Production Of High-quality Graphene Research Articles

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.

Theoretical calculation boosting the chemical vapor deposition growth of graphene film

Chemical vapor deposition (CVD) is a promising method for the mass production of high-quality graphene films, and great progress has been made over the last decade. Currently, the CVD growth of graphene is being pushed to achieve further advancements, such as super-clean, ultra-flat, and defect-free materials, as well as controlling the layer, stacking order, and doping level during large-scale preparation. The production of high-quality graphene by CVD relies on an in-depth knowledge of the growth mechanisms, in which theoretical calculations play a crucial role in providing valuable insights into the energy-, time-, and scale-dependent processes occurring during high-temperature growth. Here, we focus on the theoretical calculations and discuss the recent progress and challenges that need to be overcome to achieve controllable growth of high-quality graphene films on transition-metal substrates. Furthermore, we present some state-of-the-art graphene-related structures with novel properties, which are expected to enable new applications of graphene-based materials.

Graphene functionalized hybrid nanomaterials for industrial-scale applications: A systematic review

As of remarkable electrical, optical, magnetic, thermal and mechanical properties and large specific surface area, graphene belongs to two-dimensional material of sp2 hybridization carbon atoms, has attracted a lot of interest in the recent decades. For the enormous utilization of graphene in nanoelectronics, the production of high quality graphene in large scale is essential. The properties and applications of this 2-D carbon structure have opened up new possibilities for potential systems and devices. Due to its unique properties in relation to other carbon nanomaterials, research interest in this material grew quickly. Though there are numerous graphene generating techniques, complications in the production of large scale, highly ordered structures of graphene have triggered advanced research in this area leading to the development of a broad spectrum of graphene nanostructures. Utilities of graphene is often behaving as a composite or filler material with metals, metal oxides and polymers. The customization of graphene properties and surface chemistry is focused on controlling its performance in a polymer matrix device. Due to its unusual combination of excellent properties, graphene has evolved as one of the most innovative nanomaterials. ‘Graphene’ is so thick that not even helium, the smallest gas atom, can move through it and it is impermeable to gasses. The typical review overviews the current understanding of the properties of graphene and its derivatives such as: graphene oxide (GO), porous graphene and porous graphene oxide, graphene oxide incorporated liquid crystal (GO-LC), graphene scroll. The review emphasis on simple and effective methodologies for the development of graphene nanocomposite. Various components of smart synthesis techniques are illustrated. Furthermore systematic review explored, interesting applications diversities of graphene and its derivatives, especially in the field of electronics, energy storage were examined along with the potential prospects for their further development, key challenges and significant opportunities in the industrial potential scale.

Chlorosulfuric acid-assisted production of functional 2D materials

The use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

A Novel and Simplest Green Synthesis Method of Reduced Graphene Oxide Using Methanol Extracted Vernonia Amygdalina: Large-Scale Production

The large-scale production of high-quality graphene is the major focus of scientists and engineers recently. However, its massive manufacturing routes from its precursor graphene oxide (GO) are involved in the production of toxic gasses and consist of hazardous explosive steps that severely hurt and threaten ecological balance and human health. Therefore, in this study, we investigated the green, effective, and economical approach for the synthesis of graphene by using Vernonia amygdalina (VA) plant leaf extracts for the effective and efficient reduction of GO. The nonexplosive two-step synthesis of GO in a short period of time in the absence of an ice bath was used in this study. The appropriate solvent for the extraction of VA for the green synthesis of graphene was methanol, and the reducing and capping agent in the plant extract was identified to be terpenoids and polyphenols. The graphene/rGO obtained this way was characterized by UV-VIS, XRD, FTIR, SEM, HR-TEM, and EDAX that confirmed the successful reduction of GO to graphene under the hydrothermal process. The HR-TEM images showed the development of few layers of graphene. The FTIR result also shows the complete reduction of GO. Hence, methanol extracted VA leaves consisted of the most appropriate compounds for reducing and capping agent in the green synthesis and could be the preferred method for the large-scale production of graphene-based materials.

