Fluorination Of Graphite Research Articles

Fluorinated polymer-derived microporous carbon spheres for CFx cathodes with high energy density

Fluorinated carbon (CFx) compounds have extensive applications in lithium primary battery cathodes owing to their high energy density. In this investigation, a novel CFx compound offering superior electrochemical properties was synthesized via a low-temperature fluorination process, utilizing Pluronic F127 as a template agent and microporous carbon spheres produced through soft template-assisted high-temperature carbonization and chemical activation as precursors, and by regulating the amount of soft template F127 added. The reduction in microsphere size, narrower particle size distribution, and introduction of defects contribute to augmenting the molar ratio of F to C (F/C) of CFx while preserving the electrochemical activity of C-F bonds. The specific capacity of fluorinated polymer-derived microporous carbon spheres (FPMCSs) with a high fluorination degree rivals that of commercial fluorinated graphite (FG). The microsphere morphology and microporous structure not only furnish abundant sites for fluorination reactions in electrode processes but also facilitate Li+ diffusion, ensuring ample rate capability. The synthesized FPMCSs exhibited a peak specific capacity of 1079 mAh g–1 and a maximum energy density of 2679 Wh kg–1 (substantially surpassing the 2180 Wh kg–1 of commercial FG). Hence, the prepared FPMCSs underscore the significance of selecting suitable carbonaceous materials and designing structures deliberately, showing promising potential for achieving high energy density in CFx cathodes in the future, employing readily available and cost-effective raw materials.

Fluorinated graphite reinforced polytetrafluoroethylene/poly(butylene terephthalate) composites as friction materials for deep‐sea applications

AbstractThe application of polymer composites is one of the most effective methods for preventing lubrication failure in deep‐sea engineering. In this study, fluorinated graphite (FGr) microsheets were incorporated into polytetrafluoroethylene (PTFE) microparticle‐filled poly(butylene terephthalate) (PBT) composites. The tribological performance in the simulated deep‐sea environment at elevated seawater pressure equivalent to 3000 m ocean depth was investigated. The results showed that FGr enhances the flexural and compressive strengths, thermal stability, and seawater resistance of the PTFE/PBT composite. The wear rate was decreased to 96% at the critical FGr content of 4% by improving the transfer onto the metallic counterfaces, preventing direct contact and shear between friction couples. Moreover, the seawater pressure impedes composite transfer, leading to a 29% increase in the wear rate.

Ignition and combustion characteristics of aluminum-based fluorine-containing composite powder

To improve the combustion characteristics of micron-sized aluminum (Al) powder, a composite powder was prepared by doping a small amount (15 wt%) of magnesium fluoride (MgF2), polytetrafluoroethylene (PTFE), and fluorinated graphite (FG) into the aluminum powder through solution dispersion method. The physical phase composition, micro morphology, thermal reactivity, and combustion performance of the composite powders were also characterized. The findings suggest that the promoting effect of the three fluorides on aluminum combustion can be ranked in the following descending order: FG > PTFE > MgF2. The fluorides can to erode the Al2O3 shell layer directly, thus creating cracks and reaction pathways for the Al core enclosed within the shell. Moreover, the gasification of AlF3 within the combustion products can escape from the surface of Al particles and promote the oxidation combustion of the exposed aluminum, which enhances the diffusion reaction on the active aluminum surface.

Measurement of perfluoroalkyl substances in drinking water sources by DGT sampler with a novel fluorinated graphite binding gel

Extensive use of per- and polyfluoroalkyl substances (PFASs) has resulted in their widespread presence in natural waters. Concern for public health requires reliable measurement methods for determining their distribution and risks. Here, a sampling method based on diffusive gradients in thin films (DGT) was developed for measuring PFASs in drinking water sources. Fluorinated graphite (FG) particles were used to prepare the DGT binding gel for selective enrichment of trace PFASs in an aqueous environment. The FG-DGT method did not show sensitivity to relevant environmental parameters including pH (5.0–9.0), ionic strength (0.001–0.5 M), or DOM concentration (0–30 mg/L). The FG-DGT had enough capacity for deployment of up to four months. Six traditional and emerging PFASs including PFOS, PFOA, PFHpA, PFHxS, PFNA, and 6:2 FTSA at the ng/L level were detected in two major reservoirs serving as public drinking water sources by FG-DGT method coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS). PFOA appeared at the highest observed concentrations in the drinking water sources. The research demonstrates that FG-DGT is an effective and efficient tool for monitoring PFASs in drinking water.

