A simple mechanical technique to obtain carbon nanoscrolls from graphite nanoplatelets

A simple approach for the bulk production of carbon nanoscrolls (CNSs) is described. This method is based on the application of shear-friction forces to convert graphite nanoplatelets into carbon nanoscrolls using a bi-axially oriented polypropylene (BOPP) surface. The combined action of shear and friction forces causes the exfoliation of graphite nanoplatelets and the simultaneous roll-up of graphite layers. Evidence of the CNS formation is given by optical microscopy, scanning electron microscopy, and transmission electron microscopy. These investigations reveal that the CNSs have a long tube-like and fusiform structure with a hollow core surrounded by few layers of graphene. Micro-Raman spectroscopy shows that the produced structures are not defect free, and optical spectroscopy reveals distinctive features due to the presence of two weak absorption bands at 224 and 324 nm.     

The synthesis of graphene sheets with controlled thickness and order using surfactant-assisted electrochemical processes

An electrochemical route is reported for the production of graphene sheets using the following steps: electrochemical intercalation of sodium dodecyl sulfate (SDS) into graphite followed by electrochemical exfoliation of a SDS-intercalated graphite electrode. These electrochemical processes yield a stable colloidal graphene/SDS suspension. The potential value for SDS intercalation into graphite plays an important role in determining the structural order, size, and number of layers of synthesized graphene sheets. Raman spectroscopy and transmission electron microscopy results indicate that graphene sheets with the highest structural order and lowest number of layers can be obtained by using relatively high intercalation potentials. Average size and thickness of graphene sheets prepared at high potentials for SDS intercalation into graphite were measured to be about 500 and 1 nm, respectively, indicating presence of graphene sheets as thin as a monolayer. UV–vis spectra of graphene/SDS suspensions show that a large amount of the reduced form of graphene flakes is obtained after successive electrochemical intercalation and exfoliation processes.     

Anodic behaviour of carbon materials in NaCl saturated NaAlCl4 fused electrolyte at low temperatures: A cyclic voltammetric study

The anodic behaviour of compacted graphite, graphite powder, glassy carbon and reticulated vitreous carbon electrodes in basic sodium chloroaluminate melt in the temperature range 428–573 K was studied using cyclic voltammetry. Chlorine evolution (> + 2.1 V vs Al) alone was the predominant reaction on the compact glassy carbon and fresh RVC electrodes. On compacted graphite, chlorine-assisted chloroaluminate intercalation was found to be a competitive process to the chlorine evolution. At high sweep rates, intercalation/deintercalation near the graphite lattice edges occur faster than chlorine evolution. Subsequent intercalation, however, is a slow process. Chlorine evolution predominates at higher temperatures and at higher anodic potentials. On graphite powders, a more reversible free radical chlorine adsorption/desorption process also occurs in the potential region below chlorine evolution. The process occurs at the grain boundaries, edges and defects of the graphite powder material. Intercalation/deintercalation processes are mainly responsible for the disintegration of graphitic materials in low-temperature chloroaluminate melts. Repeated intercalation/deintercalation cycles result in the irreversible transformation of the electrode surface and electrode characteristics. The surface area of the electrode is increased substantially on cycling. Electrode materials and operating conditions suitable for chlorine generation, intercalation/deintercalation and chlorine adsorption/desorption and power sources based on these processes are identified in this work.     

界面涂层对碳纤维增强锂铝硅玻璃陶瓷复合材料力学性能影响的研究

采用溶胶凝胶法在碳纤维表面制备了Li2O/SiO2涂层,采用XRD技术对其层间结构进行了表征.结果表明在所得碳纤维的表面层形成了二阶的插层结构的石墨层间化合物,聚丙烯腈基碳纤维作宿主,锂离子作插层剂的,该插层化合物的生成提高了碳纤维增强锂铝硅玻璃陶瓷复合材料的抗弯强度.     

