Liquid-phase Exfoliation Of Graphite Research Articles

Solution-Processed Hybrid Graphene Flake/2H-MoS2 Quantum Dot Heterostructures for Efficient Electrochemical Hydrogen Evolution

We designed solution-processed, flexible hybrid graphene flake/2H-MoS2 quantum dot (QD) heterostructures, showing enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) with respect to their native individual components. The 2H-MoS2 QDs are produced through a scalable, environmentally friendly, one-step solvothermal approach from two-dimensional (2D) 2H-MoS2 flakes obtained by liquid phase exfoliation (LPE) of their bulk counterpart in 2-Propanol. This QDs synthesis avoids the use of high boiling point and/or toxic solvents. Graphene flakes are produced by LPE of graphite in N-Methyl-2-pyrrolidone. The electrochemical properties of 2H-MoS2 QDs and their HER-favorable chemical and electronic coupling with graphene enable to reach a current density of 10 mA/cm^2 at an overpotential of 136 mV, surpassing the performances of graphene flake/2H-MoS2 (1T-MoS2) flake heterostructures. Our approach provides a shortcut, viable and cost-effective method for enhancing the 2D materials electrocatalytic properties.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

Terahertz saturable absorbers from liquid phase exfoliation of graphite

Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z-scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies. Fourier-transform infrared spectroscopy provides evidence of intraband-controlled absorption bleaching. These results pave the way to the integration of graphene-based SA with electrically pumped THz semiconductor micro-sources, with prospects for applications where excitation of specific transitions on short time scales is essential, such as time-of-flight tomography, coherent manipulation of quantum systems, time-resolved spectroscopy of gases, complex molecules and cold samples and ultra-high speed communications, providing unprecedented compactness and resolution.

Perylene tetracarboxylate surfactant assisted liquid phase exfoliation of graphite into graphene nanosheets with facile re-dispersibility in aqueous/organic polar solvents

Liquid phase exfoliation (LPE) is a promising method for graphene production particularly in terms of cost effectiveness and scale up. Nonetheless, it is still challenging to synchronize prime goals of high quality, good yield, large sheet size, stable long term storage and low cost eco-friendly processing. We present a simple and inexpensive green route for large scale production of exfoliated graphene dispersions exploiting the non-covalent surface chemistry between graphene and perylene tetracarboxylate (PTCA) aromatic semiconducting surfactant. Direct sonication of graphite flakes in aqueous PTCA solutions produced high yield of single and few-layer graphene sheets with minimal basal plane defects as revealed by XPS, Raman and FTIR spectroscopy. Uniquely for LPE protocol, the lateral graphene flake dimensions extended upto 10–12 μm range. The exfoliated dispersions exhibited high colloidal stability with shelf-life exceeding a year. Facile re-dispersibility of the dried graphene/PTCA powders was observed in water as well as many polar organic solvents. Significantly, pure aromatic semiconducting nature of surfactant without dielectric moiety ensures tight electrical contact among graphene sheets in thin films. The approach exploiting the simple molecular design of aromatic charged surfactants for graphene exfoliation holds a great prospect for solution processed graphene based nanomaterials and devices.

Thermo-responsive graphene dispersions by liquid phase exfoliation of graphite aided by an alkylated Percec monodendron

Large-scale production of graphene and subsequent sample engineering is the key for fully-realizing the potential applications proposed to this intriguing two-dimensional nanomaterial. Herein, smart graphene dispersions with low defects and thermo-responsive properties can be obtained by liquid phase exfoliation of graphite using an alkylated Percec monodendron (3,4,5-trioctadecyloxybenzaldehyde, 1) as the stabilizing reagent. By simply changing the temperature, the dispersed graphene and 1 can be detached, leading to the recovery of both components. Besides noncovalent wrapping, the stabilizing reagent 1 can be also covalently attached to graphene through [3+2] cycloaddition. The covalently functionalized graphene sheets show improved dispersibility in organic solvents compared to the pristine graphene, which opens the door for their applications in various polymer matrixes. The strategy demonstrated here provides a new methodology to get smart graphene dispersions with multiple functions.

