Production Of Few-layer Graphene Research Articles

Few-layer graphene production through graphite exfoliation in pressurized CO2 assisted by natural surfactant

Graphene research has captivated researchers worldwide, propelling innovation across diverse industries. Through the liquid-phase exfoliation methodology of graphite powder, we have demonstrated a rapid route for obtaining few-layer and multi-layer graphene using a natural surfactant, cardanol. Aqueous phase exfoliation of graphite in the presence of cardanol as a surfactant was conducted to obtain pre-exfoliated graphite suspensions. The influence of different ultrasonication times, 10, 20, and 30 min, and contact times with the surfactant, 1 and 60 min, on the stability and concentration of dispersed exfoliated graphite was evaluated. Results indicate that ultrasonication for 20 min resulted in improved stability and reduced graphene flake sizes, making it suitable for scalable graphene production. Subsequently, the most stable dispersions of exfoliated graphite were subjected to CO2-pressurized treatment. Promising results were obtained when employing cardanol at its critical micelle concentration. The graphene exhibited good structural quality, low defect density, and small stacking, with an average size of 15 nm, where 40 % of the stacked graphene was smaller than 5 nm. The findings provide valuable recommendations for the scalable production of graphene with multilayers and a few layers (FLG/MLG), using cardanol, a friendly surfactant, and a novel method of exfoliation utilizing supercritical CO2. This technology represents an innovative approach, with potential applications in supercapacitors, solar cells, biosensors, polymer composites, and advanced materials.

Bubble-Mediated Production of Few-Layer Graphene via Vapor-Liquid Reaction between Carbon Dioxide and Magnesium Melt.

It is urgent to develop novel technologies to convert carbon dioxide to graphene. In this work, a bubble-mediated approach via a chemical reaction between carbon dioxide gas and magnesium melt to fabricate a few-layer graphene was illustrated. The morphology and defects of graphene can be regulated by manipulating the melt temperature. The preparation of graphene at 720 °C exhibited an excellent quality of surface and graphitization degree. The high-quality few-layer graphene can be grown under the combined effect of carbon dioxide bubbles and in-situ grown MgO. This preparation method possesses the advantages of high efficiency, low cost, and environmental protection, which may provide a new strategy for the recovery and reuse of greenhouse gases.

Rapid, Large Area Fabrication of Porous Graphene Networks Using Photothermal Flash Lamp Carbonization for High Performance Supercapacitors

Graphene materials exhibit intriguing physical, chemical, and mechanical properties. Remarkably high surface area and electrical conductivity make them excellent materials for energy storage applications, especially supercapacitors. The production of graphene requires relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involves multi-step reactions that present challenges for high-throughput fabrication of energy storage devices. Moreover, supercapacitor devices fabricated using graphene suffer from low areal capacitance mainly due to the tortuous path of electrolytes in accessing the bulk of the material, which limits charge storage and transport throughout the thickness of the device.We have developed an efficient photothermal route to large-scale production of few-layer graphene within milliseconds from polymers using high intensity xenon flash lamp on carbon fiber at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into few-layer graphene upon millisecond exposures. Specifically, photothermally heating of polyaniline, a rod like polymer with a large absorption cross-section in the emission spectra of xenon flash lamp, led to the formation of macroporous network as shown in Figure 1a. Characterization revealed the formation of few layer graphene ( ID/IG ratio less than 0.3) with good adhesion to the carbon fiber support, enabling the formation of devices in-situ. We investigated the influence of morphology as well as graphene quality on the energy storage capabilities of the obtained devices as shown in Figure 1b. The supercapacitor devices prepared with macroporous few-layer graphene network exhibited a superior areal capacitance of 200 mF/cm2 at 10 mV/s which is an order of magnitude higher than few layer graphene with a conventional film like structure. Also, it retained more than 70% of its capacitance even after increasing the scan rate to 100 mV/s. Moreover, large area processability enabled by this photothermal approach allowed us to easily produce graphene-derived high-performance supercapacitor devices over areas greater than 100 cm2 (Figure 1c) within a few milliseconds at ambient conditions. Hence, this work provides an energy efficient and scalable route to produce high-quality few layer graphene devices with superior energy storage capabilities. Figure 1

Verification of experimental results with simulation on production of few-layer graphene by liquid-phase exfoliation utilizing sonication

