氧化石墨烯的化学剥离法制备、还原与应用探索

IMR OpenIR

	氧化石墨烯的化学剥离法制备、还原与应用探索
	赵金平
学位类型	博士
导师	成会明 ; 任文才
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	氧化石墨烯化学剥离法还原透明导电膜吸附材料 Graphene Oxide Chemical Exfoliation Reduction Transparent Conducting Film Adsorption Material
摘要	"石墨烯是一种新型二维碳材料，具有独特的晶体结构特征，呈现出优异的电学、光学、热学、力学等物理化学性质，在纳电子器件、高灵敏传感器、透明导电膜、功能复合材料、储能、催化等领域有着广阔的应用前景。因此，自2004年以来石墨烯迅速成为材料科学和凝聚态物理领域的研究前沿。化学剥离法是一种低成本宏量制备石墨烯的有效方法，但所得石墨烯可控性差，并且含氧官能团的存在使其导电性较差，限制了其在电学相关领域的应用。本论文以化学剥离法控制制备石墨烯为切入点，发展其高效还原方法，并在此基础上探索其在透明导电薄膜和水净化方面的应用。取得的主要结果包括：一、发展了温和氧化剥离法，制备出尺寸可达200 μm的氧化石墨烯，并一定程度上实现了石墨烯的尺寸控制制备由于化学剥离过程中强氧化和剥离会不可避免地导致氧化石墨烯的破裂，因此采用化学剥离法制备的石墨烯的尺寸通常较小，面积大多小于100 μm2。我们系统研究了石墨原料的结构、氧化和剥离工艺及离心方式对氧化石墨烯尺寸的影响，通过使用大尺寸的天然鳞片石墨作为原料，在温和氧化剥离条件下，结合多步离心方法制备出大尺寸氧化石墨烯，其最大面积可达~40000 μm2。研究发现，氧化石墨烯的尺寸与氧化石墨中的C-O含量有密切关系：氧化石墨的C-O含量越高，所得氧化石墨烯的尺寸越小。在此基础上，通过改变氧化条件，选择性制备出面积为~100-300、~1000-3000 和~7000 μm2的氧化石墨烯，为研究尺寸对石墨烯性能的影响奠定了基础。二、提出氢碘酸低温高效无损还原方法，使用大尺寸氧化石墨烯制备出性能优异的石墨烯透明导电薄膜通过还原处理去除氧化石墨烯的含氧官能团、恢复其sp2结构是实现其在电学相关方面应用的前提。化学还原和高温热处理是两种常用的氧化石墨烯还原方法。其中，化学还原可在低温下进行，但还原效果较差；高温热处理虽然可以获得较好的还原效果，但不能在低熔点基底上实现石墨烯的还原。我们在对碳与其他元素间键合能力分析的基础上，发展了一种基于亲核取代反应的氧化石墨烯低温高效还原方法，即卤化还原法。厚度为5 μm的氧化石墨烯薄膜在100 °C、55%的氢碘酸中还原1 h后的电导率可达298 S/cm，C/O比可达12，远优于其他化学还原方法的还原效果，并且保持了氧化石墨烯薄膜原有的完整性和柔性，且强度有所提高。在此基础上采用不同尺寸氧化石墨烯，利用液-固-气自组装方法制备了氧化石墨烯薄膜，并用氢碘酸进行了还原。研究发现，所得石墨烯透明导电膜的面电阻随石墨烯尺寸的增加而降低，这主要是由于石墨烯尺寸的增加降低了石墨烯之间的搭接电阻。采用平均面积为~7000 μm2的氧化石墨烯制备的透明导电膜在透光率为78%时，面电阻为840 Ω/sq，该数值与在Ni上CVD生长的石墨烯的性能相当，为低成本制备石墨烯透明导电薄膜奠定了基础。三、采用自组装方法制备出石墨烯海绵，对染料和油类表现出优异的吸附性能，在水净化方面具有巨大的应用潜力水污染已成为全球性问题，寻找高效、廉价的方法进行污水处理对于人类的生存和发展非常重要。吸附法由于能够有效去除多种污染物、易于操作以及可得到高质量水源等优势而被广泛用于污水处理，而吸附材料的选择至关重要。我们通过在氧化石墨烯溶液中添加硫脲，用水热方法将氧化石墨烯组装成一种新型石墨烯体材料—石墨烯海绵。这种材料具有可以调控的孔结构和表面特性，并且具有很好的机械加工性能。研究表明，石墨烯海绵对于染料、有机溶剂和油类表现出很好的吸附性能，如亚甲基蓝的吸附量可达184 mg/g，柴油的吸附量可达129 g/g。通过简单处理可将吸附物有效去除，且不会造成结构的变化，因此可以循环用于水中污染物的吸附。通过研究石墨烯海绵的结构与污染物吸附性能之间的关系，发现染料的吸附性能取决于石墨烯海绵表面所带的电荷和比表面积，而油类的吸附主要取决于石墨烯海绵的比表面积，说明石墨烯海绵针对不同吸附物具有不同的吸附机制。该结果为石墨烯在水净化方面的应用奠定了基础。"
其他摘要	"Graphene, a monolayer of sp2-bonded carbon atoms, has been attracting great interest because of its fascinating electronic, optical, thermal, and mechancal properties, and a wide range of potential applications such as nanodevices, sensors, transparent conductive films, composites, energy storage and catalysis, etc. Among all the developed preparation methods, chemical exfoliation has been widely used to produce graphene for various intriguing bulk applications due to its low cost, easy scalability and high yield. However, graphene prepared by chemical exfoliation suffers from poor controllability and low conductivity because of the presence of many defects and oxygen-containing fuctional groups. In this dissertation, we mainly studied the controlled synthesis and reduction of graphene oxide by chemical exfoliation, and explored its potential applications as transparent conductive films and adsorption materials. The main results include: 1. Developed a mild chemical exfoliation method to prepare graphene oxide (GO) with a size up to 200 μm, and realized, in some extent, the size-controlled synthesis of GO sheets Because of the unavoidable breaking of GO sheets during vigorous oxidation and exfoliation processes, the GO sheets obtained by chemical exfoliation are usually small, mostly with an area in the order of 100 μm2. We systematically studied the effect of the structure and size of graphite and the oxidation, exfoliation and centrifugation conditions on the structure of GO. In order to prepare large-area GO sheets, three modifications were made in our experiments: 1) using graphite with a large lateral size (nature flake graphite with an average size of 500-600 μm) as starting material to prepare large-area graphite oxide; 2) applying mild oxidation and sonication to avoid the over-cracking of graphite during oxidation and exfoliation; 3) using a two-step centrifugation to successively remove thick multilayer flakes and small flakes. By the above modifications, we have realized the preparation of large-area GO sheets using chemical exfoliation. The maximum area of the GO sheets obtained can reach ~40000 μm2. In addition, we found that the GO area is strongly correlated with the C-O content of the graphite oxide, which enables the area of GO sheets to be controlled. By simply changing oxidation conditions, GO sheets with an average area of ~100-300, ~1000-3000 and ~7000 μm2 were selectively synthesized. 