石墨烯基无机纳米复合材料的可控合成及性能研究

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英文题名：Controllable Synthesis and Properties of Graphene-Based Inorganic Nanocomposites 作者：季振源 论文级别：博士 学科专业名称：材料学 中文关键词：石墨烯 ; 纳米复合材料 ; 制备 ; 催化 ; 超级电容器 英文关键词：graphene ; nanocomposite ; synthesis ; catalysis ; supercapacitor 学位年度：2014 导师：沈小平 学科代码：080502 学位授予单位：江苏大学 论文提交日期：2014-05-01

摘要

由于石墨烯具有独特的结构柔韧性、超高的电导率、优异的热稳定性以及巨大的比表面积,石墨烯在纳米材料的制备与应用领域具有广阔的发展前景,将拥有优异性能的石墨烯与其他功能纳米材料相结合制备石墨烯基纳米复合材料,是拓展石墨烯应用范围的有效途径。基于此,本论文旨在合成多种形貌和尺寸可控的石墨烯基二元以及三元纳米复合材料,发展制备石墨烯基纳米复合材料的新方法、探索其合成机理、考察复合结构的形貌和微结构,并将其运用于光催化、超级电容器、对硝基苯酚(4-NP)催化加氢等领域中。主要研究内容如下：
     1.利用Ag+与氧化石墨烯(GO)片层之间的静电相互作用,成功的制备出一种新颖的Ag2O/GO可见光光催化材料,并利用X-射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对所得产物进行表征。通过对亚甲基蓝(MB)的光催化降解来评价Ag2O/GO的光催化活性。结果表明,在可见光照射下,Ag2O/GO纳米复合材料光催化降解MB的催化性能明显高于单独Ag2O纳米粒子。催化活性提高的原因主要归因于与GO复合之后,Ag20纳米粒子的尺寸变小,光生电子-空穴对能有效的进行分离,吸附性能也显著提高。此外,我们研究了Ag2O/GO催化降解MB的动力学过程,提出了MB光催化降解的机理,为发展高活性的可见光响应的光催化剂提供了方向。
     2.采用原位生长与自组装的方法,成功的将Ce02纳米粒子复合到还原氧化石墨烯(RGO)片的表面。所得产物用XRD、Raman和TEM进行表征。结果表明与原位生长途径相比,采用自组装途径制备的RGO/CeO2纳米复合材料,其Ce02纳米粒子负载更为均匀,且负载密度可以通过简单的改变Ce02的起始加料量而加以调控。与RGO复合之后,Ce02纳米粒子的光生电子-空穴对能有效的进行分离,吸附性能也显著提高。在模拟太阳光的照射下,RGO/CeO2纳米复合材料光催化降解MB的活性明显优于Ce02纳米粒子。而且RGO/CeO2的光催化活性可以通过改变Ce02的负载量而简单加以调节。这种简单的自组装方法可以推广到在石墨烯表面负载分布高度均匀的其他功能纳米材料,从而在催化、传感和能源等方面得到应用。
     3.采用自组装与高温煅烧相结合的方法成功制备出具有优异超级电容性能的RGO/CeO2纳米复合材料。系统研究了其结构、形貌与组成。发现RGO作为载体能有效阻止CeO2纳米粒子在煅烧时发生团聚。在5mV s-1的扫速下,RGO/CeO2作为超级电容器电极材料的单位比电容为265F g-1,且循环1000次后电容不发生明显衰减。该复合材料电化学性能提高的原因可归因于RGO与Ce02的协同作用机制。优异的电化学性能使得RGO/CeO2纳米复合材料在超级电容器领域具有潜在的应用价值。
     4.利用十八胺(ODA)作为还原剂与分散剂,我们开发出了一种合成半导体量子点(SQDs)/石墨烯复合材料的通用方法,成功地将一系列金属氧化物与硫化物SQDs均匀的附着于RGO的表面。采用XRD, Raman,红外光谱(FT-IR),X-射线光电子能谱(XPS)与TEM等对合成产物进行了表征。通过紫外-可见(UV-vis)与光致发光(PL)光谱系统研究了制备的RGO/SQDs纳米复合材料的光学性质。我们将RGO/NiO应用于超级电容器电极材料,以探索RGO/SQDs纳米复合材料的潜在应用。研究表明,RGO/NiO显示出增强的电容特性与优异的循环稳定性能。这类RGO/SQDs纳米复合材料在能源、催化、光敏、光电等领域具有良好的应用前景。
     5.发展了一种简易的两步合成方法,将贵金属(Pt、Au和Ag)纳米粒子成功复合于CeO2修饰的RGO片表面。Pt、Au和Ag纳米粒子的尺寸分别为5、2与10nm。以NaBH4还原4-NP为模型反应,考察了制备的贵金属/RGO/CeO2二元纳米复合材料的催化性能。发现在这些三元复合体系中,CeO2的引入可以显著提高RGO/Pt、RGO/Au和RGO/Ag纳米复合材料的催化性能,同时提出了三元复合体系催化性能增强的可能机理。
     6.采用一种简易的环境友好的合成方法制备出由RGO、Fe3O4和Ag纳米粒子构成的三元复合体系。研究表明,Ag与Fe3O4纳米粒子密集而均匀的附着于RGO的表面。RGO/Ag/Fe3O4显示室温超顺磁行为。Fe3O4的引入可以调节Ag纳米粒子在RGO表面的分散,减小其粒径,同时有效提高RGO/Ag纳米复合材料对4-NP加氢的催化性能。催化反应结束后,RGO/Ag/Fe3O4可以在外磁场的作用下方便地回收再利用。我们提出了Ag纳米粒子粒径减小以及三元复合体系催化性能增强的可能机理。RGO/Ag/Fe3O4简易的制备方法以及优异的磁性与催化性能对设计合成具有多种功能的其他石墨烯基三元纳米复合材料具有参考价值。
Graphene has been emerging as a fascinating material because its remarkable structural flexibility, high electronic conductivity, superior thermal stability, large specific surface area and wide-spread potential applications in energy, environment, nanoelectronics and nanodevices. The combination of these attractive properties of graphene with the excellent characteristics of other functional nanomaterials has become a popular pathway for achieving applications in multiple fields. In this paper, we try to develop new methods to fabricate graphene-based binary and ternary nanocomposites with controlled shape and size, study the formation mechanism of the graphene-based nanocomposites, and explore their potential applications in many fields such as photocatalysis, supercapacitor and the reduction of4-nitrophenol (4-NP). The main points are as follows:
