High-quality 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.

Reproducible Preparation of Thin Graphene Films Using a Green and Efficient Liquid-Phase Exfoliation Method for Applications in Photovoltaics

This paper presents an innovative, cost-effective, and environmentally sustainable approach to producing high-quality graphene nanosheets (G-NSs) on a large scale. Particularly, we have achieved a remarkable graphene material, expertly dissolved in ethanol at an impressive concentration of 0.7 mg/mL, using a cutting-edge electrophoretic deposition method on an ITO/PET surface. This achievement holds great promise for a wide range of photovoltaic applications. The G-NSs were rigorously analyzed using advanced techniques, including FESEM, EDAX elemental mapping, X-ray diffraction (XRD), and Raman analysis. This comprehensive examination yielded a significant discovery: the thickness of the deposited films profoundly influences the material’s interaction with photons. This finding positions the synthesized graphene material as a game changer in the field of light detection sensors, with the potential to revolutionize the landscape of optoelectronics.

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.

Highly efficient dual-electrode exfoliation of graphite into high-quality graphene via square-wave alternating currents

Scalable production of high-quality graphene nanosheets is urgently needed to realize its practical applications. Here, we show that electrochemical dual-electrode exfoliation via alternating current can effectively produce high-yield solution-processable graphene. The selected molecule, tetrabutylammonium hydrogen sulfate, has the ability to diminish anodic oxidation damage to structures while also allowing for simultaneous intercalation of anion and cation species. Additionally, repeated intercalation of cations and anions with alternating current accelerates the ion intercalation and exfoliation process, leading to highly efficient graphene production with minimum destruction. After precisely controlling the intercalation process, high-yield graphene (88.6%) with uniform thickness distribution (77%, 1–3 layers) was achieved. Meanwhile, as-prepared graphene exhibits outstanding electrical conductivity (>6 × 104 S m−1), a considerably high C/O ratio of > 47.2, and a very low defect density (ID/IG < 0.045). Remarkably, the up-scaled manufacturing technique not only achieves a record high production rate (over 80 g h−1), but also improves upon the best-reported graphene quality and exfoliation efficiency (by > 60%). This rapid and scalable method will facilitate the widespread manufacture of high-quality graphene and open up a myriad of potential uses.

High-quality ultra-flat reduced graphene oxide nanosheets with super-robust lubrication performances

The development of high-performance graphene has been driven by increasingly growing industrial demands. Due to the compatibility of high-efficient and low-cost, chemical exfoliation of graphite is currently a common synthesis method of graphene. Unfortunately, there is not an effective chemical way to prepare high-quality graphene nanosheets for industry application. Working under a harsh condition is also a challenge for their engineering application. Herein, high-quality ultra-flat reduced graphene oxide (UF#G) nanosheets with near-perfect integrity were synthesized by a chemical exfoliation method. Taking the advantage of metal ion from the oxidant agent, the manganese compounds are in situ uniformly deposited on the surface of reduced graphene oxide (rGO) nanosheets in a weak alkali environment, thus protecting the nanostructure from being damaged by gaseous products during chemical reduction process. UF#G can reduce the coefficient of friction (COF) and wear depth of the lubricated interfaces by 49% and 93% at a heavy load (2.5 GPa), compared with pure grease (P.G). Especially, the UF#G-based lubricant has superior lubricating stability with long-operating life of more than 216,000 cycles, which is beyond previous results for both state-of-the-art nanocoatings and nanolubricants. UF#G together with the lubricant generate a robust chemical-mixing tribofilm consisting of a carbon-adsorbed layer and a CaSO4-deposited layer, which is contributed to the super-robust lubrication performances. The ultra-flat nanostructure of UF#G further improves the lubrication by interlayer-sliding effect. This work provides high-quality ultra-flat reduced graphene oxide nanosheets enabled by a novel chemical-exfoliation route with super-robust lubrication performances.

Graphene nanosheets derived from waste plastic for cost-effective thermoelectric applications

Herein, we report the synthesis of graphene nanosheets (GNs) derived from plastic waste for cost-effective thermoelectric (TE) applications. The synthesis of GNs was done as per our present process, where a two-step pyrolysis process was carried at the temperature range of 400 °C–850 °C by using Al2O3 as the catalytic and degradation template, while nickel metal-based catalytic beds were used to get high-quality GNs from our indigenously developed 100 Kg per batch pilot-scale plant. Raman, X-ray diffraction (XRD), and transmission electron microscopy (TEM) analysis showed the presence of 4–5 nm thick sheets of GNs. After the successful synthesis of GNs from waste plastics, the TE properties of thus synthesized GNs were investigated. GNs showed low resistivity of 3.93 × 10−2 Ω-m at room temperature, which are further decreases with an increase in temperature. The Seebeck coefficient values of the GNs show that the material behaves as a p-type semiconductor. The TE figure of merit ZT showed a signatory value of 0.1 × 10−6 at the temperature of 426 K corresponding to the TE properties within the synthesized GNs. The results of TE analysis indicate that waste plastic-derived GNs can be used for a variety of TE applications.