2. Proposed a low-temperature, highly-efficient and nondestructive HI reduction method, and prepared high-performance transparent conductive films combined with large-area GO sheets Removing oxygen-containing functional groups in GO sheets to restore their sp2 conjugated graphene network is the prerequisite for the electrical conductivity-related applications of GO. Chemical reduction and high-temperature annealing are two main reducting methods of GO sheets. Chemical reduction can operate at low temperature, but only yield moderate optoelectronic properties; high-temperature annealing at 1100 °C yields high degree of reduction, but high-temperature reduction must be avoided for GO films on substrates with low melting point, such as plastics and glass. Based on the analyses on the bond energy between carbon and other elements, we developed a low-temperature but highly-effective HI reduction method to reduce GO films based on the nucleophilic substitution reaction. GO films reduced for 1 h at 100 °C in 55 % HI acid show an electrical conductivity as high as 298 S/cm and a C/O ratio above 12, both of which are much higher than those reduced by other chemical methods. Morevoer, the reduction process maintains the good integrity and flexibility, and even improves the strength and ductility, of the original GO films. For transparent conductive film applications, thin GO films were fabricated by self-assembly on a liquid/air interface and reduced by HI acid. We found that the sheet resistance of the reduced GO (rGO) films decreases with increasing sheet area at the same transmittance because of the decrease in the number of inter-sheet tunneling barriers. The rGO film made from GO sheets with an average area of ~7000 μm2 shows a sheet resistance of 840 Ω/sq at 78% transmittance, which is comparable to that of graphene films grown on Ni foil by chemical vapor deposition. 3. Fabricated a graphene macrostructure, graphene sponges (GSs), by hydrothermal treatment of GO sheets using thiourea, and studied the use of GSs for efficient and repeatable adsorption and desorption of water contaminations One of the most pervasive problems throughout the world is inadequate access to clean water and sanitation. Therefore, seeking highly-efficient, low-cost and robust methods to disinfect and decontaminate water from source to point-of-use are highly desired. Adsorption is extensively growing in use for water treatment due to its ability to remove different types of contaminations and produce high-quality water, and ease of operation. We have modified GO sheets and assembled them into GSs by hydrothermal treatment using thiourea. These GSs show tunable pore structure and surface properties, and are mechanically strong. They show a high adsorption and desorption ability for various dyes, oils and many other organic solvents. The adsorption amount of methylene blue can reach about 184 mg/g, and the adsorption capacity of diesel oil can reach 129 g/g. Moreover, the GSs can also be repeatedly used without obvious structure and performance degradation. We also studied the relationship between the GSs structure and the contamination adsorption performance. It was found that the dye adsorption performance of GSs strongly depends on the charge concentrations on their surface and the specific surface area of GSs, but the oil adsorption capacity is mainly related to the specific surface area, indicating different adsorption mechanisms. These findings open up many possibilities for the use of graphene in water cleaning including disinfection, decontamination, re-use, reclamation and desalination. "
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64481
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	赵金平. 氧化石墨烯的化学剥离法制备、还原与应用探索[D]. 北京. 中国科学院金属研究所,2012.