Tuning Schottky diodes at the many-layer-graphene/semiconductor interface by doping

We report on the use of bromine intercalation of graphite to perform in situ tuning of the Schottky barrier height (SBH) formed at many-layer-graphene (MLG) semiconductor interfaces. The intercalation of Br into MLG simultaneously increases interlayer separation between the graphene planes, while at the same time giving rise to an increase (decrease) in the free hole carrier density (Fermi energy) because of the transfer of electrons from carbon to bromine. The associated increase in the graphite work function results in an increase of the SBH, as manifested by lower forward/reverse current densities and higher depletion capacitances. These results are quantitatively understood within the context of the Schottky–Mott model and thermionic emission theory. The presented results have important implications for sensing and high power applications as well as the integration of carbon into semiconductors and carbon/graphene electronics.     

混酸插层制备膨胀石墨研究

对采用H2SO4-HNO3-KMnO4-H2O2混酸氧化插层体系制备膨胀石墨进行了研究,采用扫描电镜（SEM）、X射线衍射（XRD）、红外光谱（IR）和热重一差热法（TG-DTA）分析产物,并提出了氧化插层过程和机理。分析表明：插入剂的插入破坏了原有鳞片石墨层的紧密结构,使碳层间距增大,高温膨胀后,膨胀石墨呈蠕虫状或手风琴状蓬松结构,一个石墨蠕虫由许多微胞连接在一起组成,微胞之间呈现较大的狭缝裂开。氧化插层破坏了鳞片石墨原有的晶体结构,但是未破坏石墨的C—C键,20=29．5。处的特征峰是由石墨插层物结晶区引起的。可膨胀石墨片层。间存在SO4^2-、NO2阴离子插层物。可膨胀石墨在500℃之前的热失重和267℃附近较小的放热峰,均是由石墨插层物的气化、分解所致。     

Graphite intercalation compounds as PEMFC electrocatalyst supports

Intercalation of metal chlorides into fine natural graphite flakes of 2 × 10⁻⁶ m in diameter was attempted. CuCl₂ was satisfactorily intercalated from the vapour phase. NiCl₂ and PdCl₂ were also intercalated from the liquid phase using chloroform solvent. The reduction products of the obtained graphite intercalation compounds were used as carbon supports of the platinum electrocatalyst for a proton exchange membrane fuel cell. Oxygen reduction activity was evaluated and it can be seen that natural graphite flakes treated using the intercalation technique provide different levels of activity from that of pristine natural graphite flakes. In particular, the catalytic activity was enormously improved when CuCl₂ was used as the intercalate.     

Chemical Fibre Gland Packing for Sealing Connections in Operation in Hot Water and Residual Fuel Oil

The positive effect of impregnating carbon fibre packings with a suspension of a fluoroplastic and graphite is demonstrated. The carbon packing impregnated with the fluoroplast—graphite suspension is recommended for sealing connections in hot water and residual fuel oil.     

Preparation of tin-filled carbon nanotubes and nanoparticles by molten salt electrolysis

This article presents a molten salt electrolytic method of synthesizing tin-filled carbon nanostructures, in which a melt of LiCl with an addition of SnCl₂ is electrolyzed between two graphite electrodes. In this process, Li intercalates into the cathodically polarized graphite while Sn is deposited onto the graphite surface. The Li intercalation causes the release of graphitic layers from the graphite, which enclose the Sn deposits, to form Sn-filled MWCNTs and carbon nanoparticles. By reversing the polarity of the graphite electrodes at regular intervals during electrolysis, the process can be extended substantially until the electrodes have been completely consumed, suggesting its suitability for production at a larger scale.     

A novel route towards high quality fullerene-pillared graphene

A new approach for the synthesis of graphite intercalation compounds (GICs), by the help of co-intercalant molecules, has been observed. In the present work, we demonstrate the successful incorporation of fullerene (C₆₀) molecules between the graphene sheets aided by the preceding intercalation of nitric acid. The presence of intercalated C₆₀ between the graphene sheets is deduced from X-ray diffraction patterns, while Raman and X-ray photoelectron spectroscopy (XPS), verify that the quality of the graphene layers is not compromised by the intercalation. A quantification of the interaction yield was derived from thermogravimetric analysis and XPS studies, giving that fullerene molecules intercalated in the pillared structure amount to about 25 wt%. The present method opens new perspectives for the intercalation of various guest molecules in graphite also because graphite nitrate allows for functionalization processes following the very well established carbon chemistry.     

