Surface Fluorination of Nuclear Graphite Exposed to Molten 2LiF-BeF2 (FLiBe) Salt and Its Cover Gas at 700 °C

This study demonstrates that the reaction of Li2BeF4 (FLiBe) with graphite both in the liquid phase and the gas phase of the molten salt leads to the formation of covalent and semi-ionic carbon-fluorine bonds at the graphite surface and is accompanied by surface microstructural changes, removal of C-O groups, and deposition of metallic beryllium, based on XPS, Raman, and glow discharge mass spectroscopy characterization. At 700 °C, the observed surface density of C-F is higher after 240 h than after 12 h of exposure to molten FLiBe salt; the kinetics of covalent C-F formation is slower than that of semi-ionic C-F formation, and the relative amount of semi-ionic C-F content increases with depth. The graphite sample exposed to the cover gas exhibits less surface fluorination than the salt-exposed sample, with predominantly semi-ionic C-F. Based on these observations and the observed LiF/BeF2 ratio by surface XPS, the hypotheses that fluorination of the salt-exposed graphite occurs via a gas-phase mechanism or that it requires salt intrusion are refuted; future studies are warranted on the transport of C-F semi-ionic and covalent species in graphite at high temperatures.

Progress in Diamanes and Diamanoids Nanosystems for Emerging Technologies

New materials are the backbone of their technology-driven modern civilization and at present carbon nanostructures are the leading candidates that have attracted huge research activities. Diamanes and diamanoids are the new nanoallotropes of sp3 hybridized carbon which can be fabricated by proper functionalization, substitution, and via Birch reduction under controlled pressure using graphitic system as a precursor. These nanoallotropes exhibit outstanding electrical, thermal, optical, vibrational, and mechanical properties, which can be an asset for new technologies, especially for quantum devices, photonics, and space technologies. Moreover, the features like wide bandgap, tunable thermal conductivity, excellent thermal insulation, etc. make diamanes and diamanoids ideal candidates for nano-electrical devices, nano-resonators, optical waveguides, and the next generation thermal management systems. In this review, diamanes and diamanoids are discussed in detail in terms of its historical prospect, method of synthesis, structural features, broad properties, and cutting-edge applications. Additionally, the prospects of diamanes and diamanoids for new applications are carefully discussed. This review aims to provide a critical update with important ideas for a new generation of quantum devices based on diamanes and diamanoids which are going to be an important topic in the future of carbon nanotechnology.

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.

Redox reactions between acetonitrile and nitrogen dioxide in the interlayer space of fluorinated graphite matrices

The interlayer space of 2D materials can be a slit reactor where transformations not typical for the gas phase occur. We report redox reactions involving acetonitrile and nitrogen oxide guests in galleries of fluorinated graphite. Fluorinated graphite intercalation compounds with acetonitrile are treated with dinitrogen tetraoxide and the synthesis products are studied by a set of experimental methods. Data analysis reveals that N2O4 dissociates in fluorinated graphite matrices to form nitrogen-containing species NO3, NO2, NO, and N2. The interaction of NO3 with acetonitrile yields HNO3, which predominates as a guest in the synthesis products independently of the fluorination degree of the matrix. This reaction is accompanied by the removal of fluorine atoms weakly bonded to the graphite layers, leading to partial defluorination of the matrices. Our work demonstrates the possibility of using fluorinated graphite as a test nanoreactor whose dimension can be controlled by fluorination of the layers.

Microwave exfoliation of organic-intercalated fluorographites

Microwave (MW) irradiation is often used in preparation of nanomaterials. Here, we investigate MW exfoliation patterns of intercalated fluorinated graphite (C₂F) depending on the nature of the "guest". The resulting highly exfoliated graphites (multi-layer graphenes) show advantageous characteristics, as compared to the products of convective heating.

Chemically induced transformation of chemical vapour deposition grown bilayer graphene into fluorinated single-layer diamond

Notwithstanding the numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film carried out to date, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer ('F-diamane'). Induced by fluorine chemisorption, the phase transition from (AB)-stacked bilayer graphene to single-layer diamond was studied and verified by X-ray photoelectron, UV photoelectron, Raman, UV-Vis and electron energy loss spectroscopies, transmission electron microscopy and density functional theory calculations.

The ways of use of multilayered graphene in engineering ecology

The applications of multilayered graphenes (MLGs), nanocomposites "MLG-decontaminant" and polydicarbonfluoride intercalation compounds for the localization and deactivation of toxic spills and gaseous emissions under technogenic accidents are investigated in this paper. The intercalation compounds contain oxidizers as intercalants, and MLGs are formed destructively by thermolysis of polydicarbonfluoride intercalation compounds. The sorptive capacity of MLGs (about 240 ml of liquid phase per 1 g of MLG) is much higher than in well-known expanded graphites (EGs) obtained from graphite oxide or graphite acid salts. Our investigation revealed the possibility of the production of the "MLG-decontaminant" nanocomposites with the neutralizator content >95% due to the extremely low (down to 0.4 g/l) apparent density of MLG and its high specific surface (about 370 m²/g). The use of these nanocomposites for the acid-base or redox neutralization of contaminants does not result in the overheating, sputtering or evaporation of liquid phases, because their neutralization products sorb into MLGs. It prevents the soil mineralization by liquid or solid deactivated spills. We revealed that polydicarbonfluoride intercalation compounds with oxidizers (ClF₃, HNO₃, N₂O₄) can be efficiently used for the deactivation of spills and gaseous emissions of nitrogen-containing base compounds.

