Production Of High-quality Graphene Research Articles

Efficient fabrication of high-quality graphene via alternating-current co-intercalation and microwave-assisted expansion

To facilitate the transformation of inexpensive and abundant graphite resources into two-dimensional graphene materials with promising applications, the development of efficient, cost-effective, and scalable technologies for large-scale production of high-quality graphene is crucial. Here, we propose an effective electrochemical dual-electrode co-intercalation exfoliation strategy. During the process, precise control of the electrochemical intercalation is achieved by adjusting the working bias and alternating current (AC) cycle, while ensuring the ion insertion rate through gradual voltage escalation. Repeated insertion of cations and anions under AC accelerates the graphite exfoliation. Following complete ion inserting, suitable microwave processing was employed to achieve rapid graphite expansion. Ultimately, ultra-sonication in NMP is employed to achieve final exfoliation between graphite layers. The resulting few-layer graphene (2–3 layers) exhibited minimal defects (ID/IG = 0.0405), low oxygen content (C/O = 44.62), high yield (95.3 %), and excellent conductivity (625 S/cm), enabling its potential commercialization and large-scale application. This outcome also serves as a significant reference for the commercial production of environmentally friendly and cost-effective graphene.

Analysis of large-scale high-quality graphene production and applications

Graphene, a single-atom-thick layer of carbon atoms arranged in a hexagonal lattice, is the thinnest and strongest material known to mankind. It has excellent electrical, thermal, and mechanical properties, making it a promising material for a wide range of applications in electronics, optoelectronics, energy storage, and more. With the increasing demand for graphene in various applications, large-scale and high-quality graphene production has become a significant challenge. While early methods of graphene production involved mechanical exfoliation, this method is limited in terms of scalability and yield. To meet the increasing demand for large-scale production of graphene, various methods have been developed in recent years, including chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent exfoliation and so on. This study aims to introduce several existing methods for the mass production of graphene with high quality and analyzes the advantages and disadvantage involve thereof. The findings in this paper may provide a valuable reference for the industrial-scale production of graphene.

Improved photoelectrochemical performance of tungsten-catalyzed graphene nanoplatelet electrodes prepared by hot-wire chemical vapor deposition at low substrate temperatures

The current increase in demand for graphene in various energy applications such as electrode materials for supercapacitors, batteries, thermoelectric, and hydrogen production via water-splitting, the production of high-quality graphene, considering its fascinating physical and electrical properties, high-yield, and large-area has becoming more challenging at the research and development level. Therefore, in this work, graphene nanoplatelets (GNPs) were directly grown on tungsten nanoparticle (W NP)-coated p-type crystalline silicon and quartz substrates using hot-wire chemical vapor deposition at low substrate temperatures (<500 °C). Prior to the GNP deposition, a plasma process was employed to induce the formation of W NPs, which act as a metal catalyst for facilitating the growth of large-area and multi-layer GNPs. The W NPs were formed at substrate temperatures ranging from 250 to 550 °C, with the largest graphene sheet was grown at 450 °C. Higher substrate temperatures promote the growth of high-quality graphene layers with high intensities of G (IG) and 2D bands (I2D), and high I2D/IG ratio values. The GNP photoelectrode prepared at 450 °C demonstrated better photoelectrochemical responses with the highest photocurrent density of 1.65 mA/cm2 at 1.5 VAg/AgCl, the lowest charge transfer resistance (14.0 kΩ), and the highest donor density (2.57 × 10 28 cm−3) compared to the tungsten carbide thin film and W NP electrodes prepared at the same temperature. The effects of substrate temperature on the optical, structural, and photoelectrochemical properties of the as-grown GNPs are discussed.

High-quality graphene devoid of oxygen functionalities as conductive ink for flexible electronics and bendable all-solid-state supercapacitors

High-yielding and scalable naphthalene-assisted ball-mill exfoliation of graphite is reported here aiming at the production of high-quality graphene cost-effectively. The Raman spectral analysis indicates less-defective graphene, whereas the few-layered nature is evident from the XRD pattern and AFM images. Monolayered graphene can also be produced upon ultrasonication, which is evident from the HRTEM images and Raman spectral analysis. XPS indicated the absence of in-plane oxygen functionalities that usually disrupt the aromatic π-conjugation. Graphene is effectively utilized here to formulate a conducting ink for polyimide tape-based wires for lighting LEDs. The supercapacitor performance of the graphene as an electrode material was also assessed, where, in the three-electrode system, graphene exhibited an excellent areal capacitance of 197.22 mF/cm2 at a current density of 2 mA/cm2 and the graphene-modified carbon paste electrode retained 100 % of initial capacitance even after 7500 charge-discharge cycles. A bendable supercapacitor was also fabricated here with graphene-coated carbon cloth electrodes that exhibited a high capacitance of 524.28 mF at 0.05 mA/cm2 with the highest energy and power densities of 14.87 μWh/cm2 and 349.76 μW/cm2 respectively. The bendable device retained 99.9 % of its initial capacitance after 3000 continuous cyclic voltammetric runs. The supercapacitor delivered the same performance as the straight device during bending, twisting and even after bending at different angles.

