Fluorinated Graphene Nanosheets Research Articles

Tuning fluorine content of fluorinated graphene by an ionothermal synthesis method for achieving excellent tribological behaviors

Fluorinated graphene (FG) has been an excellent lubricant additive due to its wider layer spacing and weaker interlayer forces, and FG with different fluorine content can exhibit different tribological performance. Herein, an ionothermal synthesis method was provided to prepare FG nanosheets with different fluorine content. Under the dual function of the ionic liquids ([C16C1im][Br]) and the temperature, the [C16C1im][Br] can work well as both an intercalation agent and polar catalyst, thus achieving tuning fluorine content of FG. Surprisingly, due to the chemical stability of [C16C1im][Br], the [C16C1im][Br] used in the exfoliated process of FG can be recycled and reused at least 5 times and still remain favorable exfoliation effect. Moreover, it can be obtained that friction coefficient and wear track width are reduced by 53.1 % and 52.8 % through adding FG nanosheets into PAO4 oil, the function generated by breaking of C–F bonds can form an adsorbed film on the friction surface, thus offering a synergistic lubricant mechanism with formation of FG tribo-film. Therefore, the FG dispersed into PAO4 oil can greatly enhance the tribological behaviors during the friction process.

Revealing the Mechano-Electrochemical Coupling Behavior and Discharge Mechanism of Fluorinated Carbon Cathodes toward High-Power Lithium Primary Batteries.

Unclear reaction mechanisms and unsatisfactory power performance hinder the further development of advanced lithium/fluorinated carbon (Li/CFx ) batteries. Herein, the mechano-electrochemical coupling behavior of a CFx cathode is investigated by in situ monitoring strain/stress using digital image correlation (DIC) techniques, electrochemical methods, and theoretical equations. The DIC monitoring results present the distribution and dynamic evolution of the plane strain and indicate strong dependence toward the material structure and discharge rate. The average plane principal strain of fully discharged 2D fluorinated graphene nanosheets (FGNSs) at 0.5 C is 0.50%, which is only 38.5% that of conventional bulk-structure CFx . Furthermore, the superior structural stability of the FGNSs is demonstrated by the microstructure and component characterization before and after discharge. The plane stress evolution is calculated based on theoretical equations, and the contributions of electrochemical and mechanical factors are examined and discussed. Subsequently, a structure-dependent three-region discharge mechanism for CFx electrodes is proposed from a mechanical perspective. Additionally, the surface deformation of Li/FGNSs pouch cells formed during the discharge process is monitored using in situ DIC. This study reveals the discharge mechanism of Li/CFx batteries and facilitates the design of advanced CFx materials.

Fabrication of Self-Rolled Fluorinated Graphene Nanosheets and Cathode Application

A simple approach of self-rolled fluorinated graphene nanosheets (srFGN) was reported in this work. Notably, the preparation of the specific srFGN showed interesting solvent-sensitive characteristics. The research findings revealed that when an aprotic solvent was used, e.g., dimethyl sulfoxide (DMSO), the interesting srFGN was obtained readily, which was characterized by different technologies. Cathode application for primary lithium-ion batteries (LIBs) of the prepared srFGN nanoscrolls was also studied in this work, which exhibited elevated energy density (e.g., 2287.9 Wh·kg−1), excellent discharge specific capacity and reliable discharge platform, indicating it a cheap and hyperdensity cathode material for primary LIBs.

Surface Engineering of Fluorinated Graphene Nanosheets Enables Ultrafast Lithium/Sodium/Potassium Primary Batteries.

Fluorinated carbon (CFx ) is considered as a promising cathode material for lithium/sodium/potassium primary batteries with superior theoretical energy density. However, achieving high energy and power densities simultaneously remains a considerable challenge due to the strong covalency of the C-F bond in the highly fluorinated CFx . Herein, an efficient surface engineering strategy combining surface defluorination and nitrogen doping enables fluorinated graphene nanosheets (DFG-N) to possess controllable conductive nanolayers and reasonably regulated C-F bonds. The DFG-N delivers an unprecedented dual performance for lithium primary batteries with a power density of 77456W kg-1 and an energy density of 1067Wh kg-1 at an ultrafast rate of 50 C, which is the highest level reported to date. The DFG-N also achieves a record power density of 15 256 and 17 881W kg-1 at 10 C for sodium and potassium primary batteries, respectively. The characterization results and density functional theory calculations demonstrate that the excellent performance of DFG-N is attributed to surface engineering strategies that remarkably improve electronic and ionic conductivity without sacrificing the high fluorine content. This work provides a compelling strategy for developing advanced ultrafast primary batteries that combine ultrahigh energy density and power density.

