利用超临界流体制备石墨烯的研究进展

石墨烯具有各种优异性能,使其成为当前研究的热点,但如何大规模、高质量、低成本的制备石墨烯是当前亟待解决的问题,利用超临界流体插层-剥离制备石墨烯是有望解决上述问题的新方法。对利用超临界流体插层-剥离制备石墨烯的过程进行了综述,包括超临界流体的选择、辅助方法(超声辅助、流体剪切辅助、添加分子楔)、超临界流体膨胀速率的影响、重复实验、实验参数的影响等,对石墨烯的表征技术进行了概述,并对该技术存在的问题进行了总结。     

超临界流体制备氮化硼纳米片的研究进展

氮化硼纳米片(BNNSs)是一种新型二维纳米材料,具有极好的绝缘导热性能、力学性能、介电性能、化学稳定性和良好的生物相容性,被广泛应用于复合材料增强、导热复合材料、储氢、药物运输、催化载体、量子点等方面,逐渐成为研究的热点。氮化硼主要有六方(h-BN)、立方(c-BN)、菱方(r-BN)和纤维矿(w-BN)四种稳定结构,其中h-BN是与石墨相类似的层状结构,但其层间范德华力更强,这也给其剥离带来困难。迄今为止,人们参照石墨烯的制备探究出许多制备氮化硼纳米材料的方法,如微机械剥离法、液相剥离法、化学气相沉积法(CVD)和二次外延生长法等。这些方法虽各有优劣,但在大规模稳定生产晶体结构较为完整的BNNSs且剥离效率较高上均存在不足。采用低成本、高效率、高质量的方法制备出氮化硼纳米片是其产业化的关键。超临界流体兼具气体的扩散性质和液体的溶解能力,自从被引入到石墨烯的制备中取得了一些成果后,许多研究者也将其运用到BNNSs的制备上。目前,利用超临界CO_2在一定的温度和压力下能制备出厚度为2～6 nm的BNNSs,且BNNSs的结晶形态与原始的h-BN基本没有太大差异,得到的BNNSs悬浮液的浓度可高达0.24 mg/mL,辅助以剪切、超声波等手段后能有效提高其剥离效率。超临界有机溶剂一般有超临界甲醇、超临界N,N-二甲基甲酰胺,它们不仅能作为插层剂打开片层间距,而且是良好的分散剂,能防止纳米材料再次团聚。超临界有机溶剂能大大简化剥离过程,反应时间只有短短15 min,就能得到2～3层的无明显缺陷的BNNSs,产率约为10%。本文综述了超临界流体制备氮化硼纳米片的方法、原理、研究现状及其表征手法,讨论了提高剥离效率的各种方法及优缺点。超临界流体制备氮化硼纳米片设备单一、条件较易达成、产品质量高,为氮化硼纳米片的工业化生产提供了新的思路。     

石墨烯的top-down方法制备研究进展

石墨烯独特的纳米片层结构使其在诸多方面性能优异,成为材料领域研究的热点。而石墨烯能否被广泛应用很大程度上依赖于高质量石墨烯的大规模生产。以石墨或氧化石墨为原料的top-down方法,是目前备受关注的低成本大规模生产石墨烯的方法之一。在对近年来有关石墨烯top-down制备方法进行总结分析的基础上,重点介绍了石墨和氧化石墨的直接剥离技术,如超声剥离、剪切剥离、球磨剥离以及超临界流体剥离等最新研究成果,并分析比较了各方法的剥离机理及优缺点;此外,介绍了近年来新的氧化石墨烯还原方法,如热还原、化学还原以及绿色还原剂等。     

液相剥离法制备石墨烯研究进展

对石墨剥离体系的选择原则,石墨在有机溶剂体系、含水表面活性剂、离子液体体系中的剥离,球磨机、高压射流机、超声波发生器、高速搅拌剪切机、超临界装置、超重力旋转床等石墨的剥离设备进行综述;认为提出液相剥离法制备的石墨烯应用前景良好;液相剥离法还存在浓度低、层数和尺寸的多分散性、剥离介质价格昂贵或沸点高、辅助剂不易分离等不足;液相剥离法规模制备石墨烯面临的挑战主要是选择和设计合适的剥离体系和剥离设备。     