Identifying and abating copper foil impurities to optimize graphene growth

Copper foil impurities are hampering scalable production of high-quality graphene by chemical vapor deposition (CVD). Here, we conduct a thorough study on the origin of these unavoidable contaminations at the surface of copper after the CVD process. We identify two distinct origins for the impurities. The first type is intrinsic impurities, originating from the manufacturing process of the copper foils, already present at the surface before any high-temperature treatment, or buried into the bulk of copper foils. The buried impurities diffuse towards the copper surface during high-temperature treatment and precipitate. The second source is external: silica contamination arising from the quartz tube that also precipitate on copper. The problem of the extrinsic silica contamination is readily solved upon using an adequate confinement the copper foil samples. The intrinsic impurities are much more difficult to remove since they appear spread in the whole foil. Nevertheless, electropolishing proves particularly efficient in drastically reducing the issue.

Production of reduced graphene oxide from activated rice husk charcoal using a high-energy ball milling method

Production of high-quality graphene at a commercial scale with low cost remains challenging. Thus, we used a high-energy ball milling approach to make reduced graphene oxide (rGO) from activated rice husk charcoal as an enriched carbon source. The as-produced rGO samples were characterized to determine the effect of various milling times (0, 50, 100, 150, and 200 min) on their structure, morphology, specific surface area, pores volume, and size distribution. The variation in the ball milling times was found to introduce the structural defects and remove the oxygen functional groups, thus improving the overall characteristics of the obtained rGO. The wrinkle sheet-like structures of rGO evolved into numerous paper balls-like transparent rumple morphologies due to the milling process-enabled compression mechanism. In addition, due to the increase of milling times, the amount of carbon in rGO was increased to 89.9 atomic%, and oxygen was reduced to 9.3 atomic%, wherein the thermal agitation-mediated collisions of particles played a significant role. The specific surface area (121.483 m2 g−1) and pore volume (0.133 cm3 g−1) of rGO prepared at a milling time of 50 min were observed to be optimum. It was asserted that a high-energy ball milling technique with controlled milling times could help produce high-quality rGO from activated rice husk charcoal at low cost, leading to the development of sustainable and environmentally friendly material required for diverse applications.

Experimental Study on Green Concrete using Graphene

The paper considers methods for concrete modification using low-layer graphene and grapheme oxide. It was found that graphene oxide and low-layer graphene obtained by liquid-phase shear exfoliation significantly increase the strength of concrete. In our opinion, low-layer graphene has better prospects since it is cheaper and its production technology is environmentally friendly. The viability and future of graphene largely depends on the availability of such a method that allows mass production of high-quality graphene at an affordable price. In this regard, liquid- phase separation of graphite with the formation of low-layer graphene, which can be used to modify concrete, turned out to be a competitive solution. The following main tasks were formulated in order to solve the organizational problems of low- layer grapheme industrial production: reducing the concentration of low-layer grapheme in concrete; increasing the concentration of low-layer graphene in suspension; developing an industrial technology for the production of concentrate with a high content of low- layer graphene; conducting full-scale experimental studies to determine the optimal concentration of low-layer graphene in concrete.

Direct conversion of CO2 to graphene via vapor–liquid reaction for magnesium matrix composites with structural and functional properties

Converting CO 2 to valuable materials is attractive in environmental protection and resource utilization. In this study, a vapor–liquid interface reaction system for mass production of high-quality graphene is reported. The graphene obtained has high crystallinity and few defects during the reaction of CO 2 and Mg melt. The growth mechanism of graphene is demonstrated in vapor–liquid interface area by combining the CO 2 bubbles as a soft template to guide growth with the confinement effect of dense MgO nanoparticles. The quality of the graphene is verified by epoxy composites with high electromagnetic shielding effectiveness. Additionally, the V–L reaction method ingeniously solves the dispersion of graphene in metal, providing a preparation strategy of Mg matrix composites with structure and function integration.

