可用于纳米填料的剥离型石墨

在密歇根州立大学（MSU）的复合材料和结构中心，科研人员的工作集中在剥离石墨纳米片层材料（xGnP）在内的几种纳米材料。知名教授兼主任Lawrence Drzal说，该中心已经开发出一种经济的方法，可以从天然石墨中剥离出单个的石墨片层。     

超薄片层石墨和多层石墨烯的真空剥离法制备及微区分析

用真空剥离法,对钢铁冶炼炉渣中的蠕虫状石墨进行处理,所得样品经过TEM微区分析,证明是一类沿C轴堆垛的多层石墨片层,其中也包含有多层石墨烯。同时说明,采用人造石墨和真空剥离法,是一种制备超薄片层石墨和多层石墨烯的可行方法,进一步可以作为用天然或人造矿物来制造二维材料的前驱处理技术。     

N-甲基吡咯烷酮与正丁醇液相剥离制备高浓度石墨烯

采用N-甲基吡咯烷酮(NMP)与正丁醇(NBA)二元溶剂体系液相剥离法制备石墨烯,探究高浓度、高质量石墨烯的制备条件,通过比较不同体积比溶剂对石墨的剥离效果,得出最佳剥离体积比为V(NMP)∶V(NBA)=1. 5∶1。通过正交试验得到初始石墨质量浓度对剥离后石墨烯的浓度影响最大,超声功率、时间、温度次之。结果表明,初始石墨质量浓度为10 mg/mL时,制备的石墨烯80%以上为少层石墨烯,结构完整,片层大小最大可达到3~4μm,石墨烯溶液质量浓度最高达到7. 2 mg/mL。该体系制备的石墨烯产率与片层大小比以往文献的报道均有大幅度提高。     

钯/石墨烯复合材料的制备及其性能表征

石墨烯常被用于储能器件的电极材料,然而采用化学方法制备的石墨烯其实际应用性能远低于其理论值。有鉴于此,本文提出了利用惰性金属钯纳米材料解决石墨烯实际应用中存在的电导率差和易产生团聚的问题。制备的钯/石墨烯复合材料具有优异的导电性能,比单一石墨烯材料具有更高的电导率,这表明金属钯纳米颗粒显著改善石墨烯片层间的堆叠团聚以及结构缺陷问题。此外,研究了金属钯纳米颗粒对于钯/石墨烯复合电极材料功率密度的影响。     

石墨烯电热薄膜材料的制备及表征

采用超临界二氧化碳剥离的方法制备了2种不同的剥离石墨烯EG-6、EG-6u,并制备了以石墨D、剥离石墨烯EG-6、EG-6u为导电填料的导电薄膜。采用扫描电镜(SEM)、拉曼光谱对原材料石墨以及导电薄膜进行表征,并对所制备薄膜进行电热特性测试。结果表明,经过超临界二氧化碳剥离之后,石墨烯片层从石墨块上剥离下来,尺寸为3～10μm。导电薄膜中石墨烯以片层方式存在,而石墨以粒状存在,片层方式的存在方式使得石墨烯片层定向排列,导电网络更丰富高效。在12 V电压下升温达到相同的空间温度,相比于导电薄膜D,导电薄膜EG-6所需功率减少22.5%,膜层温度降低9.623℃,膜层的传热效率更高,综合传热系数增大,为2.60×10~(-3)W·cm~(-2)·℃~(-1)。相比于导电薄膜D,石墨烯导电薄膜的升温速率更高,升温时间更短。导电薄膜EG-6u的初始升温速率为导电薄膜D的19.3倍,升温时间为导电薄膜D的24.7%。     

水热剥离法制备氧化石墨烯及其结构性能与应用

基于水热剥离法,以膨胀石墨为原料和阳离子表面活性剂为插层剂制备出氧化石墨烯。利用X射线衍射、红外光谱、拉曼光谱、热失重法和冷场扫描电镜等表征了水热处理后的膨胀石墨的晶体结构、表面官能团和形貌等,并初步研究了处理后的膨胀石墨对聚乙烯醇(PVA)薄膜的力学增强作用。结果表明:阳离子表面活性剂十六烷基三甲基溴化铵对膨胀石墨的剥离效果最好,97.6%的膨胀石墨形成了非晶的剥离层,即无规分散的氧化石墨烯片层,1.8%的膨胀石墨经插层剂处理后层间距增大,形成插层结构;添加质量分数为1.0%的经阴离子表面活性剂处理的膨胀石墨即可明显提高PVA薄膜的拉伸断裂强度。     

超临界CO_2流体剥离膨胀石墨制备石墨烯

以膨胀石墨为原料,利用超临界CO_2流体的方法,在高温高压的条件下,通过插层剥离膨胀石墨然后快速卸压来制备石墨烯。研究了超声时间、反应时间、反应温度和压力对石墨烯产率的影响;利用X射线衍射仪、扫描电子显微镜及透射电子显微镜对膨胀石墨及所制备石墨烯进行结构和形貌表征,通过四探针测试仪对石墨烯的电导率进行测试。结果表明:采用超临界CO_2流体的方法制备石墨烯的最佳工艺为:超声时间为2 h,反应时间为3 h,反应温度为60℃,压力为14 MPa;制备出层数在10层以内石墨烯,石墨烯片层大小为15μm左右,厚度为5 nm左右;石墨烯的平均电导率在105 S/m左右。     

