Cation-directed orientation of amines in ternary graphite intercalation compounds

1,2-Diaminopropane (1,2-DAP) provides an unusual example of an organic co-intercalate where graphite intercalation compounds (GICs) show intra-gallery orientation dependant on the identity of the alkali metal cation intercalate (Li⁺, Na⁺, or K⁺). The GIC gallery heights, K(1,2-DAP)_yC_x = 0.697 nm and Li(1,2-DAP)_yC_x = 0.782 nm, indicate 1,2-DAP long axis orientations that are parallel or perpendicular to the graphene sheets, respectively.     

The synthesis and properties of highly exfoliated graphites from fluorinated graphite intercalation compounds

A series of new highly exfoliated graphites were synthesized from fluorinated graphite intercalation compounds of compositions C₂F·xR (R = ClF₃, (CH₃)₂CO, CH₃CN, C₆H₆, CCl₄). The exfoliation degree of these materials reaches more than 2000 times, indicating a significantly higher exfoliated state than observed for the conventional expanded graphites derived from graphite bisulphate or nitrate. These exfoliated graphites have increased interlayer distances, specific surface areas as high as 170–370 m²/g, low bulk densities of 0.4–0.7 g/L, and good sorption capacities towards a range of organic and inorganic liquids. The influence of the nature of the intercalated molecules on the properties of the exfoliated graphite is discussed.     

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.     

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.     

Electrochemical behavior of graphite intercalation compounds of fluorine and metal fluorides

Ternary intercalation compounds, C_xF(AlF₃)_y and C_xF(MgF₂)_y containing active fluorine atoms adsorbed on carbon layers of host graphite were used as a cathode material of lithium cell. The discharge potentials are 2.8–2.5 V at current densities 40–400 μA cm^?2, being higher than that for graphite fluoride below 300 μA cm^?2. X-ray diffraction analysis and ESCA measurement of the discharge products indicate the formation of a new intercalation compound C_x(LiF) (MF_n)_y, (M = Al or Mg, n = 3 or 2).     

X-ray diffraction studies of electrochemical graphite intercalation compounds of ionic liquids

Electrochemical intercalation studies are used to characterize a series of ionic liquids composed of a variety of cationic and anionic species. Electrochemically, the ionic liquids are characterized by cyclic voltammograms and charge–discharge experiments for the intercalation and de-intercalation of the various cationic and anionic species into graphite. X-ray structure analysis is also performed to determine the relationship between the electrochemical behaviour of the ionic liquids, and the formation of intercalated graphitic compounds. Two different types of imidazolium cations are studied, specifically the di- and trisubstituted imidazolium. These cations are paired with the following anions: tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, bis(perfluoroethanesulfonyl)imide, nitrate and hydrogen sulfate. Results indicate stronger intercalation chemistry for the trisubstituted imidazoliums, correlating with the greater charge–discharge efficiencies found for these types of ionic liquids. Many of the anions exhibit very poor charge–discharge efficiencies, correlating to very poorly formed graphite intercalates. The exception to this is the hydrogen sulfate intercalate, which had low charge–discharge efficiencies but formed a well defined graphite intercalate. Only the imide based anions exhibited both high charge–discharge efficiencies and the formation of a clearly defined graphite intercalate.     

The first graphite intercalation compounds containing tris(pentafluoroethyl)trifluorophosphate

Graphite intercalation compounds (GICs) containing the tris(pentafluoroethyl)trifluorophosphate anion, [(C₂F₅)₃PF₃]⁻ are prepared for the first time by electrochemical oxidation of graphite in a nitromethane electrolyte. Powder X-ray diffraction (PXRD) data indicate that products are of stages 2-4 with gallery heights of 0.82-0.86 nm. Intercalate orientation is determined by using a structure model containing an energy minimized anion. GIC compositional parameters are obtained by microwave digestion followed by F elemental analysis, in combination with thermogravimetric analyses.     

新型钆石墨层间化合物复合材料的制备及表征

通过Hummers法制备氧化石墨,并以化学吸附法将氯化钆（GdCl3）饱和溶液中的钆离子引入氧化石墨（GO）,合成新型水合碳酸氧钆-氧化石墨层间化合物复合材料。采用XRD、FT-IR和TG-DTA对产物进行分析表征。表明,制备水合碳酸氧钆-氧化石墨层间化合物的最佳质量配比为m（Gd2O3）∶m（EG）=5∶1。通过TG-DTA分析确认,水合碳酸氧钆-氧化石墨层间化合物的还原温度为480℃。     

Preparation, structure and reduction of graphite intercalation compounds with hexachloroplatinic acid

Electrochemical oxidation and exchange intercalation, have been used for the production of graphite intercalation compounds (GICs) with hexachloroplatinic acid. Ternary GICs H₂PtCl₆-HNO₃-graphite and H₂PtCl₆-H₂SO₄-graphite have been synthesized by the incomplete exchange reaction between the parent HNO₃ and H₂SO₄ GICs and hexachloroplatinic acid. Irrespective of the precursor GIC stage, stage-2 GIC with H₂PtCl₆ has been obtained. Attempted synthesis of the single-phase stage-2 GIC via the electrochemical oxidation of graphite in H₂PtCl₆ solutions failed since mixtures of the target products with pure graphite have resulted in all cases. The structure and properties of the samples obtained have been examined by XRD, SEM, TG-DTG, TG coupled with FTIR and EXAFS-XANES. GIC samples were preheated to 200 °C to produce exfoliation (caused by deintercalation of nitric acid), and reduced either with boiling 5% aqueous formaldehyde or hydrogen. This approach gives rise to exfoliated graphite material with platinum nanoclusters distributed on the surface. In contrast to the most other work particles with open surfaces were obtained.     

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.     

Theoretical study of stability of graphite intercalation compounds with Brønsted acids

The instability of acceptor graphite intercalation compounds (GICs) with Brønsted acids is a main obstacle to their extensive industrial use. Electron transfer from the solvated anion to the positively charged graphene layer is considered to be the first and rate-limiting step in the decomposition process, with the ionization potential of the intercalated anion being a measure of the stability of GICs. The effects of the hydrogen bonding and Coulomb interaction on the GIC stability are discussed.