Graphite intercalation compound of magnesium fluoride and fluorine

A graphite intercalation compound of C_xF(MgF₂)_y was prepared under a fluorine atmosphere of 1 atm at temperatures of 20–350°C. The 1st stage compound has the identity period of 9.3–9.4Å. ESCA and ¹⁹F NMR spectra indicate that the chemical interaction of intercalated fluorine with carbon is similar to that for graphite fluoride, however, with C_xF(MgF₂)_y having slightly mobile fluorine atoms chemically adsorbed on carbon atoms of graphite layers.     

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).     

Permanent adsorption of organic solvents in graphite oxide and its effect on the thermal exfoliation

The dispersion of graphite oxide (GO) in organic solvents followed by their evaporation at relative high temperature resulted in a strong adsorption of the solvent molecules in the graphitic interlayers as confirmed by ¹³C magic-angle-spinning NMR. Three series of solvents, alcohols (1-methanol, 1-propanol, 1-pentanol, 1-heptanol), aromatics (benzene, toluene, p-xylene, chlorobenzene) and chloride compounds (dichloromethane, chloroform, carbon tetrachloride) were studied to understand the interaction of graphite oxide with solvents. The distribution of basal interlayer spacing changed due to solvent intercalation and this distribution was particularly different for each solvent series. Even though there was on average 1 solvent molecule per 100 carbon atoms of GO, they had a profound effect on the thermal properties of the resulting GO. The exfoliation temperature was drastically reduced by the presence of the solvents due to the increase of the interlayer spacing and the reducing power of the solvent.     

Reversible intercalation of HF in fluorine-GICs

Reversible intercalation/deintercalation processes of HF were characterized for first stage fluorine-graphite intercalation compounds with semi-ionic C-F bonds (fluorine-GICs; C_xF) by X-ray diffraction and infrared absorption spectroscopy. C_xF(HF)_δ prepared by the intercalation of HF to C_xF possesses the interlayer distance of about 0.60 nm in the composition range of 2.1<x<2.6. Absorption peaks ascribed to the vibrational modes of carbon sheets in HF-intercalated C_xF are observed at higher wavenumbers with stronger intensities than those for HF-free C_xF. Attractive interaction is suggested to exist between the intercalated HF molecules and C_xF caused by the polar characters of both the H-F bonds in the former and the semi-ionic C-F bonds in the latter.     

Pyrolytically prepared carbon from fluorine-GIC

Formation mechanism, crystallinity, porosity and chemical reactivity were studied on the carbon prepared by pyrolysis of single phase, stage-1 fluorine-graphite intercalation compound (fluorine-GIC; C_xF). The stage-1 C_2.5F directly decomposes to fluorocarbon gases and carbon above 650 K, without forming higher stage compounds. The pyrocarbon prepared from C_2.5F gives hkl diffraction peaks indicating graphite-like stacking order of graphene layers. This carbon possesses average crystallite sizes along the c- and a-axes (L_c and L_a) of about 5 and 50 nm, respectively. The specific surface area of the pyrocarbon (about 40 m² g⁻¹) is only twice as large as that of the original crystalline graphite. Chemical behavior of the pyrocarbon as an intercalation host for sodium and potassium is similar to that of crystalline graphite, but it is easily fluorinated by elemental fluorine even at 573 K to give poly(carbon monofluoride) [(CF)_n] probably due to the small crystallite size and the mesopores formed by formation/decomposition processes of C_2.5F.     

A TDS study of D adsorption on terraces and terrace edges of graphite (0 0 0 1) surfaces

Adsorption of thermal (2000 K) D atoms on (0 0 0 1) surfaces of various highly oriented pyrolytic graphite (HOPG) and natural graphite substrates was studied under ultra high vacuum (UHV) conditions with thermal desorption spectroscopy (TDS). D chemisorption on terrace and terrace edge sites of graphite (0 0 0 1) surfaces was identified. Recombinative desorption of D adsorbed on terraces was observed between 400 and 600 K. The analysis of TD spectra from various graphite surfaces reveals the existence of three desorption states intrinsic to graphite (0 0 0 1), and proposed as being due to adsorbate structures composed of one (monomer) and two neighbouring (dimer) chemisorbed D atoms, and aggregates thereof (mixed). The dimer structure is supposed to exhibit higher stability than the monomer. Reaction of D with terrace edges leads to the formation of CD, CD₂ and CD₃-groups at edge C atoms. These groups decompose during heating between 790 and 1300 K via release of gaseous D₂ and CD_x, C₂D_x and C₃D_x-hydrocarbons.     

