Fluorinated Carbon Fibers Research Articles

Rational Construction of Fluorescence Turn-Off Fluorinated Carbon Fiber/Ag Composites and Their Anticancer and Antibacterial Activities.

Although fluorinated carbon fiber/Ag composites possess unique structure and special charge distribution and exhibit great potential in numerous fields, their synthesis has long been a headache because of inert chemistry bonds, low surface energy, and easy aggregation. Herein, we first demonstrate a fresh concept of constructing the nanoscale hydrosoluble fluorinated carbon fiber oxide (FCO)/Ag composite and then integrate it as a highly effective targeting nanocarrier and photothermal therapy and antibacterial agent. Chemical introduction of oxygen allows us to controllably deposit Ag nanoparticles (AgNPs) for the first time and further facilitates surface modification with folic acid prelinked bovine serum albumin to induce targeted endocytosis toward tumor cells. The structure adjustment of FCO into nanosize and the decoration of AgNPs endow the composite with much better photothermal property than fluorinated carbon materials, and FCO/Ag also serves as an effective fluorescence quencher for doxorubicin, realizing visual monitor of drug adsorption processes by "turn-off" fluorescence. Meanwhile, both in vitro and in vivo results reveal greatly improved cancer therapeutic effects than single therapy. What is more is that the synergistic interactions of lipophilic fluorine and AgNPs also ensure highly effective antibacterial activity. Our study integrates FCO/Ag as an emerging drug carrier that exhibits excellent targeted efficiency and high photothemal property and reports its unprecedented experimental example in both antibacterial- and anticancer-combined chemo-photothermal therapy.

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics.

The characterization of fluorinated carbon fibers by water sorption has been broadly investigated in this work. In brief, a pitch-based activated carbon fiber (ACF) was submitted to a fluorination process under different conditions of partial pressure (F2:N2 ratio) and temperature. This led to samples with varied fluorine content and C-F type bonding. The effect of the fluorination treatment on the textural properties of the ACF was studied by means of nitrogen and carbon dioxide adsorption at −196 and 0°C, respectively, while the changes induced in the surface chemistry of the materials were analyzed by XPS. Also, the affinity and stability of the materials toward water was evaluated by single and cycling isotherms. The obtained results show that a mild fluorination not only can preserve most of the textural properties of the parent ACF, but enhance the water uptake at the first stages of the water sorption process, together with a shift in the upswing of the water isotherms toward lower relative humidities. This indicates that fluorination under certain conditions can actually enhance the surface hydrophilicity of carbon materials with specific properties. On the contrary, higher partial pressures led to highly fluorinated fibers with lower porosity and more hydrophobic character. Moreover, they presented a lower chemical stability as demonstrated by a change in the shape of the water isotherms after two consecutive measurements. The kinetics of water sorption in the ACFs provided further insights into the different sorption phenomena involved. Hence, water sorption can definitely help to tailor the water affinity, stability and performance of fluorinated porous carbon materials under humid conditions.

Highly Stable and Ultrahigh-Rate Li Metal Anode Enabled by Fluorinated Carbon Fibers.

The advanced energy storage of an Li metal substituted for graphite anode can provide a significant enhancement in a battery's energy density. Nevertheless, the practical implementation of metallic Li has seriously been fettered by the notorious Li dendrite growth and the huge volumetric variation of Li metal inducing poor cycling performance and safety concerns. In this regard, constructing a robust SEI layer combined with a 3D host to stabilize the Li metal is strongly in demand. Herein, a highly stable hosted Li with an LiF dominated SEI has successfully been achieved through metal-free fluorinated carbon fibers (FCF) with strong lithiophilicity. The metal-free design is cost-effective and can retain the energy density of the Li metal, minimizing the unnecessary energy sacrifice from the extra high gravimetric density lithiophilic sites. The FCF hosted Li delivers a promoted high Coulombic efficiency, homogeneous Li deposition, and ultrahigh rate stable cycling over 1000 cycles at 20mA cm-2 with a much lower voltage polarization (≈220mV). Moreover, half cells coupled with LiNi0.8 Co0.1 Mn0.1 O2 , sulfur or even thick LiCoO2 cathode demonstrate superior rate performances and enhanced cycling stability even under a lean electrolyte. This work proves the feasibility of FCF hosted Li for practical usage and provides a novel approach toward cost-effective and high performance lithium metal batteries.