Construction of fluorinated graphene/cerium oxide composite coatings using ethylenediamine as the covalent interface adhesive: Lubrication and anticorrosion performances

Integrated with friction-reduction, anti-wear, and anticorrosion capacities, a novel fluorinated graphene (FG) composite coating has been developed to address the need for effective protection of metal materials in salty and humid environments. Bound with ethylenediamine (EDA), cerium dioxide (CeO2) nanoparticles decorated FG nanosheets were rapidly in-situ coated on the stainless steel sheet. The experiments revealed that the effective combination of FG, CeO2, and EDA endowed the composite coating with a reduced friction coefficient and an extended lubrication duration. The corrosion performances demonstrated that the composite coating has the highest corrosion potential and the lowest corrosion current, which can be attributable to the physical barrier effect of the FG nanosheets and the chemical corrosion inhibition effect of CeO2 and EDA.

Exploring the Self‐Cleaning Facets of Fluorinated Graphene Nanoarchitectonics: Progress and Perspectives

AbstractThe development of graphene nanoarchitectonics, including their synthesis, surface modification, interfaces, conductivity and porosity, has moved forward rapidly and attracted attention from interdisciplinary research fields. Fluorinated graphene (FG), a rising star and a fascinating member of graphene family has been identified as a promising material for multiple applications, such as sensors, optics, catalysis and self‐cleaning technologies. In this review, we highlight the important aspects of FG pertinent to physiochemical stability and self‐cleaning technologies. We discuss the precise functionalization of FG surfaces with organic functionalities, which are promising for creating high‐performance graphene derivatives. Also, by utilizing the reactivity of few‐layered FG nanosheets, it is possible to develop coatings based on dispersions of functionalized FG inks coupled with porous solids and tubular nanomaterials with super‐wetting functions. The functional groups of the resultant hybrids are connected to innovative substrates including meshes and macroporous sponges that can be useful for super‐wetting containers and oleophilic sorbents. Furthermore, we discuss hydrophobic FG‐porphyrin hybrids with metal coordination and hydrophobicity dependent photoluminescence. Finally, the self‐cleaning action and anti‐corrosion features of FG hybrids are explored, with potential applications in triboelectric nanogenerators and water harvesting. Future development of these materials should focus on new designs, porosity control, batch uniformity, durable self‐cleaning membranes, smart textiles, eco‐compatible coatings and disposability.

Tribological properties of physically modified fluorinated graphene and soluble starch hybrid as water-based lubricating additive system

In this study, a hybrid additive system of soluble starch (SS) and physically modified fluorinated graphene (FG) with excellent friction-reduction and anti-wear properties was designed to meet the future demand for water-based lubrication. The modified FG nanosheets with amphiphilicity were obtained from the high-speed shear exfoliation of fluorinated graphite with surfactants. The modified FG significantly improves the load-bearing and boundary lubrication performances of the water-based lubricant via forming boundary lubricating film, while SS further enhances the friction-reduction and boundary film formation performances, especially during the running-in period. At the best ratio (0.3 wt% FG and 0.6 wt% SS), the hybrid lubricant synergistically reduces the corresponding friction coefficient and wear rate by around 90%.

Inverse Relationship between Thickness and Wear of Fluorinated Graphene: "Thinner Is Better".

Atomically thin two-dimensional (2D) materials are excellent candidates for utilization as a solid lubricant or additive at all length scales from macro-scale mechanical devices to micro/nano-electromechanical systems (MEMS/NEMS). In such applications, wear resistance of ultrathin 2D materials is critical for sustained lubrication performance. Here, we investigated the wear of fluorinated graphene (FG) nanosheets deposited on silicon surfaces using atomic force microscopy (AFM) and discovered that the wear resistance of FG improves as the FG thickness decreases from 4.2 to 0.8 nm (corresponding to seven layers to single layer) and the surface energy of the substrate underneath the FG nanosheets increases. On the basis of density function theory (DFT) calculations, the negative correlation of wear resistance to FG thickness and the positive correlation to substrate surface energy could be explained with the degree of interfacial charge transfer between FG and substrate which affects the strength of FG adhesion to the substrate.