The influence of three different intercalation techniques on the microstructure of exfoliated graphite

The characteristics of exfoliated graphite derived from three intercalation methods: gas phase intercalation of iron (III) chloride, modified Hummers method and an electrochemical technique, were compared.Despite the absence of strong oxidisers the electrochemical method produced a material which is very similar to that of the modified Hummers method in virtually every respect. These both produced a graphite oxide based material whilst the gas phase method resulted in a stage 1 intercalation compound. The different materials demonstrated very distinctive exfoliation behaviour.The gas phase material exhibits 3% mass loss during expansion but has a large amount of residual intercalant. The graphite oxide based methods result in mass loss of up to 25% in the expansion zone. For all three samples the residual impurities lead to a reduction in oxidative resistance. Once removed all samples exhibit nearly identical oxidation behaviour.All three methods delivered graphite nanoplatelets with a very high aspect ratio through considerable expansion. Surprisingly the gas phase method caused persistent residual damage. All three methods yielded a product with varying levels of basal and edge damage, but the purified Hummers material exhibited marginally more ‘ideal’ characteristics. The simplest but still effective technique was found to be the electrochemical approach.     

The intercalation of bromine in graphitized carbon fibers and its removal

When the bromine residue in graphite is heated and cooled between 20° and 900°C there is an emission of Br₂ over certain relatively small temperature ranges on both heating and cooling. It is shown that two of these emissions are associated with observed decreases in X-ray diffraction spacing between carbon layers—one on heating around 175°C and one on cooling around 100°C. The intercalation isotherms of Br₂ and of ICl on graphitized carbon fibers show that the threshold pressure on the residue is lower than on the original fiber. This is believed to be caused in fibers by the production of microscopic cracks in the interlocking amorphous carbon networks between the graphitized domains during the initial intercalation. Hence, when again exposed to Br₂ the compresssion-tension builds to a lower value so that the threshold pressure is lower and the rate of intercalation is higher. The anomalous bromine emission behavior in fiber is attributed to differential dimensional changes of the isotropic carbon network and the anisotropic crystallites. In natural graphites the anomalous emission originates in a differential dimensional change between the polycrystalline structure of the total sample of graphite and the anisotropic single crystal components of the graphite.     

High-quality few layer graphene produced by electrochemical intercalation and microwave-assisted expansion of graphite

Few-layer graphene is synthesized from electrochemically-produced graphite intercalation compounds in aqueous perchloric acid. Although anodic intercalation is more efficient in terms of time, cathodic pre-treatment is preferred to avoid the formation of graphite oxide. The materials are characterized by high resolution transmission electron microscopy and scanning electron microscopy, UV–visible, infrared and Raman spectroscopy. We demonstrate that the method, under the experimental conditions used in this work, does not produce damage to the sp² carbon lattice. The synthetic approach using electrochemical-potential control is very promising to obtain, in a controllable manner, graphene with different degrees of oxidation.     

Computer simulation for storage of methane and capture of carbon dioxide in carbon nanoscrolls by expansion of interlayer spacing

We perform a molecular simulation study on methane and carbon dioxide storage in carbon nanoscrolls. The effects of temperature and pressure, interlayer spacing, VDW gap and innermost radius on the gas storage have been examined extensively. It is found that the adsorption of gases on pristine carbon nanoscrolls is relatively low. However, once the interlayer spacing is expanded, both adsorption capacities of methane and carbon dioxide exhibit a significant improvement. In particular, the excess uptake of methane reaches 13 mmol/g at p = 6.0 MPa and T = 298.15 K and VDW gap Δ = 1.1 nm, which is about 3.5 times of uptake of the pristine carbon nanoscrolls; while the uptake of carbon dioxide could also be raised by 294.9% at T = 298.15 K and p = 3.0 MPa and Δ = 1.5 nm, reaching 30.21 mmol/g at 6.0 MPa. This work demonstrates that carbon nanoscrolls with an expansion of interlayer spacing may be a suitable material for methane storage and carbon dioxide capture.     