Building MoSe2-Mo2C incorporated hollow fluorinated carbon fibers for Li-S batteries

Lithium-sulfur (Li-S) batteries are severely confined by the sluggish redox kinetics and serious shuttle effect, and these disadvantages cause rapid capacity decay and low sulfur utilization efficiency. We fabricate the polar MoSe2, Mo2C coupled with F-doped carbon fibers (FC), named as MoSe2@FC@Mo2C to serve as the step multi-electrocatalysts to selectively catalyze the short chain soluble lithium polysulfides (LiPSs) conversion (Li2S4 ↔ Li2S) via the polar FC and the long chain LiPSs conversion (S8 ↔ Li2S4) via MoSe2 and Mo2C. The MoSe2@FC@Mo2C/S cathode material delivered a high specific capacity of 1359 mAh g−1 (81% of its theoretical capacity) at 0.2C and excellent cycle performance when evaluated for Li-S batteries. A high reversible capacity of 802 mAh g−1 at 5C even with a lean E/S of 5 mLg−1, and a high sulfur loading of 5.5 mg cm−2 was delivered, a favorable cycle behavior at 2C over 1000 cycles (0.029% decay per cycle) was obtained, corroborating the effective LiPSs shuttling relief and high LiPSs conversion efficacy. This work propels the further practical application of Li-S batteries, especially those which are tethered by sluggish kinetics and inferior rate performance.

Synthesis of novel nanosized fluorinated carbon fiber with high NIR absorption and its application in cancer chemo-photothermal therapy

Although fluorinated carbon fiber (FC) inherits many excellent properties of carbon materials, and holds great promise in many fields. However, chemical modification and application of FC in biomedicine have been rarely studied, mostly ascribed to large-sized needle-like structure, and inert C–F bonds with strong hydrophobicity. Herein, fluorinated carbon fiber oxide (FCO) enriched with oxygen groups with an average size of 90 nm is prepared, and this then allows us for the first time to modify FCO with biomolecule of hyaluronic acid, rendering FCO special targeting and good dispersibility in various media. Effective control over structure and surface makes FCO exhibit negligible toxicity and possess high near infrared absorption for photothermal therapy (PTT). Moreover, FCO also has high drug load capacity (1.05 mg/mg), and cell experiments confirm better therapeutic effect of the nanocarrier than single PTT or chemotherapy, making it practically valuable for cancer chemo-photothermal therapy.

Nano-sized paramagnetic and fluorescent fluorinated carbon fiber with high NIR absorbance for cancer chemo-photothermal therapy.

Nano-sized fluorinated carbon fiber possesses unique charge distribution and special chemical bonds and holds great promise in biomedicine. However, its synthesis remains a big challenge on account of the chemical inertness and strong hydrophobicity of C-F bonds. Herein, an up-bottom method to prepare nano-sized and water-soluble fluorinated carbon fiber oxide (FCO) with tunable lengths and adjustable fluorine levels was first developed. It was found that the effective control over structure and composition endowed the FCO with high photoluminescence (PL) and near-infrared (NIR) light absorbance, which was further employed to monitor the drug loading by turn-off PL and treat cancer by photothermal therapy (PTT). We also reported the first experimental example of paramagnetic FCO, whose novel paramagnetism was generated by point defects from fluorine invasion. Moreover, the FCO was noncovalently functionalized with polyvinylpyrrolidone, loaded with doxorubicin of high capacity (1.15 mg mg-1) and exhibited acid-triggered and photothermally enhanced drug release behavior. The application of FCO in cancer treatment achieved much better therapeutic effects than single chemotherapy or PTT. This work established FCO as a novel nano-carrier with high PL, NIR absorbance, paramagnetism, and drug loading capacity, and demonstrated its first application in cancer chemo-photothermal therapy.

Functionalization of graphene quantum dots by fluorine: Preparation, properties, application, and their mechanisms

Graphene quantum dots (GQDs) possess unique photoelectronic properties ascribed to quantum confinement and edge effects, which have evoked important development and wide application in the optoelectronic field. Doping GQDs with heteroatoms can further modulate the energy band structure and thus produce unexpected properties. Herein, we obtained fluorine-doped GQDs (F-GQDs) by adopting an effective preparation technique, which includes the treatment of the as-prepared reaction precursor, fluorinated carbon fibers, with ultrasonic liquid phase exfoliation. The proposed method is simple, handy, and low-cost, opening up an alternate approach to prepare F-GQDs. Through multiple characterization techniques, the effective incorporation of fluorine in GQDs was confirmed, and the as-prepared F-GQDs exhibit excellent photoelectrical properties and good ultraviolet absorption performances. Accordingly, we have fabricated a vertical photovoltaic UV detector based on F-GQDs. The unoptimized device has an exceptionally large ratio of photocurrent to dark current of magnitude ∼105, and its detectivity (D*) could stabilize at around 1012 Jones at room temperature under λ = 365 nm light irradiation and reverse bias voltage.