Adsorption from solution of large alkane and related molecules onto graphitized carbon

A reanalysis of experimental adsorption isotherms and enthalpies of adsorption is made for higher n-alkanes (C₁₆–C₃₂) adsorbed from dilute solutions of nonpolar organic solvents onto graphitized carbon. The submonolayer region of the adsorption isotherms suggests an alignment and close packing of the long-chain alkane molecules parallel to the graphite surface, and the results conform to a simple parallel-layer model with a large Flory-Huggins-type interaction parameter χ^a which is attributed to strong lateral adsorbate-adsorbate interactions. This interpretation of the adsorption isotherms is consistent with the calorimetric data, which yield a pronounced increase of the differential molar enthalpy of displacement with the fraction of surface covered by the long-chain alkane. Preliminary results on competitive adsorption of two solutes are presented in the second part of the paper. Different types of adsorption behaviour (mixed monolayer phase and two-dimensional eutectic) are observed depending on whether the individual solutes form close-packed ordered monolayers at the solution/graphite interface.     

Preparation of bimodal porous copolymer containing β‐cyclodextrin and its inclusion adsorption behavior

A novel insoluble bimodal porous polymer containing β‐cyclodextrin (β‐CD) was prepared to adsorb aromatic amine compound. The process involved copolymerization of styrene and methyl methacrylate with a maleic acid derivative of β‐CD, subsequently, above formed copolymer was foamed by supercritical CO₂. The chemical properties and physical structure of obtained copolymer was analyzed using Fourier transform infrared spectra, Thermal gravimetric analysis, X‐ray diffraction, scanning electron microscope, and N₂ adsorption techniques. The inclusion adsorption of aromatic amine compounds on β‐CD copolymer was carried out in a batch system. The quantities of aromatic amine compounds adsorbed on β‐CD copolymer reached equilibrium within 60 min. The adsorption kinetic could be fitted to a pseudo‐second‐order kinetic equation, and the linear correlation coefficients varied from 0.9828 to 0.9935. With the influence of molecular structure and hydrophobicity of the aromatic amine compound, the sequence of quantity of aromatic amine compounds adsorbed on β‐CD copolymer is p‐toluidine > aniline > benzidine > o‐toluidine. The adsorption equilibrium data of aromatic amine compound adsorbed on β‐CD copolymer were fitted to Freundlich and Langmuir models, respectively. The linear correlation coefficients of Langmuir model varied from 0.9516 to 0.9940, and the linear correlation coefficients of Freundlich varied from 0.9752 to 0.9976. It is concluded that Freundlich model fits better than Langmuir model, because the adsorption of aromatic amine compound on β‐CD copolymer is a chemical process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Promotional effect of graphite oxide on surface properties and catalytic performance of La1 − xSrxMnO3 (x = 0,0.1) for methane combustion

The effect of graphite oxide (i.e. GO)/La_1 − xSr_xMnO₃ (x = 0,0.1) catalysts on methane combustion in CNG's (compressed natural gas) exhaust was investigated in current work. GO layer was employed to realize a surface modification. The light-off temperature of methane decreased, and reached the full conversion at 540 °C. The prepared catalysts were also characterized by TEM, surface energy, XPS and H₂-TPR techniques. SEM indicated that the La_1 − xSr_xMnO₃ particles grew dispersedly on GO layer, and surface analysis suggested that the introducing of GO can enhance the adsorption of oxygen groups on the surface of the catalysts.     

In situ7Li nuclear magnetic resonance observation of the electrochemical intercalation of lithium in graphite: second cycle analysis

Graphite is used in the lithium-ion batteries as a negative electrode. We use continuous, in situ, operando ⁷Li nuclear magnetic resonance (NMR) to show, in real time, the progressive intercalation and de-intercalation of lithium in graphite when a battery is charged and discharged. We obtain all the Li–graphite intercalation compound stages through an electrochemical path. We explain the overvoltages by transient entropic and Peltier effects. The sample is a plastic cell, NMR compatible, made of commercial graphite, commercial electrolyte and lithium metal foil. We analyze the NMR characteristics of the Li–GIC stages: line shift, quadrupolar frequencies, line width (Li diffusion), line intensity and area as a function of x = Li/C₆. This allows us to estimate the lithium quantities in each stage at each step. Two facts differ from the theoretical stage n formation: for the C/20 cycling rate, we find an hysteresis in the filling/emptying of the dilute (LiC₉n) stages, and we find another NMR line synchronous with LiC₆. The lithium metal line also provides quantitative information on the lithium deposited as dendrites when x diminishes, in de-intercalation. This paper presents experimental NMR data over two cycles, and is an extension of the first cycle analysis published earlier.     