Graphene, an extraordinary tow-dimensional carbon nanostructure, has attracted global attention due to its electronic, mechanical, and chemical properties; therefore, there is a need to find out an economical mass production method to produce graphene. In the present research, the aim is to find out optimal conditions for exfoliation of few-layers graphene (FLG) in a water–ethanol green solution. We varied different parameters of the ultrasonic probe like power quantity and time duration of sonication to investigate the effects on the number of graphene layers and density of graphene in the solution. Also, an attempt has been made to predict the acoustic pressure distribution by solving the wave equation in various output powers of the ultrasonic probe (sonotrode) using numerical simulations. The simulations and experimentations verify each other. Concluding that modifying the output power at the same condition will significantly alter the acoustic pressure inside the sonoreactor. The difference in acoustic pressure at 90% output power of our experimentations is much higher than in other conditions. Experimentation results utilizing UV–visible spectra, SEM (Scanning electron microscope), TEM (Transmission electron microscope) images and Raman spectrum indicate that the minimum thickness and maximum exfoliation for these samples are acquired for sonication at 90% of the maximum effective output power of the sonicator being 264 W for 55 min.

Combination of few-layer graphene and commercial cosmetic film for tetrahydrofuran-sensitive smart film

A shear exfoliation of graphite in Arabic gum solution is one of the interesting non-toxic methods for production of few-layer graphene. While the utilization of Arabic-based graphene is mainly as conductive ink for inkjet or screen printing of circuit for sensing or electronic device, it is noted that there is lack of works reporting on the role of this polysaccharide class-based graphene for smart vapour-driven sensing film. In this brief report, the effect of Arabic gum/graphene presence on the cosmetic oil control film (Clean and Clear®) for bending-unbending performance of vapour-driven film was investigated. It is discovered that the film was able to complete a bending cycle within 13 s while the maximum recorded bending radius was measured at 0.48 cm after exposure to tetrahydrofuran (THF) in controlled environment condition (50%rh and 25 °C). By controlling the distance between THF source and the smart film, we further show the crawling motion of this film that resembling leech with a speed of 0.5 cm/48 s.

“Molecular insights into the production of few-layer graphene in N-Cyclohexylpyrrolidone + water mixtures”

The chemical exfoliation of graphite in liquids is the choice method to produce few-layer graphenes with versatility and scalability. While physical mechanisms have been described, the understanding of the graphene-medium interactions at the molecular level is still a challenge. Here, a systematic experimental and theoretical investigation of factors that control the chemical exfoliation of graphite into graphene was performed using 1-cyclohexyl-2-pyrrolidone (CHP)/water mixtures as model systems. The “molecular wedge” structure of CHP and the reduction of graphene-CHP interfacial energy are critical factors in the exfoliation of graphite, but they are not sufficient for the stabilization of the isolated graphene sheets. We propose that such stabilization occurs by steric forces with the formation of a sandwich-like structure on the surface of graphene with two layers of water molecules interleaved with a monolayer of CHP, and by electrostatic forces resulting from the hybrid surface polarization due to the CHP/H2O-graphene interaction. This stabilization is hampered in CHP/H2O mixtures containing above 10 wt% CHP due to the formation of CHP–CHP aggregates.

Aqueous solutions of carbohydrates are new choices of green solvents for highly efficient exfoliation of two-dimensional nanomaterials

Abstract Deep eutectic solvents (DESs) have found great interest among researchers due to their green nature and lower costs compared to organic solvents and ionic liquids. Water, an essential component of most DESs, poses paramount impacts on the properties of these solvents. In the present study, we found that water can modulate the molecular arrangement of the solvent and affect the synthesis efficiency of both MoS2 and graphene nanosheets considerably. Using a low-cost mechanical exfoliation approach and response surface methodology, we achieved the synthesis yield of 87% for MoS2 nanosheets. We also succeeded in the production of few-layer graphene with the average lateral dimension of 3.5 μm. We further showed that it is possible to dilute DESs by water and still retain the synthesis yield at reasonably high levels. In this way, the total cost of the exfoliation process reduces, particularly when it is aimed to synthesize large scales of two-dimensional nanomaterials.

High-Yield Production of Few-Layer Graphene via New-fashioned Strategy Combining Resonance Ball Milling and Hydrothermal Exfoliation.