MIL-101(Fe) Networks Supported on Fluorinated Graphene Nanosheets as Coatings for Oil Sorption

MIL-101(Fe) Networks Supported on Fluorinated Graphene Nanosheets as Coatings for Oil Sorption

Similar chemical composition with different tribological properties: Influences of C[sbnd]F bond strength and carbon-skeleton structure on fluorinated graphene and PTFE

Taking fluorinated graphene (FG) and polytetrafluorethylene (PTFE) as the typical models, this work aims to clarify the influences of carbon-skeleton structure and CF bond strength on their tribological performance and lubrication mechanism under extreme-pressure condition. As oil additives, the load-bearing capacity of PAO-6 increases from 300 N to 600 N with FG and 400 N with PTFE. Compared with the situation with the PTFE sub-microspheres, the wear rate of PAO-6 with FG nanosheets reduces by about 40%. Proved by the apparent difference in tribofilm formation ability of FG and PTFE, it is believed that the higher reactivity of the CF bond and adsorption ability of two-dimensional carbon-skeleton play a crucial role in FG’s excellent tribological performance.

The simple preparation of superhydrophobic sponge with fluorinated graphene and carbon nanotube

Nanomaterials have been developed to solve kinds of water pollution problems. Fluorinated graphene (FG) and multi-walled carbon nanotubes (MWCNTs) are used to improve the efficiency of oil/water separation of sponge via forming MWCNTs/FG/PU sponge in this work. The tests show that the two-dimensional FG can be adsorbed on the PU sponge, and one-dimensional MWCNTs can intertwine on the FG nanosheets as threads to fix on the skeletons of the PU sponge, which will form the micro-nano hierarchical structures and low surface energy surface. The surface contact angle of the MWCNTs/FG/PU sponge comes to the point of 158°, which indicates the MWCNTs/FG/PU sponge is superhydrophobic. The superhydrophobic MWCNTs/FG/PU sponge has outstanding ability to separate various oil/water mixtures effectively, and the corresponding absorbency of oils and organic reagents is over 15 g/g.

Fabrication of Graphene‐Based Self‐Assembly Monoliths through Reversible Fluorination and Defluorination Strategy

AbstractThe low bending stiffness and inferior self‐lubricating ability of graphene bring about flexible nanosheet and poor mobility, greatly restricting its well‐organized self‐assembly in direct solid‐phase molding. Herein, abundant fluorine atoms are introduced onto graphene nanosheet to obtain fluorinated graphene (FG). A direct dry‐compression molding achieves to rapidly fabricate highly compact FG monolith under room temperature. Tracing origins, the enhanced bending stiffness guarantees relatively flat FG nanosheet and excellent self‐lubricating ability actuates flat FG nanosheets to automatically slip, thereby accomplishing well‐organized and compact layer‐by‐layer stacking with interlock structure. Whereafter, highly compact graphene monolith is finally obtained by high‐temperature annealing, because interlock structure in FG monolith restricts graphene′s deformations during defluorination. Obtained graphene monolith owns a high conductivity of 5.5 × 104 S m−1 and compression strength of 77 MPa, while graphene without above process only forms fluffy foam with a low conductivity of 6.8 S m−1. Interestingly, transitional FG monolith presents a higher compression strength of 102 MPa, ultralow dielectric constant of 1.72 and prolongable chemical reactivity for preparing “Janus” monolith. Designing reversible fluorination and defluorination strategy offers an unexplored avenue to effectively manufacture high‐quality graphene‐based monoliths.

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.

Investigating the fluorination degree of FG nanosheets on the tribological properties of FG/PI composite coatings

In this work, fluorinated graphene (FG) nanosheets with different F/C fluorination degree were synthesized by a convenient gas phase fluorination method. Ionic liquids was used to modify the FG to improve its dispersion and compatibility in polyimide (PI). The thermal, mechanical and tribological properties of FG/PI composite coatings were investigated systematically. The morphology of FG was observed by Transmission electron microscopy (TEM) and scanning probe microscope (SPM). The physical and chemical properties of the FG were characterized by a large number of measurement methods, such as X-ray powder diffraction (XRD), Raman spectra, X-ray photo-electronic spectroscopy (XPS) and so on. Fourier transformed infrared spectra (FTIR) was used to confirm the successful modification of ILs. And the Chemical composition of the PI coating was investigated by XPS and FTIR measurements. On the basis of the stable dispersion of FG in the PI matrix, compared with pure PI, the composite coating with (reduced graphene oxide) rGO owned slightly improved thermal, mechanical and tribological properties and the composite coating with FG displayed significant improvement, especially when the F-doped degree was the highest.

Large-scale synthesis of fluorinated graphene by rapid thermal exfoliation of highly fluorinated graphite.

