Fluorographene

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Fluorographene structure in chair conformation seen from above CF 1.png
Fluorographene structure in chair conformation seen from above
Fluorographene in chair structure seen from side Fluorographene side.png
Fluorographene in chair structure seen from side
Fluorographene
CF 1.png
Identifiers
ChemSpider
  • none
Properties
CF1(.1)
Molar mass Variable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Fluorographene (or perfluorographane, graphene fluoride) is a fluorocarbon derivative of graphene. [1] [2] [3] It is a two dimensional carbon sheet of sp3 hybridized carbons, with each carbon atom bound to one fluorine. The chemical formula is (CF)n. In comparison, Teflon (polytetrafluoroethylene), -(CF2)n-, consists of carbon "chains" with each carbon bound to two fluorines.

Contents

Unlike fluorographene, graphene is unsaturated (sp2 hybridized) and completely carbon. The hydrocarbon analogue to fluorographene is sp3 hybridized graphane. Similar to other fluorocarbons (e.g. perfluorohexane), fluorographene is highly insulating. Fluorographene is thermally stable, resembling polytetrafluoroethylene; however, chemically it is reactive. It can be transformed back into graphene by reaction with potassium iodide at high temperatures. [3] During reactions of fluorographene with NaOH and NaSH simultaneous reductive defluorination and substitution are observed. The reactivity of fluorographene represents a facile way towards graphene derivatives. [4]

Preparation

The material was first created in 2010 by growing graphene on copper foil exposed to xenon difluoride at 30 °C. [1] It was discovered soon after that fluorographene could also be prepared by combining cleaved graphene on a gold grid while being exposed to xenon difluoride at 70 °C. [2] Also in 2010 Withers et al. described exfoliation of fluorinated graphite (monolayer, 24% fluorination) [5] and Cheng et al. reported reversible graphene fluorination. [6] Stoichiometric fluorographene was also prepared by chemical exfoliation of graphite fluoride. [3] It was also shown that graphene fluoride can be transformed back into graphene via reaction with iodine, which forms graphene iodide as a short lived intermediate. [3]

Structure

The structure of fluorographene can be derived from the structure of graphite monofluoride (CF)n, which consists of weakly bound stacked fluorographene layers, and its most stable conformation (predicted for the monocrystal) contains an infinite array of trans-linked cyclohexane chairs with covalent C–F bonds in an AB stacking sequence. [7] The estimated C-F distance is 136-138 pm, C-C distance is 157-158 pm and the C-C-C angle is 110°. [8] Possible fluorographene conformations have been extensively investigated computationally. [9] [10] [11] [12]

Electronic properties

Fluorographene is considered a wide gap semiconductor, because its I-V characteristics are strongly nonlinear with a nearly gate-independent resistance greater than 1 GΩ. In addition, fluorescence and NEXAFS measurements indicate band gap higher than 3.8 eV. Theoretical calculations show that estimation of fluorographene band gap is rather challenging task, as GGA functional provides band gap of 3.1 eV, hybrid (HSE06) 4.9 eV, GW 8.1 eV on top of PBE 8.1 or 8.3 eV on top of HSE06. The optical transition calculated by the Bethe-Salpeter equation is equal to 5.1 eV and points to an extremely strong exciton binding energy of 1.9 eV. [8] It has recently been demonstrated that using fluorographene as a passivation layer in Field Effect Transistors (FETs) featuring a graphene channel, carrier mobility increases significantly. [13]

Reaction

Fluorographene is susceptible for nucleophilic substitution and reductive defluorination, which makes it an extraordinary precursor material for synthesis of numerous graphene derivatives. Both of these channels can be used to chemically manipulate fluorographene, and they can be tuned by suitable conditions, e.g., solvent. [14] In 2010 it was shown that fluorographene can be transformed to graphene by treatment with KI. [3] Nucleophiles can substitute the fluorine atoms and induce partial or full defluorination. [15] The fluorographene reactivity is triggered by point defects. [16] The knowledge on fluorographene reactivity can be used for synthesis of new graphene derivatives, which contain i) mixture of F and other functional groups (like, e.g., thiofluorographene containing both -F and -SH [17] ) or ii) selectively only the functional group (and any -F groups). Alkyl and aryl groups can be selectively attached to graphene using Grignard reaction with fluorographene and this reaction leads to high-degree of graphene functionalization. [18] Very promising and selective graphene derivative cyanographene (graphene nitrile) was synthesized by reaction of NaCN with fluorographene. This material was further used for synthesis of graphene acid, i.e., graphene functionalized by -COOH groups over its surface, and it was shown that this graphene acid can be effectively conjugated with amines and alcohols. These findings open new door for high-yield and selective graphene functionalization. [19]