Graphene shows great potential applications in functional coating, electrodes, and ultrasensitive sensors, but high-yield and scalable preparation of few-layer graphene (FLG) by mechanical exfoliation method is still a formidable challenge. In this work, a novel two-step method for high-yield preparation of FLG is developed by combining resonance ball milling and hydrothermal treatment. During the resonance ball milling process, the utilization of magnetic Fe3O4 nanoparticles as a new “particle wedge” is beneficial to facilitate fragment and delamination of graphitic layers. In addition, further hydrothermal treatment can enhance ball milling product (BMP) exfoliation because of the shear force driven by the Brownian motion of various molecules at high temperature and high pressure. As expected, the two-step method can have high exfoliation efficiency up to 92% (≤10 layers). Moreover, the FLG nanosheet ink can easily achieve the formation of FLG coatings on the surface of various substrates, resulting in good electrical conductivity, which possesses potential applications in various fields including functional coating, energy storages, and electrochemical sensors, etc. Our work provides a new-fashioned strategy for mechanical large-scale production of graphene.

Morphology-selective preparation and formation mechanism of few-layer graphene on Cu substrate by liquid-phase pulsed laser ablation

This paper presented a morphology-selective preparation and formation mechanism of few-layer graphene (FLG) on a Cu substrate by pulsed laser ablation in liquid. It is a simple and controllable route to grow FLG directly on the surface of a copper foil at ambient temperature and normal pressure, which does not need other precursor materials. FLG with 3–10 layers of thickness and continuous hundreds of micrometers in lateral size is obtained. The morphology and structure of FLG were investigated by using a Raman spectrometer, scanning electron microscope, high-resolution transmission electron microscope, and atomic force microscope. The formation mechanism of FLG and the role of the plasma-produced carbon species are put forward based on the interaction between the laser, material, and substrate. Our finding, the direct deposition of FLG on the Cu substrate by pulsed laser ablation in liquid, will open a door to apply this green route to the production of FLG with controlled morphology.

Rapid production of few layer graphene for energy storage via dry exfoliation of expansible graphite

Contrasted with the excellent properties of graphene, searching for an effective industrial production method is still necessary for progressing from the laboratory to commercial applications. This study presents a rapid and mass production method to get large-scale few layer graphene using the expansivity of expansible graphite. Under a suitable thermal treatment temperature (550 °C), the interlayer spacing of expansible graphite can increase sharply, then assisted with simple mechanical crushing, large-scale few layer graphene are obtained. By this dry exfoliation method, we exfoliated expansible graphite into graphene with high quality and structural integrity. The method can be achieved with yield of 93% and the Atomic force microscopy (AFM) results show the nanosheets have a thickness about 2.3 nm. Using the availability of this method, we show the excellent application values of graphene in phase change material (PCM) field for energy storage. This work shows huge potential applications of graphene in many practical fields.

Production of few-layer graphene by wet media milling using organic solvents and different types of graphite

One of the main challenges in the exploitation of nanomaterials is their production at low cost. Mechanical milling is an alternative for the production of nanomaterials, such as graphene. In this work we have studied the effect of different solvents (methanol, ethanol, acetone, hexane, toluene and xylene) on the production of graphene by attrition milling of graphite. Among the solvents tested, methanol showed to be able to produce graphene sheets more efficiently. Computer modeling suggests that although methanol and acetone have a weaker interaction with graphene (3.95 and 7.41 kcal/mol, respectively) compared to xylene (12.73 kcal/mol), they have a higher Gibbs free energy (6.46, 3.81 and 0.33 kcal/mol for methanol, acetone and xylene, respectively), suggesting a higher mobility on its surface, thus facilitating the exfoliation of graphene. The production of graphene was corroborated by Raman spectroscopy and transmission electron microscopy, showing to be a few layers graphene (<5 layers), approximately 1–6 μm in length, with a high degree of graphitization. Additionally, we also show that through this route is feasible to produce a few-layer graphene using synthetic and amorphous graphite as more economical alternatives.