Weakly fluorinated graphene nanosheets were efficiently prepared via fast thermal exfoliation of highly fluorinated graphite. This scalable method consists of a fast temperature increase (around 10 °C s-1) of fluorinated HOPG performed under an argon atmosphere, without any post-treatment. The mechanism of exfoliation induced by the defluorination step, evolving volatile fluorocarbons, has been highlighted thanks to thermogravimetric analysis (TGA), high temperature X-ray diffraction (HTK-XRD), X-ray Photoelectron Spectrometry (XPS) studies on temperature, and Raman and infrared spectroscopy. The advantages of the described process are its high-yield for the preparation of fluorinated graphene nanosheets, its ease of implementation and scalability. Moreover, the fluorine content drastically decreases during such a process and graphene layers are slightly functionalized, i.e. conductive contrary to the precursor.

Functionalized graphene‐reinforced rubber composite: Mechanical and tribological behavior study

ABSTRACTA functionalized graphene, fluorinated graphene nanosheets (FGS), and SiO2 nanoparticles as reinforcing fillers were employed to improve the mechanical properties of the solution styrene butadiene and butadiene rubber composites (SSBR‐BR). The results showed that the mechanical properties of SSBR‐BR composite filled with FGS were substantially improved than those of the unfilled and equivalent filler loaded graphene oxide (GO) and reduced graphene oxide (rGO) filled SSBR‐BR composites. It can be ascribed to the fact that the hydrophobic surface of FGS can be endowed the good dispersion in rubber matrix and stronger interfacial interaction between rubber and fillers. The tribological properties of these composites are also investigated. The results reveal that incorporation of GO, rGO, and FGS in SSBR‐BR composites can decrease antiwear properties because the existence of layered graphene promotes to tear and peel off. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44970.

Photoexfoliation of two-dimensional materials through continuous UV irradiation

This paper describes the preparation of fluorinated graphene nanosheets (FGNs) through photoexfoliation of fluorinated graphite (FG) in the liquid phase. We discovered that UV irradiation of FG dispersions in N-methyl-2-pyrolidone facilitated exfoliation to give FGNs. Transmission electron microscopy and atomic force microscopy revealed that the average thickness of the FGNs was approximately 3 nm; they were considerably thinner than the nanosheets prepared using a conventional sonication approach. Furthermore, when the FGNs were deposited uniformly onto substrates (through spin coating), they formed effective cathode interlayers for polymer solar cells (PSCs), the efficiency of which was 60% greater than that of PSCs containing FGNs prepared through ultrasonication.

Melamine assisted solid exfoliation approach for the synthesis of few-layered fluorinated graphene nanosheets

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 2nm 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.

Transition‐Metal‐Free Magnesium‐Based Batteries Activated by Anionic Insertion into Fluorinated Graphene Nanosheets

Considering resource abundance, high volumetric energy density, and safer anodic electroplating, the Mg‐based battery is thought to be one of the most promising systems beyond current Li‐ion batteries. However, the development of Mg batteries is hindered by the narrow electrochemical window of electrolytes as well as by inapplicable cathode frameworks. In this work, it is proposed, for the first time, to utilize a fast surface redox process to replace sluggish lattice migration for improving the kinetics of Mg batteries. Taking fluorinated graphene nanosheets (FGSs) as model material, a reversible capacity higher than 100 mAh g−1 is achieved in a pseudocapacitance behavior from 2.75 to 0.5 V. Different from traditional storage mechanisms, this proof‐of‐concept Mg/FGS system is activated by a prior anionic process followed by reversible cationic storage. The dilution of charge density by forming large‐sized monovalent complex cations and the easy access to surface redox sites are responsible for the negligible voltage polarization without an evident MgF2 nucleation phenomenon.

Construction of Highly Ordered Fluorinated Graphene Composite Coatings with Various Fluorine Contents for Enhanced Lubrication Performance

The presence of fluorine makes fluorinated graphene (FG) exhibit extraordinary properties and provides effective route to engineer and modulate the surface and interface properties, which endows FG with promising prospect as ultrathin solid lubricant. Herein for the first time, a strongly integrated FG composite coating was fabricated by facile and scalable solution-based process. The pretreatment with alkali hydroxides both enhances the dispersibility of FG in aqueous medium and realizes the control of fluorine content. The incorporated dopamine could simultaneously function as adhesion and mechanical buffer layer. The as-prepared coatings almost show the full coverage (>90 %) of FG nanosheets over centimeter scale substrates with uniform thickness of 2.36–2.66 nm. The synthesis–structure–performance relationship, particularly the influence of fluorine content and coating structure on the lubricating properties, has been systematically investigated and discussed. Based on this fascinating testing platform, the results of tribological investigations demonstrate the composite coating with higher fluorine content has more stable friction state, lower friction coefficient, and longer duration.