Synthesis of high-quality graphene by electrochemical anodic and cathodic co-exfoliation method

Large-scale preparation of high-quality graphene nanosheets at low cost is critical for advancing its industrial applications. Here we propose a fast electrochemical anode and cathode co-exfoliation method to synthesize high-yield solution-processable graphene. The chosen tetrabutylammonium hexafluorophosphate molecule, with superior electrochemical stability and oxygen-free feature, could efficiently enable simultaneous anion and cation intercalation while suppressing structural damage from anodic oxidation, resulting in minimally destructive exfoliation and high-efficiency graphene synthesis. After accurately regulating the intercalation chemistry, high-yield graphene (75% and 92% for anode and cathode, respectively) with uniform thickness distribution (>75%, 1–3 layers) was obtained. Meanwhile, as-prepared graphene has ultralow defect density (ID/IG < 0.052), significantly high C/O ratio (>46.6) and exceptional electrical conductivity (>4 × 104 S m−1). Remarkably, record high production rates (over 100 g h−1) are achieved in up-scaled fabrication process, and such graphene quality and exfoliation efficiency outperform most previously reported research. Furthermore, the graphene based flexible supercapacitor exhibits a high area capacitance of 95 mF cm−2, excellent rate capability, cycling performance with 99% after 10,000 cycles and robust mechanical flexibility. This efficient and scalable process will promote the mass production of high-quality graphene, which offers great potential applications in wearable electronics.

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.

Reducing Carbonaceous Salts for Facile Fabrication of Monolayer Graphene.

Novel methods and mechanisms for graphene fabrication are of great importance in the development of materials science. Herein, a facile method to directly convert carbonaceous salts into high-quality freestanding graphene via a simple one-step redox reaction, is reported. The redox couple can be a combination of sodium borohydride (reductant) and sodium carbonate (oxidant), which can readily react with each other when evenly mixed/calcined and yield gram-scale, high-quality, contamination-free, micron-sized, freestanding graphene. More importantly, this method is applicable to a variety of input reductants and oxidants that are low cost and easily accessible. An in-depth investigation reveals that the carbonaceous oxidants can not only provide reduced carbon mass for graphene formation but also act as a self-template to guide the polymerization of carbon atoms following the pattern of the monolayer, six-carbon rings. In addition, the direct formation of graphene exhibits theoretically lower energy barriers than that of other allotropes such as fullerene and carbon nanotube. This facile, low-cost, scalable, and applicable method for mass production of high-quality graphene is expected to revolutionize graphene fabrication technology and boost its practical application to the industry level.

High-Quality Electrochemically Exfoliated Graphene Protective Layer for Metal Batteries

Graphene has attracted substantial attention due to its exceptional mechanical, thermal, electrical, and chemical properties. There has been active research for the scalable production of high-quality graphene. Among various techniques, electrochemical exfoliation is facile, fast, and cost-effective for graphene production. Our previous finding on anodic exfoliation suggested that the binding energy between the intercalator and graphene sheet plays an important role in exfoliation efficiency.1 We further extended the hypothesis to the cathodic exfoliation process to produce high-quality graphene. The characteristics and morphologies of electrochemically exfoliated graphene using alkali metals (e.g. Na, K, and Cs) are compared. Then, we will employ the exfoliated graphene on lithium metal anodes as carbon support for efficient lithium deposition in lithium metal batteries.References Lee, H.; Choi, J. I.; Park, J.; Jang, S. S.; Lee, S. W. Role of anions on electrochemical exfoliation of graphite into graphene in aqueous acids. Carbon 2020, 167, 816-825.

Cost effective production of high quality multilayer graphene in molten Sn bubble column by using CH4 as carbon source

The cost-effective production of high-quality graphene is one of the bottlenecks for wide applications. This article presents a modified Chemical Vapor Deposition (CVD) method to massively produce multilayer graphene (MLG) on gas-bubble surface in a bubble column with the molten Sn, which is utilized as the heat-transfer agent and catalyst. This method is able to provide a 70 ± 10% yield of MLG from CH4 gas at 1250 ℃，and a 0.27 ± 0.04 g/hr production rate while 300 ml molten Sn used. The produced MLG has around 15 layers with a crumpled structure. It exhibits excellent quality with few structure defects with superior electrical conductivity of ∼2.5 × 105 Sm−1. Furthermore, the polyurethane (PU)/MLG composite produced by the proposed method shows remarkable electromagnetic interference shielding effectiveness (EMI SE), which reaches 55 dB (1 mm thick) with a 3 wt% MLG content, and it has an electrical conductivity of 256.4 Sm−1. It can be concluded that the proposed method has great potential for the industrial cost-effective production of high-quality graphene sheets.

