氧化石墨烯薄膜的选择性传质机制及性能研究

发布时间：2018-04-01 00:25

本文选题：氧化石墨烯　切入点：传质　出处：《清华大学》2016年博士论文

【摘要】：清洁淡水资源的日益短缺与污染使近年来薄膜过滤与分离技术得到飞速发展。纳米技术在新材料领域取得的巨大进步为开发下一代组成与结构、过滤与分离性能可精确调控的功能薄膜提供了可能。其中以碳纳米管、石墨烯及其衍生物为代表的新型纳米碳材料的研究与发展最为迅速。本论文工作采用改进的Hummers方法及液相剥离法合成了单层氧化石墨烯纳米片。通过多种液相成膜技术(例如:滴加溶液法、真空抽滤法)制备了氧化石墨烯薄膜。研究了其选择性传质机制及过滤、分离性能。系统研究了氧化石墨烯薄膜的选择传质特性及机制。结果表明,液态水在氧化石墨烯薄膜的纳米毛细管通道中可超快速传输,扩散率比体相扩散提升约5个数量级,为氧化石墨烯薄膜在液相传质领域的应用奠定了基础。另外,氧化石墨烯薄膜对水溶液中一系列溶质分子与离子具有选择渗透性。提出并通过第一性原理计算模拟和实验证明了作用机制。氧化石墨烯薄膜的选择传质特性可用于膜分离,在污水处理与再利用及钢铁工业铁基废电解液中的高纯酸提取等领域具有应用前景。将层状双氢氧化物纳米片均匀插入氧化石墨烯薄膜层间,实现了不同种类纳米片异质超晶格复合薄膜的制备。研究了其离子传输特性,发现不同价态金属阳离子严格据其电荷数被有效分离,不受阴阳离子种类的影响。该复合薄膜的电荷驱动离子分离特性在污水处理与再利用、化工精炼及仿生选择性离子传输等领域具有应用潜力。研究了氧化石墨烯薄膜的水脱盐特性。结果表明,在浓度梯度驱动扩散过程中,氧化石墨烯薄膜具有较高的本征水/离子选择度,而在压力驱动过滤过程中,其脱盐率(即水/离子选择度)极低。通过实验和分子动力学计算模拟证实这一矛盾结果源于水/离子选择度与氧化石墨烯薄膜中纳米通道长度及外加压力间的强关联性。该结果为优化氧化石墨烯薄膜在水脱盐领域的应用奠定了基础。为进一步提升氧化石墨烯薄膜的水脱盐性能,将氧化钛纳米片均匀插入其层间,辅以紫外光催化还原,所得还原氧化石墨烯/氧化钛复合薄膜相比于未还原的情况,水通量保持60%,而盐通量降低至5%,在海水淡化领域具有应用前景。
[Abstract]:The technology of membrane filtration and separation has been developed rapidly in recent years due to the shortage and pollution of clean freshwater resources.The great progress made by nanotechnology in the field of new materials makes it possible to develop the next-generation functional films whose composition and structure, filtration and separation properties can be accurately regulated.Among them, carbon nanotubes, graphene and their derivatives are the most rapid research and development of new nano carbon materials.In this paper, graphene monolayers were synthesized by improved Hummers method and liquid phase stripping method.Graphene oxide films were prepared by a variety of liquid film forming techniques, such as dripping solution method and vacuum filtration method.The selective mass transfer mechanism, filtration and separation performance were studied.The selective mass transfer characteristics and mechanism of graphene oxide films were systematically studied.The results show that liquid water can be transported rapidly in the nano-capillary channel of graphene oxide film, and the diffusivity is about 5 orders of magnitude higher than that of bulk phase diffusion, which lays a foundation for the application of graphene oxide film in liquid phase mass transfer.In addition, graphene oxide films have selective permeability to a series of solute molecules and ions in aqueous solution.The mechanism is proved by first principle calculation, simulation and experiment.The selective mass transfer characteristics of graphene oxide films can be used in membrane separation and have a promising application in wastewater treatment and reuse and high purity acid extraction from iron based waste electrolyte in iron and steel industry.The layered double hydroxide nanostructures were uniformly inserted into the interlayer of graphene oxide films, and the heterostructure superlattice composite films of different kinds of nanostructures were prepared.The ion transport characteristics of metal cations with different valence states are studied. It is found that metal cations with different valence states are effectively separated according to their charge number and are not affected by the kinds of anions.The charge-driven ion separation characteristics of the composite film have potential applications in wastewater treatment and reuse, chemical refining and bionic selective ion transport.The characteristics of water desalting of graphene oxide films were studied.The results show that graphene oxide films have high intrinsic water / ion selectivity in the process of concentration gradient driven diffusion, but the desalinization rate (i.e. water / ion selectivity) is very low in the pressure driven filtration process.The results of experiments and molecular dynamics simulations show that this contradiction results from the strong correlation between the water / ion selectivity and the length of nanochannels and the applied pressure in graphene oxide films.The results laid a foundation for optimizing the application of graphene oxide film in the field of water desalination.In order to further improve the water desalting performance of graphene oxide films, titanium oxide nanocrystals were inserted into their layers uniformly and reduced by UV photocatalytic reduction. The results showed that the reduction of graphene oxide / titanium oxide composite films was compared with that of unreduced films.The water flux is kept at 60 and the salt flux is reduced to 5, which is promising in the field of seawater desalination.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ127.11;TB383.2

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