     1. A novel Ag2O/GO (GO=graphene oxide) nanocomposite as a visible-light induced photocatalyst has been fabricated by a simple solution route. The electrostatic interaction between positively charged Ag+and negatively charged GO sheets is responsible for the formation of Ag2O/GO nanocomposite. The well anchoring of Ag2O nanoparticles on the GO nanosheets was verified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Photocatalytic degradation of Methylene Blue (MB) under visible-light irradiation was conducted to evaluate the photocatalytic performance of the Ag2O/GO nanocomposites. Due to the enhanced adsorption performance, smaller size of Ag2O nanoparticles and improved separation of electron-hole pairs after incorporation with GO sheets, the Ag2O/GO nanocomposites show enhanced photocatalytic activity compared with bare Ag2O nanoparticles. In addition, the kinetics of the photocatalytic degradation reaction and a detailed photocatalytic mechanism were also proposed. Our study paves a way to design highly efficient visible-light responsive photocatalysts for the removal of organic pollutants for water purification.
     2. Two different strategies, including in situ growth and self-assembly approach, have been developed to load CeO2nanoparticles onto reduced graphene oxide (RGO) nanosheets. The microstructure and morphology of the as-synthesized RGO/CeO2 nanocomposites were investigated by XRD, Raman and TEM. The results revealed that CeO2nanoparticles with well-controlled size and a uniform distribution on RGO sheets with tunable density can be achieved through the self-assembly approach. The significantly enhanced photocatalytic activity of the RGO/CeO2nanocomposites in comparison with bare CeO2nanoparticles was revealed by the photocatalytic degradation of MB under simulated sunlight irradiation, which can be ascribed to the enhanced separation of electron-hole pairs and enhanced adsorption performance due to the presence of RGO. A suitable loading content of CeO2on RGO was found to be crucial for optimizing the photocatalytic activity of the nanocomposites. It is expected that this convenient assembly approach with high controllability can be extended to the attachment of other functional nanoparticles to RGO sheets, and the resultant RGO-supported highly dispersed nanoparticles are attractive for catalysis and power source applications.
     3. RGO/CeO2nanocomposites with improved capacitance performance were designed and synthesized by a facile two-step approach, the assembly followed by thermal annealing process. The structure, morphology and composition of the resulting RGO/CeO2nanocomposites were studied systematically. The presence of RGO can prevent the aggregation and control the structures of the CeO2nanocrystals in annealing process. The nanocomposites were used as electrode materials for supercapacitor application. We demonstrate that it is capable of delivering high specific capacitance of265F g-1at a scan rate of5mV s-1with excellent cycling stability. The enhanced high-rate electrochemical activity may be ascribed to the synergetic effects between RGO and CeO2. The excellent power performance offer great promise for applications in electrode material for supercapacitors.
