Chemical reactivity of C-F bonds attached to graphene with diamines depending on their nature and location

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 92.5 kW kg-1 at 50 C and an energy density of 707.6 Wh kg-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.

A Multifunctional Integrated Metal-Free MRI Agent for Early Diagnosis of Oxidative Stress in a Mouse Model of Diabetic Cardiomyopathy

Reactive oxygen species (ROS) are closely associated with the progression of diabetic cardiomyopathy (DCM) and can be regarded as one of its early biomarkers. Magnetic resonance imaging (MRI) is emerging as a powerful tool for the detection of cardiac abnormalities, but the sensitive and direct ROS-response MRI probe remains to be developed. This restricts the early diagnosis of DCM and prevents timely clinical interventions, resulting in serious and irreversible pathophysiological abnormalities. Herein, a novel ROS-response contrast-enhanced MRI nanoprobe (RCMN) is developed by multi-functionalizing fluorinated carbon nanosheets (FCNs) with multi-hydroxyl and 2,2,6,6-tetramethylpiperidin-1-oxyl groups. RCMNs capture ROS and then gather in the heart provisionally, which triggers MRI signal changes to realize the in vivo detection of ROS. In contrast to the clinical MRI agents, the cardiac abnormalities of disease mice is detected 8 weeks in advance with the assistance of RCMNs, which greatly advances the diagnostic window of DCM. To the best of the knowledge, this is the first ROS-response metal-free T2 -weighted MRI probe for the early diagnosis of DCM mice model. Furthermore, RCMNs can timely scavenge excessively produced ROS to alleviate oxidative stress.

Recent trends in covalent functionalization of 2D materials

Covalent functionalization of the surface is more crucial in 2D materials than in conventional bulk materials because of their atomic thinness, large surface-to-volume ratio, and uniform surface chemical potential. Because...

Thermal stability of C-F/C(-F)2 bonds in fluorinated graphene detected by in situ heating infrared spectroscopy

The thermal stability of fluorinated graphene (FG) plays an important role in its application and research, and thus it is necessary to conduct in-depth research on the thermal stability of the C-F bond in FG. Herein, FG with different types and distributions of C-F/C(-F)₂ bonds were synthesized, and the correlation between the C-F/C(-F)₂ bonds and thermal stability of these FG samples was monitored via in situ heating infrared spectroscopy (in situ FTIR). The stability of the different types and distributions of C-F/C(-F)₂ bonds in FG and the temperatures at which these C-F/C(-F)₂ bonds were eliminated were determined. In terms of C-F bonds in FG, the most stable type is that in C(-F)₂ of perfluorinated FG, followed by the C-F bonds in perfluorinated FG. The thermal stability of isolated C-F bonds and C(-F)₂ bonds adjacent to the conjugated structure was the worst, which would be detached from FG at low temperature (≤82 °C). Furthermore, the evolution of the conjugated structures in FG during thermal annealing was also affected by the type and distribution of the C-F bonds.

Suzuki-Miyaura reaction of C-F bonds in fluorographene

We report the first successful covalent modification of fluorographene (FG) based on Suzuki-Miyaura reaction of the C-F bond. The origin of the reaction efficiency of the C-F bond can be linked to the two-dimensional structure of FG and the synergistic effect of a phosphine ligand. This extends the application of the Suzuki reaction of the C-F bond into two-dimensional chemistry.

Immobilization of molecular catalysts for artificial photosynthesis

Artificial photosynthesis offers a way of producing fuels or high-value chemicals using a limitless energy source of sunlight and abundant resources such as water, CO2, and/or O2. Inspired by the strategies in natural photosynthesis, researchers have developed a number of homogeneous molecular systems for photocatalytic, photoelectrocatalytic, and electrocatalytic artificial photosynthesis. However, their photochemical instability in homogeneous solution are hurdles for scaled application in real life. Immobilization of molecular catalysts in solid supports support provides a fine blueprint to tackle this issue. This review highlights the recent developments in (i) techniques for immobilizing molecular catalysts in solid supports and (ii) catalytic water splitting, CO2 reduction, and O2 reduction with the support-immobilized molecular catalysts. Remaining challenges for molecular catalyst-based devices for artificial photosynthesis are discussed in the end of this review.

