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To elucidate how different spatial oxygen-containing groups influenced lithium-storage performance of graphene matrix, and further establish a clear structure-performance relationship, graphene framework was strategically functionalized with carboxylate and sulfonate groups and oxygen-free aniline ones as a reference. Due to maximum lithiation effect, spatially sulfonate functionalized graphene delivered the best electrochemical performances in lithium-ion batteries. [Display omitted] Graphene derivative materials are widely used as anode component in lithium-ion batteries. However, there is still a lack of reliable and foresighted guides helpful for designing high-performance graphene-based electrode materials. To this end, we strategically chose challenging graphite fluoride as starting material for the derivatization of graphene in order to exclude interference factors. As a result, graphene framework was functionalized with oxygen-containing carboxylate and sulfonate groups and oxygen-free aniline units at a similar functionalization degree. Due to the strong effect of lithiation, out-of-plane p -aminobenzoic acid blocks boosted the lithium-storage capacity of graphene matrix to 636 mAh g−1 at 0.1 A/g, and sulfanilic acid blocks maximized this value to 873 mAh g−1. Sadly, oxygen-free aniline functionalized graphene material only delivered a specific capacity of 88 mAh g−1. Meanwhile, spatial lithiated carboxylate and sulfonate units endowed graphene framework with better rate capability and cycling stability. Such a structure-performance relationship established herein was beneficial for the design and preparation of high-performance graphene derivative electrode materials. [ABSTRACT FROM AUTHOR]

A graphite-mediated microwave-based strategy was used for solid-state exfoliation of graphite fluoride in a few seconds, followed by a simple yet efficient separation to obtain exfoliated materials based on the density difference between graphite and graphene fluoride in solvent. The microwave-exfoliated graphene fluoride was a few layers thick and electrically conductive. The electrochemical testing of pouch-cell supercapacitors assembled by using the exfoliated graphene fluoride electrodes and a novel microemulsion-based electrolyte showed reasonable performance with typical electrical double-layer capacitance behavior and good rate capability (gravimetric specific capacitance: 3.2 F g−1 at 500 mA g−1 and 3.1 F g−1 at 5000 mA g−1). The BET specific surface areas of the as-exfoliated graphene fluoride are ~60–80 m2 g−1, which could be increased by activation using this simple yet versatile microwave-based method for further improvements on the electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] Low energy density is the major obstacle for the practical all-solid-state supercapacitors, which may be raised by the combination of the pseudocapacitance with the electrochemical double-layer capacitance. Although graphene and polyaniline have been demonstrated two effective materials, the synthetic route of graphene and their hybrid mode largely dictated the capacitive performances and cyclability of graphene/polyaniline nanocomposites. Herein , we employed commercial graphite fluoride as the precursor to obtain graphene with a well-preserved carbon lattice. After graphite fluoride functionalization by p -phenylenediamine (p PDA) and in situ oxidative polymerization of anilines, polyaniline (PANI) chains were covalently attached to graphene framework through p PDA bridges. Multiple characterizations were performed to confirm the covalent binding mode between graphene scaffolds and PANI partners, and electrochemical tests unraveled the as-prepared G– p PDA–PANI triads delivered a gravimetric capacitance as high as 638F g−1 and a further amplified volumetric capacitance (up to 759F cm−3). The bendable all-solid-state supercapacitors yielded an encouraging energy density of over 18 W h L−1 at a power density high to 5,950 W L−1, while exhibiting an exceptional rate capability, cycling stability and mechanical flexibility. [ABSTRACT FROM AUTHOR]

