【作者】 胡晓斌；

【导师】 孙成；

【作者基本信息】 南京大学 ， 环境科学， 2012， 博士

【摘要】 近年来,环境激素污染已引起人们的广泛关注,环境激素危害已成为全球性的重大环境问题。目前,非均相Fenton催化作为一种高级氧化技术正在被广泛研究用来催化降解有机污染物。开发一种易分离回收,铁流失量小,可重复使用,催化性能稳定,对水中环境激素有较好吸附能力的非均相Fenton催化剂己成为Fenton催化研究的一个重要方向。本论文通过在表面改性的MWCNTs上负载磁性四氧化三铁(Fe3O4)纳米晶体,得到Fe3O4/MWCNTs纳米复合粒子催化剂；以被广泛使用的人工环境激素甲基睾酮(MT)为目标物,研究了催化剂对水中痕量MT的吸附性能,在非均相Fenton, UV-Fenton, MW-Fenton体系中,详细考察了影响MT降解的因素,探讨了MT降解的反应机理。主要内容归纳如下：(1)采用多种氧化法对MWCNTs进行表面改性,通过液相化学沉积反应,在改性的MWCNTs表面生长出规则的正八面体构型的磁性Fe3O4纳米晶体,形成负载牢固的纳米复合物Fe3O4/MWNTs。所负载的Fe3O4粒子直径在40-100nm之间；复合物的比表面积为20.58m2/g,分散性能好,有较强的磁性,便于回收。(2)考察了Fe3O4/MWCNTs对水中痕量MT吸附能力。常温下,吸附剂用量为2gL-1,MT的初始浓度为212μgL-1时,Fe3O4/MWCNTs可吸附水中约90%的MT,而同样浓度的Fe3O4只能吸附10%左右。pH值的变化对其吸附能力无明显影响。在Fe3O4/MWCNTs-H2O2体系中,当pH=5.0；T=20℃,H2O2初始浓度为5.3mmol L-1,Fe3O4/MWNTs用量为2gL-1的条件下,初始浓度为212μgL-1的MT在8h内可降解85.9%。pH值的变化对Fe3O4/MWCNTs-H2O2体系降解MT的影响明显。在pH值2.5至8范围内,随着pH值的降低,MT的降解速率明显加快。Fe3O4/MWCNTs在Fenton反应中显示了良好的催化稳定性,在pH值为3.5,H2O2浓度为20mmol L-1时,铁流失量低于1mgL-1。7次重复使用后对MT的8h降解率为79.4%。非均相Fenton反应是MT降解的主要路径,而由催化剂的铁流失导致的溶液中均相Fenton反应是MT降解的次要路径。(3)按照准一级反应模型分别计算了MT和H2O2在Fe3O4/MWCNTs-H2O2体系中的降解速率和分解速率,估算了反应—扩散模量,认为反应物在催化剂表面的化学反应过程是整个反应的控制步骤。MT在催化剂表面附近微区内的富集有利于其与H2O2竞争·OH,从而提高了MT的降解效率。根据主要中间体的可能分子结构以及采用理论计算得到的MT分子的FEDs和C-H、O-H的键离解焓(BEDs),推测了·OH与MT分子首先发生加成和抽氢反应的位置。ELISA实验表明：Fenton氧化在降低MT的浓度的同时,也相应降低了反应体系雄激素活性。(4)微波能加速MT的降解。相比单纯的非均相Fenton, UV的协同作用可使MT更快转化为小分子化合物。紫外辐射强度的增加能加快MT的降解。更多还原

【Abstract】 In recent years, the environmental hormone pollution has attracted much attention among the people. The endangers of environmental hormones to the living things have become one of the most important environmental problems in the world at present. Nowadays, as an important advance oxidation processes (AOPs), heterogeneous Fenton method is being widely studied for the degradation of organic pollutants. To develop a heterogeneous Fenton catalyst which has good structural stability, little iron leaching, simple separation, stable catalytic activity in repetitive reaction cycle is an important trend in the Fenton catalysis.A novel Fenton oxidation catalyst, the ferroferric oxide nanoparticles decorated multiwalled carbon nanotubes (Fe3O4/MWCNTs) was successfully prepared. The widely used artificial hormone17a-methyltestosterone (MT) was chosen as a target contaminant. The adsorption capacity of the nanocomposites for trace MT in water was studied. The catalytic property of the catalyst in heterogeneous Fenton, UV-Fenton and MW-Fenton systems was investigated. The degradation mechanism and the reaction conditions that influence the MT degradation efficiency were discussed. (1) The surface of the MWCNTs was functionized by several oxidation methods. The regular growth of ferroferric oxide crystal on MWCNTs was achieved by in situ oxidation of Fe2+in hot alkaline solution. Inverse-spinel ferroferric oxide nanoparticles decorated MWCNTs (Fe3O4/MWCNTs) was obtained. The diameters of the loaded octahedron Fe3O4nanoparticles range from40to100nm. The specific surface area of the catalyst was20.58m2g-1. The catalyst has good dispersion property, strong magnetism and convenient recovery.(2) The adsorption capacity of Fe3O4/MWCNTs for trace MT in water was investigated. About90%MT was absorbed onto the catalyst when the conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2gL-1, pH=7.0and T=20℃, and just about10%of MT was absorbed by the same amount of Fe3O4. The adsorption of MT on Fe3O4/MWCNTs or Fe3O4in aqueous solution had no significant change when pH ranged from3-10. The degradation efficiency of MT in8h was85.9%for the first oxidation when the initial conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2g L-1, pH=5.0,[H2O2]=5.3mmol L-1under normal temperature and pressure. The change of pH has significant influence on the degradation efficiency of MT. The degradation efficiencies increased with the initial pH decreasing in the wide pH range of8.0-2.5. The nanocomposites displayed good catalytic stability. The leached iron concentration was lower than20mmol L-1in8h degradation time when the initial conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2g L-1, pH=3.5,[H2O2]=20mmol L-1. The MT degradation performance on the reused catalyst showed a slight difference with the first oxidation cycle. The degradation efficiency of MT was79.4%for the seventh oxidation cycle. The homogeneous reaction by the leached iron species from the catalyst just made a very small contribution to the MT degradation. The heterogeneous Fenton-like oxidation reaction occurred on the catalyst surface was the main pathway of the MT degradation.(3) The MT degradation and H2O2analysis approximately followed a pseudo-first-order reaction in kinetics under degradation conditions. The reaction-diffusion modulus implied that the average rate of the reaction of MT and H2O2on the catalyst surface was far slower than its diffusion rate to the surface through the external film. Therefore, the intrinsic reaction on the oxide surface was expected to be the rate-limiting step for the degradation process. The enriched MT in the very near vicinity of the catalyst surface might lead to a more efficient·OH scavenging action when competed with H2O2. The degradation mechanism of MT by Fe3O4/MWCNTs catalysis was discussed on the basis of analysis of the intermediates and the theoretical calculation of frontier electron densities and bond dissociation enthalpies of C-H and O-H of MT molecule. The estrogenic activity of the treated water was investigated during the catalytic reactions by human androgen ELISA test. The results showed that Fe3O4/MWCNTs-H2O2system could not only degrade MT but also remove its androgenic activity.(4) The MT degradation could be accelerated by the coupling of MW radiation with the heterogeneous Fenton reaction. The coupling of UV radiation could make MT transformed to be smaller compounds faster. The degradation efficiency increased with the rising of the UV irradiation intensity.更多还原