功能化氧化石墨烯的制备及其与共轭聚合物的相互作用

发布时间：2017-12-28 06:31

  本文关键词：功能化氧化石墨烯的制备及其与共轭聚合物的相互作用　出处：《山东大学》2017年博士论文　论文类型：学位论文

  更多相关文章： 氧化石墨烯 功能化 分散性 共轭聚合物 界面

【摘要】：石墨烯是一种单原子层厚度的二维材料,具有十分优异的力学、电学、光学、热学性质,正吸引着越来越多的研究力量致力于其基础研究与应用开发。氧化石墨烯作为石墨烯的衍生物,具有与石墨烯相似的二维结构,性质却完全不同。氧化石墨烯的结构通常由Lerf-Klinowski描述,即在石墨烯骨架的侧边修饰有羧基、羰基以及在二维平面上修饰有羟基、环氧基。含氧基团赋予了氧化石墨烯亲水性和水溶液可分散性,因而单层氧化石墨烯可由氧化石墨超声分散获得,而后者可通过Hummers法等低成本途径对石墨粉进行氧化得到。氧化石墨烯的亲水性为氧化石墨烯的制备以及水相应用提供了便利,但也限制了氧化石墨烯在有机溶剂中的分散。因此,各种各样的修饰方法,包括非共价键、共价键化学修饰,被采用来对氧化石墨烯进行功能化修饰,增加其在有机溶剂中的分散性,从而拓展它们在相关领域的应用范围。氧化石墨烯以及功能化氧化石墨烯在纳米复合材料、光催化、储能、能量转化等领域具有潜在的应用价值。作为柔性二维材料,他们具有巨大的比表面积(～2630 m2g-1),因此可以作为纳米材料的载体提供非常大的界面面积,实现复合材料的结构改性、光催化性能的提升、储能密度以及能量转换效率的提高等功能增强。氧化石墨烯中含氧官能团的碳原子以sp3杂化成键(σ键),从而引入了带隙,并且带隙的大小由含氧量决定,因此,氧化石墨烯可被当作一种带隙可调的二维半导体材料,从而在光电转换领域获得应用。近年来,以共轭聚合物为代表的有机半导体材料因其低成本、柔性、溶液可加工性在半导体照明、有机光伏等领域获得了极大的发展。其中,以共轭聚合物复合薄膜为活性层实现光电转换制备高性能的光电探测器、光伏器件等光电功能器件是目前的研究热点。利用氧化石墨烯对共轭聚合物进行掺入,实现聚合物薄膜结构及电荷传输特性的改变,是获得性能增强的有机光电功能器件的有效途径,具有非常重要的研究价值。由于大多数的共轭聚合物都只能在有机溶剂中进行加工处理,因而对氧化石墨烯进行功能化修饰以获得非极性有机溶剂可分散性是实现氧化石墨烯掺入提高有机光电功能器件性能的重要前提。为获得在非极性有机溶剂中可分散的功能化氧化石墨烯,并实现掺入提高基于共轭聚合物薄膜的光电功能器件性能,本论文针对功能化氧化石墨烯的制备方法及其与共轭聚合物的相互作用机制展开了系统研究,主要内容包括:1.氧化石墨烯的离子键修饰我们改进了一种表面活性剂——双十二烷基二甲基溴化铵(DDAB)离子键修饰氧化石墨烯的方法,在更为简易的条件下实现功能化氧化石墨烯(DDAB-GO)从水相到有机溶剂相(邻二氯苯,DCB)的转移。基于对DDAB-GO在相转移前后结构性质改变的测量,我们提出了实验条件下DDAB-GO的相转移模型。组成氧化石墨烯的结构成分——氧化碎片(OD)以及多余的DDAB分子在相转移及净化过程中被分离到水相中,使得DDAB-GO在非极性有机溶剂——DCB中形成洁净、稳定的分散液。DDAB-GO的DCB分散液与共轭聚合物——聚(3-己基噻吩-2,5-二基)(P3HT)的DCB溶液共混后可形成稳定的分散液,一定比例的P3HT分子可附着在DDAB-GO二维片层表面,在光激发下实现P3HT向DDAB-GO的电荷转移或能量传递,表明了 DDAB-GO在共混体系中作为电子受体的可能性。2.离子键功能化氧化石墨烯的可控还原基于极性有机溶剂——二甲基甲酰胺(DMF)的溶剂热还原法被用来实现对分散在邻二氯苯(DCB)中DDAB-GO的可控还原,获得在DCB中稳定分散的、具有不同还原程度的DDAB-rGO。我们提出了一种结合紫外-可见光吸收与电化学循环伏安法的能级结构(LUMO/HOMO)测试方法。测试结果表明,DDAB-GO的带隙在还原之后减小,DDAB-rGO的LUMO与HOMO能级位置随着还原程度的增加而相互靠近,并趋向于本征石墨烯的费米能级。对DDAB-GO、DDAB-rGO与共轭聚合物——P3HT共混物薄膜的光物理特性以及基于共混薄膜的光电探测器原型器件的性能研究表明,作为受体的DDAB-rGO与给体P3HT之间的能级匹配程度是决定DDAB-rGO:P3HT共混薄膜中电荷转移机制的重要因素,由此反映出调控DDAB-rGO的还原程度并通过测量给出DDAB-rGO能级结构对于实现功能化氧化石墨烯在光电转换领域高性能应用的重要价值。3.离子功能化氧化石墨烯的共价键修饰在离子键修饰的基础上,分散在DCB中的DDAB-GO通过与邻氯苯异氰酸酯(CI)进行酯化反应可得到进一步的共价键修饰,获得在DCB中稳定分散的功能化氧化石墨烯(CI-DDAB-GO)。DDAB-GO的单层分散为后续的共价键修饰提供了很大的反应界面,DDAB-GO剩余在二维片层表面的大量羟基则为CI基团的共价键修饰提供了足够的链接位置。CI-DDAB-GO相比于DDAB-GO具有与共轭聚合物——P3HT更高的兼容性,对P3HT进行掺入得到的共混薄膜拥有更均匀的形貌。CI-DDAB-GO掺入可有效降低基于P3HT薄膜的光电二极管的暗电流,并提高其开关比,显示出CI-DDAB-GO在提高共轭聚合物光电功能器件性能方面的重要价值。4.氧化石墨烯的π-π作用修饰利用共轭聚合物——P3HT辅助的GO相转移法,我们制备了 P3HT π-π作用修饰的氧化石墨烯(P-GO)。在DCB中,P3HT分子通过与GO中sp2共轭区域的π-π作用附着在GO表面,赋予了 P-GO在DCB中的良好分散性。光物理性质以及结构信息的研究表明,P-GO对P3HT:PCBM共混薄膜的掺杂可促进薄膜的相分离,以获得利于器件性能的更优化的薄膜形态结构。基于P-GO2.5%质量比掺入的P3HT:PCBM共混薄膜的体异质结有机光伏器件的性能相比于本征器件具有明显提升,其中光电转化效率(PCE)提高接近18%。
[Abstract]:Graphene is a two-dimensional material with a single atomic layer thickness. It has excellent mechanical, electrical, optical and thermal properties. It is attracting more and more research efforts for its basic research and application development. As a derivative of graphene, graphene oxide has a two dimensional structure similar to graphene, and its properties are completely different. The structure of graphene oxide is usually described by Lerf-Klinowski, that