Effect of the Fluorination of Graphene Nanoflake on the Dispersion and Mechanical Properties of Polypropylene Nanocomposites

In order to investigate the effect of fluorination of graphene nanoflake on the dispersibility in polypropylene (PP) composites, fluorinated graphene oxide (FGO) was prepared by solvo-thermal reaction and applied as a filler of the PP nanocomposite. Due to the weakened inter-particle attraction among the graphene nanoflake and reduced surface energy difference between PP and the filler, PP/FGO composites showed better exfoliation and dispersion state of the filler compared with that of PP/graphene oxide (GO) or PP/reduced graphene oxide (RGO) composites. The improved exfoliation and dispersion of graphene nanoflake resulted in a significant reinforcement on the composites. The Young’s modulus and tensile strength of PP composites filled with 2 wt% of FGO increased by 31% and 15%, respectively, compared with those of PP.

C-N Coupling Reactions on Graphene with Aromatic Macromolecules and the Spatial Conformation of Grafted Macromolecules

The fabrication of advanced graphene-based nanocomposites with high-performance polymers requires covalent modification of graphene with aromatic macromolecules. Herein, C-N coupling reactions between fluorinated graphene (FG) and aromatic polyamides containing the benzimidazole moiety are successfully achieved. The optimized conditions are presented based on the nucleophilic behavior of the C-N coupling reaction on graphene. Different from the C-N coupling reaction between two small aromatic molecules, the conformation of grafted aromatic polyamide after reaction changes from torsional to paralleled alignment on graphene with the molecular length increment. Non-covalent interactions between graphene and aromatic polyamides result in this conformational change owing to the extended π systems of graphene and aromatic polyamides, and the synergistic effect of covalent and non-covalent interactions is put forward. As a consequence, graphene dispersibility is greatly enhanced in the solution of aromatic polyamide.

One-Step Direct Fixation of Atmospheric CO2 by Si-H Surface in Solution

The efficient conversion of carbon dioxide (CO2) into useful chemicals has important practical significance for environmental protection. Until now, direct fixation of atmospheric CO2 needs first extraction from the atmosphere, an energy-intensive process. Silicon (or Si-H surface), Earth-abundant, low-cost and non-toxic, is a promising material for heterogeneous CO2 chemical fixation. Here we report one-step fixing of CO2 directly from the atmosphere to a paraformaldehyde-like polymer by Si-H surface at room temperature. With the assistance of HF, commercial silicon powder was used as a heterogeneous reducing agent, for converting gaseous CO2 to a polymer of fluorine substituted polyoxymethylene and hydroxyl substituted polyoxymethylene alternating copolymer (F-POM). Making use of the Si-H surface toward the fixation of atmospheric gaseous CO2 is a conceptually distinct and commercially interesting strategy for making useful chemicals and environmental protection.

In Situ Radical Polymerization and Grafting Reaction Simultaneously Initiated by Fluorinated Graphene

Fluorinated graphene (FG) showed interesting electrochemical, electronic, and mechanical properties, as well as chemical reactivity for multifarious functionalization of graphene material. This work reported a free radical polymerization and grafting from polymerization of a styrene monomer directly initiated by FG, which simultaneously provided free polymers and functionalized graphene with polymer chains grafted. The FG exhibited an almost comparative initiation efficiency to equivalent commercial initiator azodiisobutyronitrile under similar conditions, resulting in a high yield of free polystyrene (40.9%) with a high molecular weight ( M_n = 114.7 kg/mol). It was demonstrated that FG-triggered polymerization presented some special characteristics, such as a long lifetime of chain radical centers even when the reaction was stopped and insensitivity to oxygen molecules. The mechanistic study indicated that the polymerization was initiated by single-electron transfer reaction between FG and a monomer leading to formation of primary radicals; in addition, FG also played an important role in chain transfer and termination reactions during the polymerization process.

