Chemical Functionalization Of Graphene Research Articles

Covalent Functionalization of Graphene Sheets with Different Moieties and Their Effects on Biological Activities.

The ongoing spread of multi-drug-resistant bacteria over the past few decades necessitates collateral efforts to develop new classes of antibacterial agents with different mechanisms of action. The utilization of graphene nanosheets has recently gained attention with this respect. Herein, we have synthesized and tested the antibacterial activity of an array of graphene materials covalently functionalized with hydroxyl-, amine-, or carboxyl-containing groups. Fourier transform infrared spectroscopy and transmission electron microscopy confirmed successful functionalization of the few-layer graphene (FLG). The percentage of weight loss was measured by thermogravimetric analysis, which was found to be 22%, 23%, and 37% for FLG-TEG-OH, FLG-NH2, and FLG-DEG-COOH, respectively. In comparison with pristine graphene sheets, the functionalized few-layer graphene (f-FLG) materials gained an adequate dispersibility in water as confirmed by ζ potential analysis. Moreover, there was a significant improvement in the antibacterial activity against Staphylococcus aureus and Escherichia coli, where all f-FLG compounds were able to suppress bacterial growth, with a complete suppression achieved by FLG-DEG-COOH. The minimum inhibitory concentration (MIC) was 250 μg mL-1 for both FLG-TEG-OH and FLG-NH2, while it was 125 μg mL-1 for FLG-DEG-COOH. The glutathione oxidation test demonstrated an oxidative stress activity by all f-FLG compounds. However, FLG-DEG-COOH demonstrated the highest reduction in glutathione activity. FLG-DEG-COOH and FLG-TEG-OH showed adequate biocompatibility and hemocompatibility. The chemical functionalization of graphene might be a step toward the foundation of an effective class of antimicrobial agents.

Graphene and Carbon-Nanotube Nanohybrids Covalently Functionalized by Porphyrins and Phthalocyanines for Optoelectronic Properties.

In recent years, there has been a rapid growth in studies of the optoelectronic properties of graphene, carbon nanotubes (CNTs), and their derivatives. The chemical functionalization of graphene and CNTs is a key requirement for the development of this field, but it remains a significant challenge. The focus here is on recent advances in constructing nanohybrids of graphene or CNTs covalently linked to porphyrins or phthalocyanines, as well as their application in nonlinear optics. Following a summary of the syntheses of nanohybrids constructed from graphene or CNTs and porphyrins or phthalocyanines, explicit intraconjugate electronic interactions between photoexcited porphyrins/phthalocyanines and graphene/CNTs are introduced classified by energy transfer, electron transfer, and charge transfer, and their optoelectronic applications are also highlighted. The major current challenges for the development of covalently linked nanohybrids of porphyrins or phthalocyanines and carbon nanostructures are also presented.

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.

Preparation of chloro-functionalized reduced graphene oxide by silver-catalyzed radical reaction

It is well-known that chemical functionalization of graphene has the great significance. We report the development of a new synthesis method of chloro-functionalized reduced graphene oxide (rGOCl). The rGOCl was prepared by radical reaction, and treatment of carboxyl graphene oxide (GOCOOH) with N-chlorosuccinimide (NCS) at 90°C for 10h under an atmosphere of nitrogen, using silver nitrate as catalyst. The morphologies and structures of the prepared materials were investigated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and the thermal gravimetric. Results indicated that the rGOCl can be readily obtained from graphene oxide (GO) in three steps.

One-step functionalization of graphene by cycloaddition of diarylcarbene and its application as reinforcement in epoxy composites

Due to its novel physical, chemical and mechanical properties, graphene has great potential to be applied in composite science. However, the inert chemical structures with low surface energy and low solubility in both organic and aqueous solution are the major bottleneck for real applications. Chemical functionalization of graphene is one of the effective solutions to address the above challenges. In the present study, novel highly reactive diarylcarbene derivative is designed and synthesized. Different to previous approaches, this diarylcarbene derivative contains reactive epoxy groups, which can serve as anchoring sites for further modification. Then, reactive epoxy groups are introduced to graphene via one-step diarylcarbene cycloaddition. The modification is observed spectroscopically, and the obtained graphene (DC-GR) can be well-dispersed in organic solvent, such as acetone and dichloromethane. In order to further verify the effectiveness of modification, we use DC-GR as reinforcement to enhance epoxy resin. Both thermal and mechanical properties of the composites are improved significantly at low DC-GR content loading. The enhancement is believed to be attributed to the strong interfacial interactions between DC-GR and the matrix via epoxy groups. This study provides alternate strategy to modify the graphene, which will greatly expand the application field of graphene in composite science.

ChemInform Abstract: Graphene Oxide: Strategies for Synthesis, Reduction and Frontier Applications

AbstractReview: 263 refs.

