新型核壳结构功能材料的制备及其在环境污染物降解/分析中的应用研究
文献类型：学位论文
| 作者 | 曾滔 |
| 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 | 蔡亚岐 |
| 关键词 | 核壳式复合纳米材料，可控构建，催化还原，氧化降解，磁性固相萃取 Core-shell nanocomposite, Controllable fabrication, Catalytic reduction, Oxidative degradation, Magnetic solid-phase extraction |
| 其他题名 | Fabrication of novel core-shell functionalized nanomaterials and their applications in degradation/analysis of environmental organic pollutants |
| 学位专业 | 环境科学 |
| 中文摘要 | 本论文围绕新型核壳结构环境纳米材料的制备及其在污染物降解和分析中的应用展开研究，分四个部分进行阐述。 1）介绍了核壳结构纳米复合材料的分类、不同形态核壳结构的制备方法以及它们在不同环境领域的应用现状。 2）探讨了基于金纳米颗粒（Au NPs）的不同类型核壳式催化剂的构建及其对硝基苯类化合物还原反应的催化性能。 首先用一种简单、绿色的方法将 Au NPs负载到聚多巴胺包覆的磁性颗粒（Fe3O4@PDA）表面，制得核壳结构的磁性-金纳米复合催化剂。由于PDA中的邻苯二酚基团不但能将 Au3+还原为 Au0，还能牢固地固定生成的 Au NPs，所以本方法无需额外加入其它还原剂和稳定剂。同时，PDA层的厚度和 Au NPs的尺寸及密度可控。将制备的催化剂用于 8种不同硝基苯的催化还原反应，结果表明，这些硝基苯类化合物在被还原成相应的苯胺类化合物的过程中均有较高的转化率。由于催化剂具有较高的磁饱和强度和稳定性，在使用之后可以方便地通过磁性分离回收并重复利用，连续使用 8个循环后仍然具有优良的催化活性，其形貌也基本保持完整。 由于石墨烯的超大比表面积和优良的电子传递效率，我们以石墨烯为载体负载更多 Au NPs，结合磁性纳米颗粒，构建了一种具有高效催化活性的磁性材料-石墨烯-纳米金三元复合物。为了避免磁性颗粒和 Au NPs在石墨烯表面发生团聚和位点竞争，创造性地将两种纳米颗粒分隔在石墨烯内外两面，即将 Fe3O4颗粒包裹在石墨烯片层内部，而将 Au NPs负载到石墨烯片层外表面。在石墨烯的包覆、还原和 Au NPs的沉积等主要步骤中只使用了多巴胺一种化学试剂而无需其他的还原剂、修饰剂和稳定剂，且整个制备过程都是在水相条件、室温下进行，避免了有机溶剂对环境的污染和高温处理的能耗问题，因而技术方法极为经济、环保。由于催化剂中 Au NPs的高负载量（13.58 wt%），在用于邻硝基苯胺的催化还原时，4分钟内即可达到 99%的转化率，且能连续稳定地使用至少10个循环。 Au NPs的粒径大小对催化性能也有着重大影响，我们对铃铛型SiO2@Fe3O4/C双层壳结构进行氨基化修饰，并通过静电作用将高密度超细 AuNPs负载于内部硅球核心表面和双层壳表面，合成了一种新型催化剂。该催化剂由于负载了大量超细粒径的 Au NPs（直径约 2 nm），因此对 4-硝基酚表现出了超强的催化还原性能。此外，双层外壳中的Fe3O4内层为体系提供了磁分离特性，而碳外层除了能够对硝基苯类物质起到快速富集作用外，还为内部的 Fe3O4层提供了保护作用，使之具有更高的稳定性。 3）制备了反应器式的非均相催化剂，并考察了其对环境污染物的催化降解性能。高级氧化技术（Advanced Oxidation Processes，简称 AOPs）是一种实现有机污染物彻底降解的有效方法，因此我们试图通过改造 AOPs中传统非均相催化剂的结构来提高催化剂的稳定性和催化降解污染物的效率。 首先合成了由 Fe3O4纳米核心、Fe3O4/介孔碳双层壳以及二者之间的空腔组成的新型铃铛型 Fe3O4@Fe3O4/C纳米反应器，并将其用于氯酚类污染物的催化氧化降解。H2O2和氯酚可以通过介孔外壳进入到内部空腔，H2O2在这个充满Fe3O4活性位点的微环境中通过类 Fenton反应产生高浓度羟基自由基（OH●），并由此引发氧化降解 4-氯酚（4-CP）的反应。在优化的条件下，Fe3O4@Fe3O4/C材料能够在 60分钟内去除 97%的 4-CP，而裸 Fe3O4 NPs的去除效率仅为28%。由于材料具有超顺磁性，在反应完后可以方便地通过外加磁场进行分离回收，重复利用 4个循环依然能保持 91%的 4-CP去除效率，且保持形貌和结构不发生重大变化。 基于硫酸根自由基（SO4●-）的 AOPs是有别于 Fenton技术的另一种 AOPs，SO4●-相比于 OH●具有更强的电子传递能力，而且更为稳定、可以在更宽的 pH范围生成。我们首次提出将 Co3O4 NPs包埋于中空金属有机框架（Metal-OrganicFrameworks，MOFs）中形成铃铛型 Co3O4@MOFs催化剂，用于高效催化分解单过氧硫酸氢盐（PMS）产生 SO4●-。由于特殊的纳米空腔结构和 MOFs外壳对4-CP分子的富集作用，相对于单纯的 Co3O4NPs，铃铛型 Co3O4@MOFs催化剂在催化PMS降解 4-氯酚的过程中表现出更强的催化降解能力，进一步证实了这种特殊结构和组成的非均相催化剂的优越性。 4）建立了基于铃铛型 SiO2/Fe3O4-C/C18吸附剂的磁性固相萃取-高效液相色谱-荧光检测联用检测水溶液中多环芳烃（ PAHs）的分析方法。我们合成的SiO2/Fe3O4-C/C18吸附剂具有特殊的双壳层-空腔结构，由于外部介孔碳层和内部疏水性空腔对 PAHs具有协同吸附作用，加之介孔外壳对水样中天然有机大分子的体积排阻作用，因此吸附剂具有超强的吸附性能和抗干扰特性。在最佳条件下,5 mg的 SiO2/Fe3O4-C/C18萃取剂半小时内即可定量萃取 500 mL环境水样中的痕量 PAHs。由于具有超顺磁性，完成吸附后可以通过外加磁场方便地将吸附剂从溶液中分离出来，简化了萃取操作。对四种环境水样（河水、污水、雪水和自来水）进行了分析，5种PAHs的加标回收率在 71-108%之间，相对标准偏差在2-7%之间。 |
| 英文摘要 | This dissertation focuses on the preparation of novel core-shell environmental nanomaterials and their applications in degradation or analysis of organic pollutants.It consists of the following four sections. The first part describes the preparation of core-shell nanocomposites with different structure and their applications in a variety of environmental areas. In the second part, three Au NPs based nanocatalysts with core-shell structure are fabricated using different method and their catalytic performance for the reduction of nitrobenzene are studied. Firstly, a simple and green method for the deposition of gold nanoparticles (Au NPs)on the surface of polydopamine (PDA)-encapsulated Fe3O4 nanoparticles is proposed to fabricate a core-shell Fe3O4@PDA-Au nanocatalyst. In the current approach, PDA serves as a reductant as well as a stabilizer so that additional reagents and