is, there are carboxyl and carbonyl groups on the side of graphene skeleton, and hydroxyl and epoxy groups are modified on 2-D plane. The oxygenated group gives the graphene hydrophilicity and dispersibility of aqueous solution. Therefore, monolayer graphene oxide can be obtained by ultrasonic dispersion of graphite oxide, while the latter can be oxidized by graphite powder through low cost way such as Hummers method. The hydrophilicity of graphene oxide provides convenience for the preparation of graphene oxide and the application of water phase, but it also restricts the dispersion of graphene oxide in organic solvents. Therefore, a variety of modification methods, including non covalent and covalent chemical modifications, are used to functionalized graphene oxide and increase their dispersion in organic solvents, thereby expanding their application in related fields. Graphene oxide and functionalized graphene oxide have potential applications in the fields of nanocomposites, photocatalysis, energy storage and energy conversion. As a flexible two-dimensional material, they have a huge specific surface area (~ 2630 m2g-1), so it can be used as a carrier of nano materials provide a very large interfacial area, the structure of the composite modification and photocatalytic performance improvement, energy storage density function and improve the energy conversion efficiency enhancement. The oxygen-containing functional groups of graphene oxide in carbon atoms in SP3 hybrid orbitals (sigma bond), which introduced the band gap, and the gap is adjusted by the oxygen content decided, therefore, graphene oxide can be regarded as a kind of two-dimensional semiconductor materials with tunable band gap, which was applied in the field of photoelectric conversion. In recent years, organic semiconductor materials represented by conjugated polymers have made great progress in semiconductor lighting, organic photovoltaic and other fields because of their low cost, flexibility and solution processability. Among them, conjugated polymer thin film as active layer to achieve photoelectric conversion to prepare high-performance photoelectric detectors, photovoltaic devices and other photoelectric functional devices is the current research hotspot. Using graphene oxide to conjugate polymers, the structure and charge transfer properties of polymer films are changed. It is an effective way to obtain enhanced organic photoelectric functional devices, and has very important research value. Because most of the conjugated polymers can only be processed in organic solvents, so the functionalization of graphene oxide to obtain non-polar organic solvent dispersion of the graphene oxide incorporation is important premise to improve the performance of organic optoelectronic devices. In order to obtain non functionalized graphene oxide can be dispersed in polar organic solvents, and improve the incorporation of photoelectric devices based on the properties of conjugated polymer film and preparation method for the