Molecular dynamics study of the interfacial strength between carbon fiber and phenolic resin

The interfacial strength between carbon fiber and phenolic resin is studied using molecular dynamics simulations to demonstrate that carbon fiber-reinforced carbon matrix composites (C/C composites) have improved tensile strength. Simulations are performed using two carbon fiber models, one of which has only carbon atoms and the other has carbon atoms and some fluorinated carbon groups. The carbon fiber models are regarded as two-layer graphite, and the phenolic resin model is treated as cross-linked structures. All force field parameters are based on the Dreiding force field. The tensile stress and interfacial fracture energy are calculated for the estimation of the interfacial strength. The results show that the model including the fluorinated carbon groups has lower interfacial strength than the model having only carbon atoms, up to a certain coating ratio of fluorinated carbon groups. Similarly, within the limits of the coating ratio, the interfacial fracture energy of the fluorinated carbon fiber model is lower than that of carbon fiber model having only carbon atoms.

Fluorinated carbon fiber as a novel nanocarrier for cancer chemo-photothermal therapy.

Although biomedical applications of carbon materials such as fullerenes, carbon nanotubes and graphene have been intensively studied in recent years owing to their unique chemical and physical properties, fluorinated carbon fiber (FC) has been rarely explored in biomedicine, mostly because of it's large-size, needle-like structure and strong hydrophobicity. In this study, for the first time we developed a novel FC-based nano-carrier with good biocompatibility, high drug-loading capacity and enhanced photo-thermal performance. A simple and feasible strategy is first employed to transform commercial FC into nano-sized ones with good solubility in both water and culture medium. The changes in surface wettability then facilitated us to load doxorubicin (DOX) onto the FC viaπ-π stacking interactions. Successful regulation of structure and composition also endows FC with an enhanced photothermal response in the near-infrared (NIR) region. Moreover, cell experiments indicate that the constructed nanocarrier can be easily transferred into cells by endocytosis, showing low toxicity and exhibiting excellent cancer therapy effects resulting from a good combination of chemotherapy and photothermal therapy. Considering the low cost, high synthesis efficiency and outstanding properties of FC, the newly developed nanocarrier may find widespread applications in biomedicine and other related fields.

Synthesis and Reaction Mechanism of Novel Fluorinated Carbon Fiber as a High-Voltage Cathode Material for Rechargeable Na Batteries

While a rechargeable battery based on Na/CFx has been proposed, its reversible mechanism has remained unclear. Here, a new fluorinated carbon fiber material with the formula CF0.75 is used as a cathode material for rechargeable sodium batteries, delivering an initial discharge capacity of 705 mA·h g–1 with a high discharge plateau of 2.75 V and a reversible high discharge capacity of 350 mA·h g–1 at 20 mA g–1. The first discharge plateau of 2.75 V is the highest value reported in this family of materials so far, even slightly higher than that of commercial fluorinated graphite tested in a lithium battery (2.7 V). The origins of the observed high voltage of the material are explored by a combination of theoretical calculations and galvanostatic intermittent titration technique data and determined to be related to the disordered structure of the carbon fiber. Soft X-ray absorption spectroscopy and 19F magic angle spinning nuclear magnetic resonance characterization results disclose a full view of the conver...

Enhanced performance of Li-O2 battery based on CFx/C composites as cathode materials

A hybrid air-electrode composed of a mixture of fluorinated carbon (CFx) and Ketjen black (KB) active carbon composite materials was prepared to improve performance of Li-O2 battery. In the hybrid air-electrodes, four kinds of CFx materials including fluorinated graphite, fluorinated carbon fiber, fluorinated coke and fluorinated black carbon were utilized as lithium insertion materials. The physical properties and morphologies of the KB and CFx carbon materials were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM) measurements. Compared with the conventional KB air-electrode, all the CFx/KB hybrid air-electrodes in Li-O2 batteries showed higher specific discharge capacity, especially at high current density. Among these CFx/KB hybrid air-electrodes, the fluorinated graphite based electrode showed the best electrochemical performance in Li-O2 battery due to its highest discharge capacity of the fluorinated graphite material in the Li/CFx primary battery, highest specific surface area, and highest total pore volume. The electrochemical performance of Li-O2 and Li-air batteries using the hybrid air-electrodes with the different fluorinated graphite: KB weight ratio, including specific charge and discharge capacity, cycling stability and rate capability were systematically investigated. At a current density of 0.5mAcm−2, the fluorinated graphite based air-electrode delivered a high specific discharge capacity of 1138mAhg−1 in Li-O2 batteries, which was more than four times than that of the conventional KB air-electrode (265mAhg−1) under same testing conditions. The battery assembled with the fluorinated graphite based air-electrode exhibited better cycling stability than that of the battery assembled with the conventional KB air-electrode.

