Synthesis,Properties, and Dispersion of Few‐Layer Graphene Fluoride

We have fluorinated few‐layer graphene (FLG) by using a low‐temperature fluorination route with gaseous ClF₃. The treatment process resulted in a new graphene derivative with a finite approximate composition of C₂F. TEM studies showed that the product consisted of thin transparent sheets with no more than 10 fluorographene layers stacked together. Spectroscopic methods revealed a predominantly covalent nature of the C? F bonds in the as‐synthesized product and we found no evidence for the existence of so‐called “semi‐ionic” C? F bonds, as observed in bulk C_xF. In contrast to the case of graphite and typical (thick) expanded graphites, fluorination of FLG did not lead to the intercalation of ClF₃ molecules, owing to the lack of a 3D layered structure. The approximate “critical” number of graphene layers that were necessary to form a phase of intercalated compound was estimated to be more than 12, thus providing a “chemical proof” of the difference between the properties of few‐layered graphenes and bulk graphites. Fluorographene C₂F was successfully delaminated into thinner layers in organic solvents, which is an important property for its integration into electronic devices, nanohybrids, etc.     

Intercalation of halogen fluorides into graphite

IF₇ intercalates into graphite accompanied by the partial fluorination of the graphite host. The intercalated species was identified as IF₅ by IR and ¹⁹F nmr spectroscopies. Mass spectrometric analyses of the gases evolved from the intercalate showed only IF₅ and fluorocarbons. Iodine pentafluoride intercalates only in the presence of HF, yielding a compound with the stoichiometry C₈IF₅ and no fluorination of the graphite host. Careful elimination of even traces of HF resulted in no intercalation. Evolved gas analysis showed that the only species recovered from the intercalation was IF₅. The remaining interhalogens, ClF₅, ClF₃, BrF₅ and BrF₃ all intercalate into graphite with extensive fluorination of the lattice. In the case of these four compounds, the intercalate proved to be more difficult to characterize, e.g. stoichiometry was often variable, and ¹⁹F nmr yielded resonances that did not agree with any known halogen fluorides. Thermal decomposition of these intercalates showed little or no gas evolution until relatively high temperatures were reached, whereupon Cl₂ or Br₂ was evolved, followed by fluorocarbons.     

Facile preparation of graphite intercalation compounds in alkali solution

Graphite intercalation compounds are often prepared by flake graphite, oxidants, inorganic acids, organic acids and intercalated ions which are usually hydrogen protons between the graphene planes. They are also known as the acid-treated graphite intercalation compounds. In this work, alkaline graphite intercalation compounds were prepared by flake graphite, K₂Cr₂O₇, concentrated H₂SO₄ and NaOH, and the morphology and structure were characterized by Electron microscopy and X-ray techniques. The results display that the combination of neutralisation heat and oxidation capability produced by K₂Cr₂O₇ can break the bonds to produce the spaces between the graphene planes and hydroxyl ions also intercalate into the graphene planes to form alkaline graphite intercalation compounds in alkali solution. The morphology and structure of alkaline graphite intercalation compounds are analogous to the ones of the acid-treated graphite intercalation compounds, but the intercalated ions and the expansion volume are different. The results show that the method is an innovation.     

Synthesis,structure and properties of fluorinated graphite

Fluorine-graphite intercalation compounds, C₂F to C₁₆F were synthesized by various methods. C-F bonds range from ionic to semi-covalent. These properties of C-F bonding give to fluorinated graphite metallic conductivity, higher hydrophilicity than graphite and high reduction potential. The c-axis and in-plane structures are governed by C-F bonding, fluorine intercalation rate and host graphites.     

Structural characteristics of dicarbon polyfluoride

In chemical analysis and XRPA studies, it has been found that the products of fluorination of graphite, graphite bifluoride, and tetracarbon polyfluoride with gaseous and liquid fluorooxidants (ClF₃, ClF₅, XeF₂, and FNO₃) and their solutions in anhydrous hydrogen fluoride and freon-113 at 20–100°C, having a limiting composition, are second stage intercalated compounds based on dicarbon polyfluoride with the corresponding fluorooxidant, or the reduced form of fluorooxidant, or a fluorooxidant and a solvent. The degree of C-F bond ionicity in C₂F was higher than in CF, but lower than in C₄F. However, the bond is closer in character to the covalent C-F bond in monocarbon polyfluoride.     