超临界CO2射流空化法制备石墨烯及其在金属复合散热器上的应用研究

为了提高金属散热器的散热效率,利用自制超临界CO2射流空化装置制备高质量的石墨烯纳米粉,将该纳米粉制备成高散热性能的石墨烯复合涂料,并且用喷涂法制备了表面具有石墨烯复合散热涂层的金属复合散热器.结果 显示:利用超临界CO2射流空化法剥离制备的石墨烯纳米粉纯度高、片层大、层数少,具有良好的导热性能,使用该石墨烯纳米粉体制备的石墨烯复合材料涂层,在室温环境下能够将原金属散热器的温度降低16.13℃,使金属散热器的散热效率提高15.6％～21.6％.     

石墨烯的制备方法

目的探究和比较制备石墨烯的两种常见方法,即氧化还原法和液相剥离法。方法采用液相剥离法,在N-甲基吡咯烷酮中超声剥离膨胀石墨制备单层和多层石墨烯,与氧化还原法制备得到的石墨烯在微观形貌和结构表征方面进行比较,并在此基础上比较不同有机溶剂液相剥离制备的石墨烯分散液的浓度和稳定性。结果液相剥离法得到的石墨烯具有更好的片层结构,分子结构含有较少的杂团和含氧基团,石墨烯片层间距较宽,热稳定性更好。在N-甲基吡咯烷酮中液相剥离制备的石墨烯质量浓度可达0.15 mg/m L,稳定性相对较好,该方法在一系列应用中也更易制备导电薄膜和复合材料。结论相较氧化还原法,液相剥离法制备的石墨烯性能更好。     

电化学法制备石墨烯的研究进展EI北大核心CSCD

石墨烯优异的导电、导热、光学和力学性能,使其成为制造新一代电子、光电装置材料的理想选择。因此,高质量、规模化、低成本的石墨烯制备技术研究开发尤为重要。电化学剥离石墨制备石墨烯是一种很有前途的湿化学方法,具有可扩展性、溶液加工性和环境友好性等优点。本文综述了电化学法制备石墨烯技术的研究进展,阐述了电化学法制备石墨烯的机制,重点分析了石墨阳极氧化和阴极剥离过程涉及因素变化对石墨烯的剥离效率及产率、形貌、质量和缺陷程度的影响,简要介绍了电化学法制备功能化石墨烯材料及其应用,并指出电化学法制备石墨烯技术的未来发展方向是电解质体系设计、电解条件优化、剥离机理认识及电解池合理设计等。     

机械剥离法制备石墨烯及其在石墨烯/陶瓷复合材料制备中的应用

扼要介绍了石墨烯特殊的二维结构及因这种结构导致石墨烯所具有的极其优异的电学、光学和力学性质.回顾了石墨烯的研究历史以及微机械剥离法在其中所起到的重要作用,并对主要制备方法进行了简要的介绍.然后,阐述了以机械磨为剥离工具的新型机械剥离法的发展和已取得的成果.最后,对利用机械剥离法制备石墨烯/陶瓷复合材料粉体的探索进行了总结和概括.同时,展望了机械剥离法在制备石墨烯及其复合材料中的应用前景.     

MPCVD法制备石墨烯的研究进展

微波等离子体化学气相沉积（MPCVD）法是近年来发展起来的制备石墨烯的新方法,具有低温生长、基底材料选择广泛、容易掺杂等优点,逐渐成为制备高质量石墨烯的主要方法。首先通过分析制备石墨烯的几种主要方法（微机械剥离法、sic外延生长法、化学剥离法、化学气相沉积法）得出MPCVD法相对于其他方法的优势,然后综述了MPCVD法制备石墨烯的研究进展,最后简要列举了MPCVD法制备的石墨烯的应用并对MPCVD法制备石墨烯的发展趋势进行了展望。     

电化学法制备石墨烯的研究进展

石墨烯优异的导电、导热、光学和力学性能,使其成为制造新一代电子、光电装置材料的理想选择。因此,高质量、规模化、低成本的石墨烯制备技术研究开发尤为重要。电化学剥离石墨制备石墨烯是一种很有前途的湿化学方法,具有可扩展性、溶液加工性和环境友好性等优点。本文综述了电化学法制备石墨烯技术的研究进展,阐述了电化学法制备石墨烯的机制,重点分析了石墨阳极氧化和阴极剥离过程涉及因素变化对石墨烯的剥离效率及产率、形貌、质量和缺陷程度的影响,简要介绍了电化学法制备功能化石墨烯材料及其应用,并指出电化学法制备石墨烯技术的未来发展方向是电解质体系设计、电解条件优化、剥离机理认识及电解池合理设计等。     