Regulating cations and solvents of the electrolyte for ultra-efficient electrochemical production of high-quality graphene

Electrochemical exfoliation of graphite has been regarded as a potential approach to produce graphene on a large scale. Despite recent progress in the production of graphene with few defects by cathodic exfoliation, current methods suffer from uncontrolled thicknesses and limited yield. Here we devise a novel cathodic exfoliation method using diverse tetraalkylammonium cations in various non-aqueous solvents toward efficient preparation of high-quality graphene. Sandwich-structured graphite electrode enables sufficient ion intercalation and uniform exfoliation into few-layer graphene (>80%, 1–3 layers), along with remarkable yield (91.5%) and ultralow defect density (ID/IG = 0.05). The interplay of electrolyte cation and solvent on its intercalation efficiency and electrochemical stability was also studied, which are in direct correlation with the exfoliation ability. Further mechanism investigation demonstrates that tetrabutylammonium cations in propylene carbonate can intercalate into graphite efficiently under reducing condition. Adjacent layers were then taken apart rapidly due to gas formation reactions, resulting in non-destructive exfoliation. The preparation process can be easily scaled up and yield a high production rate (exceeding 50 g h−1), demonstrating its potential to facilitate the mass production of high-quality graphene for extensive applications.

Catalytic graphitization: A bottom-up approach to graphene and quantum dots derived therefrom – A review

Catalytic graphitization as a simple, scalable method for a bottom-up approach to the production of high-quality graphene is presented. The product is then converted into graphene laced with graphene quantum dots. In brief, the method involves dissolution of precursor carbon forms such as petroleum coke in a molten metal like iron to produce a saturated solution of carbon. The molten mass teeming with individual carbon atoms then bond themselves into honeycomb-structured graphite, which is thermodynamically the most stable form of carbon. The conversion of disconnected carbon atoms to graphitic forms is aided by catalytic graphitization by iron as the melt is slowly cooled. Upon cooling, the light graphitic precursors float on the molten mass, which may be skimmed out with a ladle. This product is found to be highly pure forms of single-, bi- and few-layer graphenes. The graphene may be further processed to yield quantum dots.

Hydrogen-Assisted Fast Growth of Large Graphene Grains by Recrystallization of Nanograins.

Chemical vapor deposition has been highlighted as a promising tool for facile graphene growth in a large area. However, grain boundaries impose detrimental effects on the mechanical strength or electrical mobility of graphene. Here, we demonstrate that high-pressure hydrogen treatment in the preannealing step plays a key role in fast and large grain growth and leads to the successful synthesis of large grain graphene in 10 s. Large single grains with a maximum size of ∼160 μm grow by recrystallization of nanograins, but ∼1% areal coverage of nanograins remains with 28–30° misorientation angles. Our findings will provide insights into mass production of high-quality graphene.

Production of High-Quality Graphene Using a Novel Electrochemical Intercalation-Exfoliation Approach

Large scale production of graphene has recently received a great deal of attention because of its interesting properties and wide range of potential applications. Conventional chemical exfoliation approaches, such as Hummer’s method,provides cost-effective pathway for large scale production, however, the method suffers from several key challenges such as the usage of corrosive and toxic solution, high processing temperature, long duration, and the poor quality of graphene produced which severely affects its potential applications. Recently, electrochemical exfoliation of graphene has been proposed for a high production yield with better quality. The electrochemical method involves two steps: 1) intercalation of ionic species between the graphene layers, followed by 2) oxidation of these ionic species under an anodic voltage into gas molecule enabling exfoliation of graphene flakes from the graphite electrode.1 In this study we examine a new approach to the intercalation, using an intercalating ion that has received very little attention and has not been evaluated for electrochemical exfoliation. The intercalation was followed by exfoliation in (NH4)2SO4 solution leading to the production of graphene flakes. The resultant graphene was found to have less disrupted sp2 lattice structure, with a high yield of about 95 % of graphene, along with high electrical conductivity and a low oxidation level (with a C:O ratio of about 15, determined by XPS). In addition, the presence of nitrogen and sulfur moieties in the resulting graphene structure can act as an electrocatalyst2 for applications such as the oxygen reduction reaction. Thus, the as-prepared graphene could be used for a range of electrochemical applications.