Green and facile production of high-quality graphene from graphite by the intercalation and decomposition of oxalic acid

• A green and environmentally friendly chemical exfoliation method was developed. • Oxalic acid is used for the first time alone for chemical intercalation exfoliation of natural flake graphite. • No water-washing and effluent-treatment are involved during the whole chemical exfoliation process. • The 9-μm-thick-graphene film exhibits excellent electrical conductivity (5.05 × 10 5 S/m) and EMI shielding property (53.9 dB). The environmentally friendly preparation of graphene remains a great challenge. Herein, a novel and green preparation method for graphene has been developed. Graphene sheets were successfully exfoliated from graphite by intercalation and decomposition of oxalic acid for the first time. The whole chemical exfoliation process does not involve any waste liquid disposal, and, more importantly, the decomposed products by oxalic acid are CO 2 and H 2 O, respectively, demonstrating that the exfoliation method is environmentally friendly. The obtained graphene sheets exhibit high-quality and large-size with a yield of about ∼ 100%. The prepared graphene film exhibits excellent electrical conductivity (5.05 × 10 5 S/m) and EMI shielding property (53.9 dB with a thickness of 9.0 μm), suggesting a great prospect for miniaturized electronic devices and flexible wearable applications.

An electrochemical route to exfoliate vein graphite into graphene with black tea

The study is focused on exfoliating vein graphite into graphene using an unsophisticated and low-cost process through a non-oxidative production route. High-quality graphene production with low-cost methods that give high yields and suitable for large-scale production, using vein graphite is a challenge to address, though there are many methods for graphene production. Vein graphite directly received from the mining site was electrochemically exfoliated to small particles which were further exfoliated by ultrasonic vibration. In addition, commonly used highly toxic, expensive solvents were substituted by inexpensive and nontoxic aqueous black tea solution, in the exfoliation by ultrasonic vibration process. Four different tea types were used to compare the quality and quantity of yields. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and Raman spectroscopy were utilized for the characterization, and the study uncovers a low-cost, nontoxic, promising and nonoxidative route to exfoliate vein graphite into either single or double-layer graphene. The study uncovers that the four different tea types tested can be used to successfully exfoliate graphite. The suitability of the exfoliated graphene for applications was checked by utilizing them to prepare electrochemical double layer supercapacitors (EDLC). Electrochemical properties of fabricated EDLC were investigated by cyclic voltammetry (CV) and Galvanostatic charge-discharge curves (GCD). Graphene based EDLC exhibited energy density of 0.385 W h kg−1 and a power density of 17.3 W kg−1 for the 0.01 V s−1 scan rate.

Towards High-quality graphite oxide from graphite – Systemization of the balance in oxidative and mechanical forces for yield enhancement

Despite intensive research on graphene, large-scale production of high-quality graphene oxide/graphite oxide (GO) is challenging. The labour-intensive oxidative mechanical exfoliation is frequently found to be the rate-limiting step. In this study, we report ways to improve GO quality and yield by modifying two promising scalable process variants of Hummers method, viz., Kim’s and Tour’s method for GO production. To achieve a desired crystallite size with minimal defects, we report possible adjustments to the exfoliation process by evaluating the oxidation mechanism against GO’s structural integrity. The modifications such as altering the quantity of the oxidant, the duration of ultrasonic-assisted oxidation and the order of washing cycles improved the oxidation efficiency resulting in yield enhancement of defect-free GO. The structure and quality of the synthesized GO were found to depend on the rigorousness of washing cycles and the quantity of oxidant used rather than on the nature of the oxidant alone.

Electrochemically exfoliated functionalized graphene flakes: Facile synthesis, 3rd order optical nonlinearity and optical limiting response

High quality graphene production is prerequisite for good performance in nonlinear optics application such as fast optical communications, all-optical switching, and optical limiting. Graphene journey begins with the method of synthesizing graphene which need to be simple, fast, and environmentally friendly. Hence, we introduce the method by exfoliating graphite by electrochemical route to produce good quality functionalized graphene for various nonlinear optics application. In this work, functionalized graphene flakes are synthesis by using two different electrodes; furnaced graphite rod (Gr-FG) and non-furnaced graphite electrode (Gr-NFG). Visual inspection on the synthesized Gr-FG and Gr-NFG show dark murky color solutions give the impression of high yield functionalized graphene flakes. Further observation under transmission electron microscopy (TEM), selected area electron diffraction (SAED), and UV–vis and Raman analysis confirm the good quality functionalized graphene structure. The nonlinear optical behavior of the functionalized graphene was accessed via Z-scan technique with 637 nm laser source operating in continuous mode with simultaneous monitoring of the close and open aperture signal. Close aperture profile of Gr-FG and Gr-NFG display nonlinear refraction, whereas open aperture profile shows reverse saturable absorption (RSA). Equation fitting reveals higher n2 magnitude for Gr-FG compared to Gr-NFG, but the later possess higher magnitude of β. Further analysis on the 3rd order of optical nonlinearity by z-scan technique reveal the admirable value at the range of 10−6 esu. Optical limiting performance conducted via transmittance-based measurement shows superior limiting of Gr-NFG compared to Gr-FG.