科学家首次用碳纳米管制造出石墨烯带可广泛应用于太阳能电池、计算机等电子工业产品的开发

美国两组科学家成功地使用圆柱状的碳纳米管制造出了几十纳米宽的石墨烯带。这些石墨烯带的应用范围涵盖太阳能电池、计算机等。一直以来，科学家都认为石墨烯带比碳纳米管还要难以制造，石墨烯是从石墨材料中剥离出的单层碳原子材料，其厚度只有0．335nm，把20万片石墨烯叠加到一起，也只有一根头发丝那么厚。     

低温热剥离制备石墨烯及其电化学性能研究

以石墨为原料,采用改进的Hummers法制备了氧化石墨,300℃下热剥离氧化石墨制备得到石墨烯.采用红外光谱、扫描电镜表征了石墨烯的还原程度及形貌结构,运用循环伏安、恒流充放电等测试方法研究了石墨烯的电容性能.结果表明:石墨烯片层之间被充分剥离开来,拥有一定的孔道结构.在1 mol·L-1的硫酸电解液中,石墨烯制备的电...     

定向制备不同尺寸的3D掺氮石墨烯及其表征

利用改进的Hummers方法经冷冻干燥制备氧化石墨(GO),通过温和磁力搅拌、普通超声和大功率超声3种剥离方式,经一步水热法合成了3D掺氮石墨烯。通过FT-IR、XRD、FESEM、EDS、Raman、XPS、TGA、AFM对样品的微观形貌和结构进行表征。结果表明,通过不同的剥离方式可以得到不同形貌、不同尺寸、不同厚度、不同掺氮含量的掺氮石墨烯。温和磁力搅拌不会对片层结构有较大破坏,可制备微米级大尺寸掺氮石墨烯,厚度约为1.1 nm。在普通超声下,掺氮石墨烯片层开始产生孔状结构,厚度约为0.8 nm。在大功率超声波的空化效应作用下,片层剥离程度较普通超声更为明显,更易形成较小尺寸的3D多孔网络结构,厚度约为0.6 nm。     

Ammonia borane assisted solid exfoliation of graphite fluoride for facile preparation of fluorinated graphene nanosheets

Fluorinated graphene, which combines the unique properties of graphite fluoride and graphene, has attracted considerable attention in recent years. Here, we developed a facile, efficient, and scalable method for high-yield exfoliation of graphite fluoride into fluorinated graphene (fluorographene) nanosheets. The exfoliation approach consists of solid ball milling of graphite fluoride with ammonia borane and followed washing with ethanol to get rid of ammonia borane from the products. The majority of the as-synthesized fluorographene nanosheets consist of 1–6 atomic layers with grain sizes in the range of 0.3–1 μm. X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy demonstrated that fluorographene has the same structure as pristine graphite fluoride.     

One-step scalable preparation of graphene nanosheets and high-thermal-conductivity flexible graphene films

It is well known that graphene nanosheets (GNSs) have many excellent properties. However, it has been a difficult thing to exfoliate graphite into GNSs in a controllable and scalable manner. In this research, a new strategy named xylitol-assisted ball milling exfoliation (XABME) was developed for the scalable preparation of GNSs. The experimental results characterized by a series of measurements showed that GNSs were successfully exfoliated by the XABME strategy. The structure of the prepared nanosheets was featured by large lateral size and ultra-small thickness. Furthermore, the prepared GNSs easily achieved high production yield (≈54%). Lastly, the as-obtained GNSs and cellulose nanofibers (CNF) were compounded to form some nanomaterial films. The prepared films exhibited excellent flexibility and higher thermal conductivity, with the in-plane thermal conductivity of 90 wt% GNS film (8.0 W/(m·K)) being 11.4 times higher than that of the film without GNSs. This shows that GNSs could effectively enhance the thermal conductivity of the CNF matrix and indicate that these prepared films have great potentials in the thermal management of portable mobile devices.     

Van der Waals epitaxy and characterization of hexagonal boron nitride nanosheets on graphene

Graphene is highly sensitive to environmental influences, and thus, it is worthwhile to deposit protective layers on graphene without impairing its excellent properties. Hexagonal boron nitride (h-BN), a well-known dielectric material, may afford the necessary protection. In this research, we demonstrated the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by chemical vapor deposition, using borazine as the precursor to h-BN. The h-BN nanosheets had a triangular morphology on a narrow graphene belt but a polygonal morphology on a larger graphene film. The h-BN nanosheets on graphene were highly crystalline, except for various in-plane lattice orientations. Interestingly, the h-BN nanosheets preferred to grow on graphene than on SiO₂/Si under the chosen experimental conditions, and this selective growth spoke of potential promise for application to the preparation of graphene/h-BN superlattice structures fabricated on SiO₂/Si.     