Enhancing Liquid-Phase Exfoliation of Graphene with Addition of Anthracene in Organic Solvents

In this work, graphene is synthesized via liquid-phase exfoliation of graphite in organic solvents with addition of anthracene. Graphene concentration is enhanced by adding anthracene in organic solvents. Anthracene intercalates into the edges of graphite and results in graphene concentration enhancement. By adding anthracene in benzonitrile (BZN) solvent, the graphene concentration is increased from 0.01 to 0.03 mg/ml. The effect of anthracene in concentration enhancement is most prominent in 1-methyl-2-pyrrolidone (NMP), orthodichlorobenzene (ODCB) and BZN solvents as compared to others. With addition of anthracene, the graphene concentration in NMP and ODCB solvents is increased to 0.04 mg/ml. This facile method of concentration enhancement is highly suitable for preparing conducting graphene films and composites for various electronics device applications such as field-effect transistors, flexible paper supercapacitors.

Enhancing the liquid phase exfoliation of graphite in both aqueous and organic mixtures

Enhancing the liquid phase exfoliation of graphite in both aqueous and organic mixtures

식물추출액을 이용한 흑연으로부터 그래핀 생산 특성

Recently, numerous studies have utilized graphene in biomedical applications such as drug delivery, cancer therapy, and bioimaging. In this study, graphene was eco-friendly prepared by liquid phase exfoliation of graphite using plant extracts in water. Initially, 12 different plants or plant parts were screened for the characteristic graphene peak at near 268 nm using UV-Vis spectrophotometric analyses. The ability to form stable black graphene dispersion was highest using Xanthium strumarium extract. Transmission electron microscopy images showed that about 5 layer-graphene was produced from 1 g/L of graphite, while more than 5 layers were formed from 2 g/L of graphite. The optimum X. strumarium concentration for graphene production was 2 g/100 mL.

Carbon Nanostructures Produced by Liquid Phase Exfoliation of Graphite in the Presence of Small Organic Molecules

Abstract We report on the formation of different carbon nanostructures by ultrasonication of graphite in DMF upon the addition of 3 different small molecules: ferrocene carboxylic acid, dimethylamino methyl-ferrocene, and benzyl aldehyde. Our results confirm that acoustic cavitation in organic solvents generates free radicals which enable or are involved in secondary reactions. During the ultrasonication process, the addition of small molecules induces the formation of different carbon nanostructures mainly depending on the chemical nature of the molecule, as observed by transmission electron microscopy (TEM). Raman spectroscopy analysis confirms that small molecules act as radical scavengers reducing the damage caused by cavitation to graphene sheets producing long nanoribbons, squared sheets, or carbon nanoscrolls. Importantly, this strategy allows the production of different carbon nanostructures in liquid-phase making them readily available for their chemical functionalization or for their incorporation into hybrids materials enabling the development of new advanced biological applications.

Production of Ni(OH)2 Nanosheets By Liquid Phase Exfoliation: High Performance Oxygen Evolution Catalysts and Supercapacitor Electrodes

2D materials have generated much excitement in recent years.1-2 Although these can now be produced in a number of ways, many applications, particularly in the energy arena, require liquid dispersions of 2D nanosheets. Liquid phase exfoliation3-4(LPE) is a very simple processing method which allows layered crystals to be exfoliated in liquids to give suspensions of good quality nanosheets. One strength of this process is its versatility. It has been used to exfoliate graphene and a number of inorganic 2D materials such as BN, MoS2 and GaS. Another is its simplicity – it is straightforward and easy to replicate. Here we bring together these two strengths by demonstrating that LPE can be used to exfoliate a new family of 2D materials, the layered double hydroxides (LDHs). This family of materials have been exfoliated previously using chemical exfoliation techniques. These techniques work well but are time consuming, take multiple steps and use harsh chemicals. Here, LPE method method involves sonication of commercially available powders in aqueous surfactant solutions and so is mild and potentially scalable. More specifically, we demonstrate that LPE can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities. TEM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin and of good quality. Size selection allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resulting strong size dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. Prior to use we perfomed an activation procedure of polarising the electrode at 10 mA/cm2 in 1 M NaOH which significantly increased both the capacitance and catalytic activity towards the oxygen evolution reaction (OER). While the resultant capacitance was reasonably high at ~1200 F/cm3 (20 mV/s), the catalytic performance was exceptional. We observed currents of 10 mA/cm2 at overpotentials as low as 297 mV for the OER, which is close to the state of the art. Fig 1 (a) A) Structure of nickel hydroxide, Ni(OH)2. Blue, Ni; yellow, O; silver, H. B) Photograph of typical Ni(OH)2 dispersion in surfactant solution (H2O + sodium cholate) showing distinctive green colour. C) Representative low resolution TEM image of Ni(OH)2 nanosheets (b) Polarisation curves, 1 M NaOH (1 mV/s), for OER from Ni(OH)2 electrodes fabricated from Ni(OH)2films on Ni foam current collector before and after activation with the equivalent curve for the bare Ni foam shown for comparison. 1. Chowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H., The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nature Chemistry 2013,5, (4), 263-275. 2. Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotechnology 2012,7, (11), 699-712. 3. Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun'ko, Y. K.; Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.; Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N., High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotechnology 2008,3, (9), 563-568. 4. Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, (6017), 568-571. Figure 1