Rational Design of Binary Alloys for Catalytic Growth of Graphene via Chemical Vapor Deposition

Chemical vapor deposition is the most promising technique for the mass production of high-quality graphene, in which the metal substrate plays a crucial role in the catalytic decomposition of the carbon source, assisting the attachment of the active carbon species, and regulating the structure of the graphene film. Due to some drawbacks of single metal substrates, alloy substrates have gradually attracted attention owing to their complementarity in the catalytic growth of graphene. In this review, we focus on the rational design of binary alloys, such as Cu/Ni, Ni/Mo, and Cu/Si, to control the layer numbers and growth rate of graphene. By analyzing the elementary steps of graphene growth, general principles are summarized in terms of the catalytic activity, metal–carbon interactions, carbon solubility, and mutual miscibility. Several challenges in this field are also put forward to inspire the novel design of alloy catalysts and the synthesis of graphene films bearing desirable properties.

Polymer-Assisted Electrophoretic Synthesis of N-Doped Graphene-Polypyrrole Demonstrating Oxygen Reduction with Excellent Methanol Crossover Impact and Durability.

The design and synthesis of metal-free catalysts with superior electrocatalytic activity, high durability, low cost, and under mild conditions is extremely desirable but remains challenging. To address this problem, a polymer-assisted electrochemical exfoliation technique of graphite in the presence of an aqueous acidic medium is reported. This simple, cost-effective, and mass-scale production approach could open the possibility for the synthesis of high-quality nitrogen-doped graphene-polypyrrole (NG-PPy). The NG-PPy catalyst displays an improved half wave potential (E1/2 =0.77 V) in alkaline medium compared with G-PPy (E1/2 =0.66 V). Most importantly, this catalyst demonstrates excellent stability with high methanol tolerance, and it outperforms the commercial Pt/C catalyst and other previously reported metal-free catalysts. The content of graphitic nitrogen atoms is the key factor for the enhancement of electrocatalytic activity towards oxygen reduction reactions (ORR). Interestingly, the NG-PPy catalyst can be used as a cathode material in a zinc-air battery, which demonstrates a higher peak power density (59 mW cm-2 ) than G-PPy (36.6 mW cm-2 ), highlighting the importance of the low-cost material synthesis approach towards the development of metal-free efficient ORR catalysts for fuel cell and metal-air battery applications. Remarkably, the polymer-assisted electrophoretic exfoliation of graphite with a high yield (≈88 wt %) of few-layer graphene flakes could pave the way towards the mass production of high-quality graphene for a variety of applications.

Interface between graphene and liquid Cu from molecular dynamics simulations.

Controllable synthesis of defect-free graphene is crucial for applications since the properties of graphene are highly sensitive to any deviations from the crystalline lattice. We focus here on the emerging use of liquid Cu catalysts, which have high potential for fast and efficient industrial-scale production of high-quality graphene. The interface between graphene and liquid Cu is studied using force field and ab initio molecular dynamics, revealing a complete or partial embedding of finite-sized flakes. By analyzing flakes of different sizes, we find that the size-dependence of the embedding can be rationalized based on the energy cost of embedding vs bending the graphene flake. The embedding itself is driven by the formation of covalent bonds between the under-coordinated edge C atoms and the liquid Cu surface, which is accompanied by a significant charge transfer. In contrast, the central flake atoms are located around or slightly above 3 Å from the liquid Cu surface and exhibit weak van der Waals-bonding and much lower charge transfer. The structural and electronic properties of the embedded state revealed in our work provide the atomic-scale information needed to develop effective models to explain the special growth observed in experiments where various interesting phenomena such as flake self-assembly and rotational alignment, high growth speeds, and low defect densities in the final graphene product have been observed.