Utilization of multiple graphene nanosheets in fuel cells: 2. The effect of oxidation process on the characteristics of graphene nanosheets

Structural properties of graphene nanosheets that will be used as electrode material in fuel cells were investigated at different oxidation times. As the oxidation time was increased, the strong bonding between graphene layers in graphite was reduced and graphene layers started to exfoliate forming clusters with a few number of graphene layers. The variations in interplanar spacings, layer number and percent crystallinity indicated how stepwise chemical procedure influenced the morphology of graphite. It was possible to produce relatively flat graphene clusters with definite number of layers by controlling the oxidation time. Graphene nanosheets were characterized in detail by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and thermal gravimetric analyzer.     

Graphene nanosheets production using liquid-phase exfoliation of pre-milled graphite in dimethylformamide and structural defects evaluation

The non-oxidation-based procedure is proposed for the production of high-quality graphene nanosheets using graphite as the raw materials. This research demonstrated a hybrid two-step production method by liquid-phase exfoliation (LPE) of Premilled graphite in Dimethylformamide (DMF) and compared it with the purely milled and just sonicated samples. However, a simple physical separation procedure composed of two centrifuge processes also designed for the separation of the products in each step. By this process, the exfoliated graphite, less-exfoliated ones and produced nanoparticles are separated, and the less-exfoliated ones are reused again in moderate sonication process. Two grades of graphene nanosheets and a grade of graphitic nanoparticles result at the end. The quality and the nature of defects in all graphene samples produced from LPE, wet milling of graphite and a combination of both, was investigated and discussed by Raman spectroscopy related indices. Raman spectra analysis indicates the adverse effect of sonication power on the in-plane defects formation in the graphene nanosheets which could be hindered by the reduction in power of sonication along with the pre-milling of the graphite. Also inductively-coupled plasma (ICP) and field emission scanning electron microscopy (FE-SEM) analysis used for further characterization of the milled-sonicated sample.     

Enhanced interfacial interaction of epoxy nanocomposites with activated graphene nanosheets

The interfacial properties of epoxy nanocomposites reinforced by thermally exfoliated graphene nanosheets (TEG) and activated thermally exfoliated graphene nanosheets (a‐TEG) were compared. The specific surface area (SSA) of a‐TEG with well‐defined micro‐mesopore size distribution was 1000 m²/g, which was much higher that of TEG (550 m²/g). The interfacial interaction between a‐TEG and epoxy was stronger than that of TEG/epoxy owing to their higher SSA and pore size which was proved by dynamic mechanical analysis. As a result, the tensile strength of a‐TEG/epoxy was increased compared with that of TEG/epoxy for all concentrations. In particular, the tensile and flexural strength of a‐TEG/epoxy was increased up to 20 and 50% in comparison to that of TEG/epoxy at 0.05 wt % graphene, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41164.     

The effect of graphene nanosheets as an additive for anode materials in lithium ion batteries

A small amount of graphene nanosheets was added to commercial graphite as an anode active material in lithium ion batteries and its effects were examined through a variety of physical and electrochemical characterization techniques: FE-SEM, XRD, Raman, BET, and EIS. Compared to a commercial graphite electrode, a composite electrode containing 1 or 5 wt% graphene nanosheets showed higher reversible capacity and enhanced cyclability. This was attributed to the large surface area and low charge transfer resistance of the graphene nanosheets.     

NiO nanosheets grown on graphene nanosheets as superior anode materials for Li-ion batteries

This paper reports a hydrothermal preparation of NiO-graphene sheet-on-sheet and nanoparticle-on-sheet nanostructures. The sheet-on-sheet nanocomposite showed highly reversible large capacities at a common current of 0.1 C and good rate capabilities. A large initial charge capacity of 1056 mAh/g was observed for the sheet-on-sheet composite at 0.1 C, which decreased by only 2.4% to 1031 mAh/g after 40 cycles of discharge and charge. This cycling performance is better than that of NiO nanosheets, graphene nanosheets, NiO-graphene nanoparticle-on-sheet, and previous carbon/carbon nanotube supported NiO composites. It is believed that the mechanical stability and electrical conductivity of NiO nanosheets are increased by graphene nanosheets (GNS), the aggregation or restacking of which to graphite platelets are, on the other hand, effectively prevented by NiO nanosheets.     

Preparation and characterization of graphite nanosheets from ultrasonic powdering technique

Natural flake graphite was exfoliated into exfoliated graphite via an acid intercalation procedure. The resulting exfoliated graphite was a worm-like particle composed of graphite sheets with thickness in the nanometer scale. Subjecting it to ultrasonic irradiation, the exfoliated graphite was effectively further foliated into isolated graphite nanosheets. SEM, TEM, SAD, laser counting, and BET measurements revealed that the graphite nanosheets prepared with 10 h irradiation were about 52 nm in thickness and 13 μm in diameter. FTIR examination showed that there were oxygen-containing groups presented on the surface of the exfoliated graphite. This result substantiated the statement reported in the literature that acid treatment could result in oxidization of carbon bonds on graphite surface.     

Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp² domains of graphene nanosheets obtained after the reduction of graphite oxide.