In situ X‐ray Diffraction Studies of Cation and Anion Inter­calation into Graphitic Carbons for Electrochemical Energy Storage Applications

Graphite is a redox‐amphoteric intercalation host and thus capable to incorporate various types of cations and anions between its planar graphene sheets to form so‐called donor‐type or acceptor‐type graphite intercalation compounds (GICs) by electrochemical intercalation at specific potentials. While the LiC_x/C_x donor‐type redox couple is the major active compound for state‐of‐the‐art negative electrodes in lithium‐ion batteries, acceptor‐type GICs were proposed for positive electrodes in the “dual‐ion” and “dual‐graphite” cell, another type of electrochemical energy storage system. In this contribution, we analyze the electrochemical intercalation of different anions, such as bis(trifluoromethanesulfonyl) imide or hexafluorophosphate, into graphitic carbons by means of in situ X‐ray diffraction (XRD). In general, the characterization of battery electrode materials by in situ XRD is an important technique to study structural and compositional changes upon insertion and de‐insertion processes during charge/discharge cycling. We discuss anion (X^–) and cation (M⁺) intercalation/de‐intercalation into graphites on a comparative basis with respect to the M_x⁺C_n^– and C_n⁺X_n^– stoichiometry, discharge capacity, the intercalant gallery height/gallery expansion and the M–M or X–X in‐plane distances.     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(CnTAB)对其进行插层处理;通过改变CnTAB的链长、浓度,得到系列CnTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及CnTAB插入量进行表征。结果表明,随着Cn TAB链长的增长、CnTAB浓度的增大,CnTAB/GO插层复合物的最大底面间距逐渐增大。CnTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即CnTAB以单分子层吸附在GO片层上。根据CnTAB/GO插层复合物最大底面间距及CnTAB插入量的变化规律分析,得出CnTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(C_nTAB)对其进行插层处理;通过改变C_nTAB的链长、浓度,得到系列C_nTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及C_nTAB插入量进行表征。结果表明,随着C_nTAB链长的增长、C_nTAB浓度的增大,C_nTAB/GO插层复合物的最大底面间距逐渐增大。C_nTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即C_nTAB以单分子层吸附在GO片层上。根据C_nTAB/GO插层复合物最大底面间距及C_nTAB插入量的变化规律分析,得出C_nTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

石墨烯和铂/石墨烯的合成及其表征

以天然鳞状石墨为原料,采用化学氧化法合成氧化石墨,在此基础上采用低温热解膨胀结合微波加热乙二醇还原法合成石墨烯(Gr)以及铂/石墨烯(Pt/Gr)复合材料。SEM和TEM显示所制备的石墨烯为层状结构的半透明薄膜。采用X射线光电子能谱(XPS)和傅立叶转换红外光谱(FTIR)分别确定氧化石墨、膨胀石墨及石墨烯表面含氧官能团的数量和性质。以所制备的碳氧原子比5.94的石墨烯作为载体制备出可用于质子交换膜燃料电池的高负载量的Pt/Gr催化剂,在铂载量高达60%时,表面铂粒子依然具有高分散性,平均粒径为3.8 nm。     

On the Structure of Graphite Fluoride

The structure of graphite fluoride, (C₂F)_n has been investigated by X-ray analyses, solid state ¹⁹F-n.m.r., and electron microscopy for well characterized and crystallized samples obtained from natural graphite or HOPG (highly oriented pyrolytic graphite). On the basis of the present results and structural properties derived from previous works, (C₂F)_n has a layered structure of stage-2 which belongs hexagonal to the system with C_3h symmetry. Detailed discussions on the symmetry both for (CF)_n and (C₂F)_n have led to possible stacking sequences each unit cell of graphite fluoride should require. The ideal structure of (C₂F)_n is a hexagonal crystal lattice with a = b = 2.5 Å; c = 16.2 Å, and a plausible stacking sequence of AB/B′A′/ with I_c (identity period) = 8.09 Å. The layered structure of (CF)_n is of stage-1 with A/A′/ stacking sequence.     

Acceptor-type graphite intercalation compounds and new carbon materials based on them

The problems of synthesis and study of the physicochemical properties of graphite intercalation compounds (GIC) formed upon insertion of various molecules into the interplanar space of graphite are considered. Binary and ternary intercalation compounds with protonic acids (HNO₃, CH₃COOH, H₃PO₄, H₂SO₄, etc.) are described. The results of systematic research into graphite intercalation by potentiometry, calorimetry, powder X-ray diffraction, conductivity measurements, DTA, chemical analysis, and other methods are given. These results underlie elucidation of the characteristic and peculiar features of acid insertion into graphite. The physicochemical properties and practical applications of GIC and low-density carbon materials are analyzed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1699–1716, August, 2005.     