Fluorine-Enriched Graphdiyne as an Efficient Anode in Lithium-Ion Capacitors

Lithium-ion capacitors (LICs) have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with low energy density or power density owing to the lack of active storage sites and ion diffusion limitation. In this study, fluorine-enriched graphdiyne (F-GDY) is prepared by a solvothermal reaction. Owing to the 42-C hexagonal porous structure, abundant sp and sp² hybrid carbon atoms, and even distribution of fluorine, F-GDY has enormous potential as an anode for lithium-ion storage. The outstanding rate performance (1825.9 mAh g^-1 at 0.1 A g^-1 , 979.2 mAh g^-1 at 5 A g^-1 ) and stable cycling stability of F-GDY in the lithium-ion battery inspire the assembly of a LIC with F-GDY as an anode and activated carbon (AC) as a cathode. When the AC/F-GDY mass ratio is 7:1, the LIC gives the largest energy density of 200.2 Wh kg^-1 , corresponding to a power density of 131.17 W kg^-1 . This LIC also shows excellent long-term cycling stability with a retention of approximately 80 % after 5000 cycles at 2 A g^-1 and a retention of more than 80 % after 6000 cycles at 5 A g^-1 .

Low temperature preparation of highly fluorinated multiwalled carbon nanotubes activated by Fe3O4 to enhance microwave absorbing property

Conventional approaches to preparing highly fluorinated multiwalled carbon nanotubes (MWCNTs) always require a high temperature. This paper presents a catalytic approach to realizing the effective fluorination of MWNCTs at room temperature (RT). Fe₃O₄/MWCNTs composites with Fe₃O₄ loaded on MWCNTs were first prepared using the solvothermal method, followed by fluorination treatment at RT. The attachment of Fe₃O₄ changes the charge distribution and dramatically improves the fluorination activity of MWCNTs. Consequently, the fluorine content of fluorinated Fe₃O₄/MWCNTs (F-Fe₃O₄/MWCNTs) can reach up to 17.13 at% (almost six times that of the unloaded sample) only after fluorination at room temperature, which leads to an obvious decrease in permittivity. Besides, the partial fluorination of Fe₃O₄ brings about abnormally enhanced permeability due to strengthened exchange resonance. Benefiting from the lower permittivity and higher permeability, F-Fe₃O₄/CNTs composite exhibits increased impedance matching and thus an enhanced microwave absorption property with a minimal reflection loss of -45 dB at 2.61 mm when the filler content is 13 wt%. The efficient absorption bandwidth (<-10 dB) reaches 4.1 GHz when the thickness is 2.5 mm. This work illustrates a novel catalytic approach to preparing highly fluorinated MWCNTs as promising microwave absorbers, and the design concept can also be extended to the fluorination of other carbon materials.

The Friedel-Crafts reaction of fluorinated graphene for high-yield arylation of graphene

Herein, we report the Friedel-Crafts reaction of fluorinated graphene with aryl molecules including methylbenzene, chlorobenzene and polystyrene. The reaction achieved the high-yield arylation functionalization of graphene under mild reaction conditions and extends the range of the Friedel-Crafts reaction to the field of two-dimensional materials.

2D Chemistry: Chemical Control of Graphene Derivatization

Controllable synthesis of graphene derivatives with defined composition and properties represents the holy grail of graphene chemistry, especially in view of the low reactivity of graphene. Recent progress in fluorographene (FG) chemistry has opened up new routes for synthesizing a plethora of graphene derivatives with widely applicable properties, but they are often difficult to control. We explored nucleophilic substitution on FG combining density functional theory calculations with experiments to achieve accurate control over the functionalization process. In-depth analysis revealed the complexity of the reaction and identified basic rules for controlling the 2D chemistry. Their application, that is, choice of solvent and reaction time, enabled facile control over the reaction of FG with N-octylamine to form graphene derivatives with tailored content of the alkylamine functional group (2.5-7.5% N atomic content) and F atoms (31.5-3.5% F atomic content). This work substantially extends prospects for the controlled covalent functionalization of graphene.

