Fluorographene Modified by Grignard Reagents: A Broad Range of Functional Nanomaterials

Emerging graphene derivatives as active 2D coordination platforms for single-atom catalysts

Single-atom catalysts (SACs) based on graphene derivatives are an emerging and growing class of materials functioning as two-dimensional (2D) metal-coordination scaffolds with intriguing properties. Recently, owing to the rich chemistry of fluorographene, new avenues have opened toward graphene derivatives with selective, spacer-free, and dense functionalization, acting as in-plane or out-of-plane metal coordination ligands. The particular structural features give rise to intriguing phenomena occurring between the coordinated metals and the graphene backbone. These include redox processes, charge transfer, emergence, and stabilization of rare or otherwise unstable metal valence states, as well as metal-support and metal-metal synergism. The vast potential of such systems has been demonstrated as enzyme mimics for cooperative mixed-valence SACs, ethanol fuel cells, and CO₂ fixation; however, it is anticipated that their impact will further expand toward diverse fields, e.g., advanced organic transformations, electrochemical energy storage, and energy harvesting.

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...

Recent Advances in Fluorinated Graphene from Synthesis to Applications: Critical Review on Functional Chemistry and Structure Engineering

Fluorinated graphene (FG), as an emerging member of the graphene derivatives family, has attracted wide attention on account of its excellent performances and underlying applications. The introduction of a fluorine atom, with the strongest electronegativity (3.98), greatly changes the electron distribution of graphene, resulting in a series of unique variations in optical, electronic, magnetic, interfacial properties and so on. Herein, recent advances in the study of FG from synthesis to applications are introduced, and the relationship between its structure and properties is summarized in detail. Especially, the functional chemistry of FG has been thoroughly analyzed in recent years, which has opened a universal route for the functionalization and even multifunctionalization of FG toward various graphene derivatives, which further broadens its applications. Moreover, from a particular angle, the structure engineering of FG such as the distribution pattern of fluorine atoms and the regulation of interlayer structure when advanced nanotechnology gets involved is summarized. Notably, the elaborated structure engineering of FG is the key factor to optimize the corresponding properties for potential applications, and is also an up-to-date research hotspot and future development direction. Finally, perspectives and prospects for the problems and challenges in the study of FG are put forward.

Halogen Functionalization in the 2D Material Flatland: Strategies, Properties, and Applications

Given the electronegativity and bonding environment of halogen elements, halogenation (i.e., fluorination, chlorination, bromination, and iodination) serves as a versatile strategy for chemical modifications of materials. The combination of halogens and 2D materials has triggered extensive interests since the first report on graphene fluorination in 2008. Subsequently, scholars consistently conduct pre-, in-process, or posthalogenation modifications of emerging 2D materials to achieve desired properties and broad device applications. They also continuously explore the role of halogens in 2D material functionalization. The multiple advantages introduced by halogen decoration make 2D materials outstanding from each subclass. In this review, an overall retrospect is provided on the research advances in the area of 2D material halogenation, including experimental halogenation strategies, halogen-triggered novel physics and properties, and advanced applications across the studied objects. Future research directions in this area are also proposed.

Tunable one-step double functionalization of graphene based on fluorographene chemistry

Double functionalized graphene derivatives were synthetized by a one-pot reaction of fluorographene with organometallic nucleophiles. Their nucleophilicity governed the preference for grafting and was utilized for tuning the functionalization. This approach paves the way toward the facile, up-scalable and controllable multifunctionalization of graphene.

Deoxofluorination of graphite oxide with sulfur tetrafluoride

In this study, deoxofluorination of graphite oxide (GO) using sulfur tetrafluoride (SF₄) at a temperature below the decomposition temperature of GO (∼200 °C) was investigated for the first time with and without HF catalysis. At 25 °C, the reaction proceeds only at high SF₄ pressures (≥8 atm) when not catalyzed by HF and at 1 atm SF₄ under the catalysis of HF. The degree of fluorination increases at higher temperatures and SF₄ pressures. Hydroxy and carbonyl groups are replaced by fluorine following this reaction, and SF₄ and SOF₂ are introduced into the product, while the epoxy groups do not react. SF₄ and SOF₂ in the products are removed by washing with water. The obtained product is less hygroscopic than pristine GO owing to the hydrophobicity of the fluorine atom. The interlayer separation of the product is increased after deoxofluorination despite the smaller size of fluorine than the sizes of the oxygen-containing functional groups. When compared with direct fluorination using elemental fluorine, deoxofluorination using SF₄ has the advantages of high reactivity with hydroxy groups and the preservation of the carbon skeleton, and the reaction results in the formation of graphite oxyfluoride.

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.

Alkynylation of graphene via the Sonogashira C-C cross-coupling reaction on fluorographene

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes.

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes. Theoretical calculations revealed that fluorographene can efficiently bind and oxidize the palladium catalyst on electrophilic sites activated by fluorine atoms. This paves the way towards conductive and mechanically robust 3D covalent networks.

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.

Hydrogenation of Fluorographite and Fluorographene: An Easy Way to Produce Highly Hydrogenated Graphene

Fluorographene is an excellent precursor for the synthesis of graphene derivatives. Relative to pure graphene, fluorographene possesses higher reactivity and, in comparison with graphene oxide, is also homogenous in composition, which enables the preparation of well-defined materials. Recently, it has been shown that several graphene derivatives can be synthesized from fluorographene, thus yielding various products such as graphene acid or alkylated graphene. This study focuses on the hydrogenation of fluorographene by using various hydrogenation reactions, including the use complex hydrides and solvated electrons in different media. In addition, a comparison of these reactions shows that fluorinated graphite has significantly lower reactivity than fluorographene. The conversion rates of these reactions are higher when fluorographene is used relative to fluorographite. These reactions can be used to tune the hydrogen/fluorine composition on a graphene backbone.

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.

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

We report a novel strategy to synthesize nano-sized, water-soluble and functionalized fluorinated carbon fiber oxide with high fluorescence, paramagnetism and NIR absorption for cancer chemo-photothermal therapy.

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.

Current and future directions in electron transfer chemistry of graphene

The participation of graphene in electron transfer chemistry, where an electron is transferred between graphene and other species, encompasses many important processes that have shown versatility and potential for use in important applications.

Towards stoichiometric analogues of graphene: graphane, fluorographene, graphol, graphene acid and others

Stoichiometric derivatives of graphene, having well-defined chemical structure and well-defined chemical bonds, are of a great interest to the 2D materials research.