Inherent Electrochemistry and Activation of Chemically Modified Graphenes for Electrochemical Applications

Graphene research is currently at the frontier of electrochemistry. Many different graphene‐based materials are employed by electrochemists as electrodes in sensing and in energy‐storage devices. Because the methods for their preparation are inherently different, graphene materials are expected to exhibit different electrochemical behaviors depending on the functionalities and density of defects present. Electrochemical treatment of these “chemically modified graphenes” (CMGs) represents an easy approach to alter surface functionalities and consequently tune the electrochemical performance. Herein, we report a preliminary electrochemical characterization of four common chemically modified graphenes, namely: graphene oxide, graphite oxide, chemically reduced graphene oxide, and thermally reduced graphene oxide. These CMGs were compared with graphite as a reference material. Cyclic voltammetry was used to ascertain the chemical functionalities present and to understand the potential ranges in which the materials were electroactive. Electrochemical treatment with either an oxidative or a reductive fixed potential were then carried out to activate these chemically modified graphenes. The effects of such electrochemical treatments on their electrocatalytic properties were then investigated by cyclic voltammetry in the presence of well‐known redox probes, such as [Fe(CN)₆]^4?/3?, Fe^3+/2+, [Ru(NH₃)₆]^2+/3+, and ascorbic acid. Thermally reduced graphene oxide exhibited the best electrochemical behavior amongst all of the CMGs, with the fastest rate of heterogeneous electron transfer (HET) and the lowest overpotentials. These findings will have far‐reaching consequences for the evaluation of different CMGs as electrode materials in electrochemical devices.     

The relationship of graphite/AsF5 intercalation compounds to Cx+AsF6− salts

Graphite intercalated by AsF₅ has been reported to give compounds of formula C_8nAsF₅ where n is the stage. It is doubtful however if materials of exact composition C_8nAsF₅ have ever been obtained. The intercalation of graphite by AsF₅ is associated with electron oxidation of the graphite according to the equation: 3AsF₅ + 2e^? → 2AsF₆^? + AsF₃. Because of the easy removal or displacement of AsF₃ the As:F ratio is readily increased beyond 5. By treating graphite with excess AsF₅, removing volatiles under vacuum and repeating the cycle seven times a first stage salt C₁₀⁺AsF₆^? (C_o = 7.96 ā) is made. Interaction of graphite with AsFs in the molar ratio 8:1, within a small volume reactor, yields a material of approximate composition C₈AsF₅. The major component of the volatiles at the onset of their removal is AsF₅,, but, at a composition close to C₁₀AsF₅, is AsF₃. ‘Graphite AsF₅’ can be prepared by adding AsF₃ to C_xAsF₆ salts. The electrical conductivities of ‘AsF₅’ and AsF₆ relatives will be compared and discussed.     

Isostructural organic–inorganic hybrid compounds: triethylcholine tribromidocadmate and triethylcholine tribromidomercurate

In order to search for new anionic architectures and develop useful organic–inorganic hybrid materials in halometallate systems, two new crystalline organic–inorganic hybrid compounds have been prepared, i.e. catena‐poly[triethyl(2‐hydroxyethyl)azanium [[bromidocadmate(II)]‐di‐μ‐bromido]], {(C₈H₂₀NO)[CdBr₃]}_n, (1), and catena‐poly[triethyl(2‐hydroxyethyl)azanium [[bromidomercurate(II)]‐di‐μ‐bromido]], {(C₈H₂₀NO)[HgBr₃]}_n, (2), and the structures determined by X‐ray diffraction analysis. The compounds are isostructural, crystallizing in the space group P2₁/n. The metal centres are five‐coordinated by bromide anions, giving a slightly distorted trigonal–bipyramidal geometry. The crystal structures consist of one‐dimensional edge‐sharing chains of MBr₅ trigonal bipyramids, between which triethylcholine counter‐cations are intercalated. O—H...Br hydrogen‐bonding interactions are present between the cations and anions.     

