Sodide and Organic Halides Effect Covalent Functionalization of Single-Layer and Bilayer Graphene

Direct Electrochemical Functionalization of Graphene Grown on Cu Including the Reaction Rate Dependence on the Cu Facet Type

We present an electrochemical method to functionalize single-crystal graphene grown on copper foils with a (111) surface orientation by chemical vapor deposition (CVD). Graphene on Cu(111) is functionalized with 4-iodoaniline by applying a constant negative potential, and the degree of functionalization depends on the applied potential and reaction time. Our approach stands out from previous methods due to its transfer-free method, which enables more precise and efficient functionalization of single-crystal graphene. We report the suggested effects of the Cu substrate facet by comparing the reactivity of graphene on Cu(111) and Cu(115). The electrochemical reaction rate changes dramatically at the potential threshold for each facet. Kelvin probe force microscopy was used to measure the work function, and the difference in onset potentials of the electrochemical reaction on these two different facets are explained in terms of the difference in work function values. Density functional theory and Monte Carlo calculations were used to calculate the work function of graphene and the thermodynamic stability of the aniline functionalized graphene on these two facets. This study provides a deeper understanding of the electrochemical behavior of graphene (including single-crystal graphene) on Cu(111) and Cu(115). It also serves as a basis for further study of a broad range of reagents and thus functional groups and of the role of metal substrate beneath graphene.

Band Gap Engineering in Two-Dimensional Materials by Functionalization: Methylation of Graphene and Graphene Bilayers

Graphene is well-known for its unique combination of electrical and mechanical properties. However, its vanishing band gap limits the use of graphene in microelectronics. Covalent functionalization of graphene has been a common approach to address this critical issue and introduce a band gap. In this Article, we systematically analyze the functionalization of single-layer graphene (SLG) and bilayer graphene (BLG) with methyl (CH₃) using periodic density functional theory (DFT) at the PBE+D3 level of theory. We also include a comparison of methylated single-layer and bilayer graphene, as well as a discussion of different methylation options (radicalic, cationic, and anionic). For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e., the fully methylated analogue of graphane) are considered. We find that up to a coverage θ of 1/2, graphene readily accepts CH₃, with neighbor CH₃ groups preferring trans positions. Above θ = 1/2, the tendency to accept further CH₃ weakens and the lattice constant increases. The band gap behaves less regularly, but overall it increases with increasing methyl coverage. Thus, methylated graphene shows potential for developing band gap-tuned microelectronics devices and may offer further functionalization options. To guide in the interpretation of methylation experiments, vibrational signatures of various species are characterized by normal-mode analysis (NMA), their vibrational density of states (VDOS), and infrared (IR) spectra, the latter two are obtained from ab initio molecular dynamics (AIMD) in combination with a velocity-velocity autocorrelation function (VVAF) approach.

The Covalent Functionalization of Surface-Supported Graphene: An Update

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

Low-voltage-hysteresis aluminum-sulfur battery with covalently functionalized mesoporous graphene

A pyridyl-functionalized mesoporous graphene is developed to accommodate sulfur for Al-S batteries, which can significantly reduce the voltage hysteresis to ∼0.43 V. The reaction kinetics of the Al-S battery are accelerated by the catalyst-free carbon host, ascribed to both the mesoporous graphene structure and the covalently functionalized pyridyl groups.

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.

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...

Alkalide-Assisted Direct Electron Injection for the Noninvasive n-Type Doping of Graphene

Although the doping of graphene grown by chemical vapor deposition is crucial in graphene-based electronics, noninvasive methods of n-type doping have not been widely investigated in comparison with p-type doping methods. We developed a convenient and robust method for the noninvasive n-type doping of graphene, wherein electrons are directly injected from sodium anions into the graphene. This method involves immersing the graphene in solutions of [K(15-crown-5)₂]Na prepared by dissolving a sodium-potassium (NaK) alloy in a 15-crown-5 solution. The n-type doping of the graphene was confirmed by downshifted G and 2D bands in Raman spectra and by the Dirac point shifting to a negative voltage. The electron-injected graphene showed no sign of structural damage, exhibited higher carrier mobilities than that of pristine graphene, and remained n-doped for over a month of storage in air. In addition, we demonstrated that electron injection enhances noncovalent interactions between graphene and metallomacrocycle molecules without requiring a linker, as used in previous studies, suggesting several potential applications of the method in modifying graphene with various functionalities.

Exfoliation of 2D Materials for Energy and Environmental Applications

The fascinating properties of single-layer graphene isolated by mechanical exfoliation have inspired extensive research efforts toward two-dimensional (2D) materials. Layered compounds serve as precursors for atomically thin 2D materials (briefly, 2D nanomaterials) owing to their strong intraplane chemical bonding but weak interplane van der Waals interactions. There are newly emerging 2D materials beyond graphene, and it is becoming increasingly important to develop cost-effective, scalable methods for producing 2D nanomaterials with controlled microstructures and properties. The variety of developed synthetic techniques can be categorized into two classes: bottom-up and top-down approaches. Of top-down approaches, the exfoliation of bulk 2D materials into single or few layers is the most common. This review highlights chemical and physical exfoliation methods that allow for the production of 2D nanomaterials in large quantities. In addition, remarkable examples of utilizing exfoliated 2D nanomaterials in energy and environmental applications are introduced.