Two-Dimensional Fluorinated Graphene: Synthesis, Structures, Properties and Applications

Fluorinated graphene, an up-rising member of the graphene family, combines a two-dimensional layer-structure, a wide bandgap, and high stability and attracts significant attention because of its unique nanostructure and carbon-fluorine bonds. Here, we give an extensive review of recent progress on synthetic methods and C-F bonding; additionally, we present the optical, electrical and electronic properties of fluorinated graphene and its electrochemical/biological applications. Fluorinated graphene exhibits various types of C-F bonds (covalent, semi-ionic, and ionic bonds), tunable F/C ratios, and different configurations controlled by synthetic methods including direct fluorination and exfoliation methods. The relationship between the types/amounts of C-F bonds and specific properties, such as opened bandgap, high thermal and chemical stability, dispersibility, semiconducting/insulating nature, magnetic, self-lubricating and mechanical properties and thermal conductivity, is discussed comprehensively. By optimizing the C-F bonding character and F/C ratios, fluorinated graphene can be utilized for energy conversion and storage devices, bioapplications, electrochemical sensors and amphiphobicity. Based on current progress, we propose potential problems of fluorinated graphene as well as the future challenge on the synthetic methods and C-F bonding character. This review will provide guidance for controlling C-F bonds, developing fluorine-related effects and promoting the application of fluorinated graphene.

The Influence of Dimensional Effects on the Composition and Properties of Polydicarbonfluoride

The influence of dimensional effects on the compositions and properties of polydicarbonfluoride (C2 F)n prepared from multilayered graphenes was investigated. Multilayered graphenes were produced by destructive thermal decomposition of intercalation compounds of "idealized" (C2 F)n that were obtained by reaction of gaseous ClF3 with natural graphite at a room temperature. The precursors of multilayered graphenes have a common formula (C2 F⋅xR)n where R is an organic or inorganic component. It was shown that polydicarbonfluoride prepared from multilayered graphene does not form stable intercalation compound with ClF3 , in contrast to polydicarbonfluoride prepared from graphite, that forms its intercalation compound with ClF3 during fluorination of initial graphite in the ClF3 excess. Investigations of polydicarbonfluoride prepared from multilayered graphene showed that it cannot form intercalation compounds with different classes of organic and inorganic compounds as polydicarbonfluoride prepared from graphite can do. The absence of such intercalation activity for polydicarbonfluoride prepared from multilayered graphene can be explained by high exfoliation degree of multilayered graphene (3-4 nm) along the c-axis that results in the presence of two-dimensional (2D) structure properties in multilayered graphene. Dimensional effects transformed the chemical properties of polydicarbonfluoride prepared from multilayered graphene and lowered its decomposition temperature by 150 K in comparison with polydicarbonfluoride prepared from graphite.

Heteroatom substituted and decorated graphene: preparation and applications

The electronic structure and surface chemistry of graphene can be tuned subtly by doping with heteroatoms, which induces unique applications.

Energetics of defects on graphene through fluorination

Functionalized graphene sheets (FGSs) comprise a unique member of the carbon family, demonstrating excellent electrical conductivity and mechanical strength. However, the detailed chemical composition of this material is still unclear. Herein, we take advantage of the fluorination process to semiquantitatively probe the defects and functional groups on graphene surface. Functionalized graphene sheets are used as substrate for low-temperature (<150 °C) direct fluorination. The fluorine content has been modified to investigate the formation mechanism of different functional groups such as C-F, CF2, O-CF2 and (C=O)F during fluorination. The detailed structure and chemical bonds are simulated by density functional theory (DFT) and quantified experimentally by nuclear magnetic resonance (NMR). The electrochemical properties of fluorinated graphene are also discussed extending the use of graphene from fundamental research to practical applications.

Halogenated graphenes: rapidly growing family of graphene derivatives

Graphene derivatives containing covalently bound halogens (graphene halides) represent promising two-dimensional systems having interesting physical and chemical properties. The attachment of halogen atoms to sp(2) carbons changes the hybridization state to sp(3), which has a principal impact on electronic properties and local structure of the material. The fully fluorinated graphene derivative, fluorographene (graphene fluoride, C1F1), is the thinnest insulator and the only stable stoichiometric graphene halide (C1X1). In this review, we discuss structural properties, syntheses, chemistry, stabilities, and electronic properties of fluorographene and other partially fluorinated, chlorinated, and brominated graphenes. Remarkable optical, mechanical, vibrational, thermodynamic, and conductivity properties of graphene halides are also explored as well as the properties of rare structures including multilayered fluorinated graphenes, iodine-doped graphene, and mixed graphene halides. Finally, patterned halogenation is presented as an interesting approach for generating materials with applications in the field of graphene-based electronic devices.