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Graphites covalently intercalated with fluorine to form (C 2 F) n structural type compounds shows a dramatic increase of the interlayer distance up to by a factor of almost 3 to reach ∼9 Å. Such graphite fluoride compounds containing only carbon and fluorine offer the rare opportunity to bridge the so-called gap in the reflectivity of neutron reflectors. Slow neutron reflectors are of great interest in designing neutron sources as well as in fundamental and applied science; they require synthesizing high thermal and chemical compound stability graphite fluorides. In this work, a new strategy is proposed for synthesizing (C 2 F) n compounds in a well-controlled method. Our results show that the outcome (C 2 F) n has a covalent character with only sp3 hybridized carbon atoms. Moreover, C–F bonds in the fluorocarbon sheets and CF 2 groups on the sheet edges lead to the desired stability and hydrophobic character. A dedicated home-made neutron diffractometer was built for measurements of double-differential neutron cross sections of crystals with specific large interlayer distances found in (C 2 F) n compounds. We demonstrate that the synthesized fluorine intercalated graphites developed effectively cover the gap in the reflectivity for the new generation of neutron reflectors. [Display omitted] [ABSTRACT FROM AUTHOR]

Fluorinated graphene-like materials are currently attracting much attention due to the tuning of their properties by changing the fluorine content and pattern on the graphene lattice. In this work, we report the redshift of absorption bands and the suppression (increase) of green (yellow-orange) photoluminescence (PL) in the spectra of transparent CF x crystallites as x decreases from ∼0.44 to ∼0.33. Time-dependent density functional theory (TDDFT) calculations reveal that the aromatic regions and polyene chains in the CF x layers are mainly responsible for the optical absorption of the samples in the ultraviolet and visible regions, respectively. The electron-hole recombination within branched aromatic rings or long carbon chains produces orange-red emission, while green-yellow PL is due to transitions of excited polyene electrons to half-occupied levels of aromatic carbon. Our results show that the optical properties of partially fluorinated graphite layers are determined by the size and shape of the remaining sp2 carbon regions, which can be varied by changing the fluorination conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Rechargeable batteries based on graphite are considered as promising alternatives for energy storage applications. The charge/discharge mechanisms of these batteries results from the intercalation and de-intercalation driven electrochemically by the atoms or molecules of the electrodes in contact with a liquid electrolyte. These solutions are often complex systems engineered to stabilize and allow the transport of the evolving moieties. In this article, we isolate the effect on the graphite structure of a chemical component of novel electrolytes, the aluminum fluoride (AlF 3), by dosing this pure compound in the gas phase over high oriented pyrolitic graphite (HOPG) substrates at 10−9 mbar and 300 K. We performed an extensive experimental study involving surface characterization and beam analysis techniques, and developed a model of the sorption substantiated in ab-initio calculations. We found a preferential interlaminar absorption when dosing in the direction transversal to the carbon planes. The intercalation in the HOPG is spontaneous and non-reactive, and increases the interplanar spacing by 20%. A charge transfer of 0.65 e− per formula from graphite to AlF 3 is calculated for the intercalate. Since the absorption depends on the roughness of the substrate we may infer that the intercalation proceeds through the step-edges. These features may contribute to the development of novel quasi-2D devices for special applications. [Display omitted] ● We isolate the effects of the AlF 3 over the crystalline structure and chemistry of HOPG by studying the system AlF 3 /HOPG in UHV by STM, XPS, RBS, and using DFT calculations to build an absorption model. ● The AlF 3 aggregates diffuse into the substrate, separating the carbon layers locally, and in turn generate changes in the density of electronic states of neighboring regions. ● The AlF 3 and HOPG retain their chemical identity ruling out the formation of metallic Al formation on the surface and any type of covalent bond between C and AlF 3 ● Surface defects and rsubstrate roughness are parameters that control the thickness of the fluoride intercalates. ● The calculated intercalation energy favours this process over adsorption, predicting a value of 4.41 V for its deintercalation potential. [ABSTRACT FROM AUTHOR]

Fluorinated single-layer diamond ("F-diamond") is a new form of two-dimensional (2D) carbon allotrope. Herein, poly(dicarbon monofluoride) (C 2 F) n which is essentially made of stacked layers of "F-diamane" has been synthesized and exfoliated in a variety of solvents to yield well-dispersed ultrathin sheets. Microscopic and spectroscopic analyses revealed that the exfoliated nanosheets retained the "F-diamane"-like structure. The experimental results are also supported by density functional theory (DFT) calculations. Image 1 • Poly(dicarbon monofluoride) (C 2 F) n was synthesized by the fluorination of graphite. • The (C 2 F) n is essentially made of stacked layers of "F-diamane". • Liquid-phase exfoliation of (C 2 F) n yielded ultrathin nanosheets. • The "F-diamane"-like structure was retained after exfoliation. • Density functional theory calculations support the experimental results. [ABSTRACT FROM AUTHOR]

