Liquid-phase Exfoliation Of Graphite Research Articles

Preparation and anticorrosion performance of graphene-reinforced epoxy powder coating

Existing studies have reported that graphene can enhance the corrosion resistance of solvent-based organic coatings. However, the role of graphene in organic powder coatings remains to be obscure. In the present study, the graphene powder was prepared through liquid-phase exfoliation of graphite followed by freeze drying and the effects of graphene on structures, anticorrosion performance and adhesion strength of epoxy powder coatings were investigated. Scanning electron microscopy (SEM) demonstrated that graphene reduced surface micropores and enhanced structural compactness of the epoxy powder coatings. Electrochemical impedance spectra, Tafel polarization measurement and salt spray test indicated that a small amount (0.0125, 0.025 and 0.05 wt%) of well-dispersed graphene powder would be sufficient to effectively reinforce the anticorrosion performance of the epoxy powder coatings, especially for the coating with 0.025 wt% graphene, of which the impedance modulus maintained the highest values of nearly 107 and 105.8 Ω cm2 after immersion in 3.5 % NaCl solution for 21 and 30 days. Pull-off test confirmed that graphene enhanced the adhesion strength of coatings after salt spray test for 240 h, while the coating with 0.025 wt% graphene exhibited the highest adhesion strength up to 3.88 MPa. In addition, differential scanning calorimetry (DSC) indicated that graphene sheets could improve the thermal conductivity and promote curing reactions of epoxy powder. The mechanism for the reinforcement of epoxy powder coating by graphene has also been proposed.

Liquid-Phase Exfoliation of Graphite in a Low-Boiling-Point Solvent Using 2,6-Azulene-Based Conjugated Copolymers as Stabilizers

Liquid-Phase Exfoliation of Graphite in a Low-Boiling-Point Solvent Using 2,6-Azulene-Based Conjugated Copolymers as Stabilizers

Liquid-Phase Exfoliation of Graphite Using the Serum from Skim Natural Rubber Latex

Liquid-Phase Exfoliation of Graphite Using the Serum from Skim Natural Rubber Latex

The The Impact of Sodium Perylene-3, 4, 9, 10-Tetracarboxylate Surfactant Concentration on the Yield of Liquid Phase Exfoliated Graphene Sheets

The graphene sheets were aqueous processed via simple method liquid phase exfoliation. Sodium perylene-3, 4, 9, 10-tetracarboxylate (NaPTCA) were used as surfactant to assist the exfoliation process. The purpose of this research is to investigate the impact of NaPTCA concentration on the yield of liquid phase exfoliation of graphite to graphene sheets. The degree of exfoliation was found to be greatly influenced upon the concentration of NaPTCA surfactant. 1.0 mgmL-1 was identified as the optimal NaPTCA concentration as the graphene produced had a distinct x-ray diffraction crystallinity, scanning electron microscopic image features, high concentration of graphene dispersion (0.154 mgmL-1) and high conductivity values (751.88 Sm-1) in 2-probe electrical measurements, all of which comparison are much favourably with typical values obtained for multi-layer graphene. Hence, this simple approach for liquid-phase graphite exfoliation provides decent potential for mass production of high-quality graphene for a wide range of applications in energy storage, optical, and electronic areas.

An eco-friendly solution for liquid phase exfoliation of graphite under optimised ultrasonication conditions

Ultrasonic assisted liquid phase exfoliation (ULPE) is a promising method for the large scale production of 2D materials. Currently, toxic solvents such as N-Methyl-2-pyrrolidone (NMP) are commonly used for the production of graphene. In this paper four solvents; three green solvents (water, ethanol and water/ethanol) plus NMP for comparison, were sonicated and examined in terms of their bubble dynamics and acoustic emissions. Advanced fundamental analysis was conducted using high-speed imaging synchronised with acoustic pressure measurements complemented by shadowgraphic photography of the emitted shockwaves, in order to determine a suitable eco-friendly solvent medium from a cavitation bubbles dynamics perspective. Thereafter, ULPE of graphite in the optimum solvent took place for 2 h under controlled ultrasonication parameters. The produced graphene samples were characterised by employing a series of techniques consisting of Ultraviolet–visible (UV–Vis) and Raman spectroscopy as well as transmission electron microscopy (TEM). A mixture of deionised water and ethanol was shown to produce a yield twice that of pure water, comprising of high quality few layer graphene (3–5 Ls) with an average area of ∼1.15 (μm)2 and stability of ∼78% for the duration of six months. This combination is a promising eco-friendly substitute for future commercial manufacturing of graphene.