thermo treatment are not necessary. Both the size of Au NPs and the thickness of PDA layer are tunable. The Au content on Fe3O4@PDA-Au nanocomposites is about 4.3 wt%, which endows the nanocatalyst with high catalytic performance in the reduction of o-nitroaniline to benzenediamine by NaBH4 (with a conversion of 99% in 7 min).Most importantly, the catalyst can be easily recycled by using an external magnetic field due to the high magnetization (39.6 emu g-1) and shows excellent reusability (8cycles with a conversion of >98%). The as-prepared catalyst also show good activity for the reduction of other nitrobenzene analogues. These facilitate the practical application of the catalyst in reduction of nitroaromatic compounds. Graphene is an ideal catalyst support because of its two-dimensional platelike structure, large specific surface area and excellent electron transport property. A novel Fe3O4-graphene-Au multifunctional nanocomposite is therefore synthesized. To integrate Fe3O4 NPs and metal NPs with graphene without any interference or sites competition, Au NPs are decorated on the surface of graphene-encapsulated magnetic icrospheres. The coating and reduction of RGO, as well as the deposition of Au NPs, are greatly simplified by using dopamine as reductant and coupling agent. The overall synthetic procedureis conducted in aqueous solution at room temperature and dopamine is the only reagent involved, which reduce the energy consumption and avoid the possible contamination of the toxic chemicals. The high Au content (13.58 wt%) endows the nanocatalyst with great catalytic performance towards the reduction of o-nitroaniline to benzenediamine by NaBH4 (completely transform within 4 min). Furthermore, the as-prepared catalyst can be easily recovered and reused at least ten times due to the high magnetization and stability. Generally, the catalytic activity of Au NPs depends on the size, loading amount,stability, and gold-support interaction. A facile methodis proposed to load ultra-fine Au NPs (~ 2 nm) onto novel double-shelled yolk-like SiO2@Fe3O4/C nanostructure.The presented strategy involves the one-step coating of a Fe3O4-carbon double-layered shell, the partially etching of the silica cores and the in situ immobilization of Au NPs. The large number of catalytic active sites, together with the advantages of the yolk-shell architecture, make the nanocomposite a perfect catalyst for the reduction of 4-nitrophenol into 4-aminophenol in the presence of NaBH4 (completely transform within 200 s). The outer carbon layer not only protects the Fe3O4 layer from outside harsh condition but also provides additional adsorption sites for Au NPs besides the interior space. Moreover, the inner Fe3O4 layer of the double-layered shell endows the composites with superparamagnetism and thereby simplifys the isolation procedure of the magnetic composite. Therefore, the synthesized catalyst can be easily recovered and reused for at least nine cycles due to the magnetically separable feature and good stability. In the third part, two yolk-like heterogeneous nanocatalysts were synthesized for the catalytic degradation of some environmental pollutants. Advanced oxidation processes (AOPs) are generally recognized as one of the innovative water treatment technologies for degradation of organic pollutants owing to the creation of highly reactive radicals. Hence, we try to design novel and well-defined heterogeneous nanocatalysts to improve the catalytic performance for degradation of pollutants. Yolk-shell nanostructure, whose core and shell both composed of magnetite (designated