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题名: 纳米Fe3O4的非均相Fenton反应动力学过程和微界面机制
作者: 何洁
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: 王东升
关键词: 非均相Fenton反应,反应动力学,微界面机制,原位ATR-FTIR,Fe3O4,heterogeneous Fenton reaction, reaction kinetics, micro-interfacial mechanisms, in-situ ATR-FTIR, Fe3O4
其他题名: Kinetic Process and Micro-interfacial Mechanisms of Heterogeneous Fenton Reactions Catalyzed by Nano-Fe3O4
中文摘要:       非均相Fenton反应能在中性pH条件下,利用固体催化剂与H2O2反应产生的活性氧物种(ROS),高效去除水中难生物降解的有机物,且催化剂可重复利用,因而在水处理领域具有巨大应用前景。自二十世纪九十年代以来,非均相Fenton反应的研究不断涌现,主要集中在高效催化剂的研发,但对于反应体系的作用机理尚不明确。深入研究典型的铁基材料催化的非均相Fenton反应机理,将有助于研发高效催化剂,早日实现非均相Fenton反应的工业化应用。
     本文基于Fe3O4催化的非均相Fenton反应动力学过程和微界面机制,系统地研究了Fe3O4的表面性质、有机物的特性、以及不同共存配体对于非均相Fenton反应的影响机制。主要研究工作和成果如下。
(1)通过化学共沉淀法制备了纳米级Fe3O4(nano-Fe3O4),对比研究了自制纳米级Fe3O4和商品微米级Fe3O4分别催化的非均相Fenton体系的反应动力学过程。结果表明,Fe3O4通过表面反应催化H2O2分解。Fe3O4/H2O2氧化邻苯二酚也为非均相反应机制主导。具有大比表面积的nano-Fe3O4,能提供更多表面活性位,加速H2O2活性分解,产生更多·OH和大量HO2·/O2·-,从而加速邻苯二酚的氧化。但两种Fe3O4/H2O2氧化邻苯二酚体系的DOC去除率和氧化效率E值相当,可能由Fe3O4本身的化学特性决定。
(2)分别研究了邻苯二酚、4-氯邻苯二酚,在nano-Fe3O4催化的非均相Fenton体系中的氧化动力学过程和界面反应过程。结果表明,nano-Fe3O4/H2O2体系可在3 h内完全去除水中邻苯二酚或4-氯邻苯二酚,目标有机物的氧化曲线遵循二级反应动力学方程。4-氯邻苯二酚的氧化速率更大,可能与其略低的吸附量和本身的化学特性有关。氧化产生的氯代有机物,可能导致了其较低的矿化度。邻苯二酚的氧化伴随醚类、二聚体类物质的产生与吸附,以及碳中心自由基的产生,可能与其较高的矿化程度有关。两种有机物的非均相Fenton氧化体系中,H2O2主要通过表面反应产生·OH和大量HO2·/O2·-,进攻近催化剂表面溶液相中的目标有机物。并且伴随羧酸类物质的产生和吸附。
(3)将配体磷酸盐引入nano-Fe3O4/H2O2氧化邻苯二酚的体系。结果表明,磷酸盐能强烈吸附于nano-Fe3O4表面,与H2O2竞争表面位,抑制H2O2的分解和·OH的生成,从而降低邻苯二酚的氧化速率和DOC去除率。吸附的磷酸盐虽然会与邻苯二酚竞争Fe3O4表面吸附位,但并不影响界面上有机物的氧化反应。随着非均相Fenton反应的进行,磷酸盐与溶出铁形成磷酸铁沉淀,沉积于Fe3O4表面,也可能影响非均相Fenton反应。
(4)溶液中的EDTA和表面吸附的EDTA均可加速nano-Fe3O4/H2O2体系中邻苯二甲酸二甲酯(DMP)的氧化。溶液中的EDTA通过与Fe3O4表面络合,促进Fe3O4溶出,从而引发由Fe2+/3+-EDTA增强的均相Fenton反应。同时,溶液中的EDTA也会被反应产生的ROS进攻。另一方面,吸附的EDTA会与H2O2竞争Fe3O4表面活性位,明显抑制H2O2分解。但是, H2O2活性分解产生的·OH和HO2·/O2-·并未明显减少。吸附的EDTA通过加强,近催化剂表面区域的DMP对ROS的有效利用,而加速DMP的氧化。
英文摘要:       Heterogeneous Fenton reactions can generate reactive oxygen species (ROS) from H2O2 decomposition catalyzed by solid catalysts in neutral pH range, so as to remove nonbiodegradable organic compounds in water with reusable catalysts. Therefore, it has become a potential technology in the field of water treatment. There has been more and more researches on heterogeneous Fenton reactions since 1990s, mainly focusing on the development of highly efficient catalysts. However, the mechanisms of heterogeneous Fenton reactions remains unclear. It is of great importance to further investigate the mechanisms of heterogeneous Fenton reactions catalyzed by characteristic iron based materials for its industrial applications and for the development of highly efficient catalysts.     