Chemistry of graphite intercalation by nitric acid

Gas-phase intercalation of graphite by nitric acid is accompanied by evolution of a brown gas which has been identified as nitrogen dioxide by chemiluminescence measurements. The reaction is inhibited by the presence of oxygen or water vapor, but not by nitrogen. These results, and the existence of induction times of 5–20 min before intercalation begins, is interpreted as evidence that intercalation is effected by oxidation of graphite by adsorbed nitronium ions with the release of NO₂. The graphite lattice then intercalates NO₃^? ions along with neutral HNO₃ molecules.     

Electrochemical insertion of sodium into graphite in molten sodium fluoride at 1025 °C

The electrochemical insertion of sodium into graphite was studied in molten sodium fluoride at 1025 °C. The results obtained evidenced two mechanisms for sodium insertion into graphite: sodium intercalation between the graphite layers and sodium sorption into the porosity of the material. Subsequent internal rearrangement of inserted sodium occurred, via transference from the pores towards the intercalation sites. In addition, the intercalation compound was found to undergo a fast decomposition process (k = 2.55 × 10⁻⁹ mol s⁻¹). X-ray diffraction analysis was used to confirm the formation of a high stage compound (Na_0.1C₈), the composition of which was consistent with compositions observed in the case of chemical vapor and electrochemical insertion of sodium, during experiments in the sodium perchlorate-ethylene cabonate electrolyte.     

HETEROGENEOUS REACTIONS OF OH RADICALS WITH PARTICULATE-PYRENE AND 1-NITROPYRENE OF ATMOSPHERIC INTEREST

The heterogeneous reactivity of OH radicals with pyrene and 1-nitropyrene adsorbed on model particles has been investigated using a discharge flow reactor, in the presence of a large excess of NO ₂ . Graphite was chosen as a simple model of carbonaceous particles, whereas silica was chosen as a representative surrogate of mineral atmospheric aerosol. The reaction kinetics was investigated by measuring the remaining pyrene and 1-nitropyrene adsorbed on particles after pressurized fluid extraction and gas chromatography/mass spectrometry analysis. Pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Rate constants were measured at room temperature for reactions of OH radicals with, respectively, pyrene, 1-nitropyrene, both adsorbed on silica, and 1-nitropyrene adsorbed on graphite, in the presence of NO ₂ .     

Adsorption and reaction behavior for the simultaneous adsorption of NO-NO2 and SO2 on activated carbon impregnated with KOH

This study examined the individual and simultaneous adsorption of NO_x (NO-NO₂) and SO₂ on activated carbon impregnated with KOH (KOH-IAC). For individual component adsorption, KOH-IAC showed a higher adsorption capacity in NO-NO₂ rich air than in SO₂-air. In the simultaneous adsorption of NO-NO₂-SO₂, SO₂ showed a greater adsorption affinity than NO-NO₂. The smaller the amount of NO-NO₂ adsorbed, the more SO₂ was adsorbed. XPS analysis of the adsorption of NO-NO₂ rich SO₂-air on KOH-IAC revealed that the adsorbed SO₂ was predominantly found on the external surface, producing mainly K₂SO₄ and, additionally, H₂SO₄ and K₂SO₃. Depth profile analysis showed that the amount of SO₂ adsorbed decreased regularly away from the surface, while the amount of adsorbed NO-NO₂ increased irregularly. We confirmed that the presence of the impregnant in KOH-IAC is a determining factor in the adsorption of NO-NO₂ and SO₂ by chemical reaction, clarifying the surface chemical behavior.     

Catalytic activity of graphite-based nanofillers on cure reaction of epoxy resins

The strong influence of graphite oxide (GO) nanofiller on the glass transition temperature (T_g) of epoxy resins, generally attributed to restricted molecular mobility of the epoxy matrix by the nanofiller or to the crosslinking of GO layers via the epoxy chains, is investigated. The study confirms that large increases of the glass transition temperature of the nanocomposite can be observed in presence of GO. However, similar T_g increases are observed, when the filler is a high-surface-area graphite (HSAG), lacking oxidized groups. Moreover, these T_g differences tend to disappear as a consequence of aging or thermal annealing. These results suggest that the observed T_g increases are mainly due to a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine), rather than to reaction of the epoxide groups with functional groups of GO. This hypothesis is supported by investigating the catalytic activity of graphite-based materials on reactions between analogous monofunctional epoxide and amine compounds.     