Graphene Trails on PECVD Hydrogenated Amorphous Silicon Carbide Films SiC-a: H by Laser Writing at Room Temperature

The production of high quality graphene without the need for catalyst metals as in the case of chemical vapor deposition (CVD) techniques remain a challenge. Silicon carbide is one of the materials with potential to form graphene films on its surface through thermal decomposition when subjected to high temperatures and ultrahigh vacuum. This technique is highly desirable since it enables the elimination of corrosion and transfer steps, which can leave residues in the graphene structure and alter its quality, as well as its electrical proprieties, however it is a costly and time consuming method. In this work, we present the production of graphene trails by direct laser radiation writing at room temperature and atmospheric pressure on hydrogenated amorphous silicon carbide films (SiC-a:H) produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). Graphene trails of approximately 1cm x 4μm were obtained with patterns designed by computer Aided Design (CAD) software. Variations were made in both scanning speed and laser focal length, identifying a great dependence on the graphene quality with these two parameters. The best results of the Raman Spectroscopy Mappings showed high quality graphene with distance between point defects (LD) of 20nm, crystallite size (La) of 25nm and few layers (2-3). In addition, the electrical measurements from Au/Ti (20nm/100nm) electrodes deposited by electron beam evaporation showed high conductivity, with sheet resistances (Rs) from 0.7kΩ to 1.3 kΩ per square. This technique opens a great possibility of manufacturing devices for applications in electronics, being a fast, efficient and low cost method.

Strategies for Scalable Gas-Phase Preparation of Free-Standing Graphene

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

Production of High-Quality Graphene Using a Novel Electrochemical Intercalation-Exfoliation Approach

Large scale production of graphene has recently received a great deal of attention because of its interesting properties and wide range of potential applications. Conventional chemical exfoliation approaches, such as Hummer’s method,provides cost-effective pathway for large scale production, however, the method suffers from several key challenges such as the usage of corrosive and toxic solution, high processing temperature, long duration, and the poor quality of graphene produced which severely affects its potential applications. Recently, electrochemical exfoliation of graphene has been proposed for a high production yield with better quality. The electrochemical method involves two steps: 1) intercalation of ionic species between the graphene layers, followed by 2) oxidation of these ionic species under an anodic voltage into gas molecule enabling exfoliation of graphene flakes from the graphite electrode.1 In this study we examine a new approach to the intercalation, using an intercalating ion that has received very little attention and has not been evaluated for electrochemical exfoliation. The intercalation was followed by exfoliation in (NH4)2SO4 solution leading to the production of graphene flakes. The resultant graphene was found to have less disrupted sp2 lattice structure, with a high yield of about 95 % of graphene, along with high electrical conductivity and a low oxidation level (with a C:O ratio of about 15, determined by XPS). In addition, the presence of nitrogen and sulfur moieties in the resulting graphene structure can act as an electrocatalyst2 for applications such as the oxygen reduction reaction. Thus, the as-prepared graphene could be used for a range of electrochemical applications.

A novel chemical reduction/co-precipitation method to prepare sulfur functionalized reduced graphene oxide for lithium-sulfur batteries

The higher theoretical specific capacity with considerable cell potential, Lithium–Sulfur batteries (LSBs) are considered to be high-energy storage strategies near future. However, the practical realization of LSBs is being hindered owing to low cell capacity risen from poor electronic-conductivity of elemental sulfur. To enhance the electronic-conductivity and thus to improve the specific cell capacity, commonly conducting carbons such as reduced graphene oxide, carbon nanotubes etc. are used as additives in the electrodes. Here, we report a unique in-situ synthesis strategy to prepare a composite of sulfur-functionalized reduced graphene oxide (SFRGO) encapsulating monodisperse sulfur nanoparticles using a low-cost deep eutectic solvent (DES) derived from choline chloride and sodium thiosulfate. The DES serves as an effective reductant as well as dopant. Moreover, during formation of SFRGO, a major fraction of the DES degrades to elemental sulfur. The SFRGO composite has been applied as cathode material in LSBs. The cathode material delivered a maximum specific capacity of 1265 mA h g−1 during initial cycle and retains 903 mA h g−1 after 100 cycles, with a usual capacity decay rate 0.28% each cycle. This facile chemical reduction method is an alternative to the large-scale and cost-effective production of high-quality graphene for energy storage application.

Ultrafast, Low-Cost, and Mass Production of High-Quality Graphene.