The work reports a study of the processes of multilayer graphene (MLG) preparation using the action of microwave (MW) radiation on polyfluoridedicarbon intercalation compounds with general composition C2F·xR (R is chlorine trifluoride, acetone, acetonitrile, carbon tetrachloride, and benzene). Under the action of MW heating, these intercalation compounds undergo exfoliation (splitting) at temperature values that are 40–55% lower than in the case of traditional convective heating. It is shown that microwave heating increases the exfoliation degree and specific surface area of fluorinated graphite and decreases residual content of fluorine and chlorine in MLG. A key role in the process of MW exfoliation is due to the absorption of MW radiation by the polar dielectric intercalated into the interlayer space of fluorinated graphite. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The naked-eye NH 3 sensor based on fluorinated graphene was obtained. • The effect of F atoms on the adsorption ability and charge transfer were identified. • The sensitivity of the NH 3 sensor can reach to 4.05% ppm−1. • The naked-eye NH 3 sensor needs no device fabrication, power supply or measuring equipment. Abstract Graphene has aroused continual and tremendous interest in gas sensing applications because of its unique properties. However, the graphene-based sensors still meet limitations such as inconvenient device fabrication, sustained power supply, specific measuring equipment, etc. Here, we find that fluorinated graphene (FG) shows an obvious color change (from white to dark yellow) in the presence of NH 3 which can be observed directly by the naked eye. PL measurement shows that the sensitivity of color change can reach a high value of ca. 4.05% ppm−1. The density functional theory calculations reveal that the F atoms on FG increase the adsorption ability and charge transfer of NH 3 molecules, resulting in the efficient color change. This work develops a naked-eye sensor which needs no device fabrication, power supply or measuring equipment, thus, can be potentially used to manufacture a cheap, sensitive and miniaturized NH 3 sensor. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we investigate the adsorption of water monomer on fluorinated graphene using state-of-the-art first-principles methods within the framework of density functional theory (DFT). Four different types of methods are employed to describe the van der Waals (vdW) interactions between water molecule and the carbon surface: The traditional DFT calculations within the generalized gradient approximation (GGA), and three additional types of calculations using respectively the semi-empirical DFT-D2 method, the original van der Waals density functional (vdW-DF) method, and one of its variants. Two situations and totally four adsorption configurations are considered. Compared with the adsorption on pristine graphene, the adsorption energies of water on fluorinated graphene are significantly increased, and the orientations of water diploe moment are notably changed. The most stable configuration is found to stay right above the top site of the C atom which is bonded with F, and the dipole moment of water molecule aligns spontaneously along the surface normal. Highlights • The adsorption of water on fluorinated graphene is studied using state-of-the-art first-principles methods. • The water-carbon interactions are enhanced due to F decoration. • The dipole moment of water molecule aligns spontaneously along the surface normal. [ABSTRACT FROM AUTHOR]

Graphene materials including porous few-layered graphenes are under focus of scientific community today. The great attention towards them is caused by their remarkable properties. Here, we use two different fluorinated graphite intercalation compounds with different fluorine content in their matrices to prepare thermally exfoliated fluorinated graphites and to investigate them in terms of their structural, spectroscopic and electrochemical properties as materials for use in supercapacitors. A higher temperature of low-fluorinated graphenes preparation resulted in higher exfoliation degree and higher gravimetric capacitance in supercapacitor appliances. More dramatic leap of gravimetric capacitance was observed after a treatment in a concentrated acid mixture of graphene material samples prepared at the highest temperature of thermolysis with highest exposition time. [ABSTRACT FROM AUTHOR]

Graphene sheets as nanostructured membranes with various functional groups (fluorine or hydrogen atoms) and different pore sizes were studied to separate nitrate anions from water molecules using molecular dynamics simulation method. Three systems with different functionalized graphene membranes were simulated to purified water from contamination. These three functionalized graphenes which two of them had fluorinated graphene pores with various diameters and one of them had hydrogenated graphene pore that its pore size was smaller than one of the fluorinated graphene pores, were located at the middle of the simulation boxes which contained sodium nitrate aqueous solution. Water molecules crossed from all functionalized graphenes but nitrate ions only passed across the fluorinated graphene with large size pore. In addition to the exerted pressures and the sizes of the graphene pores, the type of the functional groups based on their chemical nature had influence on water permeation and ion rejection. [ABSTRACT FROM AUTHOR]

Fluorinated graphene (FG) has been obtained by a fluorination of thermally exfoliated graphite fluoride C2F layers using a gaseous mixture of BrF3 and Br2 at room temperature. Comparative study of electromagnetic (EM) response of thin FG films after recovering their conductivity via different methods is presented in microwave (GHz) and terahertz (THz) frequency ranges. We discovered that fluorination can be used as promising tool for producing tunable EM interference (EMI) shielding materials, combining reflective and absorptive layers. [ABSTRACT FROM AUTHOR]

Fluorinated graphene was irradiated by electron beam, and the changing of fluorinated graphene after electron beam irradiation was found by several detection techniques of Raman, electrical characterization and X-ray photoelectron spectroscopy (XPS). Raman spectra and electric characterization confirmed that the crystal structure and electrical performance of graphene was recovered partially after electron beam irradiation. XPS results indicated that the concentration of fluorine quickly dropped from 35% to 15% just after 30 min irradiation, and then dropped, slowly to 10% with the irradiation time to 150 min. The results indicate that stimulate fluorine desorption from fluorinated graphene used electron beam completely is difficult, which means a big challenge for ESD to fabricate all graphene electronics. [ABSTRACT FROM AUTHOR]

The effect of the amount of sp3 defects in graphene on the graphene enhanced Raman scattering (GERS) is studied using gradual fluorination of chemical vapour deposition grown graphene covering the Rhodamine 6G molecules. While upon a mild fluorination the GERS effect is preserved, the GERS enhancement disappears in case of a strong fluorination. After partial removal of the fluorine from the strongly fluorinated graphene by water vapor treatment, the GERS effect is restored. [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]