        This thesis systematically investigated the mechanisms of the effects of Fe3O4 surface characteristics, the characteristics of organic compounds, and the ligands on the heterogeneous Fenton reactions, based on kinetic process and micro-interfacial mechanisms of the heterogeneous Fenton reactions catalyzed by Fe3O4. The primary researches and results are as follows.
(1) Nano sized Fe3O4 was prepared by chemical coprecipitation method. The reaction kinetics of the heterogeneous Fenton systems catalyzed by nano-Fe3O4 and micro-Fe3O4 respectively were compared. Results showed that H2O2 decomposition was catalyzed by the surface of Fe3O4. And the oxidation of catechol in Fe3O4/H2O2 system was also controlled by heterogeneous reactions. Due to its large surface area, nano-Fe3O4 could provide with more active sites, thus promoting the active decomposition of H2O2 to generate more ·OH and large amounts of HO2·/O2·-, leading to the enhanced oxidation of catechol. However, the DOC removal and oxidation efficiency (E value) were similar in the two systems, probably due to the characteristic of Fe3O4.
(2) The oxidation kinetic process and the interfacial reaction process of catechol and 4-chlorocatechol in the heterogeneous Fenton systems catalyzed by nano-Fe3O4 were investigated respectively. Results showed that catechol or 4-chlorocatechol could be completely removed within 3 h in nano-Fe3O4/H2O2 system. And the oxidation curves of the target organics could be well fitted by the second order kinetic equations.4-chlorocatechol was oxidized faster, possibly due to the unique redox properties and its lower adsorption amount. The generated chloro-byproducts probably led to the lower mineralization. On the other hand, ethers or dimers were generated and adsorbed during the oxidation of catechol, together with the generation of carbon-centered radicals, all of which might lead to the higher mineralization. In both heterogeneous Fenton oxidation systems, ·OH and HO2·/O2·- were generated by surface decomposition of H2O2, and attacked the target organics in the close proximity of Fe3O4 surface. Meanwhile, carboxyl acids were generated and adsorbed.
(3) Phosphate was then introduced to the oxidation of catechol in nano-Fe3O4/H2O2 system. Results showed that phosphate adsorbed on nano-Fe3O4 surface strongly, and competed with H2O2 for the surface sites, leading to the inhibited H2O2 decomposition and ·OH generation. Therefore, the oxidation rate of catechol and DOC removal was reduced in the presence of phosphate. Though the adsorbed phosphate competed with catechol for the surface adsorption sites, it didn’t affect the oxidation of organics on the interface. As the heterogeneous Fenton reactions continued, iron phosphate precipitation was formed by the reaction between phosphate and the leached iron, and precipitated on nano-Fe3O4 surface, which might also influence the heterogeneous Fenton reactions.
(4) Both the EDTA in solution and the EDTA adsorbed on the surface could accelerate the oxidation of dimethyl phthalate (DMP) in nano-Fe3O4/H2O2 system. EDTA added in solution could complex with Fe3O4 surface, promoting the dissolution of Fe3O4, which led to the enhanced homogeneous Fenton reaction catalyzed by Fe2+/3+-EDTA complex. Meanwhile, the aqueous EDTA was also attacked by the generated ROS. On the other hand, though the adsorbed EDTA competed with H2O2 for the surface active sites and inhibited H2O2 decomposition, the generations of ·OH and HO2·/O2-· from H2O2 decomposition were not obviously inhibited. Therefore, the adsorbed EDTA accelerated DMP oxidation by increasing the efficient utility of ROS by DMP in the close proximity of the catalysts surface.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34329
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
何洁. 纳米Fe3O4的非均相Fenton反应动力学过程和微界面机制[D]. 北京. 中国科学院研究生院. 2015.
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