Reactivity of fluorographene is triggered by point defects: beyond the perfect 2D world

Preparation of graphene derivatives using fluorographene (FG) as a precursor has become a key strategy for the large-scale synthesis of new 2-D materials (e.g. graphene acid, cyanographene, allyl-graphene) with tailored physicochemical properties. However, to gain full control over the derivatization process, it is essential to understand the reaction mechanisms and accompanying processes that affect the composition and structure of the final products. Despite the strength of C-F bonds and high chemical stability of perfluorinated hydrocarbons, FG is surprisingly susceptible to reactions under ambient conditions. There is clear evidence that nucleophilic substitution on FG is accompanied by spontaneous defluorination, and solvent-induced defluorination can occur even in the absence of any nucleophilic agent. Here, we show that distributed radical centers (fluorine vacancies) on the FG surface need to be taken into account in order to rationalize the defluorination mechanism. Depending on the environment, these radical centers can react as electron acceptors, electrophilic sites and/or cause homolytic bond cleavages. We also propose a new radical mechanism of FG defluorination in the presence of N,N'-dimethylformamide (DMF) solvent. Spin-trap experiments as well as 19F NMR measurements unambiguously confirmed formation of N,N'-dimethylformyl radicals and also showed that N,N'-dimethylcarbamoyl fluoride plays a key role in the proposed mechanism. These findings imply that point defects in 2D materials should be considered as key factor determining their chemical properties and reactivity.

Chemistry of Graphene Derivatives: Synthesis, Applications, and Perspectives

The chemistry of graphene and its derivatives is one of the hottest topics of current material science research. The derivatisation of graphene is based on various approaches, and to date functionalization with halogens, hydrogen, various functional groups containing oxygen, sulfur, nitrogen, phosphorus, boron, and several other elements have been reported. Most of these functionalizations are based on sp³ hybridization of carbon atoms in the graphene skeleton, which means the formation of out-of-plane covalent bonds. Several elements were also reported for substitutional modification of graphene, where the carbon atoms are substituted with atoms like nitrogen, boron, and several others. From tens of functional groups, for only two of them were reported full functionalization of graphene skeleton and formation of its stoichiometric counterparts, fluorographene and hydrogenated graphene. The functionalization of graphene is crucial for most of its applications including energy storage and conversion devices, electronic and optic applications, composites, and many others.

Fluorographite to hydroxy graphene to graphene: a simple wet chemical approach for good quality graphene

Good quality graphene is prepared in a scalable manner from fluorographite by nucleophilic substitution of F with OH⁻ ions.

Radical mechanism of a nucleophilic reaction depending on a two-dimensional structure

The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C-F bond, and a spin center was generated on the nanosheet and fluorine anion. Moreover, neither the S_N1 nor S_N2 mechanism was suggested to be appropriate for the substitution reaction of FG with a 2D structure due to the corresponding kinetics or thermodynamics disadvantage; hence, its nucleophilic substitution was proved to occur via a radical mechanism initiated by the defluorination step. The proposed substitution mechanism of FG demonstrates that nucleophilic substitution via a radical mechanism can also be applied to the attacking process of common nucleophiles without any particular conditions. Furthermore, it has been discovered that triethylamine without active hydrogen can be covalently attached to graphene nanosheets via a nucleophilic substitution reaction with FG; this further indicates a radical process for the nucleophilic substitution of FG rather than an S_N1 or S_N2 mechanism. The detailed process of the nucleophilic substitution reaction of FG was revealed to occur via a radical mechanism depending on the 2D structure of FG, which could also represent the typical characteristic of 2D chemistry.

Chemistry, properties, and applications of fluorographene

Fluorographene, formally a two-dimensional stoichiometric graphene derivative, attracted remarkable attention of the scientific community due to its extraordinary physical and chemical properties. We overview the strategies for the preparation of fluorinated graphene derivatives, based on top-down and bottom-up approaches. The physical and chemical properties of fluorographene, which is considered as one of the thinnest insulators with a wide electronic band gap, are presented. Special attention is paid to the rapidly developing chemistry of fluorographene, which was advanced in the last few years. The unusually high reactivity of fluorographene, which can be chemically considered perfluorinated hydrocarbon, enables facile and scalable access to a wide portfolio of graphene derivatives, such as graphene acid, cyanographene and allyl-graphene. Finally, we summarize the so far reported applications of fluorographene and fluorinated graphenes, spanning from sensing and bioimaging to separation, electronics and energy technologies.

Effects of the oxygenic groups on the mechanism of fluorination of graphene oxide and its structure

The influence of the chemical structure of graphene oxide on its fluorination reaction and on the structure of the products was investigated.