Synthesis of in situ N‐, S‐, and B‐doped few‐layer graphene by chemical vapor deposition technique and their superior glucose electrooxidation activity

At present, N-, S-, and B-doped grapheme-modified indium tin oxide (ITO) electrodes are produced and doping method effect on the glucose electrooxidation is investigated. Firstly, few-layer graphene is produced by chemical vapor deposition (CVD) method. Then, N, S, and B doping is carried out after graphene produced by CVD to prepare N-doped, B-doped, and S-doped few-layer graphene. N, S, and B doping is carried out by two different ways as (a) doping after synthesis of few-layer graphene and (b) in situ doping during few-layer graphene production. These materials are characterized by X-ray diffraction, scanning electron microscopy-energy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). One could note that graphene and nitrogen networks are clearly visible from SEM images. Raman spectra show that B, N, and S are doped on few-layer graphene/ITO successfully. XPS results of graphene, N-doped graphene, and in situ N-doped graphene reveal that graphene and nitrogen atoms used in the preparation of the electrodes obtain mainly in their elemental state. Then, these N-, S-, B-doped and in situ N-, S-, B-doped few-layer graphene materials are coated onto indium tin oxide (ITO) to obtain N-, S-, B-doped and in situ N-, S-, B-doped ITO electrodes for glucose (C6H12O6) electrooxidation. C6H12O6 electrooxidation measurements are investigated with cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements. As a result, in situ N-doped few-layer graphene/ITO electrode displays the best C6H12O6 electrooxidation activity with 9.12 mA.cm−2 current density compared with other N-, S-, B-doped graphene and in situ doped S and B grapheme-modified ITO electrodes. Furthermore, this current density value for in situ N-doped few-layer graphene/ITO is highly above the values reported in the literature. In situ N-doped few-layer graphene/ITO electrode is a promising electrode for C6H12O6 electrooxidation because it exhibits the best electrocatalytic activity, stability, and resistance compared with other electrodes.

Simultaneous electrochemical-assisted exfoliation and in situ surface functionalization towards large-scale production of few-layer graphene

Functionalized graphene manufacturing usually consists of two consecutive steps of graphene production and functionalization, which are mainly accompanied with several reaction routes and waste generation. Herein, we demonstrated a facile one-step method for the simultaneous exfoliation of graphite and surface functionalization of the resulting graphene using electrochemical approach. We showed that presence of a water soluble acrylate monomer e.g., n-butyl acrylate in an ammonium sulphate electrolyte solution can functionalize graphene through in situ polymerized n-butyl acrylate monomers during electrochemical exfoliation. Overall yield for electrochemically synthesized and functionalized graphene nanosheets was ~25% with respect to as-received natural graphite, which contain at least 80% few-layer nanosheets with a thickness less than 7 nm. It was found that these electrochemically produced and functionalized nanosheets can serve as a potential reinforcing agent in fabrication of thermoset and thermoplastic-elastomer polymer nanocomposites with enhanced mechanical performance.

Производство нескольких слоев графена в синтетическом масле с помощью стержневой барабанной мельницы

Производство нескольких слоев графена в синтетическом масле с помощью стержневой барабанной мельницы

The Effect of Solvent Viscosity on Production of Few-layer Graphene from Liquid-phase Exfoliation of Graphite

Abstract:Prior research into the liquid-phase exfoliation of graphite to produce few-layer graphene has focused primarily on the surface energy matching between graphite and solvent; however, the effect of other solvent properties, such as liquid viscosity, have not been systematically explored. In principle, a higher viscosity solvent should enable the production of graphene and other graphitic nanomaterials by liquid-phase exfoliation at lower shear rates than traditionally used organic solvents of low viscosity, such as N-methyl-2-pyrrolidone (NMP). Thus, at a given shear rate, more material should be exfoliated in the higher viscosity solvent. Hence, graphite suspensions in NMP, benzyl benzoate, and propylene glycol were exfoliated at various shear rates in a rheometer. Exfoliant concentrations were measured by ultraviolet- visual (UV-vis) spectroscopy and quality characterization was performed by Raman spectroscopy and scanning electron microscopy (SEM). Graphite exfoliation in the more viscous propylene glycol solvent resulted in a higher exfoliant concentration than in the less viscous NMP and benzyl benzoate solvents across all shear rates. Benzyl benzoate lowered exfoliant levels, likely due to a poor surface energy match, resulting in particle attraction and aggregation. Characterization showed that at least some of our material is few-layer graphene.

Water Dispersible Few-Layer Graphene Stabilized by a Novel Pyrene Derivative at Micromolar Concentration.

The search for graphene or few-layer graphene production methods that are simple, allow mass production, and yield good quality material continues to provoke intense investigation. The present work contributes to this investigation through the study of the aqueous exfoliation of four types of graphene sources, which are namely graphite and graphite nanoflakes with different morphologies and geographical origins. The exfoliation was achieved in an aqueous solution of a soluble pyrene derivative that was synthesized to achieve maximum interaction with the graphene surface at low concentration (5 × 10−5 M). The yield of bilayer and few-layer graphene obtained was quantified by Raman spectroscopic analysis, and the adsorption of the pyrene derivative on the graphene surface was studied by thermogravimetric analysis and X-ray diffraction. The whole procedure was rationalized with the help of molecular modeling.