Other halogenated graphenes

Recent studies have also revealed that, similar to fluorination, full chlorination of graphene can be achieved. The resulting structure is called chlorographene. [20] [21] However other theoretical calculations questioned stability of chlorographene under ambient conditions. [22]

Also graphene can be fluorinated or halofluorinated by CVD-method with fluorocarbons, hydro- or halofluorocarbons by heating while in contact of carbon material with fluoroorganic substance to form partially fluorinated carbons (so called Fluocar materials). [23] [24]

An overview on preparation, reactivity and properties of halogenated graphenes in available in ACS Nano journal free of charge. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Fluorocarbon</span> Class of chemical compounds

Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are commercial polymers, refrigerants, drugs, and anesthetics.

<span class="mw-page-title-main">Carbon tetrafluoride</span> Chemical compound

Tetrafluoromethane, also known as carbon tetrafluoride or R-14, is the simplest perfluorocarbon (CF4). As its IUPAC name indicates, tetrafluoromethane is the perfluorinated counterpart to the hydrocarbon methane. It can also be classified as a haloalkane or halomethane. Tetrafluoromethane is a useful refrigerant but also a potent greenhouse gas. It has a very high bond strength due to the nature of the carbon–fluorine bond.

Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers.

<span class="mw-page-title-main">Carbon monofluoride</span> Chemical compound

Carbon monofluoride (CF, CFx, or (CF)n), also called polycarbon monofluoride (PMF), polycarbon fluoride, poly(carbon monofluoride), and graphite fluoride, is a material formed by high-temperature reaction of fluorine gas with graphite, charcoal, or pyrolytic carbon powder. It is a highly hydrophobic microcrystalline powder. Its CAS number is 51311-17-2. In contrast to graphite intercalation compounds it is a covalent graphite compound.

Bromine compounds are compounds containing the element bromine (Br). These compounds usually form the -1, +1, +3 and +5 oxidation states. Bromine is intermediate in reactivity between chlorine and iodine, and is one of the most reactive elements. Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. This can be seen from the standard electrode potentials of the X2/X− couples (F, +2.866 V; Cl, +1.395 V; Br, +1.087 V; I, +0.615 V; At, approximately +0.3 V). Bromination often leads to higher oxidation states than iodination but lower or equal oxidation states to chlorination. Bromine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Br bonds.

Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain a carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refrigerants, and reagents in catalysis. In addition to these applications, some organofluorine compounds are pollutants because of their contributions to ozone depletion, global warming, bioaccumulation, and toxicity. The area of organofluorine chemistry often requires special techniques associated with the handling of fluorinating agents.

<span class="mw-page-title-main">Carbon–fluorine bond</span> Covalent bond between carbon and fluorine atoms

The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry, and relatively short, due to its partial ionic character. The bond also strengthens and shortens as more fluorines are added to the same carbon on a chemical compound. As such, fluoroalkanes like tetrafluoromethane are some of the most unreactive organic compounds.

The Fowler process is an industry and laboratory route to fluorocarbons, by fluorinating hydrocarbons or their partially fluorinated derivatives in the vapor phase over cobalt(III) fluoride.

<span class="mw-page-title-main">Fluorine</span> Chemical element, symbol F and atomic number 9

Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactive, as it reacts with all other elements except for the light inert gases.

Electrochemical fluorination (ECF), or electrofluorination, is a foundational organofluorine chemistry method for the preparation of fluorocarbon-based organofluorine compounds. The general approach represents an application of electrosynthesis. The fluorinated chemical compounds produced by ECF are useful because of their distinctive solvation properties and the relative inertness of carbon–fluorine bonds. Two ECF synthesis routes are commercialized and commonly applied: the Simons process and the Phillips Petroleum process. It is also possible to electrofluorinate in various organic media. Prior to the development of these methods, fluorination with fluorine, a dangerous oxidizing agent, was a dangerous and wasteful process. ECF can be cost-effective, but it may also result in low yields.

<span class="mw-page-title-main">Graphane</span> Chemical compound

Graphane is a two-dimensional polymer of carbon and hydrogen with the formula unit (CH)n where n is large. Partial hydrogenation results in hydrogenated graphene, which was reported by Elias et al in 2009 by a TEM study to be "direct evidence for a new graphene-based derivative". The authors viewed the panorama as "a whole range of new two-dimensional crystals with designed electronic and other properties".