Liquid-Phase Exfoliation of Graphite into Single- and Few-Layer Graphene with α-Functionalized Alkanes

Graphene has unique physical and chemical properties, making it appealing for a number of applications in optoelectronics, sensing, photonics, composites, and smart coatings, just to cite a few. These require the development of production processes that are inexpensive and up-scalable. These criteria are met in liquid-phase exfoliation (LPE), a technique that can be enhanced when specific organic molecules are used. Here we report the exfoliation of graphite in N-methyl-2-pyrrolidinone, in the presence of heneicosane linear alkanes terminated with different head groups. These molecules act as stabilizing agents during exfoliation. The efficiency of the exfoliation in terms of the concentration of exfoliated single- and few-layer graphene flakes depends on the functional head group determining the strength of the molecular dimerization through dipole-dipole interactions. A thermodynamic analysis is carried out to interpret the impact of the termination group of the alkyl chain on the exfoliation yield. This combines molecular dynamics and molecular mechanics to rationalize the role of functionalized alkanes in the dispersion and stabilization process, which is ultimately attributed to a synergistic effect of the interactions between the molecules, graphene, and the solvent.

Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors.

Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (ID/IG ∼ 0.12), and high conductivity (6.2 × 10(4) S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags.

Catalyst-Free Growth of Three-Dimensional Graphene Flakes and Graphene/g-C₃N₄ Composite for Hydrocarbon Oxidation.

Mass production of high-quality graphene flakes is important for commercial applications. Graphene microsheets have been produced on an industrial scale by chemical and liquid-phase exfoliation of graphite. However, strong-interaction-induced interlayer aggregation usually leads to the degradation of their intrinsic properties. Moreover, the crystallinity or layer-thickness controllability is not so perfect to fulfill the requirement for advanced technologies. Herein, we report a quartz-powder-derived chemical vapor deposition growth of three-dimensional (3D) high-quality graphene flakes and demonstrate the fabrication and application of graphene/g-C3N4 composites. The graphene flakes obtained after the removal of growth substrates exhibit the 3D curved microstructure, controllable layer thickness, good crystallinity, as well as weak interlayer interactions suitable for preventing the interlayer stacking. Benefiting from this, we achieved the direct synthesis of g-C3N4 on purified graphene flakes to form the uniform graphene/g-C3N4 composite, which provides efficient electron transfer interfaces to boost its catalytic oxidation activity of cycloalkane with relatively high yield, good selectivity, and reliable stability.

Liquid-phase exfoliation of flaky graphite

The majority of currently available methods of graphene production have certain drawbacks limiting its scaling. Unlike the others, liquid-phase exfoliation of graphite is a promising technique for high-yield graphene production. In this work, we present our results on one- to four-layer graphene production using various solvents and surfactants from flaky graphite. We suppose that the initial graphite in the form of millimeter-size flakes can be more advantageous for extended graphene flake acquisition than graphite powder consisting of tiny particles used in previous works. Half-centimeter–size graphene films were obtained by depositing exfoliated flakes on an arbitrary substrate. Such films can be useful for electronic and photonic applications.

Foam stabilisation using surfactant exfoliated graphene

Liquid–air foams have been stabilised using a suspension of graphene particles at very low particle loadings. The suspension was prepared through the liquid phase exfoliation of graphite in the presence of the non-ionic tri-block surfactant, Pluronic® F108. The graphene particles possess an extremely high aspect ratio, with lateral dimensions of between 0.1 and 1.3μm as evidenced by TEM imaging. The particles were shown to exhibit a number of other properties known to favour stabilisation of foam structures. Particle surface activity was confirmed through surface tension measurements, suggesting the particles favour adsorption at the air–water interface. The evolution of bubble size distributions over time indicated the presence of particles yielded improvements to foam stability due to a reduction in disproportionation. Foam stability measurements showed a non-linear relationship between foam half-life and graphene concentration, indicative of the rate at which particles adsorb at bubble surfaces. The wettability of the graphene particles was altered upon addition of alkali metal chlorides, with the stability of the foams being enhanced according to the series Na+>Li+>K+>Cs+. This effect is indicative of the relative hydration capacity of each salt with respect to the surfactant, which is adsorbed along the graphene plane as a result of the exfoliation process. Thus, surfactant exfoliated graphene particles exhibit a number of different features that demonstrate efficient application of high-aspect ratio particles in the customisation and enhancement of foams.