as yolk-like Fe3O4@Fe3O4/C), is prepared as nanoreactor to accommodate the Fenton-like reaction into its void space for degradation of chlorophenols.Benefiting from the mesoporous shell and the perfect interior cavity of this composite,reactants (H2O2 and chlorophenols) can access and be abundantly confined within the microenvironment where Fe3O4 sites are distributed on the entire cavity surfaces, thus leading to a higher catalytic efficiency compared with the conventional solid catalysts in bulk solution. Under the optimal reaction conditions, 4-chlorophenol (4-CP) can be degraded >97% in the Fe3O4@Fe3O4/C nanoreactor, while only 28% of the degradation were achieved using bare Fe3O4 particles within 60 min. Furthermore,owing to the existence of outermost carbon layer and high-magnetization property, the nanoreactor can be well guarded in long-term use and be easily recovered for several runs. SO4●- based AOPs (SR-AOPs) have attracted increasing research interests as an alternative for conventional Fenton processes because SO4●- is more efficient and stable than OH● to decompose some refractory organic contaminants. Yolk-shell Co3O4@metal-organic frameworks (MOFs) nanoreactor is first proposed through the encapsulation of Co3O4 NPs within hollow MOFs. The mesoporous and adsorptive MOFs shells allow the rapid diffusion of reactant molecules to the encapsulated Co3O4 active sites and the confined high instantaneous concentration of reactants in the local void space is anticipated to facilitate the SR-AOPs. As a proof of concept, the nanoreactor was fully characterized and applied for catalytic degradation of 4-CP in the presence of peroxymonosulfate (PMS). The enhancement of SR-AOPs in the nanoreactor is demonstrated by the result that degradation efficiency of 4-CP reached almost 100% within 60 min by using the yolk-shell Co3O4@MOFs catalysts, as compared to only 59.6% under the same conditions for bare Co3O4 NPs. In the last section, we propose a magnetic solid-phase extraction-high performance liquid chromatography equipped with fluorescence detector (MSPE-HPLC-FLD)analysis method on the basis of magnetic rattle-type sorbent to determine polycycline aromatic hydrocarbons(PAHs) in water samples. The nanomaterial(SiO2/Fe3O4-C/C18) is composed of a SiO2 core, a C18-modified interior cavity and a functional double-layered shell (a magnetic inner shell and a mesoporous carbon outer layer). This material exhibits excellent extraction performance to hydrophobic compounds due to the combined function of the outer carbon shell and the interior hydrophobic cavity. Since the mesoporous shell can allow the diffusion of small molecule targets in and out the hydrophobic cavity while prevent the NOM from entering, the material also exhibits good anti-interference ability. Under the optimized conditions, 5 mg of the sorbent is sufficient to extract the targets from 500 mL of water solution within 30 min. After preconcentrating the targets from water sample,the sorbent could be conveniently isolated from the matrix owing to the inner magnetic layer. Recoveries of PAHs are in the range of 71-108% for four spiked water samples (tap water, snow water, river water, and wastewater) with low relative standard deviation (2-7%), demonstrating the satisfactory recoveries and good method precision. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34116]  |
| 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 | 曾滔. 新型核壳结构功能材料的制备及其在环境污染物降解/分析中的应用研究[D]. 北京. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：生态环境研究中心
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