Fluorinated Carbon Nanohorns as Cathode Materials for Ultra-High Power Li/CFx Batteries.

Fluorinated carbon (CFx) has ultrahigh theoretical energy density among cathode materials for lithium primary batteries. CFx, as an active material in the cathode, plays a decisive role in performance. However, the performance of commercialized fluorinated graphite (FG) does not meet this continuously increasing performance demand. One effective way to increase the overall performance is to manipulate carbon-fluorine (C─F) bonds. In this study, carbon nanohorns are first used as a carbon source and are fluorinated at relatively low temperatures to obtain a new type of CFx with semi-ionic C─F bonds. Carbon nanohorns with a high degree of fluorination achieved a specific capacity comparable to that of commercial FG. Density functional theory (DFT) calculations revealed that curvature structure regulated its C─F bond configuration, thermodynamic parameters, and ion diffusion pathway. The dominant semi-ionic C─F bonds guarantee good conductivity, which improves rate performance. Fluorinated carbon nanohorns delivered a power density of 92.5kWkg-1 at 50 C and an energy density of 707.6Whkg-1 . This result demonstrates the effectiveness of tailored C─F bonds and that the carbon nanohorns shorten the Li+ diffusion path. This excellent performance indicates the importance of designing the carbon source and paves new possibilities for future research.

Mechanochemical Degradation of SF6 for Realizing Simultaneous Disposal of Super Greenhouse Gas and Manufacture of Fluorinated Graphite Materials

As the most potent greenhouse gas, SF6 can cause persistent harm to the environment if discharged directly to the air. Therefore, it is necessary to develop an efficient approach for its disposal and resource utilization. Here, we discovered the mechanochemical degradation of SF6 by graphite under mild conditions, along with the formation of an S-containing fluorinated graphitic carbon material (SFGCM) with over 8% of sulfur and 12% of fluorine, being a “one-stone-two-birds” strategy. The unexpected reaction between SF6 and graphite with least reactivity may be ascribed to the intensive mechanical stress and grinding on graphite for its size miniaturization and radical formation at the cutting edges, as well as their synergistic activation for SF6. The resultant SFGCM is composed of few-layered graphite nanomaterial with rich porosity, high specific surface area (380 m2 g–1), good amphiphilicity, and excellent adsorptivity for heavy metals (Hg2+) from aqueous solution. This study provides a viable way for the resource utilization of SF6, and sheds light on the massive degradation of various greenhouse F-gases in the future.

Photochemical degradation of fluorinated graphite stimulated by embedded nitrogen oxides

Layered fluorinated graphite material can become an efficient nanoreactor for photochemical reactions. In this work, we compared the photochemical behavior of partially fluorinated graphite (FG) and FG containing nitrogen oxides in the interlayer space (NOx@FG) under the action of a high-intense polychromatic photon beam from the synchrotron radiation source BESSY II. Analysis of the chemical and electronic states of the samples was performed using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Density functional theory calculations were used to interpret and analyze the experimental data. It was found that nitrogen oxides promote the photo-induced degradation of the FG matrix, namely, its partial defluorination, formation of vacancies and doping with nitrogen, while the empty FG had a high photoresistance to synchrotron radiation. The results obtained can be used in the development of new approaches to the modification of graphene layers and in the creation of photostable materials for optical elements.

Fluorinated microporous carbon spheres for Li/CFx batteries with high volumetric energy density

Carbon fluorides (CFx) have the highest theoretical energy density among current cathode materials for lithium primary battery. Although fluorinated graphite (FG) has been successfully commercialized, its energy density is difficult to meet the continuously increasing demand. In this study, porous carbon spheres are prepared as starting materials to obtain a new type of CFx compound with improved electrochemical performance. The fluorinated microporous carbon spheres (FMCSs) with a high fluorinated degree achieve a comparable specific capacity as that of the commercial FG. The spherical morphology and hierarchically porous structure prompt the diffusion of Li+ and the reaction with fluorinated active sites. The FMCSs fluorinated at 250 °C deliver a specific capacity of 955 mAh g−1 and a maximum energy density of 2428 Wh kg−1, and could operate stably at discharge rate as high as 10C. Unlike nanostructured CFx, the desirable true density of FMCSs enable their practical applications without sacrificing the volumetric energy density. Therefore, the assembled pouch cell using FMCSs as the cathode material exhibits superior electrochemical performance. In particular, the alleviated volume expansion and heat release further promoted the applicability of FMCSs and strengthen their capability as a favorable alternative to commercial FG.