Characteristics and microstructure of aqueous colloidal dispersions of graphite oxide

A highly oxidized graphite oxide was synthesized from natural graphite powder by oxidation with KMnO₄ in concentrated H₂SO₄ followed by hydrolysis, washing and centrifugation. Concentrated gel-like colloidal dispersions were obtained. The corresponding filtrates, supernatants, GO dispersions, and solid GO films obtained from them, were investigated by various chemical analyses, small angle X-ray scattering, X-ray diffraction, light scattering (LS), Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, ¹³C Nuclear Magnetic Resonance and Thermo-Gravimetric Analysis. The spectroscopic analysis shows besides the common peaks assigned to water molecules, hydroxyl and carboxyl groups, elimination of CC bonds due to strong oxidation and presence of bands assigned to sulfate. Data of Gas Chromatography/Mass Spectrometry experiments confirm the presence in GO of water and an abundance of carboxyl groups. Scattering measurements confirm that the structure of the GO colloids consists of plate-like objects, mostly containing only a few layers, with a small population of thicker aggregates. SEM images of cross sections of dried GO film, obtained by freeze fracture, demonstrate that a continuous film-like structure was successfully achieved by elimination of water localized within exfoliated GO particles in the swelled GO aqueous colloidal dispersions.     

Etude par diffraction des rayons X de la penetration du benzene dans KC24

The intercalation of benzene in KC₂₄ is fast (less than half an hour) and lead to the disorganization of the lamellar binary compound crystal structure. The second stage lamellar compound is dismutated to the first stage one. The latter is modified to give a benzene inserted first stage which is called the first phase.The reorganization is very slow: several weeks are needed to the disappearance of the second stage binary compound and of the first phase one. At the end appear the third stage binary compound, and a second phase product, which is the result of the intercalation of one molecule of benzene in the first phase (Table 1). The increases of the thickness of filled layers in lamellar compounds is explained in Fig. 2 by the benzene molecule behaving as an extra graphite layer.At low temperature (? 100°C), we get the hkl reflections which confirm our hypothesis (Table 2).The first phase has an identity period of 18.8 Å which is corresponding to a 9.4 Å thickness of filled layer: the molecule of benzene is intercalated between the potassium unit and the graphite layer.The second phase has an identity period of 25.8 Å, corresponding to a thickness of filled layer of 12.9 Å, the potassium unit is then inserted between two molecules of benzene, the latter being parallel to the graphite layers.     

On the role of fatty acid in adsorption and corrosion inhibition of iron by amine—fatty acid salts in acidic solution

A study has been made of the adsorption and corrosion inhibition of iron by triethanolamine salts of 18C unsaturated fatty acids in 0.5 M deaerated H₂SO₄ solution. The adsorption was considered in terms of the competitive coadsorption of acid molecules and amine cations, being the main species in this solution. From measurements of differential double layer capacitance and dissolution kinetic of iron, the preferential adsorption of fatty acids over amine has been found. The orientation of acids appeared decisive for the formation of inhibitory effective adsorbates. Such adsorbates were originated by vertically oriented oleic acid molecules. Less effective were the layers based on salts of acids possessing a greater number of Π bonds. The double, horizontal and vertical orientation was found for these acids. The main role of amine was the cross-linkage of acid chains adsorbed on the iron surface.     

Water vapor adsorption and the microporous structures of carbonaceous adsorbents

The principal role in adsorption of almost all vapors organic and inorganic substances on nonporous and microporous carbonaceous adsorbents is played by dispersion interactions. They are characterized by a considerable increase in adsorption potentials as a result of superposition of the fields of the opposite pore walls. This effect determines the entire specifics of adsorption in micropores and, in particular, the substantial increase in adsorbability. A theoretical estimate of the adsorption potentials of benzene and water in adsorption on graphite, and a comparison of the differential heats of adsorption of water vapors on a non-porous carbon black previously heated in a vacuum at 950°C and on an active carbon show that water adsorption is due to the formation of hydrogen bonds both between the oxygen complexes on the surface of carbonaceous adsorbents and between the adsorbed molecules themselves. Dispersion interactions are weak and can be neglected to a first approximation. It has been shown for microporous structures and the slitlike model that one can calculate, from the parameters W₀ and E₀ of the adsorption equation of the theory of volume filling of micropores (determined from the adsorption isotherm of a standard vapor, benzene) the volume of the micropores, their halfwidth, and the specific surface area of the micropore walls. The latter are in good agreement with the specific surface areas of the micropores, as estimated by the independent method of similarity of the adsorption isotherms of water in micropores and on the surface of a nonporous carbonaceous adsorbent. The application of the BET and t-methods to microporous carbonaceous adsorbents is physically unsubstantiated.