With the development of portable and flexible electronic devices, demends for high-performance thermal management materials with high thermal conductivity and electrical insulation are growing. Recently, graphene fluoride has received numerous attention from science community due to its high thermal conductivity and electrical insulation. Here, we report an advanced exfoliated graphene fluoride (EGF) film as a high performance heat spreader and thermal interface material for flexible electronic devices, which simultaneously exhibits ultrahigh thermal conductivity, excellent electrical insulation, and satisfactory flexibility. Commercially available graphite fluoride was directly exfoliated into graphene fluoride solution using ball milling method, followed by preparing ultrathin graphene fluoride films to take full advantage of graphene fluoride properties for heat dissipating applications. The resultant films show a tunable thermal conductivity by altering the thickness of films and show a superior in-plane thermal conductivity of 242 W m−1 K−1 and exceptional through-plane thermal conductivity of 21.8 W m−1 K−1 at the thickness of 10 μm. More interestingly, the graphene fluoride films possess excellent flexibility. The newly developed EGF film provides a creative opportunity for fabrication of multifunctional highly flexible materials, which may promote the development of heat dissipation materials in next generation flexible electronics. Image 1 [ABSTRACT FROM AUTHOR]

In the present paper, graphite fluoride compounds C x F with various degrees of fluorination (x = 4, 2 and 1), i.e., with different C-F bonding characteristics, were systematically investigated using X-ray Raman Spectroscopy (XRS) and X-ray and neutron diffraction by means of Pair Distribution Function (PDF) analysis. For both techniques, ab-initio calculations allow the experimental results and structural/bonding assignments to be explained and/or confirmed. Presented here for the three stoichiometries are results for the carbon and fluorine first-neighbour distances, the evolution of the electronic band structure due to the change of the carbon hybridization upon fluorination, and also the nature of the final states for 1s core-electron excitations. Since fluorination is limited by the diffusion of fluorine in the carbon lattice, the process is less effective in the bulk, where a graphitic core remains. The cross-checked XRS, PDF data and Density Functional Theory (DFT) simulations appear also to be a powerful method to highlight the presence of a residual graphitic core, even at the highest fluorine content, in such semi-disordered and structurally complex compounds. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Fluorine Graphite Intercalation Compounds are one of the most common cathode used in primary lithium batteries, mainly for their high delivering potential. Nevertheless, to increase their capacities, fluorine can be partially substituted by oxygen. Oxifluorides offer then versatility to design cathode materials delivering the upmost performances. Combining the choice of the precursor (either graphite oxide or sub-fluorinated graphite fluoride) and two-step synthesis processes, which include Hummers' oxidation and direct fluorination, allow the tuning of the fluorine and oxygen atoms distribution. According to the sequence, i.e. fluorination/oxidation or oxidation/fluorination, several oxifluorides were then prepared. On one hand, direct fluorination using F 2 gas resulted in homogeneous fluorine dispersion when precursor was graphite oxide. On the other hand, Hummers' oxidation was modulated according to the temperature parameter. C OH, C O C, COOH, CF, CF 2 and CF 3 were identified through multinuclear solid-state MAS-NMR. Covalence and environment, especially in-plane organization of those chemical groups, were assessed. When oxifluorides are then used as cathode in primary lithium battery, the better performances are obtained for 3 phases compounds where fluorinated part insured high potential whereas oxygenated part allowed durability to be reached; carbonaceous region providing conductivity. A maximum of about 2400 Wh/kg of energy density is attempted. Graphical abstract High performances of cathode materials for primary lithium battery have been obtained through bifunctionalization by fluorine and oxygen of graphite. Two steps synthesis: gas solid fluorination/Hummer's oxidation or oxidation/fluorination allow to get various functional groups and their repartition in graphite structure. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Ice formation on surfaces is a fascinating phenomenon with a major impact on a huge range of human activities from airplanes and shipping to wind mill parks, power transmission and telecommunication. A significant amount of work has been dedicated to the development of icephobic surfaces, often with the basis in superhydrophobicity. However, most surfaces investigated so far have not been very robust (an issue for operation in harsh and high humidity environments). Anti-icing strategies for practical applications in harsh environments have therefore mainly been related to the development of heatable coatings and/or mechanical removal or, in the case of airplanes, de-icing with glycol. Here we present a robust and lightweight anti-icing coating based on fluorinated graphene. The new coating delays ice formation for a striking 90 min at −15 °C up to 6 h and 45 min at −5 °C. All experiments were carried out at high humidity (50–55%). We also present first experiments of anti-icing on pure graphene. The very superior performance of the fluorinated graphene can be explained as a favourable combination of very low surface energy and nanoscale roughness. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Hydrogenated graphite was synthesized through a Birch−type reduction by treating fluorinated graphite ((CF x ) n , x ∼ 1.1) with a solution of Li in liquid NH 3 followed by the addition of H 2 O as the proton donor. The conversion was evaluated by Fourier transform infrared spectroscopy, Raman spectroscopy and powder X−ray diffraction. X−ray photoelectron spectroscopy and combustion elemental analysis were used to determine and quantify the chemical composition, giving an empirical formula of C 1 H 0.60 O 0.0 6 N 0.01 for the product with no more than 2 at.% of fluorine atoms remaining. Thermal dehydrogenation of the hydrogenated material – as investigated by thermogravimetric analysis coupled to mass spectrometry – predominately occurs over the range of 350–600 °C. The product was also analyzed using scanning electron microscopy, atomic force microscopy and transmission electron microscopy, which collectively supported the formation of hydrogenated graphene sheets through a wet−chemical route. To elucidate the structure of the hydrogenated sample, the material was investigated by solid−state nuclear magnetic resonance spectroscopy. Direct pulse and cross−polarization nuclear magnetic resonance measurements, including spin counting, spectral editing and 2D heteronuclear correlation experiments, revealed the nature of the sp 3 − and sp 2 −hybridized carbon nuclei, and indicated that methine, methylene and quaternary sp 3 −carbon atoms were present in the hydrogenated material. [ABSTRACT FROM AUTHOR]