Superhydrophobic composite asymmetric electrospun membrane for sustainable vacuum assisted air gap membrane distillation

Membrane distillation (MD) relies on superhydrophobic membranes that must achieve the competing goals of high liquid entry pressure (LEP) and high permeability. In this study, we developed the first superhydrophobic composite electrospun asymmetric membrane using fluorinated graphite (FG). We also provided among the first comparisons of the relative benefits of membrane asymmetry and composite coatings via 3D electrospinning and spraying. FG particles increased the roughness and reduced the zeta potential of the membranes. Superhydrophobic composite membranes had a contact angle of 157° (sliding angle of 7°) and an LEP of 327 kPa. Long-term MD testing revealed that FG particles could increase MD's sustainability while decreasing membrane wetting. Vacuum-assisted air gap membrane distillation (V-AGMD) showed that the composite asymmetric membrane outperformed the non-asymmetric version (composite nanofiber) membrane by 21 % in average water flux and 25 % in average thermal efficiency because of the asymmetric structure of the membrane. The numerical model developed for the V-AGMD system also successfully predicted the water flux generated experimentally from the composite nanofiber and composite asymmetric membranes. Our results confirmed that electrospun asymmetric FG membranes with high contact angle, low sliding angle, high permeability, and high gained output ratio (GOR) would be promising candidates for sustainable MD.

Breaking the Electronic Conductivity Bottleneck of Manganese Oxide Family for High-Power Fluorinated Graphite Composite Cathode by Ligand-Field High-Dimensional Constraining Strategy.

Primary lithium fluorinated graphite (Li/CFx ) batteries with superior energy density are an indispensable energy supply for multiple fields but suffer from sluggish reaction kinetics of the CFx cathode. Designing composite cathodes emerges as a solution to this problem. Despite the optimal composite component for CFx , the manganese oxide family represented by MnO2 is still faced with an intrinsic electronic conductivity bottleneck, which severely limits the power density of the composite cathode. Here, a cation-induced high-dimensional constraining strategy from the perspective of ligand-field stacking structure topological design, which breaks the molecular orbital hybridization of pristine semiconductive oxides to transform them into the high-conductivity metallic state while competitively maintaining structural stability, is proposed. Through first-principles phase diagram calculations, mixed-valent Mn5 O8 ( ) is explored as an ideal high-dimensional constraining material with satisfied conductivity and large-scale production feasibility. Experiments demonstrate that the as-proposed CFx @ Mn5 O8 composite cathode achieves 2.36times the power density (11399 Wkg-1 ) of pristine CFx and a higher CFx conversion ratio (86%). Such a high-dimensional field-constraining strategy is rooted in the established four-quadrant electronic structure tuning framework, which fundamentally changes the orbital symmetry under the ligand field to overcome the common conductivity challenge of wide transition metal oxide materials.

Combustion mechanism of fluorinated organic compound-modified nano-aluminum composite particles: Towards experimental and theoretical investigations

Fluorinated Organic Compounds (FOCs) are commonly used as modifiers for Aluminum (Al) powder to improve its ignition, combustion, and agglomeration characteristics. However, the effects of FOCs on combustion and inhibition mechanisms of agglomeration of Al powder are not well understood. In this paper, based on the experimental study of Fluorinated Graphite (FG)-modified Al matrix composite particles, the combustion and aggregation inhibition mechanisms of FOCs on Al particles were studied by the quantum chemical calculation at B3LYP/6-311+G(d,P) and G3//B3LYP/6-311+G(d,p) levels. The flame behavior and single particle burning behavior of FG-modified samples were compared through ignition experiments, and the characteristic spectra of Al related oxides of different samples in the initial ignition stage were captured. It is found that FG increases the burning intensity of Al composite samples significantly, while it decreases the emission intensity of Al secondary oxides. Quantum chemical calculation results show that the thermal decomposition intermediates of FOCs, namely C2F4, can react with AlO and Al2O, which weakens the characteristic emission intensity of AlO and Al2O in the sample, and thus inhibits the formation of Al2O3 in the combustion process. These results contribute to enriching the combustion dynamics model of Al-FOCs reaction system.

