209存在四种竞争性发生的反应路径,即加氢脱氯、C–C桥键断裂、氧化和结合反应。且 CB-209的氧化降解路径在 NiFe2O4体系中比在 Fe3O4体系中更易发生,而其加氢脱氯降解路径在Fe3O4体系中更易发生。这与NiFe2O4降解 CB-209过程中产生的 O2−•有关,而 Fe3O4在反应过程中会部分转变为Fe2O3,为CB-209的加氢脱氯反应提供更多的电子。生成的九氯联苯(NoCB)同分异构体相对含量关系为:CB-207>CB-208>CB-206,表明不同取代位上 Cl的活性相对大小为:间位>对位>邻位,推测这与不同取代位上 C-Cl键解离能和产物的稳定性有关。 3.研究了NiFe2O4催化降解 CB-209过程中对二恶英类(PCDD/Fs)副产物生成的影响,并与 Fe2O3反应体系和 CB-209空白加热体系进行比较。结果显示,各反应体系中2,3,7,8-PCDFs的生成均显著高于2,3,7,8-PCDDs。在30-120 min内,NiFe2O4体系中生成的 2,3,7,8-PCDFs的总浓度和WHO-TEQ比CB-209空白加热体系分别减少了 75.9-99.7%和86-98.4%,且均低于Fe2O3反应体系。NiFe2O4对 PCBs降解过程中 PCDD/Fs副产物生成的阻滞作用与其对 PCBs这一前生体表现出的高降解活性及其本身稳定的化学性质有关。 NiFe2O4对生成的 PCDFs还具有降解作用,其中 OCDF的主要加氢脱氯路径为:OCDF→1,2,3,4,6,7,8-HpCDF→1,2,3,6,7,8-HxCDF→1,2,3,7,8-PeCDF→2,3,7,8-TCDF,加氢脱氯优先发生在 1-和 9-取代位上。 4.通过水热法合成了三元铁基复合氧化物材料,并对材料进行了一系列表征。结果显示,合成的材料为具有高比表面积、高表面活性氧量和丰富表面 B酸、L酸性位的磁性纳米材料。合成的材料在 300 °C下对一氯联苯(CB-1)表现出非常高的降解活性和稳定性,连续反应 10 h后 CB-1的降解效率仍维持在 98%左右,这与材料稳定的物理化学性质及丰富的表面活性氧和酸性位有关。CB-1在三元铁基复合氧化物催化下能发生加氢脱氯、C-C桥键断裂、矿化和氯化反应,且可能以矿化反应为主。 |
英文摘要 | Polychlorinated biphenyls (PCBs) are persistent organic pollutants. The production and use of PCBs have been prohibited, but large amounts of PCBs still exist in closed industrial equipment and large amounts of PCBs have been emitted into the environment. In the environment, PCBs have harmful effects on the health of humans and other biota. Because of the costs involved, the technology available,and public opinion, practical ways of disposing of PCBs are currently limited.Therefore, there is an urgent need for the development of PCB disposal techniques that are economic, safe, effective, and energy efficient. Degradation using novel multicomponent metal oxides might be a new way of disposing of PCBs. In this study, a series of binary and ternary iron-based composite oxides were prepared using oprecipitation, polyol-mediated, and hydrothermal methods, and the PCB degradation activities of the materials produced and the mechanisms involved were studied. The methods used and the main results are described below. 1. A series of NiFe composite oxides, synthesized by coprecipitation, were used to degrade decachlorobiphenyl (CB-209), which was used as a model PCB compound. The results were compared with those found using Fe3O4 prepared by a polyol-mediated process. NiFe2O4 had a larger specific surface area and more abundant surface active oxygen than did the other NiFe composite oxides that were synthesized. Of the materials that were tested, NiFe2O4 had the highest and Fe3O4 had the second highest CB-209 degradation activity. The high activity of NiFe2O4 was attributed to the physicochemical properties of the material and synergistic effects between Ni and Fe in the material. 2. The degradation pathways involved in the thermal catalytic destruction of CB-209 by NiFe2O4 were studied by identifying the intermediate products and superoxide radicals and using theoretical calculations. The results were compared with the results found when CB-209 was degraded using Fe3O4. Less-chlorinated biphenyls, chlorobenzenes, hydroxyl species, and organic compounds were found after performing the degradation tests. This suggested that hydrodechlorination, C–C bridge bond cleavage, and oxidation, accompanied by a combination reaction,occurred competitively during CB-209 degradation by both NiFe2O4 and Fe3O4. The oxidation reaction was more favored when NiFe2O4 was used than when Fe3O4 was used, while the hydrodechlorination was more favored over Fe3O4. The reason would be that the NiFe2O4 reaction system contained highly reactive O2−•species, whereas the Fe3O4 reaction system provided more electrons for hydrodechlorination by the transformation of Fe3O4 into Fe2O3. The amounts produced nonachlorobiphenyl congeners decreased in the order CB-207>CB-208>CB-206, indicating that the activities of the substituent chlorine atoms in CB-209 decreased in the order meta > para > ortho. These activities will have been related to the energy required to break the C–Cl bonds at the different positions. 3. The amounts of PCDD/F byproducts formed during the thermal degradation of CB-209 by NiFe2O4 and Fe2O3 and in a catalyst-free system were evaluated. The total 2,3,7,8-substituted PCDF concentrations and toxic equivalents were 75.9–99.7% and 86–98.4% lower, respectively, after CB-209 had been degraded for 30–120 min in the NiFe2O4 catalyst system than in the catalyst-free reaction system, and were lower than those in the Fe2O3 catalytic system. These results indicate that NiFe2O4 suppressed the formation of PCDFs, and this was attributed to the stability of the chemical structure of NiFe2O4 and the strong activity of NiFe2O4 for degrading biphenyl-like constituents in PCB mixtures. The initial hydrodechlorination of octachlorodibenzofuran formed during the degradation of CB-209 was found to occur at the 1- and 9-positions in preference to the 4- and 6-positions. This initial step will have been followed by subsequent hydrodechlorination steps, the main pathway being 1,2,3,4,6,7,8-HpCDF →1,2,3,6,7,8-HxCDF → 1,2,3,7,8-PeCDF → 2,3,7,8-TCDF. 4. A ternary iron-based composite oxide was prepared using a hydrothermal method and characterized using a number of techniques. The material synthesized was a magnetic nanomaterial with a high surface area, abundant surface active oxygen, and Lewis and Brønsted acid sites. The ternary iron-based composite oxide that was prepared had an excellent activity for the degradation of monochlorobiphenyl (CB-1) at 300 °C and was stable through the degradation process. The activity of the material could be attributed to its stability, abundant surface active oxygen, and acid sites. CB-1 could have been degraded during the thermal catalytic process through hydrodechlorination, C–C bond cleavage,mineralization, and chlorination, and mineralization appears likely to have been the dominant pathway. |
内容类型 | 学位论文 |
源URL | [http://ir.rcees.ac.cn/handle/311016/34332] |
专题 | 生态环境研究中心_环境化学与生态毒理学国家重点实验室 |
推荐引用方式 GB/T 7714 | 黄林艳. 多元铁基复合金属氧化物材料的制备与多氯联苯的降解研究[D]. 北京. 中国科学院研究生院. 2015. |
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