We studied the high pressure behavior of poly(dicarbon monofluoride) (C 2 F) n up to 37 GPa both theoretically, within the first-principle framework of the density functional theory, taking into account van der Waals corrections to the total energy, and experimentally, combining in situ Raman spectroscopy, XRD and X-ray photoelectron spectroscopy (XPS) measurements. The (C 2 F) n structure has a complex mixed sp 2 sp 3 character where graphene layers are intercalated among sp 3 carbon hybridized structural domains. We observed three phase transitions in the high pressure range explored. The first transition is observed around 12 GPa and is dominated by strain effects. Above 16 GPa the intercalated graphene layers corrugate and change from the sp 2 to sp 3 hybridization state. Above 25–27 GPa the new pressure-induced phase becomes unstable. We find that, by varying applied pressure or by changing the hybridization due to the fluorination of graphite, the band structure of (C 2 F) n can be modified, resulting in valence and conduction bands touching at the K point, as in graphene, thus turning (C 2 F) n into a semimetal. This could provide a new pathway to reversibly engineer the band structure and conductivity for applications in high energy density batteries. [ABSTRACT FROM AUTHOR]

In this study, we report a potentially scalable strategy for the cost/time-efficient production of water-soluble functionalized few layered graphene (FcG) through the mild defluorination of graphite fluoride (GF) at room temperature (RT). The strategy includes mechanical milling which is of high simplicity and operability, and subsequently water purification. By using heteroatom-containing alkaline such as NaNH 2 and Na 2 S, N or S dopants can be functionalized into the defluorinated graphene, leading to the formation of N- and S-doped FcG, respectively. Our methodology of defluorination of GF allows the fabrication of water soluble FcG in much safer ways relative to the conventional Hummers' method that involves strong acidic/oxidative ambience and disposal of large amount of salt wastes. Meanwhile, the abundance of GF and the simplicity of processibility may also facilitate the practical uses of FcG obtained via our methodology. [ABSTRACT FROM AUTHOR]

The structural properties of graphite fluoride are not well characterized despite many experimental and theoretical studies. Computational investigations have indicated the existence of several possible stacking sequences for this material, but the methods used were incapable of adequately describing the dispersive interactions between graphite-like layers. We studied the structural and surface properties of graphite fluoride using the random phase approximation method, which provides dispersive (van der Waals) interactions with the correct asymptotic decay. The chair conformation with the AA stacking sequence is predicted to be the most stable structure, having lattice parameters of a = 2.58 Å, and c = 5.75 Å. The energetic difference between AB and ABC stacking is small, so a statistical ensemble of several stacking arrangements can be expected in graphite fluoride samples. The energy needed for the exfoliation of graphite fluoride into individual CF layers is 190 mJ/m 2 , which is lower than the corresponding energy for graphite. The predicted surface energy of graphite fluoride is 100 mJ/m 2 . We also measured the surface energy of graphite fluoride powder experimentally using inverse gas chromatography, yielding a value of 79 ± 7 mJ/m 2 that agreed well with the computational result. [ABSTRACT FROM AUTHOR]