functionalization of graphene oxide and its interaction mechanism with conjugated polymers developed system were studied, the main contents include: ion key 1. graphene oxide modified we improved a surfactant - alkyl two methyl bromide (DDAB) method of modified graphene oxide ionic bond, the more function of the oxidation of graphene simple conditions (DDAB-GO) from the aqueous phase to the organic phase (o two chlorobenzene, DCB transfer). Based on the measurement of the structural properties of DDAB-GO before and after phase transfer, we propose a phase transfer model of DDAB-GO under experimental conditions. The structural components of graphene oxide -- oxidized debris (OD) and redundant DDAB molecules are separated into water phase during phase transfer and purification process, making DDAB-GO form a clean and stable dispersion in non-polar organic solvents DCB. DDAB-GO DCB dispersions and conjugated polymer poly (hexylthiophene: 3- -2,5- two) (P3HT) DCB solution can be formed after the dispersion stability of P3HT molecules, a certain proportion can be attached to the DDAB-GO two-dimensional sheet surface, the realization of P3HT to DDAB-GO charge transfer and energy transfer in the light show the possibility of DDAB-GO in the blends as electron acceptor. Controllable 2. ionic bond functionalized graphene oxide reduction of polar organic solvent - two methyl formamide (DMF) method was used based on the realization of the dispersion in the adjacent two chlorobenzene solvent thermal reduction (DCB) controlled the reduction of DDAB-GO, obtain stable dispersion in DCB, with different degree of reduction of DDAB-rGO. An energy level structure (LUMO/HOMO) method combining ultraviolet visible light absorption and electrochemical cyclic voltammetry is proposed. The test results show that the band gap of DDAB-GO decreases after reduction. The location of LUMO and HOMO level of DDAB-rGO is close to each other with the increase of reduction degree, and tends to the Fermi level of intrinsic graphene. The photophysical properties of DDAB-GO, DDAB-rGO and P3HT blends of conjugated polymer films and shows that the performance of the photoelectric detector prototype device based on the blend film, as the receptor DDAB-rGO and P3HT to the level between the degree of matching is an important factor in determining the charge transfer mechanism of DDAB-rGO:P3HT blend thin films, thus reflecting the reduction degree of regulation of DDAB-rGO and by measuring the energy level structure of DDAB-rGO is given for the functionalization of graphene oxide to achieve an important value in high performance applications in the field of photoelectric conversion. 3., the covalent bond modification of ion functionalized graphene oxide is based on ionic bond modification. The DDAB-GO dispersed in DCB can be further covalent modified by esterification with CI, and stable dispersion of DCB is achieved.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.71;O631
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本文编号：1344955