Composites of (C4F)n and (CF)n Synthesized by Uncatalyzed Fluorination of Graphite

A new solid-state 19F magic-angle spinning NMR signal at an isotropic 19F chemical shift of −53 ppm is measured from graphite fluoride synthesized by reaction of graphite with F2 at temperatures above 750 K with no catalyst. Two-dimensional NMR suggests the −53 ppm 19F NMR signal originates from covalent fluoromethanetriyl groups belonging to ordered (CyF)n bulk domains composited with the major (CF)n domains. Quantitative 19F and 13C NMR find y=4.32±0.64. DFT calculations of NMR chemical shifts for unsaturated fluorographene models show that a (C4F)n phase with fluorine bound covalently to a single side of the carbon layer best explains the observed NMR chemical shifts. We assign the new phase to this (C4F)n structure, which constitutes up to 15% of the carbon in our graphite fluoride composites. The (C4F)n content of the composite affects bulk electrochemical properties in a manner similar to graphite fluorides produced by conventional, catalyzed fluorination processes.

Fast formation kinetics of methane hydrate promoted by fluorinated graphite

Achieving rapid and high gas storage is the primary goal of solidified natural gas storage (SNG) using hydrate. In this study, the formation and decomposition process of hydrate were visualized on the fluorinated graphite (FG) layer for the first time by sapphire visible vessel. The results show that, the addition of FG alone can promote the formation of hydrate. After adding fluorinated graphite into SDS system, the gas storage capacity can be further increased to 165.2 cm3 STP/g H2O, and the average gas storage rate can be further increased to 20.84 cm3·g−1·min−1, which were 154.7% and 507.7% of SDS system, respectively. Meanwhile, the decomposition speed was faster than SDS system. After optimizing the experimental conditions, it was found that FG-1 with superhydrophobicity could stably exist in the gas–liquid interface and cover it when the dosage reached 1 wt% (13.95 mg·cm−2), and the combination with 300 ppm SDS could greatly promote the growth of hydrate. In addition, the excellent stability of FG made the performance of FG + SDS system remain at about 90% after 10 cycles. The unique growth phenomenon of hydrate in fluorinated graphite system was interesting. By building a hydrate formation platform, FG made water pumped from below to the gas phase and hydrate grow upward continuously. In comparison with other reported carbon nanoparticles, FG system maintained similar gas storage and had excellent gas storage speed, which was 1.35 ∼ 40.67 times faster under similar conditions. Therefore, the reusable FG + SDS system with high gas storage capacity and fast growth rate without induction time and mechanical agitation was a promising alternative to hydrate-based SNG technology.

Fluorinated Graphite (FG)-Modified Li-S Batteries with Superhigh Primary Specific Capacity and Improved Cycle Stability.

Lithium-sulfur (Li-S) batteries have received extensive attention because of their high theoretical energy density and low cost. However, the low sulfur utilization and the shuttle effect of polysulfide cause low initial capacity and serious capacity decay. Herein, fluorinated graphite (FG) is introduced to the cathode to alleviate these issues. The results indicated that the FG could provide additional capacity during the first discharge process and increase the porosity and polarity of the cathode via in situ formation of lithium fluoride (LiF) nanocrystals, which can enhance the infiltration of electrolyte and polysulfide adsorption. As a result, the as-prepared cathode containing FG shows a high initial specific capacity of 1602 mA h g-1 and the reversible specific capacity is 650 mA h g-1 at 0.5C after 300 cycles. Moreover, its specific capacity remains at 860 mA h g-1 at 5C, which is 367% higher than that of the sample without FG. This paper provides a new strategy to improve the energy density and the cycle stability of Li-S batteries.

Chemiresistive Properties of Imprinted Fluorinated Graphene Films.

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.

Large-scale, green, and high-efficiency exfoliation and noncovalent functionalization of fluorinated graphene by ionic liquid crystal

In this study, green and high-efficient ionic liquids crystal (ILC)-assisted hydrothermal exfoliation method was developed for exfoliation and functionalization of fluorinated graphene (FG). The proposed method was efficient for exfoliating FG from bulk fluorinated graphite (FGi) at yield reaching 48%. Meanwhile, the reliable interaction between FG and ILC led to noncovalent functionalization of exfoliated nanosheets, where exfoliated FG suspensions were highly stable at room temperature for more than three months without formation of agglomerates. The tribological properties of exfoliated FG nanosheets were then tested as lubricating additive and showed significant decrease in friction coefficient by 82% when compared to pure water. On the other hand, well-dispersed homogeneous FG/-poly (vinyl alcohol) (PVA) composite film with robust mechanical properties and photothermal effects were fabricated thanks to the excellent dispersibility of the FG nanosheets.