Modulating charge carrier density and mobility in doped graphene by covalent functionalization

Covalent B-functionalization of B-doped graphene has been performed for the first time. The electronic properties and Hall effect of functionalized N- and B-doped graphene can be tuned by tailoring the electron-donating/-withdrawing properties of the organic addend.

Conductive Polyamide-Graphene Composite Fabric via Interface Engineering

Conductive fabrics have received significant attention because of their widespread applications from smart textiles to energy storage devices. Conductive colloidal materials are preferred as a coating on the fabric to achieve desirable electronic conductivity; however, obtaining a uniform coverage with a simple and effective route is a challenge. Herein, we report exfoliated graphene nanoplatelets (GNPs) in low boiling point solvents and their subsequent coating onto a polyamide fabric surface. Few-layered (average <7 layers) GNPs were obtained by optimizing solubility parameters of solvent mixtures and sonication time. Raman spectroscopy showed that the I_D/ I_G ratio changed from 0.33 to 0.38 in the GNP solution before and after the sonication, confirming an insignificant increase in defects on the basal plane of graphene after sonication treatment. Uniform coating of GNPs was obtained by optimizing concentration and sonication times. Scanning electron microscopy showed a uniform coverage of GNPs, and the surface resistivity of the polyamide fabric decreased from infinity to ∼40 kΩ after 4 h of coating. X-ray diffraction analysis confirmed the minimal effect on the fabric crystallinity during processing. This interface engineering approach is simple and scalable, and it is applicable for the coating of different polymeric fabrics with a great promise in electronic textiles.

N-Doped graphene/C60 covalent hybrid as a new material for energy harvesting applications

N-Doped graphene (N-G) was chemically functionalized by N-alkylation with the well-known electron acceptor C60. The degree of functionalization and the key structural features of the N-G/C60 hybrid were systematically investigated by a number of techniques including thermogravimetric analysis, X-ray photoelectron and Raman spectroscopies and transmission electron and atomic force microscopies. Absorption and electrochemical studies revealed interactions between the N-G and C60 while the fluorescence of C60 within the hybrid was found to be fully quenched. Evidence for the occurrence of excited state charge transfer from the singlet excited C60 to N-G in the hybrid was obtained from femtosecond transient absorption studies covering the visible-near-IR regions. Electron-pooling experiments performed in the presence of a sacrificial electron donor and a second electron acceptor, methyl viologen, revealed the accumulation of the one-electron reduced product of methyl viologen upon continuous irradiation of the N-G/C60 nanohybrid, thus revealing the utility of this material in photocatalytic energy harvesting applications.

Orientation-Dependent Strain Relaxation and Chemical Functionalization of Graphene on a Cu(111) Foil

Epitaxial graphene grown on single crystal Cu(111) foils by chemical vapor deposition is found to be free of wrinkles and under biaxial compressive strain. The compressive strain in the epitaxial regions (0.25-0.40%) is higher than regions where the graphene is not epitaxial with the underlying surface (0.20-0.25%). This orientation-dependent strain relaxation is through the loss of local adhesion and the generation of graphene wrinkles. Density functional theory calculations suggest a large frictional force between the epitaxial graphene and the Cu(111) substrate, and this is therefore an energy barrier to the formation of wrinkles in the graphene. Enhanced chemical reactivity is found in epitaxial graphene on Cu(111) foils as compared to graphene on polycrystalline Cu foils for certain chemical reactions. A higher compressive strain possibly favors lowering the formation energy and/or the energy gap between the initial and transition states, either of which can lead to an increase in chemical reactivity.

Constructing two-dimensional CuFeSe2@Au heterostructured nanosheets with an amorphous core and a crystalline shell for enhanced near-infrared light water oxidation

Although substantial efforts have been made toward the synthesis of noble metal-semiconductor heteronanostructures, direct in situ synthesis of two-dimensional (2D) core-shell semiconductor@noble metal heterostructured nanosheets remains largely unexplored. Herein, we report the synthesis of a novel 2D core-shell CuFeSe₂@Au heterostructured nanosheet with an amorphous core and a crystalline shell based on the reversed growth of Au nanosheets on the CuFeSe₂ frameworks under near-infrared (NIR) illumination. The nanosheet exhibits strong absorbance in the NIR region, and the valence band top of CuFeSe₂@Au nanosheets is higher than the oxidation potential of O₂/H₂O. Owing to the unique structural features, the resulting nanosheets show excellent photocatalytic activity and high stability toward water oxidation with an O₂ generation rate up to 3.48 mmol h^-1 g^-1 compared to those of the constituent materials under NIR light irradiation (λ > 850 nm). This work brings new opportunities to prepare 2D core-shell semiconductor@noble metal heterostructured nanosheets, which can be applied as photocatalysts toward water splitting and solar energy conversion at long wavelengths.

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.

Chemical functionalization and characterization of graphene-based materials

This review offers an overview on the chemical functionalization, characterization and applications of graphene-based materials.