Production of graphene nanosheets by supercritical CO2 process coupled with micro-jet exfoliation

A facile and cost-effective method which combines supercritical CO₂ and micro-jet exfoliation has been developed for producing graphene nanosheets with high-quality. CO₂ molecules can intercalate into the interlayer of graphite because of their high diffusivity and small molecule size in supercritical operation. The tensile stress induced by graphite interfacial reflection of compressive waves exert on the graphite flakes, which lead to further exfoliation of graphite. Scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM), Raman spectrum and X-ray diffraction (XRD) are used to identify morphology and quality of the exfoliated graphene nanosheets, which reveal that the graphite was successfully exfoliated into graphene and more than 88% of graphene nanosheets are less than three layers. The yield of graphene nanosheets is about 28 wt% under optimum conditions, which can be greatly improved by repeated exfoliation of the graphene sediment. The pure graphene film has a high conductivity of 2.1 × 10⁵ S/m.     

化学气相沉积法制备大面积石墨烯及其光谱学表征

化学气相沉积（CVD）法是近年来发展起来的制备石墨烯的新方法。该方法产物具有生长面积大、质量高等优点,逐渐成为制备石墨烯的主要方法。用CVD法在常压下通过全面优化实验参量,以镍箔为基底制备了大面积少数层和单层石墨烯,用拉曼光谱,场发射扫描电子显微镜（SEM）和原子力显微镜（AFM）手段表征,通过分析常压下不同温度、不同载气成分比等实验参数,最终获得制备高质量、大面积、少数层石墨烯的最佳参量,用双共振理论解释少数层和单层石墨烯的拉曼光谱中2D峰强度随石墨烯层数变化而变化的原理。CVD法制备的石墨烯具有面积大、低成本、可测量性强、可用于大批量生产的优点,为工业用途石墨烯的制备提供了有效途径。     

Prospects of Supercritical Fluids in Realizing Graphene‐Based Functional Materials

Supercritical‐fluids science and technology predate all the approaches that are currently established for graphene production by several decades in advanced materials design. However, it has only recently been proposed as a plausible approach for graphene processing. Since then, supercritical fluids have emerged into contention as an alternative to existing technologies because of their scalability and versatility in processing graphene materials, which include composites, aerogels, and foams. Here, an overview is presented of such materials prepared through supercritical fluids from an advanced materials science standpoint, with a discussion on their fundamental properties and technological applications. The benefits of supercritical‐fluid processing over conventional liquid‐phase processing are presented. The benefits include not only better performances for advanced applications but also environmental issues associated with the synthesis process. Nevertheless, the limitations of supercritical‐fluid processing are also stressed, along with challenges that are still faced toward the achievement of the great expectations from graphene materials.     

A New Facile Route to Flexible and Semi‐Transparent Electrodes Based on Water Exfoliated Graphene and their Single‐Electrode Triboelectric Nanogenerator

Wearable technologies are driving current research efforts to self‐powered electronics, for which novel high‐performance materials such as graphene and low‐cost fabrication processes are highly sought.The integration of high‐quality graphene films obtained from scalable water processing approaches in emerging applications for flexible and wearable electronics is demonstrated. A novel method for the assembly of shear exfoliated graphene in water, comprising a direct transfer process assisted by evaporation of isopropyl alcohol is developed. It is shown that graphene films can be easily transferred to any target substrate such as paper, flexible polymeric sheets and fibers, glass, and Si substrates. By combining graphene as the electrode and poly(dimethylsiloxane) as the active layer, a flexible and semi‐transparent triboelectric nanogenerator (TENG) is demonstrated for harvesting energy. The results constitute a new step toward the realization of energy harvesting devices that could be integrated with a wide range of wearable and flexible technologies, and opens new possibilities for the use of TENGs in many applications such as electronic skin and wearable electronics.     