A green approach for cohesive recycling and regeneration of electrode active materials from spent lithium-ion batteries

The implementation of the green energy transition by reducing reliance on fossil fuels has fueled the burgeoning demand for lithium-ion batteries in grid-level energy storage systems and electric vehicles. The growth of portable electronic devices has also contributed to this exponential demand, creating both logistical and environmental challenges in the supply of raw materials such as lithium and the management of end-of-life batteries. Current recycling methods for spent batteries are both energy-intensive and inefficient. To address these issues, a green approach using organic acid mixtures has been proposed to reclaim lithium from spent cathodes and recover and purify graphite from spent anodes, while also regenerating its structure. The effectiveness of this method is demonstrated through the use of organic acid mixtures to leach and reclaim lithium from NCM 622 batteries. On the anode side, a curing–leaching strategy using organic acids is employed to purify spent graphite, which is subsequently calcined to enhance its interlayer structure conducive to better intercalation of Li⁺ and improve electrochemical performance. Additionally, recovered graphite is tailored with carbon using water bath carbonization to repair structural defects caused by lithium intercalation and improve electrochemical performance while augmenting the regenerated graphite's quality, equipping it to be reused in batteries or upcycled applications.     

气相扩散法制备石墨层间化合物述评

本文从碱金属-石墨层间化合物、碱土金属-石墨层间化合物、稀土金属-石墨层间化合物、金属卤化物-石墨层间化合物、卤素-石墨层间化合物以及其他类型的石墨层间化合物六个方面简要介绍了气相扩散法在石墨层间化合物制备中的应用,指出了气相扩散法存在的问题和进一步的发展方向.     

Calcium oxide and potassium hydroxide catalysed low temperature methane production from graphite and water Comparison of catalytic mechanisms

An experimental study was carried out to obtain information on the catalytic mechanisms involved in the methanation of graphite using, separately, potassium and calcium as catalysts, and water and/or hydrogen as reactants. The mechanisms for the potassium-catalysed graphite—water reaction appear to be the same in the wide temperature range from 473 to 873 K as indicated by the constant activation energy, 46 kJ mol^?1, found for methane production. The intercalation of potassium into the graphite as a possible step in the methane synthesis has been investigated and ruled out. XPS studies indicate the formation of an active form of more positively charged carbon from graphite when graphite is heated at low temperature in the presence of a calcium catalyst and water vapour. The activation energy for this carbon depolymerization reaction is 68.1 kJ mol^?1. Methane formation occurs only in the presence of hydrogen due to its reaction with the active carbon with an activation energy of 106.6 kJ mol^?1.     

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.     

Electrical resistivity and magnetoresistance of carbon/graphite fibers intercalated with nitric acid and arsenic pentafluoride

A series of high performance, experimental carbon/graphite fibers was intercalated and examined with respect to their metallic conductivity behavior by resistivity and magnetoresistance versus temperature measurements. One fiber was a polyacrylonitrile (PAN)-type precursor and three were pitch base precursors. All four types showed substantially similar behavior in the pristine state with respect to room temperature resistivity and the sign and magnitude of the temperature coefficient of resistivity. After intercalation with either nitric acid or nitric acid followed by AsF₅, the PAN-based fibers displayed a resistivity versus temperature behavior qualitatively similar to their pristine counterparts but displaced to lower resistivity. On the other hand, the pitch fibers with the same intercalation treatment exhibited metallic behavior (a positive temperature coefficient of electrical resistivity and a small magnetoresistance). These manifestations of metallic behavior are usually indicative of some three dimensional graphite structure in the carbon fibers.     

锂离子电池碳负极材料的结构与嵌锂行为

介绍了按炭素材料的定向程度和定向方式的结构特征对其进行分类的方法;综述了近年各种炭材料作为锂离子电池负极的较新研究进展,着重分析了石墨、焦碳和不可石墨化碳在放电容量、不可逆容量损失、充放电电位和充放电速率等主要性能上的差异及与他们的结构之间的联系;并简要介绍了各自可能的嵌入机理。