Unidirectional carbon fibre reinforced poly (vinylidene fluoride): Impact of atmospheric plasma on composite performance

A powder impregnation process with integrated inline continuous atmospheric plasma fluorination (APF) of carbon fibres to produce unidirectional carbon fibre/polyvinylidenefluoride (PVDF) tapes with a fibre volume fraction of 60% was developed. Carbon fibre/PVDF tapes were processed into test laminates by compression moulding and interface dominated composite properties were studied. The short beam strength of composites containing fluorinated carbon fibres improved by up to 200%. Flexural strength and modulus of laminated carbon fibre/PVDF composites containing APF treated carbon fibres increased by 110% and 37.5%, respectively. Critical energy release rate at initial crack determined using Mode I (DCB) and Mode II (ENF) tests for composites containing fluorinated carbon fibres exhibited about four times and two times enhancement, respectively, over composites made with as-received carbon fibres. Essential and non-essential work of fracture of composites containing fluorinated carbon fibres determined using the trousers test increased by 140% and 104%, respectively.

Composites based on fluorinated carbon fiber and polytetrafluoroethylene: Adsorption properties and heat stability

In this work, the methods of gas chromatography, IR spectroscopy, and thermogravimetry are used to study the adsorption properties, the chemistry of the surface, and the heat stability of composites based on fluorinated carbon fiber (FCF) and polytetrafluoroethylene (PTFE) as a binding agent. It is found that the increase in the PTFE content in the composite from 10–15 wt % has a slight effect on values of the thermodynamic characteristics of adsorption and the form of IR spectra. The increase in the Henry constants and the heats of absorption upon the introduction of binding agent into FCF results from additional lateral interactions with the polymer, which fills a small part of the adsorbing surface of FCF. In addition, the general nature of the intermolecular interactions with the prevalence of the dispersion component under adsorption on FCF and composites on its basis is observed. The adsorbents are found to be heat stable when heated to 400°C in airflow.

Chemistry of the surface and structural and adsorption properties of fluorinated carbon fiber and an adsorbent based on it

The chemistry of the surface and structural and adsorption properties of fluorinated carbon fiber were studied by IR spectroscopy, gas chromatography, and static adsorption of vapors and dyes from aqueous solutions. Also, the quantitative characteristics of the influence of a binder (polytetrafluoroethylene) used to prepare a granulated adsorbent on the basis of the fiber were determined. The functional properties of the adsorbent were found to be largely determined by the properties of the initial fluorocarbon fiber. Fluorocarbons were shown to possess a developed porous structure and highly hydrophobic chemically homogeneous nonpolar surface for the adsorption of most of the organic compounds studied.

Adsorption of oxygen-containing compounds at fluorinated graphite and fluorinated carbon fiber

The surface properties of fully fluorinated samples of natural graphite (FG) and carbon fiber (FCF) were studied by gas chromatography, IR spectroscopy, and static adsorption. It was found that for fluorocarbons, the contributions from the O atom (for ethers) and the OH group (for alcohols) are comparable with the contribution from the methylene unit to the retention parameters, which is typical only of highly homogeneous, hydrophobic, and nonpolar surfaces. Unusual properties of fluorocarbons compared to known hydrophobic adsorbents include weaker adsorption of secondary alcohols than ketones, their dehydrogenation products. An analysis of the retention parameters of isomeric propanols and butanols revealed that the FCF surface is accessible to the adsorption of these molecules, and is mainly formed by planar homogeneous fragments. In contrast, the FG structure is porous; the pore width is comparable with the molecule size, which makes the adsorption equilibrium more difficult to reach.