Growth and characterization of 7,7,8,8-tetracyano-quinodimethane crystals on chemical vapor deposition graphene

Chemical functionalization of graphene could pave the way for favorably modifying its already remarkable properties. Organic molecules have been utilized to this end as a way to alter graphene's structural, chemical, electrical, optical and even magnetic properties. One such promising organic molecule is 7,7,8,8-tetracyano-quinodimethane (TCNQ), a strong electron acceptor which has been shown to be an effective p-dopant of graphene. This study explores the thermal evaporation of TCNQ onto graphene transferred onto SiO2/Si substrates. Using two different home-made thermal evaporators, a wide range of TCNQ growth regimes are explored, from thin films to bulk crystals. The resulting graphene/TCNQ structure is characterized via optical microscopy, Raman spectroscopy and atomic force microscopy (AFM). Films are found to be comprised of TCNQ and the oxidized product of TCNQ, α,α-dicyano-p-toluoylcyanide (DCTC), which confirms the electron charge transfer from graphene to the TCNQ films. AFM measurements of these films show that after forming a rather smooth layer covering the graphene surface, small clusters start to form. For higher TCNQ coverage, the clusters agglomerate, becoming quite large in size and forming ripples or wrinkles across the surface.

Light-assisted recharging of graphene quantum dots in fluorographene matrix

In the present study, the charge transient spectroscopy was used to analyze the transient relaxation of charges in graphene and bilayer-graphene quantum dot (QD) systems formed by chemical functionalization of graphene and few-layer graphene layers. A set of activation energies (one to three different values) for the emission of charges from QDs sized 50 to 70 nm, most likely proceeding via the thermal activation of charge carriers from QD quantum confinement levels, were deduced from measurements performed in the dark. Daylight illumination of samples during measurements was found to result in a strong decrease of the activation energies and in an involvement of an athermal process in the charge relaxation phenomenon. The time of the light-assisted emission of charge carriers from QDs proved to be two to four orders of magnitude shorter than the time of their emission from QDs under no-illumination conditions.

Chemical modification of graphene via hyperthermal molecular reaction.

Chemical functionalization of graphene is achieved by hyperthermal reaction with azopyridine molecular ions. The one-step, room temperature process takes place in high vacuum (10(-7) mbar) using an electrospray ion beam deposition (ES-IBD) setup. For ion surface collisions exceeding a threshold kinetic energy of 165 eV, molecular cation beams of 4,4'-azobis(pyridine) covalently attach to chemical vapor deposited (CVD) graphene. A covalent functionalization degree of 3% of the carbon atoms of graphene is reached after 3-5 h of ion exposure of 2 × 10(14) azopyridinium/cm(2) of which 50% bind covalently. This facile approach for the controlled modification of graphene extends the scope of candidate species that would not otherwise react via existing conventional methods.

Graphene quantum dots in fluorographene matrix formed by means of chemical functionalization

In the present study, we examined the creation conditions and the properties of graphene or multi-layer graphene (MLG) quantum dots (QDs) self-formed in insulating dielectric fluorographene matrix. The QD arrays were obtained using chemical functionalization of graphene or MLG films in an aqueous solution of hydrofluoric acid. The formation of a fluorographene network in the films caused their transition from conducting to insulating state; this transition was a result of partitioning of the films into isolated graphene islands accompanied by an increase of the resistance of the films by 7–8 orders of magnitude. Experimentally, it was shown that the characteristic time required for the formation of QD arrays in the films depended linearly on the initial film thickness, on the solution concentration, and on temperature. The atomic force microscopy lateral force measurements have allowed us to evaluate the sizes and densities of formed QDs, and to trace the evolution of both QDs and fluorinated barriers between them in the functionalization process. A possibility to achieve QD sizes ranging from 70–20nm (at QD density ∼(4–6)×1010cm−2) to 10–20nm (at QD density ∼1×1010cm−2) has been demonstrated. The activation energies of electrical conductivity in the films with QDs have been evaluated.

Chemical functionalization of graphene by carbene cycloaddition: A density functional theory study

Abstract In this work, we have systematically studied the structural, energetic and electronic properties of graphene functionalized with carbene groups by using density functional theory. Introducing a low concentration of CCl 2 group in graphene was studied in detail by DFT, and closed cyclopropane-like three-membered ring structure was formed, meanwhile, the potential candidate carbene groups CR 2 (R = H, F, CH 3 , CN, NO 2 , OCH 3 , CCH, C 6 H 5 ) were added to graphene sheet, and CR 2 (R = H, NO 2 , CH 3 ) groups were expected to be good reactive species to covalently modify graphene. The graphene functionalization with carbene groups above can open graphene's band gap. More CCl 2 molecules were added to graphene, and different concentrations of CCl 2 group can tune graphene's band gap. In addition, the addition of CCl 2 group to graphene edges was investigated, and the stronger binding energy was found. Multiple CCl 2 molecules preferred to be bound with the same edge of graphene nanoribbon. This work provides an insight into the detailed molecular mechanism of graphene functionalization with carbene groups.