Cardanol surfactant/ultrasound-assisted exfoliation of graphite in a water/ethanol solution

Graphene has high electrical and thermal conductivity, high transparency, and chemical stability that stand out compared to those of other materials. An efficient technique for producing few-layers graphene (<5 layers) is the liquid-phase exfoliation of graphite (LPE). LPE is a simple, cost-effective, ecologically friendly technique that without the use of hazardous solvents can produce graphene without defects in its basal plane. The influence of natural surfactant (cardanol), time and type of ultrasound on the properties of exfoliated graphite was studied. The use of tip ultrasound promotes graphite exfoliation in relatively shorter time (20 min) than ultrasonic bath time (360 min). Another factor that determines the effectiveness of the exfoliation is the concentration of cardanol, which, when used at the critical micelle concentration (CMC) value promotes the formation of micelles that help in the exfoliation and stability of the exfoliated graphite. Few-layers graphene with a concentration of 3.00 ± 0.01 mg mL−1 and an average stacked graphene height of up to 3 nm for 30% of the product were produced by combining the appropriate time of tip ultrasound with the use of cardanol at an equal concentration to its CMC. Furthermore, stable suspension of graphene in aqueous medium was achieved for more than 6 months without significant sedimentation. These results are related to the π-π and hydrophobic-hydrophobic interactions between the cardanol molecules and the graphene surface, which promote the adsorption of cardanol molecules on the graphene surface, and the re-stacking and agglomeration can be reduced due to electrostatic repulsion. Few-layers graphene produced from a new green-surfactant is an innovative technology that transforms low cost products into materials with higher added value for applications in supercapacitors, solar cells, and biosensors.

Optimizing the structure and molecular weight of polymers for graphene dispersants

Graphene is an allotrope of carbon consisting of a single-atom-thick honeycomb lattice nanostructure. Among the various preparation methods for graphene, the liquid-phase exfoliation of graphite is mass-producible and cost-effective. To facilitate the exfoliation of graphite in organic solvents, polymers can be employed as dispersants. We synthesized polymer dispersants with various monomer ratios and molecular weights and investigated the efficient acquisition of graphene from graphite. Graphene with a uniform thickness was obtained when graphite was exfoliated using an optimized polymer dispersant. The optimized polymer enabled a high yield and concentration of graphene using liquid-phase exfoliation.

An Eco-Friendly Solution for Liquid Phase Exfoliation of Graphite Under Optimised Ultrasonication Conditions

An Eco-Friendly Solution for Liquid Phase Exfoliation of Graphite Under Optimised Ultrasonication Conditions

Bilayer-favored intercalation induced efficient and selective liquid phase production of bilayer graphene

A novel strategy for the scalable liquid phase exfoliation of graphite into bilayer graphene under ambient conditions was developed. The selectivity and yield for bilayer graphene reached record-breaking values of 86.5% and 52.3%, respectively.

Production of Graphene-Containing Suspensions and Concentrates by Cascade Exfoliation of Graphite

Various technologies and equipment for the production of graphene-containing suspensions by liquid-phase exfoliation of graphite are considered. The prospects of using liquid-phase graphite shear exfoliation in a continuous mode are shown. Taking into account the analyzed shortcomings of existing technologies, a technology for the production of graphene-containing suspensions and concentrates by cascade exfoliation of graphite and a device for its implementation are proposed. In particular, the following are proposed: a new method for two-stage dosing of graphite powder; new design of rod drum mill for mechanical activation of graphite; a new design of the rotary apparatus with compound movable blades, providing an increase in shear forces acting on graphite particles in the process of exfoliation. The kinetics of the exfoliation process has been studied. Experimental studies on the modification of concrete with graphene have been carried out and an increase in compressive strength of at least 33% has been proven.

Influence of C=O groups on the optical extinction coefficient of graphene exfoliated in liquid phase

Liquid phase exfoliation of graphite is currently one of the most promising graphene production methods at large scale. For this reason, an accurate calculation of the concentration in graphene dispersions is important for standardization and commercialization. Here, graphene dispersions, at high concentrations, were produced by electrochemical exfoliation. Furthermore, a cleaner methodology to obtain graphene oxide by electrochemical exfoliation at high acid concentrations was implemented. The absorption coefficient for graphene and graphene oxide was determined in the optical range (α 660 nm = 1414 (±3%) ml mg−1 m−1 and α 660 nm = 648 (±7%) ml mg−1 m−1, respectively) with an exponential dependence with the wavelength. The difference in α for both materials is attributed to an increased presence of C=O groups as evidenced by Fourier transform infrared spectroscopy (FTIR), UV–vis and Raman spectroscopy, as well as, in the calculation of the optical extinction coefficient and optical band-gap via Tauc-plots.