     4. A facile and general method was developed for the first time to synthesize a variety of semiconductor quantum dots (SQDs) supported on reduced graphene oxide (RGO) sheets, including RGO/metal oxides and RGO/metal sulfides nanocomposites. The obtained nanocomposites were investigated by Raman spectroscopy, XRD, Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS) and TEM. It was found that by using octadecylamine (ODA) as both reductive and dispersing agent, the resulting metal oxides and sulfides SQDs were all homogeneously deposited on the surface of RGO sheets. The optical properties of the as-synthesized RGO/SQDs nanocomposites were studied through Ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy. To demonstrate one potential application, the RGO/NiO nanocomposites were used as electrode materials for electrochemical supercapacitor, which exhibit enhanced capacitive activity and long cycle life. It is expected that our prepared RGO/SQDs nanocomposites could serve as promising candidates for power source, catalysis, optical sensitizer and optoelectronic applications.
     5. We developed a facile two-step approach to disperse noble metal (Pt, Au and Ag) nanoparticles on the surface of CeO2functionalized reduced graphene oxide (RGO) nanosheets. It was shown that Pt, Au and Ag with average diameters of about5,2and10nm are well dispersed on the surface of RGO/CeO2. The reduction of4-NP to4-aminophenol (4-AP) by NaBH4was used as a model reaction to quantitatively evaluate the catalytic performance of the as-synthesized RGO-based ternary nanocomposites. In such triple-component catalysts, CeO2nanocrystals provide unique and critical roles for optimizing the catalytic performance of noble metallic Pt, Au and Ag, allowing them to express enhanced catalytic activities in comparison with RGO/Pt, RGO/Au and RGO/Ag catalysts. In addition, a possible mechanism for the enhanced catalytic activities of the ternary catalysts in the reduction of4-NP was proposed.
     6. A three-component composite composed of RGO, Fe3O4and Ag nanoparticles was designed and synthesized by a simple and environmentally friendly strategy. It was shown that Ag and Fe3O4nanoparticles are uniformly dispersed on the surface of RGO sheets. Magnetic studies revealed a room-temperature superparamagnetic behavior of the RGO/Ag/Fe3O4nanocomposites. The results revealed that the presence of Fe3O4not only has a great influence on the size of the Ag nanoparticles formed on RGO, but also can significantly improve the catalytic activity and stability of them towards the reduction of4-NP. Moreover, after completion of the reaction the nanocomposit catalysts can be easily re-collected from the reaction system by a magnet. Possible mechanisms for the reduced size of Ag nanoparticles and the enhanced catalytic performance of RGO/Ag nanocomposites after combining with Fe3O4were proposed. The facile synthesis of RGO/Ag/Fe3O4nanomaterials together with their superior magnetic and catalytic performance provides a potentially new approach for the design and construction of graphene-based ternary nanostructured composites with various functions.

引文

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