In situ LiFePO4 nano-particles grown on few-layer graphene flakes as high-power cathode nanohybrids for lithium-ion batteries

We have realized a Lithium Iron Phosphate (LFP)-graphene nanohybrid obtained by a direct LFP crystal colloidal synthesis on few-layer graphene (FLG) flakes produced by the liquid phase exfoliation (LPE) of pristine graphite. This hybrid material has been tested as a cathode in Li-ion batteries, achieving fast charge/discharge responses to high specific currents. We demonstrate a specific capacity exceeding 110 mAh g−1 at 20 C, with no electrode damaging. Our LFP-FLG electrodes display a low charge transfer resistance, chemical stability and steady electrochemical behavior even under stressful conditions, such as impulsive charges at a high-rate (5 C) and long cycles at 1 C (> 700 cycles). The LFP colloidal synthesis combined with the FLG production by LPE allows for tuning both the LFP-platelets like and FLG flake morphologies in order to promote an optimal connection between the LFP and FLG flakes, ensuring fast charge transfers and consequently high-rate electrochemical performances. The method here proposed yields a scalable production path, which can be easily extended to silicate-, phosphate- and fluorophosphates-based cathode materials for the next generation of high-power lithium batteries.

Production of Few-Layer Graphene via Enhanced High-Pressure Shear Exfoliation in Liquid for Supercapacitor Applications

A novel method for producing graphene via enhanced shear exfoliation in a high-pressure fluid has been developed. In the process of exfoliation, graphite flakes, dispersed in a solution of N-methyl-2-pyrrolidone (NMP), were pushed through the exfoliation tube by a high-pressure pump, which produces high shear stresses on the graphite flakes due to the turbulent flow, causing the peeling-off of graphene sheets from the graphite flake. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that produced graphene sheets have thicknesses ranging from monolayer to about 12 layers. The results of X-ray photoelectron spectroscopy (XPS) and Raman and infrared (IR) spectroscopy analyses reveal that neither basal-plane defects nor oxides were noticeably introduced to graphene sheets in the process. The graphite solution can be continuously treated in a circular loop. At a pressure of 100 MPa and after 2 h of treatment, exfoliated graphene was obtained with a yield of about 15 ± 0.3%. T...

A comparative study on different aqueous-phase graphite exfoliation methods for few-layer graphene production and its application in alumina matrix composites

Four different methods (attrition milling, shear mixing, low-power bath sonication and tip sonication) used for the aqueous-phase, surfactant-assisted exfoliation of graphite were compared. Few-layer graphene (FLG) concentration, yield and production rate were measured for each method at different production times and the quality of the as produced FLG was determined using Raman spectroscopy and X-ray diffraction. It was inferred from the results that a combined method comprising tip sonication and shear exfoliation would offer the best balance between quality and quantity of FLG for relatively short processing times (<6h). FLG dispersions produced with this method were used to fabricate 1wt.% FLG/Al2O3 nanocomposites by ball milling and extrusion, followed by pressure-less sintering. The influence of the FLG addition on the microstructure and mechanical properties was studied, with observed increases of 26.4% and 67.6% in flexural strength and fracture toughness,respectively, and a 25.3% decrease in average grain size.

Efficient solvent systems for improving production of few-layer graphene in liquid phase exfoliation

Liquid-phase exfoliation (LPE) of graphite is a promising method to produce few-layer graphene (FLG) in large quantities. Selection of the solvent or surfactant is the most important factor in determining the productivity of LPE and the stability of the liquid FLG dispersion. To find efficient solvent systems for improving the production of FLG, various approaches based on previous research, including addition of a surfactant and use of binary solvents, are investigated using a pressure homogenizer. Over the range of solvents and surfactants used in our study, we find that the greatest improvement in the production of FLG results from the addition of an alkaline aqueous solution (pH 11) into organic solvents. Moreover, we find that this approach works for the probe-sonication method of FLG production as well as for various types of natural graphite. Solvent molecular size and electrostatic repulsion of graphene in liquid play important roles in improving the production of FLG because they mitigate the restacking of FLG during exfoliation.