Liquid-Phase Exfoliation of Graphene in Organic Solvents with Addition of Picric Acid

In this work, graphene was produced by liquid-phase exfoliation of graphite in different organic solvents with addition of picric acid. The graphene was easily produced by one step ultra-sonication of graphite powder in the organic solvents. The addition of picric acid has increased the graphene production yield in most of the solvents tested in this work. Picric acid serves as a “molecular wedge” to intercalate into the edge of graphite, which plays a key role during sonication and significantly improves the production yield of graphene. The products were analyzed by microscopic techniques, including atomic force microscopy (AFM) and scanning electron microscope (SEM). The AFM images indicate that the exfoliation efficiency and amount of graphene increased by addition of picric acid in organic solvents. Moreover, the AFM images also indicate presence of bilayer graphene. SEM analysis also shows that the addition of picric acid into the organic solvent favors the exfoliation process. The produced graphene was also analyzed by XRD, FTIR, Raman and UV-visible spectroscopy. The XRD results illustrate that exfoliation was best achieved in N-methyl-2-pyrrolidone (NMP) as a solvent. FTIR and Raman results indicate that addition of picric acid has slightly defected the produced graphene surface. The amount of graphene concentration was calculated by using Beer Lambert law, and it was observed that the graphene production yield was increased by using picric acid in most of the solvents. The maximum amount of graphene concentration (0.159 mg/ml) was achieved by adding 30 mg of picric acid in NMP.

(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing.

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterial-fraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔEp = 28mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and β-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1µM, L.R. 0.5-150µM; NADH: LOD = 0.6µM, L.R. 2.5-200µM) at low overpotential (+ 0.15V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.

Vapour Diffusion Sitting Drop Method to Induce Nucleation of Calcium Phosphate on Exfoliated Graphene and Graphene Oxide Flakes

The preparation of graphene/apatite and graphene oxide/apatite hybrid nanocomposites has recently attracted great attention in the biomaterial community. The sitting drop vapor diffusion technique has been assessed as a preparative method for such nanocomposites in this work. The technique has been employed to induce heterogeneous nucleation and growth of calcium phosphate in the presence of exfoliated graphene and commercial graphene oxide flakes, both labeled with L-Alanine. Exfoliated multilayered graphene flakes were produced by sonication-assisted liquid-phase exfoliation of graphite. In both composites, the apatite nanocrystals displayed similar size and shape, but different labile and B-type carbonation contributions. Graphene and graphene oxide flakes also influenced the carbonation degree of the apatite, which was almost half that measured for the apatite blank, as well as the aggregation state of their composites. In this regard, those composites with graphene oxide formed larger aggregates because of their wider size distribution, with a high-volume percentage of nanosheets (of about 4 nm length). Overall, the method is very useful to prepare small amounts of nanocomposite with high reproducibility.

The electrochemistry of size dependent graphene via liquid phase exfoliation: capacitance and ionic transport.

Recently, graphene-based materials have become ubiquitous in electrochemical devices including electrochemical sensors, electrocatalysts, capacitive and membrane desalination and energy storage devices. However, many of the electrochemical properties of graphene (particularly the capacitance and ionic transport) are not yet fully understood. This paper explores the capacitance and ionic transport properties of size dependent graphene (from 100 nm to 1 μm) prepared through the liquid phase exfoliation of graphite in which the size of graphene was finely selected using a multi-step centrifugation technique. Our experiment was then expanded to include basal plane graphene using highly ordered pyrolytic graphite as a model electrode, describing the assumed theoretical graphene capacitance (quoted as 550 F g-1 or 21 μF cm-2) and the electrochemical surface area of the carbon-based materials. This work improves our understanding of graphene electrochemistry (capacitance and ion transport), which should lead to the continuing development of many high-performance electrochemical devices, especially supercapacitors, capacitive desalination and ion-based selective membranes.

Seaweed biomass derived bio solvents for the large scale production of few layered graphene nanosheets from graphite

Large-scale production of graphene sheets by liquid-phase exfoliation of graphite is a challenging task from a sustainability point of view. Certain bio-derived solvents were found to exfoliate graphite to produce single-layered graphene sheets but the high cost of the solvent is always a deterring factor towards upscaling of the process. Herein, Kappaphycus alvarezii, a cultivable red seaweed is demonstrated as a sustainable resource for producing a bio solvent for exfoliation and to produce graphene sheets from graphite. A solvent system consisting of levulinic acid, acetic acid, and γ-valerolactone was prepared from the polysaccharide obtained from the seaweed biomass through acid hydrolysis under pressure and the mixture was found to exfoliate graphite to produce few-layered pristine graphene nanosheets. The process is scalable and cost-effective and the seaweed biomass-derived solvent mixture can be recovered and reused in the subsequent cycles of exfoliation for large-scale production of graphene nanosheets.