借助聚合物实现石墨烯转移的技术进展

高质量、低成本、绿色制备石墨烯及其高效转移技术是促进石墨烯应用和行业发展的关键。目前制备大面积高质量石墨烯的主流方法是基于金属表面催化生长的化学气相沉积法。薄膜转移技术作为连接石墨烯制备和应用的重要桥梁,在实现石墨烯产业化应用中发挥着重要作用。当前石墨烯薄膜的转移技术主要是利用各种聚合物作衬底或支撑材料的直接和间接转移技术。分类介绍了借助单一聚合物转移、复合结构聚合物转移和其他聚合物转移等石墨烯薄膜的转移方法,并对各自的特点进行了分析和总结,比较了各自的优劣势,给出了对应的适用场合。最后展望了石墨烯转移技术的发展方向。     

石墨烯的制备方法及其应用特性

近3年来,石墨烯以其独特的结构和优异的性能,在化学、物理和材料学界引起了轰动。引用大量最新的参考文献,介绍了石墨烯的研究现状,通过评述石墨烯的合成、功能化以及近期应用概况,展望了石墨烯的发展前景和研究方向,认为借鉴各种方法的优势,综合运用,可以制备单层、结构完整和高电导率的石墨烯,并进一步将其功能化,拓展其应用领域并已取得较大的进展,这一途径被认为是石墨烯规模化应用的战略起点。     

Hysteresis I–V nature of mechanically exfoliated graphene FET

Graphene is an attractive material for device applications due to its excellent electrical and mechanical properties. The mechanical exfoliation is an attractive method to fabricate graphene devices using mono and multilayer graphene flakes. As the graphene is very sensitive to atmosphere the occurrence of hysteresis and p-doping is common. This paper reports electrical characterization and hysteresis effect of graphene field effect transistor (FET) fabricated using mechanically exfoliated graphene flakes. Raman spectra and atomic force microscopy techniques have been used to examine the quality and thickness of the exfoliated graphene. This fabricated graphene FET has shown hysteresis nature with p-type doping. The possible reason for the observed hysteresis and p-doping has been explained.     

Chemical vapor deposition-derived graphene with electrical performance of exfoliated graphene

While chemical vapor deposition (CVD) promises a scalable method to produce large-area graphene, CVD-grown graphene has heretofore exhibited inferior electronic properties in comparison with exfoliated samples. Here we test the electrical transport properties of CVD-grown graphene in which two important sources of disorder, namely grain boundaries and processing-induced contamination, are substantially reduced. We grow CVD graphene with grain sizes up to 250 μm to abate grain boundaries, and we transfer graphene utilizing a novel, dry-transfer method to minimize chemical contamination. We fabricate devices on both silicon dioxide and hexagonal boron nitride (h-BN) dielectrics to probe the effects of substrate-induced disorder. On both substrate types, the large-grain CVD graphene samples are comparable in quality to the best reported exfoliated samples, as determined by low-temperature electrical transport and magnetotransport measurements. Small-grain samples exhibit much greater variation in quality and inferior performance by multiple measures, even in samples exhibiting high field-effect mobility. These results confirm the possibility of achieving high-performance graphene devices based on a scalable synthesis process.     

Fine particle formation using supercritical fluids

The use of supercritical fluids as solvents for the formation of micro- and nano-particles has shown tremendous over the past few years due to increased demands from industry for materials with high performance specifications and high or unique functionality. Supercritical fluids allow synthesis of many types of particles since the solvent's chemical and physical properties can be varied with temperature or pressure, both of which can affect the degree of supersaturation and nucleation. In this review, we describe methods for the formation of fine particles using supercritical fluids CO₂ and water. Basic principles and specific features of each solvent are described, and the advantages and limitations are discussed.     

六方氮化硼的剥离及其在导热复合材料中的应用

六方氮化硼(h-BN)是一种石墨烯类二维材料,具有很高的导热性。当将其剥离成二维氮化硼纳米片(BNNSs)时,因其层状材料特殊的电子性能和高比表面积,使其制备技术受到很多研究人员的关注,其剥离方法以机械球磨和液相超声为主。综述了氮化硼二维纳米材料的几种剥离方法、原理及其优缺点,将在塑料导热材料中呈现较好的应用前景。