Production Of Graphene Nanosheets Research Articles

Improving the liquid phase exfoliation efficiency of graphene based on the enhanced intermolecular and interfacial interactions

The liquid phase exfoliation (LPE) technique presents significant advantages and potential for the large-scale production of high-quality graphene nanosheets (GNs) with minimal defects. Nevertheless, the Hansen solubility parameters and surface tension matched principle were limited the range of suitable solvents for LPE process. As a result, commonly employed solvents such as N-methyl-2-pyrrolidone (NMP) and N, N-Dimethylformamide (DMF) exhibit low viscosity, leading to a low transmission efficiency of shear force from solvent to graphite, resulting in inadequate shear force and low exfoliation efficiency. In this work, to break through limitations of existing solvent systems, we investigate the influence of solvent viscosity on the LPE efficiency in various pyrrolidone solvents, which share similar structures with NMP but have longer molecular chains and higher viscosity. When compared to the NMP system, the concentration of GNs in the N-octyl-2-pyrrolidone (NOP) suspension system exhibits a significant increase of approximately 70 %, which primarily attributed to the higher intermolecular and interfacial interactions in NOP suspension. Moreinterestingly, the interactions could be further intensified by reducing the operating temperature in the NOP suspension system, which leading to an about 150 % improvement in LPE efficiency when compared to the NMP system at standard temperature. Given the remarkable conductivity of GNs, the prepared Cellulose nanofibers/graphene nanosheets (CNF/GNs) composite film exhibits lightweight and efficient electromagnetic shielding performance of 2.4 × 104 dB cm2 g−1.This work is expected to establish a universal and efficient pathway for the economical and high-yield production of GNs, elucidating the microscopic mechanism by which molecular conformation at the solid–liquid interface influences the transfer of shear forces from solvent to graphite, thereby promoting the development of widespread applications of GNs ang other two-dimensional (2D) nanomaterials.

Low contents of graphite improving general properties of poly(vinylidene fluoride)

Studies on graphite flakes with a lateral size greater than 50 μm, having a large number of stacked collapse blocks, are neglected and replaced by graphene nanosheets or by powdered graphite, which can be obtained from graphite through chemical or physical exfoliation, as filler in polymer composites. Besides, the production of graphene nanosheets or the purification of powdered graphite uses a high concentration of strong and toxic acids that pollutes the environment. These processes are extremely time-consuming and generate an expensive product. Composites of poly(vinylidene fluoride) (PVDF) were prepared via extrusion with graphite flakes with up to 60 μm thick and 700 μm lateral size, in the range from 0.1 to 5% m/m. The quality of graphite flakes was analyzed by thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The increase in the graphite content in the PVDF matrix improved thermal resistance while showed an increase in the degree of crystallinity up to 25% by XRD and 43% by differential scanning calorimetry, approximately. Although the graphite acted as a nucleating agent, the content of the PVDF beta phase did not change. In the composites with up to 2.0% of graphite, a significant increase in mechanical properties, 13% modulus, and 36% in the storage modulus, evaluated by thermodynamic-mechanical analysis and tensile tests. In the analyses of time-domain nuclear magnetic resonance and oscillatory rheology in parallel plates, it was noticed that the increase of mechanical properties is due to the reinforcing effect along with the lubricant protection of stacked graphene sheets, attenuating the stress and friction between the polymer chains. Therefore, even though graphite flakes are inexpensive, that filler without any treatment at low contents are capable of significantly improving the performance of PVDF. This work suggests that these composites could be employed in applications such as electrical insulator with less energy dissipation, and also in oil pipelines, specifically to replace PVDF-based terpolymers or mixtures thereof, and polyamide-11 in flexible risers as a barrier layer, improving their performance.

Scotch-tape-like exfoliation effect of graphene quantum dots for efficient preparation of graphene nanosheets in water

As a simple and eco-friendly strategy, the production of graphene nanosheets (GNs) by liquid-phase exfoliation (LPE) faces a challenge to the improvement of exfoliation yield for scalability, as well as the stable dispersibility for application. Herein, we electrochemically prepare a kind of graphene quantum dots (GQDs) with undestroyed crystalline structure on basal plane and a number of hydrophilic functional groups at edge, to exfoliate and disperse GNs in water with a high yield of 89–100%. The obtained GNs show a conductivity of 1.2 × 105 S m−1 and water dispersibility of 1.0 mg mL−1 for over one month, due to the firm adsorption of amphiphilic GQDs, which have non-covalent π-π bond interaction with graphene basal plane and strong H-bonds with water. The lateral size, functional groups and defect nature of GQDs have great influence on GNs and a scotch-tape-like exfoliation mechanism is proposed. GQDs as green stabilizer and exfoliation agent can effectively acquire the high-quality GNs and promote their potential application.