ПОЛУЧЕНИЕ ГРАФЕНОВЫХ СТРУКТУР И НАНОПОЛИМЕРОВ С ИСПОЛЬЗОВАНИЕМ УЛЬТРАЗВУКОВЫХ КОЛЕБАНИЙ

Graphene-based polymer nanocomposites are considered a promising class of future materials. The degree of filling, the filler and binder nature, and the shape, size, and mutual arrangement of filler particles determine the properties of a polymer composite material. The destruction of nanoparticles aggregates occurs most effectively in liquid media under the action of ultrasonic vibrations. The authors proposed the technique and designed laboratory equipment for ultrasonic treatment of the finely-dispersed graphite suspension, carried out the ultrasonic treatment (UST) of finely-dispersed graphite powder. The suspensions based on graphite with a solvent were obtained. The authors carried out the experiments on producing graphene using the graphite liquid-phase exfoliation method at the ultrasonic treatment with different ultrasonic treatment times, analyzed experimental data, and selected the UST optimal time. The paper contains the results of the study of the effect of the graphite suspension base on the degree of ultrasonic liquid-phase exfoliation of graphite. The most effective synthesis of graphene structures using UST is synthesis from graphite suspensions based on dichloroethane, benzol, and dichlorobenzene. Graphene structures’ output ratio amounts to up to 66 %. The authors developed the technology for producing polymers modified with graphene structures using ultrasonic dispersion. Based on graphene synthesized by the graphite liquid-phase exfoliation, the authors obtained nanopolymers using ultrasonic vibrations, carried out DSC measurements, and studied their strength properties. The limit strength of elastic polymers is from 1.9 to 3.6 MPa at different concentrations of graphene inclusions. The residual elongation of samples within the deviation did not change and amounted to 200 %.

The production of graphene by direct liquid phase exfoliation of graphite at moderate sonication power by using low boiling liquid media: The effect of liquid media on yield and optimization

There are many production methods for graphene production. One of the most successful production methods in terms of scale-up is liquid phase exfoliation (LPE) method. In this study, after optimizing the sonication time and sonication power that are effective in the production to increase the efficiency of the LPE method, the experiments were continued at moderate sonication powers and the effect of liquid media, another important parameter, was examined. In this study, hexagonal graphite powders were subjected to direct liquid phase exfoliation process by using different liquid media (N-Methyl-2-Pyrrolidone (NMP), N,N-Dimethylformamide (DMF), ethanol, 2-propanol, acetone, methanesulfonic acid, ethanol + Sodium dodecyl sulphate (SDS), 2-propanol + SDS) and the obtained samples were characterized. As a result of the characterization, the liquid media with the highest efficiency was determined to be NMP. Besides, it was observed that a new hybrid solvent obtained by adding a surfactant such as SDS into low-cost and environmentally friendly liquid media such as ethanol and 2-propanol showed a higher efficiency than NMP. It was observed that 3–5 layer graphene ranged between 15 and 19 wt% in either graphene produced by using hybrid solvents containing NMP or SDS. The amount of double or single-layer graphene was negligibly small. The production with the lowest efficiency was observed in the use of acetone. The produced graphenes were dispersed in the liquid and their sedimentation time was observed. The sedimentation time of graphenes, produced using NMP and SDS-doped hybrid solvents, in liquid was more than 120 days. The sedimentation time of graphene produced using acetone was less than 20 days. In the use of graphene as a reinforcing material or adsorbent, large amounts of graphene are needed. In such applications, mass production of graphene is important rather than the number or quality of sheets of graphene. Therefore, optimization of production parameters of LPE method, which is suitable for mass production, is significance.

Structural Optimization of Alkylbenzenes as Graphene Dispersants

Among the several methods of producing graphene, the liquid-phase exfoliation of graphite is attractive because of a simple and easy procedure, being expected for mass production. The dispersibility of graphene can be improved by adding a dispersant molecule that interacts with graphene, but the appropriate molecular design has not been proposed. In this study, we focused on aromatic compounds with alkyl chains as dispersing agents. We synthesized a series of alkyl aromatic compounds and evaluated their performance as a dispersant for graphene. The results suggest that the alkyl chain length and solubility in the solvent play a vital role in graphene dispersion.

Raman spectroscopy analysis of number of layers in mass-produced graphene flakes

A metrological framework for statistical analysis of number of layers and stacking order in mass-produced graphene using Raman spectroscopy is presented. The method is based on two complementary protocols, denominated by 2D and G. The 2D–protocol is based on the parameterized principal component analysis of the two-phonon 2D band, and it measures interlayer coupling. A neural-network algorithm for spectral denoising was also developed to improve the outcome. The G–protocol explores the intensity of the bond-stretching G band, and provides information about the number of layers. The method is suitable for automated statistical analysis of heterogeneous graphene-based systems with relatively low computational cost, as shown here for graphene flakes prepared by the liquid-phase exfoliation of graphite.