Producing arrays of graphene and few-layer graphene quantum dots in a fluorographene matrix

Conductive islands (quantum dots) of graphene and few-layer graphene in a fluorinated graphene matrix were produced by chemical functionalization of graphene in aqueous hydrofluoric acid. The structures formed were investigated by measuring the current-voltage characteristics and by means of an atomic-force microscope used to measure the surface topography and lateral forces. The presence of conductive islands in the fluorinated matrix was shown, and their sizes were determined.

Enhanced properties of aryl diazonium salt-functionalized graphene/poly(vinyl alcohol) composites

Abstract The impediments to incorporating graphene into poly(vinyl alcohol) (PVA) are intrinsically inhomogeneous dispersion and agglomeration during mixing. Two types of PVA composites containing reduced graphene oxide (r-GO) and a novel aryl diazonium salt functionalized graphene (ADS-G) as nanofiller were successfully prepared by a simple solution casting. Fourier transform infrared spectroscopy showed the reduction of graphene oxide (GO), chemical functionalization of graphene by ADS, and formation of graphene-based PVA composites. Field emission scanning electron microscopy and transmission electron microscopy image analyses indicated that r-GO and ADS-G were fully incorporated into the PVA matrix. ADS-G formed better dispersion than r-GO and acted as good reinforcing filler to enhance the mechanical and dielectric properties of PVA. The tensile strength and modulus of the resulting PVA/ADS-G composites were improved by about 181% and 198%, respectively. In contrast, the tensile strength and modulus of PVA/r-GO composites were enhanced by 125% and 160%, respectively. The electrical conductivities were increased by ∼10 7 orders of magnitude in the composites with only 1.0 wt.% of filler loadings as compared to that of neat PVA. PVA/ADS-G composites showed greater improvement in thermal stability than PVA/r-GO composites, as evidenced from thermogravimetric and differential scanning calorimetric analyses. These results demonstrated that the ADS-G acted as good reinforcing filler compared to r-GO when using PVA as a polymer matrix.

Scalable enhancement of graphene oxide properties by thermally driven phase transformation

Chemical functionalization of graphene is promising for a variety of next-generation technologies. Although graphene oxide (GO) is a versatile material in this direction, its use is limited by the production of metastable, chemically inhomogeneous and spatially disordered GO structures under current synthetic protocols, which results in poor optoelectronic properties. Here, we present a mild thermal annealing procedure, with no chemical treatments involved, to manipulate as-synthesized GO on a large scale to enhance sheet properties with the oxygen content preserved. Using experiments supported by atomistic calculations, we demonstrate that GO structures undergo a phase transformation into prominent oxidized and graphitic domains by temperature-driven oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. Our thermal processing method offers a suitable way to tune and enhance the properties of GO, which creates opportunities for various applications.

ChemInform Abstract: Covalent Chemistry on Graphene

AbstractReview: 45 refs.

Graphene in Light: Design, Synthesis and Applications of Photo‐active Graphene and Graphene‐Like Materials

Graphene functionalized with photo-active units has become one of the most exciting topics of research in the last few years, which remarkably sustains and expands the graphene boom. The rise of photo-active graphene in photonics and optoelectronics is evidenced by a spate of recent reports on topics ranging from photodetectors, photovoltaics, and optoelectronics to photocatalysis. For these applications, the fabrication of photo-active graphene through appropriate chemical functionalization strategies is essential as pristine graphene has zero bandgap and only weak absorption of photons. Written from the chemists' point of view, up-to-date chemical functionalization of graphene with various small organic molecules, conjugated polymers, rare-earth components, and inorganic semiconductors is reviewed. Particular attention is paid to the development of graphene functionalized with light-harvesting moieties, including materials synthesis, characterization, energy/charge-transfer processes, and applications in photovoltaics. Challenges currently faced by researchers and future perspectives in this field are also discussed.