Microscopic characterization of the C–F bonds in fluorine–graphite intercalation compounds

The structures of fluorine–graphite intercalation compounds (F-GICs, C2.8F and C3.5F) have been analyzed by high-resolution transmission electron microscopy (TEM). Cross-sectional TEM images of the F-GICs indicate that the interlayer distance increases by insertion of fluorine with randomly buckled carbon layers. Such a structure can form by alternation in the bond angle at a carbon atom covalently bonded with fluorine. Electron energy loss spectroscopy combined with TEM indicates that the π-orbital network over the graphitic carbon layer reduces with fluorination. The C–F bond is essentially covalent.

Enamel Surface Remineralization Effect by Fluorinated Graphite and Bioactive Glass-Containing Orthodontic Bonding Resin.

All orthodontic appliances are potentially cariogenic. The plaque around the orthodontic appliance can make demineralization on tooth surface causing white spot lesion (WSL). The most effective method to prevent WSL is Fluoride appliance and gargling, but this requires patient cooperation, which consumes additional treatment time and cost. As suggested in this study, biomaterials like bioactive glass and fluorinated graphite (FGt) having antibacterial and anti-demineralization ability effective and easy to use in the clinic. To clinically use orthodontic bonding resins containing Graphite Fluoride BAG (FGtBAG), its properties, biological stability, antimicrobial activity, and remineralization effect must be verified. BAG was mixed with 2.5% FGt containing 51 to 61% fluorine. This mixture was mixed with the CharmFill Flow (CF) in the ratios of 1, 3, and 5 wt%. Microhardness and shear bond strength tests were performed to evaluate its mechanical properties. MTT (3-(4, 5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetra) assay was performed for evaluating its safety. Streptococcus mutans, which is major cariogen by producing lactic acid, was evaluated for antibacterial ability of reducing WSL. In addition, x-ray images were obtained by CBCT (Cone beam computed tomography) after a pH cycle. The remineralization effect was verified in vivo and by Image J. FGtBAG did not differ significantly from CF in mechanical tests. The MTT assay found no significant differences between the groups. The antibacterial activity of FGtBAG at 24 h and 48 h was significantly higher than that of CF. The fluoride release rate tended to increase with the FGtBAG content. The pH cycle results showed that FGtBAG had higher concentration-dependent remineralization effect than CF. The results of this study suggests that orthodontic resins containing FGtBAG can prevent WSL owing to their antibacterial activity and remineralization effect.

Study on relaxation process of fluorinated graphite/poly(vinylidene fluoride-hexafluoropropylene) composites by dielectric relaxation spectroscopy

The Fluorinated Graphite (FG)/poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] composites with different FG contents were prepared using the solution casting method, and the dielectric relaxation behaviors of the composites were systematically investigated by dielectric relaxation spectroscopy (DRS) with the frequency range of 20 Hz–5M Hz at the temperature range of 25 °C–200 °C. The dielectric constant of these FG/P(VDF-HFP) composites markedly increased and the dielectric loss decreased with the FG content. The electric modulus and Cole-Cole plots were employed to analyze the experimental complex dielectric constant, indicating that all the samples exhibited non-Debye relaxation process, especially in FG/P(VDF-HFP) composites. The temperature dependencies of relaxation time obtained from electric modulus analysis and conductivity relaxation obeyed the Arrhenius equation. Compared with pure P(VDF-HFP), the DC conductivity relaxation and the activation energies (Eτ and Eσ) of FG/P(VDF-HFP) composites gradually decreased with increasing FG composition because the mobility of charge carriers can be confined and merely fast hopped between the insulating fluorine atom layer.

Tuning fluorine and oxygen distribution in graphite oxifluorides for enhanced performances in primary lithium battery

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 F2 gas resulted in homogeneous fluorine dispersion when precursor was graphite oxide. On the other hand, Hummers’ oxidation was modulated according to the temperature parameter. COH, COC, COOH, CF, CF2 and CF3 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.