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题名: 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
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.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34116
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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.
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