Atomic Covalent Functionalization of Graphene

Although graphene's physical structure is a single atom thick, two-dimensional, hexagonal crystal of sp(2) bonded carbon, this simple description belies the myriad interesting and complex physical properties attributed to this fascinating material. Because of its unusual electronic structure and superlative properties, graphene serves as a leading candidate for many next generation technologies including high frequency electronics, broadband photodetectors, biological and gas sensors, and transparent conductive coatings. Despite this promise, researchers could apply graphene more routinely in real-world technologies if they could chemically adjust graphene's electronic properties. For example, the covalent modification of graphene to create a band gap comparable to silicon (∼1 eV) would enable its use in digital electronics, and larger band gaps would provide new opportunities for graphene-based photonics. Toward this end, researchers have focused considerable effort on the chemical functionalization of graphene. Due to its high thermodynamic stability and chemical inertness, new methods and techniques are required to create covalent bonds without promoting undesirable side reactions or irreversible damage to the underlying carbon lattice. In this Account, we review and discuss recent theoretical and experimental work studying covalent modifications to graphene using gas phase atomic radicals. Atomic radicals have sufficient energy to overcome the kinetic and thermodynamic barriers associated with covalent reactions on the basal plane of graphene but lack the energy required to break the C-C sigma bonds that would destroy the carbon lattice. Furthermore, because they are atomic species, radicals substantially reduce the likelihood of unwanted side reactions that confound other covalent chemistries. Overall, these methods based on atomic radicals show promise for the homogeneous functionalization of graphene and the production of new classes of two-dimensional materials with fundamentally different electronic and physical properties. Specifically, we focus on recent studies of the addition of atomic hydrogen, fluorine, and oxygen to the basal plane of graphene. In each of these reactions, a high energy, activating step initiates the process, breaking the local π structure and distorting the surrounding lattice. Scanning tunneling microscopy experiments reveal that substrate mediated interactions often dominate when the initial binding event occurs. We then compare these substrate effects with the results of theoretical studies that typically assume a vacuum environment. As the surface coverage increases, clusters often form around the initial distortion, and the stoichiometric composition of the saturated end product depends strongly on both the substrate and reactant species. In addition to these chemical and structural observations, we review how covalent modification can extend the range of physical properties that are achievable in two-dimensional materials.

Crumpled Nitrogen‐Doped Graphene Nanosheets with Ultrahigh Pore Volume for High‐Performance Supercapacitor

Continuous scientifi c endeavors have been directed toward the optimization of graphene by manipulating its electronic, mechanical, chemical, and structural properties, such as surface area, pore geometry, and functional sites, in order to advance various potential applications, including nanoelectronics, energy storage/conversion, and catalysis. [ 1 ] The structural reformation of graphene, from pore generation to morphology transformation, is receiving growing attention, because the reconstruction of graphene could potentially result in localized highly reactive regions and thus unexpected properties for specifi c applications. [ 2 ] For instance, it was reported that crumpled graphene allows for the fabrication of polymer-graphene nanocomposite fi lms with low O 2 permeability and effective reduction of transparency. [ 3 ] Chemical functionalization of graphene (e.g., graphene oxide or GO) is another effective method for manipulating physical and chemical properties of graphene, because enriched reactive oxygen functional groups in GO can provide ample covalent bonding sites for the chemical functionalization. The functionalized GO can be easily converted to graphene-like materials through chemical or thermal reduction of GO. [ 4 ] For instance, nitrogen-doped graphene (NG) can be synthesized through thermal annealing of GO in ammonia, and the resulting NG showed some unique properties including improved conductivity and excellent catalytic activity. Actually, NG has been intensively investigated as electrode materials for lithium-ion batteries, catalysts for oxygen reduction reac-

SIMULATION OF THE ELASTIC PROPERTIES OF REINFORCED KEVLAR-GRAPHENE COMPOSITES

The compressive strength of unidirectional fiber composites in the form of Kevlar yarn with a thin outer layer of graphene was investigated and modeled. Such fiber structure may be fabricated by using a strong chemical bond between Kevlar yarn and graphene sheets. Chemical functionalization of graphene and Kevlar may be achieved by modification of appropriate surface-bound functional (e.g., carboxylic acid) groups on their surfaces. In this report we studied elastic response to unidirectional in-plane applied load with load peaks along the diameter. The 2D linear elasticity model predicts that significant strengthening occurs when graphene outer layer radius is about 4% of kevlar yarn radius. The polymer chains of Kevlar are linked into locally planar structure by hydrogen bonds across the chains, with transversal strength considerably weaker than longitudinal one. This suggests that introducing outer enveloping layer of graphene, linked to polymer chains by strong chemical bonds may significantly strengthen Kevlar fiber with respect to transversal deformations.

Chemical functionalization of graphene by H adsorption on Stone-Thrower-Wales defects

Using first-principles calculations, we investigate the adsorption of H atoms on a graphene substrate with Stone–Thrower–Wales (STW) defects. Energetically, H atoms are preferred to adsorb onto the defect sites. The presences of a rotated C–C bond (a STW defect) with the H atom adsorption in graphene quench spin and band gap, while H atoms adsorption on the top of C atoms adjacent two H adsorbed carbon atoms in the “rotated” bond show ferromagnetism and band gap. Electronic and magnetic structures associated with H atomic adsorptions on STW defects in graphene are discussed.