Fluorinated graphene is a promising material for electronic applications, and its thermal properties are of high importance. Here, the resilience of fluorinated graphene to a range of temperatures is presented. The heating/cooling cycles were carried out on fluorinated monolayer, fluorinated bilayer graphene and non-fluorinated graphene as well, for comparison. In order to follow the changes of the properties of the material, in situ Raman spectra were acquired at different temperature steps. The results show that most of fluorine bonded to graphene can be removed at unusually mild temperatures, but not completely, as some fluorine can still be traced even upon heating at 800 K. Additionally, despite monolayer graphene has a higher level of fluorination than bilayer graphene, after the first heating/cooling cycle a similar amount of fluorine is found on both fluorinated graphene samples. [ABSTRACT FROM AUTHOR]

We show that irradiation of room-temperature fluorinated graphite of C 2 F composition by electron beam with a kinetic energy of 500 eV detaches the fluorine atoms from two or three top layers. The dielectric property of C 2 F prevents effective penetration of the beam in depth of the sample, and electrons are accumulated between the interior layers. Comparative study of the initial C 2 F sample and that after irradiation by means of X-ray photoelectron, X-ray absorption near edge structure, Raman and reflection optical spectroscopy detects a partial recovering of the π-bonds which increases the surface conductivity by more than three orders. The mechanism responsible for removal of fluorine atoms from dielectric matrix under electron irradiation is proposed and substantiated by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two few-layer graphene materials, strongly distinguished in structure, were compared as electrode materials for supercapacitor. The stacks of flat sheets with basal size of a few microns have been obtained as the result of ultrasonication of bromine intercalated graphite dispersion. The highly crumpled large-size layers have been produced by rapid heating of bromine intercalated graphite fluoride. The average number of layers and in-plane crystalline size in the materials were evaluated from Raman spectroscopy. The functional composition was studied using X-ray photoelectron and Infrared spectroscopy. Electrochemical testing of the graphene materials detected re-stacking of thin crumpled layers during the electrode preparation. Furthermore, graphene material produced from the fluorinated graphite showed poor wettability. The mild oxidation of the material in a mixture of sulfuric and nitric acids allowed increasing the capacitance in several times. [ABSTRACT FROM AUTHOR]

The thermal exfoliation of graphite fluoride was investigated using two starting materials: fluorinated HOPG and powdered room temperature graphite fluoride (RTGF) post-treated in pure F2 gas in order to adjust the relative contents of intercalated species, the carbon hybridization and the C-F bonding. Firstly, the thermal exfoliation of HOPG sample (of composition CF0.57) at the nanoscale is highlighted using scanning tunneling microscopy (STM). Such process involves a defluorination, which is accelerated by disruption of the graphene sheets. Similar breaking occurs during the exfoliation of post-treated RTGF and evolves CF4 and C2F6 gases. Moreover, the exfoliation using a thermal shock is assisted by the fast deintercalation of the catalyst species in the region where the covalence of the C-F bonds is weakened. In such way, exfoliation occurs with the quasi-total defluorination. [ABSTRACT FROM AUTHOR]

Abstract: Intercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF3 and a set of intercalant exchange reactions. It was found that composition of the compound is CF0.40(C7H16)0.04 and the guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04nm and the unfilled layers are separated by ∼0.60nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the π conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp 2 carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3nm. These π electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of ∼2.5eV. Variation in the size and the shape of π electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials. [Copyright &y& Elsevier]

Abstract: 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 170–370m2/g, low bulk densities of 0.4–0.7g/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. [Copyright &y& Elsevier]

The reaction mechanisms of a stage-1 fluorine–graphite intercalation compound (GIC), C2.5F, with 0.10 MPa of fluorine gas have been studied at 573–773 K. The original stage-1 structure of C2.5F with semi-ionic C–F bonds and planar sp2 carbon sheets is maintained in most part of the compound after the reaction at 573 K, although a large number of covalent C–F bonds are formed on the surface. This compound is partially or completely converted to poly(carbon monofluoride), (CF)n, with covalent C–F bonds and puckered sp3 carbon sheets at 673 or 773 K, respectively. Single-phase (CF)n obtained at 773 K possesses remarkably small BET specific surface area, 61 m2/g carbon, almost unchanged from the value of the precursor C2.5F (69 m2/g carbon). In this reaction, the accommodation of fluorine atoms supplied from the atmosphere into the galleries of C2.5F is facilitated by the rearrangement of originally intercalated fluorine atoms in the GIC, forming (CF)n with fewer defects compared to those by the conventional direct fluorination of graphite. [Copyright &y& Elsevier]

Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO4–EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F2 atmosphere for 2 h at 150 °C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g−1 in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li+/Li limiting the useful capacity. [Copyright &y& Elsevier]