Few-layer graphene samples have been obtained by a thermal expansion of bromine-intercalated fluorinated graphite with a ∼C2F matrix composition at 600, 700, and 800 °C. X-ray photoelectron spectroscopy detected that the products contained almost the same quantities of foreign atoms independently on the exfoliation temperature. However, the Raman spectra showed a progressive increase in the relative intensity of the D mode with the temperature growth. This was attributed to more edge states developed in graphene planes at the higher temperature. Thin films from obtained samples were tested as sensors using 1000 ppm nitrogen dioxide (NO2) in argon. The film from few-layer graphene produced at 800 °C had the largest relative response, while its recovery was quite low at room temperature. The sensor performances were related with the structural characteristics of the exfoliated graphenes. Left: Relative response of gas sensors based on few-layer graphene products of an expansion of fluorinated graphite at 600, 700, and 800 °C toward 1000 ppm NO2. Right: Proposed structures of the products. [ABSTRACT FROM AUTHOR]

The behavior of n-Si(111) photoanodes covered by monolayer sheets of fluorinated graphene (F-Gr) was investigated under a range of chemical and electrochemical conditions. The electrochemical behavior of n-Si/F-Gr and np+-Si/F-Gr photoanodes was compared to hydride-terminated n-Si (n-Si−H) and np+-Si−H electrodes in contact with aqueous Fe(CN)63-/4- and Br2/HBr electrolytes as well as in contact with a series of outer-sphere, one-electron redox couples in nonaqueous electrolytes. Illuminated n-Si/F-Gr and np+-Si/F-Gr electrodes in contact with an aqueous K3(Fe(CN)6/K4(Fe(CN)6 solutions exhibited stable short-circuit photocurrent densities of ∼10 mA cm-2 for 100,000 s (>24 h), in comparison to bare Si electrodes, which yielded nearly a complete photocurrent decay over ∼100 s. X-ray photoelectron spectra collected before and after exposure to aqueous anodic conditions showed that oxide formation at the Si surface was significantly inhibited for Si electrodes coated with F-Gr relative to bare Si electrodes exposed to the same conditions. The variation of the open-circuit potential for n-Si/F-Gr in contact with a series of nonaqueous electrolytes of varying reduction potential indicated that the n-Si/F-Gr did not form a buried junction with respect to the solution contact. Further, illuminated n-Si/F−Gr electrodes in contact with Br2/HBr(aq) were significantly more electrochemically stable than n-Si−H electrodes, and n-Si/F−Gr electrodes coupled to a Pt catalyst exhibited ideal regenerative cell efficiencies of up to 5% for the oxidation of Br- to Br2. [ABSTRACT FROM AUTHOR]

Fluorinated graphene (fluorographene) has attracted increasing attention due to the combination of unique properties of graphite fluoride and graphene. Development of fluorographene-based technology relies on the availability of fluorographene nanosheets in large quantities. Here, a melamine assisted solid exfoliation method is developed for the synthesis of fluorographene nanosheets. Under optimized solid ball milling condition, micrometer-sized ultrathin (less than 2 nm in thickness) fluorographene nanosheets can be exfoliated from graphite fluoride in the presence of melamine. The melamine assisted solid ball milling method is facile and highly efficient, and holds great promise for the large-scale preparation of few-layered fluorographene nanosheets. [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]

Few-layer graphene materials have been produced by decomposition of fluorinated graphite intercalated with acetonitrile (CH3CN) or isopropylamine ((CH3)2CHNH2) in the conditions of thermal shock. Electronic structure of the samples before and after exfoliation was studied using near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy. Analysis of the spectroscopic data revealed the same set of nitrogen species in both exfoliation products that indicates decomposition of the intercalated molecules to the atomic state. Most of the nitrogen atoms were incorporated at the edges of graphene layers in pyridinic and protonated nitrogen forms. A difference in the electrochemical performance of the graphene materials was related with the exfoliation degree and the defect density in the graphene layers. Schematic representation of a process of thermal exfoliation of acetonitrile-intercalated fluorinated graphite. [ABSTRACT FROM AUTHOR]

Herein, a new strategy has been developed through combining a microwave-assisted technique with hydrothermal treatment to reduce graphene waste and improve production yield of graphene quantum dots (GQDs) prepared by top-down methods. By using fluorinated graphene oxide (FGO) as a raw material, fluorinated GQDs and nonfluorinated GQDs can be synthesized. Additionally, in the fluorinated GQDs, the protective shell supplied by fluorine improves the pH stability of photoluminescence and the strong electron-withdrawing group, F, reduces the π- electron density of the aromatic structure; thus inhibiting reactivity toward singlet oxygen produced during irradiation and improving the photostability. Therefore, the as-prepared fluorinated GQDs with excellent photo- and pH stability are suitable for long-term cellular imaging. [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]