Revealing Factors Governing Self-Assembly Morphology of Fatty Acid on Graphene Synthesized by Surfactant-Assisted LPE: A Joint MD, SAPT(DFT), and Experimental Study

The production of graphene nanosheets from graphite with the assistance of biological molecules in water medium as well as understanding the morphology of the resulting self-assembly are important in fields of drug delivery, cell imaging, and photothermal therapy. Hence, in this contribution, we have applied docosahexaenoic acid (DHA) fatty acid to disperse graphite. The morphology of self-assembly on the graphene surface and the factors tailoring the morphology were surveyed in light of classical molecular dynamic (MD) and symmetry-adapted perturbation theory (SAPT). The factors such as surface density, environment pH, substrate size, and number of layers were taken into account. The results show that the decrease in pH transmutes the nature of the classical electrostatic interaction between the surfactants from repulsion to attraction, leading to a decline in the stability of the colloidal systems. When the lateral size of the graphene sheet is three times larger than the length of DHA, hemicylinder str...

Production of graphene nanosheets by supercritical CO2 process coupled with micro-jet exfoliation

ABSTRACTA facile and cost-effective method which combines supercritical CO2 and micro-jet exfoliation has been developed for producing graphene nanosheets with high-quality. CO2 molecules can intercalate into the interlayer of graphite because of their high diffusivity and small molecule size in supercritical operation. The tensile stress induced by graphite interfacial reflection of compressive waves exert on the graphite flakes, which lead to further exfoliation of graphite. Scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM), Raman spectrum and X-ray diffraction (XRD) are used to identify morphology and quality of the exfoliated graphene nanosheets, which reveal that the graphite was successfully exfoliated into graphene and more than 88% of graphene nanosheets are less than three layers. The yield of graphene nanosheets is about 28 wt% under optimum conditions, which can be greatly improved by repeated exfoliation of the graphene sediment. The pure graphene film has a high conductivity of 2.1 × 105 S/m.

Temel Bilimlerin Tekstil ve Moda Üzerine İzdüşümü: Nano-Teknoloji ve Şarj Edilebilir Kumaş Örneği

This proceeding provides readers with an overview of our multidisciplinary approach to technical textile research through reviewing recent preliminary results of an example project aiming at developing super-capacitor fabric structures. The fundamental idea of the project is based on, production of graphene nano-sheets and their application onto textile fabric, growing the oxides of manganese on graphene coating and utilization of the final fabric within a suitable electrolyte as electrode material. Graphene nano-sheet production and characterization methods, application to textile fabric and surface resistance measurements as well as construction of super-capacitor architecture and characterization of the final device capacitance via electro-chemistry are presented.

Rapid and efficient synthesis of soluble graphene nanosheets using N-methyl-p-aminophenol sulfate as a reducing agent

Mass production of soluble graphene still remains a challenge, although several methodologies have been proposed. Here we report a rapid and efficient method for the synthesis of soluble graphene nanosheets (GNSs) with long-term dispersion stability in both aqueous and common organic solvents. Within only 12 min at 95 °C, exfoliated graphite oxide in ammonia solution (pH 10) was reduced to soluble GNSs using N-methyl-p-aminophenol sulfate (metol) as a reducing agent without external stabilizers. The prepared GNSs were characterized by different techniques and a comparison of metol and hydrazine hydrate as reducing agents was made. The results indicated that, with the advantages of being rapid, efficient, inexpensive and relatively environmentally friendly, the reduction of graphite oxide into soluble GNSs by metol is a promising substitute for hydrazine hydrate in the mass production of soluble GNSs.

One-pot synthesis of large scale graphene nanosheets from graphite–liquid crystal composite via thermal treatment

An easy and cost effective route for mass production of graphene nanosheets (GNSs) is an essential requirement for design of different sensors, conductive composites and future nanoelectronic devices. Scalable and large area GNSs were synthesized by a thermal treatment of a graphite–ionic liquid crystal composite as a starting material. This composite was heated in a furnace with a flow of argon gas at 700 °C for 1 h. Intercalation of ionic liquid crystals between graphite layers, their decomposition and evolution of gases assist in exfoliation of graphite and separation of layers. The proposed method extends the scope for production of high-quality, high-yield, unoxidized and defects free GNSs for a wide range of applications. The ability to produce bulk GNSs from a graphitic precursor with an easy and relatively low-cost approach can propel us to real-world applications of GNSs.

A green and ultrafast approach to the synthesis of scalable graphene nanosheets with Zn powder for electrochemical energy storage

We developed a novel and ultrafast method to reduce graphene oxide (GO) with Zn powder in mild alkaline conditions under ultrasonication only for 10 min at room temperature. The as-prepared graphene nanosheets (GNs) are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and so on. Moreover, we proposed the reducing mechanism under which Zn powder and GO formed numerous Zn-GO primary batteries in the presence of ammonia solution, which can effectively remove a significant fraction of the oxygen-containing functional groups and yield a C/O ratio as high as 8.09 and 8.58 reduced by ultrasonication for 10 min and 60 min, respectively. A maximum specific capacitance of 116 F g−1 in an aqueous KOH electrolyte solution has been obtained. This approach presents us with a possibility for an environmentally friendly, ultrafast, low-cost and large-scale production of GNs and great potentials in electrochemical energy storage applications of graphene-based materials.