Structural diversity of a series of chlorocadmate(II) and chlorocuprate(II) complexes based on benzylamine and its N-methylated derivatives

Protonated benzylamine and its N-methylated derivatives, [C₆H₅CH₂NH_3?n(CH₃)_n]⁺ (n?=?0?3), have been adopted as cations in chlorocadmate(II) and chlorocuprate(II) complexes, showing inorganic–organic hybrid architectures. For the Cd(II) compounds, the anionic structures vary from perovskite-type layers (n?=?0) to chains (n?=?1–3). For Cu(II) compounds, the anionic structures range from perovskite-type layers (n?=?0), chains (n?=?1) to mononuclear species (n?=?2–3). Coordination geometries of the metal ions and intermolecular interactions have been analyzed. Their dielectric properties have been measured.     

The relationship between properties of fluorinated graphite intercalates and matrix composition

Inclusion compounds (intercalates) of fluorinated graphite matrix with acetone (C₂F _x Br _z ·y(CH₃)₂CO, x = 0.49, 0.69, 0.87, 0.92, z ≈ 0.01) were prepared by guest substitution from acetonitrile to acetone. The kinetics of the thermal decomposition (the first stage of filling → the second stage of filling) was studied under isothermal conditions at 292–313 K. The relationship of the host matrices structure with inclusion compounds thermal properties and kinetic parameters is discussed.     

Preparation,spectral, thermal,and biological properties of zinc(II) 4-chloro- and 5-chlorosalicylate complexes with methyl 3-pyridylcarbamate and phenazone

New zinc(II) 4-chloro- and 5-chlorosalicylate complex compounds of the general formula ((4- or 5-Cl)C₆H₃(2-OH)COO)₂Zn · L _n (where L = methyl 3-pyridylcarbamate, phenazone; n = 2, 4) were prepared and characterized by elemental analysis, thermal analysis (TG/DTG, DTA), and IR spectroscopy. During thermal decomposition, mpc, phen, chlorosalicylic acid, chlorophenol, carbon dioxide, and carbon monoxide were released. Volatile products of the thermal decomposition were confirmed by mass spectrometry. The final solid product of the thermal decomposition up to 700°C was zinc oxide or metallic zinc. Antimicrobial activity of the compounds prepared was tested against various strains of bacteria, yeasts and filamentous fungi. The highest antimicrobial effect was determined against the G⁺ bacteria S. aureus.     

Molecular Intercalation and Electronic Two Dimensionality in Layered Hybrid Perovskites

In layered hybrid perovskites, such as (BA)₂PbI₄ (BA=C₄H₉NH₃), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb–I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.     

Über die Einlagerung von Antimonfluoridchloriden in Graphit Versuche zur Darstellung von Metallfluorid-Graphitverbindungen

The reaction between graphite and SbF₃ in Cl₂ atmosphere or SbF₃Cl₂in inert atmosphere gives antimony fluoride-chloride graphite compounds. The first intercalation stage is deep blue and contains 67–68% SbF_xCl_y. The ideal composition is near [C₂₇]_GrSbF₃Cl₂ · 2 SbF₃Cl₂. SbF₃Cl₂ can be substituted partly by SbF₃ or SbF₅. The layer distance decreases with increasing F:Cl ratio from 8.87 to 8.36 Å. There exist also a second and third intercalation stage.     

1‐(4‐Chloro­phenyl­sulfanyl)‐2‐nitro‐4‐(tri­fluoro­methyl)­benzene and 1‐(4‐chloro­phenyl­sulfanyl)‐4‐nitro‐2‐(tri­fluoro­methyl)­benzene

Two chemical isomers of 3‐nitro­benzotrifluoride, namely 1‐(4‐chloro­phenyl­sulfanyl)‐2‐nitro‐4‐(tri­fluoro­methyl)­benzene, C₁₃H₇ClF₃NO₂S, (I), and 1‐(4‐chloro­phenyl­sulfanyl)‐4‐nitro‐2‐(tri­fluoro­methyl)­benzene, C₁₃H₇ClF₃NO₂S, (II), have been prepared and their crystal structures determined with the specific purpose of forming a cocrystal of the two. The two compounds display a similar conformation, with dihedral angles between the benzene rings of 83.1 (1) and 76.2 (1)°, respectively, but (I) packs in P while (II) packs in P2₁/c, with C—H⋯O interactions. No cocrystal could be formed, and it is suggested that the C—H⋯O associations in (II) prevent intermolecular mixing and promote phase separation.