First-principle band gaps and optical absorption spectra of single- and double-layer fluorographene with bulk graphite fluoride are compared. The electronic properties are calculated using the many-body GW approximation and the optical spectra using the Bethe-Salpeter equation (BSE). The inclusion of electron-hole interactions is crucial for predicting low energy excitonic absorption peaks. The position of the first exciton peak is identical in single-, double- and multilayer fluorographene, which may indicate that the onset of the absorption spectra does not differ in these materials. [ABSTRACT FROM AUTHOR]

We investigate the effect of cell culture conditions, using functionalized graphene sheets with oxygen (-O) or fluorine (-F) as growth surfaces, on the human nerve cell line (SH-SY5Y). We applied the fluorescence microscopy of cells stained with Hochest 33342, Calcein AM, and MTT assay to evaluate cell viability and morphology. The effect of the graphene on the cells in culture was dependent on the atomic state of the graphene sheet. SH-SY5Y cells exhibited approximately 138% viability (MTT assay) on the oxygenated graphene sheets and 50% viability on the fluorinated graphene sheets, as compared to the data from culturing on pristine graphene. [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]

Silicene is the graphene-like silicon nanosheet, which has been synthesized very recently [B. Lalmi, H. Oughaddou, H. Enriquez, A. Kara, S. Vizzini, B. Ealet, and B. Aufray, Appl. Phys. Lett. 97, 223109 (2010)]. Using first-principles calculations, we systematically investigate the structures and properties of fluorinated and hydrogenated silicene, the silicon analogues of graphane. Different from the carbon-counterpart, the fluorination prefers the conformation with a zigzag-line buckling, while the hydrogenation keeps the chair conformation similar to graphane. A direct band gap is opened in the silicene fluoride, and the gap values can be continuously modulated by the strain. While for the hydride, a strain-induced indirect-to-direct band gap transition is found. [ABSTRACT FROM AUTHOR]

The electrical conductivity of graphene materials is strongly sensitive to the surface adsorbates, which makes them an excellent platform for the development of gas sensor devices. Functionalization of the surface of graphene opens up the possibility of adjusting the sensor to a target molecule. Here, we investigated the sensor properties of fluorinated graphene films towards exposure to low concentrations of nitrogen dioxide NO2. The films were produced by liquid-phase exfoliation of fluorinated graphite samples with a composition of CF0.08, CF0.23, and CF0.33. Fluorination of graphite using a BrF3/Br2 mixture at room temperature resulted in the covalent attachment of fluorine to basal carbon atoms, which was confirmed by X-ray photoelectron and Raman spectroscopies. Depending on the fluorination degree, the graphite powders had a different dispersion ability in toluene, which affected an average lateral size and thickness of the flakes. The films obtained from fluorinated graphite CF0.33 showed the highest relative response ca. 43% towards 100 ppm NO2 and the best recovery ca. 37% at room temperature. [ABSTRACT FROM AUTHOR]

Graphite fluoride‐launched graphene functionalization has attracted increasing interest in recent years. Highly basic nucleophiles are normally employed for ultrastrong CF bonding. However, frequently, an appreciable majority of C–F units of graphite fluoride are reductively eliminated, leading to low functionalization degrees. It is hypothesized that graphite fluoride could likely be functionalized to a larger degree by lowering the basicity of the nucleophiles. Herein, ultraweakly basic NH3·H2O is adopted as a nucleophile to react with extremely inert graphite fluoride, and the resulting reaction affords amino/hydroxyl cofunctionalized graphene (NH2–G–OH). As expected, the NH2/OH functionalization degree and the ratio of substituted C–F units to reduced ones reach high values of 0.34 and 1.62, respectively. Due to the dual energy‐storage mechanisms of the electrochemical double‐layer capacitance coupled with Faradaic pseudocapacitance, the NH2–G8–OH‐based all‐solid‐state supercapacitors are flexible and robust and deliver state‐of‐the‐art capacitive characteristics, while exhibiting high rate capability and electrochemical cycling stability. In addition, NH2/OH moieties remain highly reactive to be post‐functionalized by versatile electrophiles, not only achieving an umpolung of graphite fluoride, but also enabling NH2–G8–OH a competitive alternative to monopolistic GO, and opening up an innovative pathway for development of high‐performance graphene derivatives amenable to multifarious applications. [ABSTRACT FROM AUTHOR]