Surface and bulk properties of severely fluorinated carbon fibres

The development of ultra-inert composites using fluorinated carbon fibres as the reinforcement requires fluorinated carbon fibres with a durable surface composition. Here we report the effect of direct fluorination using an F 2/N 2 mixture at 653 K on the surface and bulk properties of two types of high strength carbon fibres. These were treated up to a surface fluorine content of ∼64 at.% and a bulk fluorine content of ∼15 mass%. A colour change was observed after fluorination caused by the changes in the graphitic band structure of the carbon fibres by the introduction of carbon sp 3 hybridisation. The tensile strength and Young's modulus decrease after fluorination by up to 33 and 22%, respectively. XRD shows marginal changes in the interlayer distance but the crystallite size increases. Changes in the electrical conductivity of the fluorinated carbon fibres indicate that the modification is confined to the near surface volume. Predominantly covalent C–F bonds are formed as shown by X-ray photoelectron spectroscopy (XPS) and measured zeta ( ζ)-potentials. Hence the fluorinated fibres are hydrophobic and have low surface tensions. This and the large increase in fibre surface area, as determined by nitrogen adsorption, is expected to facilitate interfacial interaction between fluorinated carbon fibres and fluoropolymers.

Effect of fluorination on the surface properties of carbon materials as probed by gas chromatography

The surface properties of graphite, carbon fiber, and their fluorination products were studied using gas chromatography. The retention volumes and Kovatz indices for saturated and aromatic hydrocarbons and oxygenated and nitrogenated compounds were determined. Regardless of the properties of the matrix, fluorination produces materials with chemically homogeneous and apolar surfaces. For fluorinated graphite, the decrease in the retention of branched alcohols compared to that of linear alcohols is more significant than for fluorinated carbon fiber.

Fluorinated carbon fibres and their suitability as reinforcement for fluoropolymers

The interaction between direct fluorinated carbon fibres and various fluoropolymers (ethylene-chlorotrifluoroethylene, poly vinylidene fluoride, fluorinated ethylene propylene copolymer and tetrafluoroethylene-perfluoro alkoxy vinyl ether copolymer) was studied by means of direct wetting measurements between fibres and the polymer melts and single fibre pull-out tests. The results of both techniques allow the adhesion behaviour between the fibres and the matrices to be predicted. The results obtained show that a low degree of surface fluorination of carbon fibres leads to an improved wettability between the fibres and fluoropolymer melts and this is an indicator for an improved thermodynamic work of adhesion. The apparent interfacial shear strength as measure of practical adhesion, determined by the single fibre pull-out test, increases with increasing degree of surface fluorine content up to a maximum, which depends on the degree of fluorination of the matrix used. The improved interaction between the fibre and the matrix is due to an enhanced compatibility at the fibre/matrix interface.

Adhesion and friction behavior between fluorinated carbon fibers and poly (vinylidene fluoride)

The potential use of fluorinated, polyacrylonirtile-based, high strength carbon fibers as reinforcement for a fluorocarbon polymer, namely poly (vinylidene fluoride) (PVDF), was investigated by means of the single fiber pull-out test. The apparent interfacial shear strength as a measure of practical adhesion was determined and the fracture and friction behavior of the model composites characterized. It was shown that the fracture behavior of the model composites is predominately brittle in nearly all cases. Fluorination of carbon fibers has a positive impact on the adhesive strength to PVDF. The apparent interfacial shear strength increases with increasing degree of fiber surface fluorination and becomes maximal at a degree of fiber fluorination (F/C-ratio) of around 0.8, determined by ESCA, which is close to that of PVDF. This result points to the fact that the increased “practical” adhesion is due to a physical compatibilization between the fluorinated fibers and the surrounding PVDF matrix. It was found that, even though the interfacial shear strength increases with increasing degree of fiber surface fluorination, the friction between fluorinated carbon fibers and the surrounding PVDF decreases.

Surface characteristics of fluorine-modified PAN-based carbon fibers

Different fluorination methods were applied to modify the surface properties of carbon fibers. The relationship between the degree of fluorination and the physicochemical properties of carbon fibers was studied using a combination of mechanical tests, elemental analysis (EA), X-ray photoelectron spectrometry (XPS), and X-ray diffraction (XRD). EA and XPS analyses of fluorinated carbon fibers showed that treatment with mixtures of F 2/O 2 introduced a much higher fluorine concentration than that with F 2 only. However, XRD analysis showed that there was no increase in the interlayer distance, due to the mild fluorination condition applied. Consequently, the oxyfluorination was one of the more effective methods to increase surface polarity of carbon fibers, which probably played an important role in improving the tensile properties of the fibers in the epoxy resin system.