Non-Enzymatic H2O2 Sensor Using Liquid Phase High-Pressure Exfoliated Graphene

Importance of graphene-based nanomaterials in electrochemical sensors has increased due to their exceptional electrochemical properties and electrocatalytic activity. Despite the significant amount of work on graphene exfoliation, there is a need for large-scale, environmental friendly production of high-quality graphene for electrochemical sensing applications. This work describes the use of liquid phase mechanical (high-pressure) exfoliation for synthesis of graphene and its application in H2O2 electrochemical sensors. The basic electrochemical characterizations of exfoliated graphene samples have shown great enhancement in electrochemical activity due to their improved ion adsorption ability as a result of increased electroactive surface area and the presence of functional groups (defective sites). The developed H2O2 sensors showed excellent sensitivity and limit of detection (LOD). The repeatability, reproducibility, and stability studies of liquid phase mechanical exfoliated graphene-based H2O2 sensors showed consistent results suggesting the potential usage of the exfoliated graphene in electrochemical sensors. The interference study of fabricated sensors revealed the selective H2O2 sensing nature of exfoliated graphene and confirmed its potential for H2O2 determination in real samples.

Highly Water-Dispersible Graphene Nanosheets From Electrochemical Exfoliation of Graphite.

The electrochemical exfoliation of graphite has been considered to be an effective approach for the mass production of high-quality graphene due to its easy, simple, and eco-friendly synthetic features. However, water dispersion of graphene produced in the electrochemical exfoliation method has also been a challenging issue because of the hydrophobic properties of the resulting graphene. In this study, we report the electrochemical exfoliation method of producing water-dispersible graphene that importantly contains the relatively low oxygen content of <10% without any assistant dispersing agents. Through the mild in situ sulfate functionalization of graphite under alkaline electrochemical conditions using a pH buffer, the highly water-dispersible graphene could be produced without any additional separation processes of sedimentation and/or centrifugation. We found the resulting graphene sheets to have high crystalline basal planes, lateral sizes of several μm, and a thickness of <5 nm. Furthermore, the high aqueous dispersion stability of as-prepared graphene could be demonstrated using a multi-light scattering technique, showing very little change in the optical transmittance and the terbiscan stability index over time.

Very-few-layer graphene obtained from facile two-step shear exfoliation in aqueous solution

A defect-free graphene with 1–3 layers (very-few-layer graphene, VFLG) has been successfully produced using a facile and environmentally friendly two-step shear exfoliation method in rotating-blade mixer (kitchen blender) and in high shear rotor–stator mixer. An aqueous solution containing an inexpensive and safe anionic surfactant of sodium lauryl sulphate (SLS) was deployed as the working fluid. Raman spectroscopy (RS) and Raman imaging (RI), density functional theory (DFT) simulation, transmission electron microscopy and high-resolution transmission electron microscopy (TEM-HRTEM), as well as Fourier-transform infrared spectroscopy (FTIR) analyses were used to characterize the samples. Some configurations of mixer setting were applied, and the exfoliation mechanisms were discussed. RS analysis revealed that the exfoliation process in rotating-blade mixer continued by high shear in rotor–stator mixer for 3 h had produced VFLG dominated by a single layer of graphene. The Lorentzian peak fitting of 2D band was well-fitted by a single Lorentzian component at Raman shift of 2651.317 cm−1. The produced VFLG endured the lowest peak intensity ratio of D and G bands (ID/IG) of 0.146 which corresponded with the highest lateral size. RI analysis showed that produced VFLG had edge chirality of armchairs and zigzag terminations. TEM-HRTEM confirmed the presence of VFLG with the highest mean lateral size of ~375.4 nm. DFT calculations provided pertinent optical/electronic properties of graphene in terms of Raman Spectra, density of states (DOS) curve and nuclear magnetic resonance (NMR) shielding tensor. FTIR analysis showed that the exfoliation process did not cause any oxidation, sulphonation, or functional defects on the VFLG. The turbulence and hydrodynamic force in liquid were the critical factors in the exfoliation processes. High-quality VFLG, with a facile, inexpensive, and environmentally friendly synthesis process, rendered this process to be a promising route for large-scale high-quality graphene production.