<span class="mw-page-title-main">Vanadium pentafluoride</span> Chemical compound

Vanadium(V) fluoride is the inorganic compound with the chemical formula VF5. It is a colorless volatile liquid. It is a highly reactive compound, as indicated by its ability to fluorinate organic substances.

For inorganic compounds of carbon, chlorographene is fully chlorinated graphene with the chemical formula of (CCl)n. Upon reaction with chlorine, graphene's sp2 planar lattice structure is transformed to sp3 hybridized buckled structure, this structure is similar to hydrogenated graphene (graphane) and fluorinated graphene (fluorographene).

Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.

Radical fluorination is a type of fluorination reaction, complementary to nucleophilic and electrophilic approaches. It involves the reaction of an independently generated carbon-centered radical with an atomic fluorine source and yields an organofluorine compound.

<span class="mw-page-title-main">Perfluorocycloalkene</span> Class of chemical compounds

A perfluorocycloalkene (PFCA) fluorocarbon structure with a cycloalkene core. PFCAs have shown reactivity with a wide variety of nucleophiles including phenoxides, alkoxides, organometallic, amines, thiols, and azoles. They or their derivatives are reported to have nonlinear optical activity, and be useful as lubricants, etching agents, components of fuel cells, low dielectric materials, and super hydrophobic and oleophobic coatings.

<span class="mw-page-title-main">Jaqueline Kiplinger</span> American inorganic chemist

Jaqueline Kiplinger is an American inorganic chemist who specializes in organometallic actinide chemistry. Over the course of her career, she has done extensive work with fluorocarbons and actinides. She is currently a Fellow of the Materials Synthesis and Integrated Devices group in the Materials Physics and Applications Division of Los Alamos National Laboratory (LANL). Her current research interests are focused on the development of chemistry for the United States’ national defense and energy needs.

<span class="mw-page-title-main">Regional Centre of Advanced Technologies and Materials</span>

The Regional Centre of Advanced Technologies and Materials is a scientific and research centre connected to the Faculty of Science, Palacký University, Olomouc. Its chief objective is to produce superlative research and to transfer high-tech products and technologies to medical, industrial and environmental practice with a pronounced emphasis on connecting the Centre to international networks and collaborations. The center was established on 1 October 2010, and since October 2013 is housed in a high-tech new building in Palacky University campus at Šlechtitelů street.

Graphene is the only form of carbon in which every atom is available for chemical reaction from two sides. Atoms at the edges of a graphene sheet have special chemical reactivity. Graphene has the highest ratio of edge atoms of any allotrope. Defects within a sheet increase its chemical reactivity. The onset temperature of reaction between the basal plane of single-layer graphene and oxygen gas is below 260 °C (530 K). Graphene combusts at 350 °C (620 K). Graphene is commonly modified with oxygen- and nitrogen-containing functional groups and analyzed by infrared spectroscopy and X-ray photoelectron spectroscopy. However, determination of structures of graphene with oxygen- and nitrogen- functional groups requires the structures to be well controlled.

References

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  12. ↑ Tang, Shaobin; Zhang, Shiyong (2011). "Structural and Electronic Properties of Hybrid Fluorographene–Graphene Nanoribbons: Insight from First-Principles Calculations". The Journal of Physical Chemistry C. 115 (33): 16644–16651. doi:10.1021/jp204880f.
  13. ↑ Ho, Kuan-I; Boutchich, Mohamed; Su, Ching-Yuan; Moreddu, Rosalia; Marianathan, Eugene Sebastian Raj; Montes, Laurent; Lai, Chao-Sung (2015). "A Self-Aligned High-Mobility Graphene Transistor: Decoupling the Channel with Fluorographene to Reduce Scattering". Advanced Materials. 27 (41): 6519–6525. Bibcode:2015AdM....27.6519H. doi:10.1002/adma.201502544. PMID   26398725. S2CID   205262203.
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  17. ↑ Urbanová, Veronika; Holá, Kateřina; Bourlinos, Athanasios B.; Čépe, Klára; Ambrosi, Adriano; Loo, Adeline Huiling; Pumera, Martin; Karlický, František; Otyepka, Michal; Zbořil, Radek (2015). "Thiofluorographene-Hydrophilic Graphene Derivative with Semiconducting and Genosensing Properties". Advanced Materials. 27 (14): 2305–2310. Bibcode:2015AdM....27.2305U. doi:10.1002/adma.201500094. PMID   25692678. S2CID   624468.
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