Graphene Based Functional Hybrid Nanostructures: Preparation, Properties and Applications

The intent of this chapter is to provide a basic overview of recent advances in graphene based hybrid nanostructures including their preparation, properties and potential applications in various field. The development of graphene based functional materials, has shown their tremendous interest in areas of science, engineering and technology. These materials include graphene supported inorganic nanomaterials and films, graphene-metal decorated nanostructures, Core/shell structures of nanocarbon-graphene and graphene doped polymer hybrid nanocomposites etc. They have been prepared by various methods like chemical vapor deposition of hydrocarbon on metal surface, liquid phase exfoliation of graphite, chemical reduction of GO, silver mirror reaction, catalysis, in-situ hydroxylation and sono sol-gel route, respectively. The attractive properties of graphene and their derivatives filled with metal nanoparticles (e.g. Au, Ag, Pd, Pt, Ni, and Cu) have made them ideal templates. Graphene and their derivatives have also been decorated with various semiconductor nanomaterials (e.g. metal oxides and dioxides, metal sulfides). These metal decorated graphene nanostructures can be useful as functional hybrid nanomaterials in electronics, optics, and energy based products like solar cells, fuel cells, Li-ion batteries and supercapacitors, ion exchange and molecular adsorption.

Facile synthesis of graphene using a biological method

A new, facile, low cost, environmentally safe process is demonstrated for the production of few layer graphene by liquid phase exfoliation of graphite using extracts of medicinal plants in water.

Facile Large Scale Production of Few-Layer Graphene Sheets by Shear Exfoliation in Volatile Solvent.

Few layer graphene sheets were synthesized from natural graphite through mechanical shear mixer in 1-butanol as solvent. The liquid phase exfoliation of graphite through the shear mixer generated incising forces for 20 minutes which changed the large amount of graphite's flake into few layer graphene. The removal of solvent from the deposited dispersion was performed immediately by keeping at the room temperature. The deposited graphene thin films were characterized by AFM, HR-TEM, XRD, FT-IR and Raman Spectroscopy. The HR-TEM results showed the formation of few layers and well dispersed graphene. The Raman spectroscopy and XRD characterization confirmed the good quality and non-oxidized state of graphene.

Enhancing the Liquid-Phase Exfoliation of Graphene in Organic Solvents upon Addition of n-Octylbenzene.

Due to a unique combination of electrical and thermal conductivity, mechanical stiffness, strength and elasticity, graphene became a rising star on the horizon of materials science. This two-dimensional material has found applications in many areas of science ranging from electronics to composites. Making use of different approaches, unfunctionalized and non-oxidized graphene sheets can be produced; among them an inexpensive and scalable method based on liquid-phase exfoliation of graphite (LPE) holds potential for applications in opto-electronics and nanocomposites. Here we have used n-octylbenzene molecules as graphene dispersion-stabilizing agents during the graphite LPE process. We have demonstrated that by tuning the ratio between organic solvents such as N-methyl-2-pyrrolidinone or ortho-dichlorobenzene, and n-octylbenzene molecules, the concentration of exfoliated graphene can be enhanced by 230% as a result of the high affinity of the latter molecules for the basal plane of graphene. The LPE processed graphene dispersions were further deposited onto solid substrates by exploiting a new deposition technique called spin-controlled drop casting, which was shown to produce uniform highly conductive and transparent graphene films.

Multi-scale characterization of graphenic materials synthesized by a solvothermal-based process: Influence of the thermal treatment

Owing to its exceptional properties and a large range of possible applications, graphene gives rise to a great interest. Several major methods, as mechanical cleavage, liquid phase exfoliation of graphite and supported growth, have been developed these last years. However, it remains difficult to yield industrial quantities of graphene-based materials. Besides the research for the improvement of these major ways of synthesis, we focused on a much less common method: solvothermal synthesis. Graphenic powders can be obtained by a solvothermal reaction between ethanol and sodium followed by a thermal treatment step. We performed the solvothermal reaction and pyrolyzed the as-obtained sodium ethoxide with different temperature and time conditions, in order to study the influence of these two parameters on the final carbon-based sample. Various characterization techniques revealed the obtaining of graphenic materials with large aspect ratio, containing multi-layer graphene (MLG) regions. This study shows the strong influence of temperature and time of pyrolysis on purity, crystallinity and thickness of the samples, and goes toward an optimization of the thermal treatment step.