Fast, mass, and low-cost production of high-quality graphene, which is alluring, remains a great challenge, even though some approaches have shown potential for mass synthesis of graphene. Very recently a great breakthrough was made by Tour and co-workers (Nature 2020, 577, 647-651): in just a second, easily exfoliated and highly crystalline graphene was produced from abundant carbon-containing species by cost-effective flash Joule heating with a low energy input of 7.2 kJ per gram graphene. Such an ultrafast, economic, and scalable process for high-quality graphene production can be considered as a milestone in the graphene field and is highlighted in this article.

Substrate Placement inside CVD Tube for Graphene Production

Electronics and energy storage industry demand production of high-quality graphene which currently still a challenge. Chemical vapor deposition (CVD) has shown promises for high-quality graphene production. However, it involves control of many parameters from different aspects such as thermal fluid, mass transport, and chemical reaction. Thermal fluid aspect plays a significant role in CVD production of graphene but yet to be explored extensively. For a tubular hot-wall CVD with the heating reactor, issue of flow instability that will prolong the existence of vortices and spiral flow until the substrate required attention. Therefore current study aims to find the optimum substrate position inside the furnace. For that purpose the gas flow streamline will be observed, and minimum axial distance of the substrate will be determined. The tubular CVD is modeled using ANSYS Fluent®. The current model will not consider the chemical reaction involves and only single gas is used. This should be enough to seek the influence of thermal fluid aspects involves in CVD. The CVD tube will be divided into 3 sections where the middle part (furnace) was heated up to 1273K and the other two sections were kept at 300K. Gas was supplied to the tube and the distance from the furnace inlet to the point where the flow is fully developed is measured. Streamlines for the flow is also observed. The streamline shows that there is an induced secondary flow starting at the inlet which lasted until a certain axial distance. For flow with 50 sccm of flowrate needs an axial distance of 5 cm while flow with 250 sccm of flowrate needs 7 cm in order to become a smooth flow. Our results show that the placement of the substrate in the tubular hot-wall CVD required attention in CVD design. For flow with higher flowrate, it requires longer distance for the flow to become smooth and laminar and vice versa.

An intermittent microwave-exfoliated non-expansive graphite oxide process for highly-efficient production of high-quality graphene

Redox methods represented by Hummers’ method are the most frequently-used pathways to prepare graphene, but to date still very low-efficient, because of its time-consuming washing and hard reduction process. Here we report an intermittent microwave-exfoliated non-expansive graphite oxide (GtO) process to prepare a wrinkled graphene with a high reduction degree (C/O: 19.0), a high defect degree, and a high specific surface area (1333.7 m2 g−1). Findings show that the non-expansive GtO without water washing indicates an almost 100% exfoliated success rate during this intermittent microwave process. The obtained graphene shows easy dispersity in organic solvents, and excellent supercapacitor performance in specific capacitance, rate capacity, and especially in cycling lifetime with no decay after 80,000 cycles at 30 A g−1. Consequently, this special microwave process successfully solves the problems of tedious washing and hard reduction in redox methods, thus exponentially boosting the efficiency of preparing graphene.

SMA-Assisted Exfoliation of Graphite by Microfluidization for Efficient and Large-Scale Production of High-Quality Graphene.

In this paper, the sodium salt of styrene-maleic anhydride copolymer (SMA) was used as a stabilizer in the process of graphite exfoliation to few-layer graphene using the technique of microfluidization in water. This method is simple, scalable, and cost-effective, and it produces graphene at concentrations as high as 0.522 mg mL−1. The generated high-quality graphene consists of few-layer sheets with a uniform size of less than 1 μm. The obtained graphene was uniformly dispersed and tightly integrated into a polyamide 66 (PA66) matrix to create high-performance multifunctional polymer nanocomposites. The tensile strength and thermal conductivity of 0.3 and 0.5 wt% EG/PA66 composites were found to be ~32.6% and ~28.8% greater than the corresponding values calculated for pure PA66, respectively. This confirms that the new protocol of liquid phase exfoliation of graphite has excellent potential for use in the industrial-scale production of high-quality graphene for numerous applications.