Preparation of Ni-W-eGO composite coatings and investigation of its mechanical properties and corrosion resistance

In this paper, we explore the use of electrochemically prepared edge-oxidized graphene oxide (herein after referred to as eGO) as nano-materials doped in Ni-W electrolyte solution. Here, eGO with high dispersion properties was successfully applied to the Ni-W plating solution system, and high-performance Ni-W-eGO coating was prepared on P110 carbon steel by pulse electrodeposition method. In addition, by exploring the content of eGO in the electrolyte solution, we evaluated the comprehensive performance of different Ni-W-eGO composite coatings. Compared with the original Ni-W coating, the Ni-W-eGO composite coating can significantly improve the corrosion resistance of the P110 steel sheet in a 3.5 wt% NaCl solution. The corrosion resistance was measured by the electrochemical method, and the wear resistance was measured by friction experiment. Finally, the appropriate amount of eGO was 0.5 g/L. In this article, we explore the use of electrochemically prepared edge-oxidized graphene oxide as nano-filler, and successfully prepared Ni-W-eGO composite coating on P110 steel sheet by pulse electrodeposition. The eGO material itself has good mechanical enhancement properties, and at the same time has good dispersibility in the electrolyte solution, showing excellent solution stability. This is because only the oxidation of the graphene edges to obtain hydrophilic groups does not destroy the integrity of the graphene structure. The prepared Ni-W-eGO composite coating has a flatter surface than the Ni-W coating, and has better corrosion resistance and wear resistance. • The first use of water-dispersed high-quality graphene nano-sheets (eGO) in the field of electroplating. • The Ni-W-eGO (eGO 0.5 g/L) composite coating has excellent wear resistance and corrosion resistance. • In this work, we used a variety of characterization methods such as XRD, SEM, EDS, EIS and mechanical performance testing. • Provide new ideas for the preparation of high-performance graphene-based coatings.

Strong adhesion and high optoelectronic performance hybrid graphene/carbon nanotubes transparent conductive films for green-light OLED devices

Carbon nanotubes (CNTs) and graphene (Gr) are promising materials for flexible transparent conductive films (TCFs) in optoelectronic application because of their exceptional electrical, optical, and mechanical properties. Here, high-quality graphene nanosheets were synthesized by the one-step green method which using natural polyphenols-gallic acid (GA) as the exfoliation medium through high-pressure homogenization; besides, GA molecules can also be used as a non-covalent modifier to obtain GA modified CNTs (GCNTs). Then, the Au decorated Gr/GCNT-PET (Au-Gr/GCNT-PET) TCFs were obtained by a simple spray-coating process. The TCFs exhibited an excellent optoelectronic performance (Rs = 45.6 Ω/sq., T = ca. 80% at 550 nm), relatively flat surface (roughness = 12.43 nm), good bending resistance (the ΔR Au-Gr/GCNT-PET TCF/R0 was 0.07 after 1000 times bending tests) and strong adhesion (the fT of all Au-Gr/GCNT PET films was higher than 0.8). Finally, the Au-Gr/GCNT-PET films were used as an anode to prepare flexible green-light OLED devices; the maximum luminance of the Au-Gr/GCNT-PET device was 6554.1 cd/m2 at 15V, and the maximum current efficiency was 4.03 cd/A. It confirmed that this type of TCFs has considerable potential application in photovoltaic devices.

The adsorption of aromatic macromolecules on graphene with entropy-tailored behavior and its utilization in exfoliating graphite

Aromatic macromolecules tend to form a compact conformation after physically adsorbed on graphene and it brings about great entropy loss for physisorption, due to the strong interaction between aromatic macromolecules and graphene. However, previous researches have validated the availability of aromatic macromolecules to stabilize graphene based on physisorption. In order to clarify the underlying mechanism of this physisorption process on graphene, a series of aromatic polyamide copolymers are used as models in this research. Apart from their adsorbed conformations on graphene, the conformations of these copolymers as the free states in diluted solutions are taken into consideration. Although these copolymers present the fully extended conformation on graphene, their conformations in diluted solutions vary largely with the copolymer composition. It is verified that the copolymer with smaller conformational change could have the better stabilization effectiveness for graphene, rather than the one having stronger interaction with graphene. Therefore, the entropy-tailored behavior for the adsorption of aromatic macromolecules on graphene is put forward. Based on this mechanism, the chemical structure of aromatic polyamide is optimized and furthermore it is utilized to directly exfoliate natural graphite flakes. Eventually, high-quality graphene nanosheets with a large dimension and low defects are obtained. Moreover, its exfoliating effectiveness is superior to those of the commonly used exfoliating agents nowadays.

Scalable Preparation of Low-Defect Graphene by Urea-Assisted Liquid-Phase Shear Exfoliation of Graphite and Its Application in Doxorubicin Analysis.

The mass production of graphene is of great interest for commercialization and industrial applications. Here, we demonstrate that high-quality graphene nanosheets can be produced in large quantities by liquid-phase shear exfoliation under ambient conditions in organic solvents, such as 1-methyl-2-pyrrolidinone (NMP), with the assistance of urea as a stabilizer. We can achieve low-defect graphene (LDG) using this approach, which is relatively simple and easily available, thereby rendering it to be an efficient route for the mass production of graphene. We also demonstrate the electrochemical sensing of an LDG-modified electrode for the determination of doxorubicin (DOX). The sensor shows an enhanced electrocatalytic property towards DOX, leading to a high sensitivity (7.23 × 10−1 μM/μA) with a detection limit of 39.3 nM (S/N = 3).

Facile synthesis of paper based graphene electrodes for point of care devices: A double stranded DNA (dsDNA) biosensor

The demand for high-quality graphene for electronic applications is increasing due to its high carrier mobility and electrical conductivity. In this connection, printing technology is a reliable method towards the fabrication of conductive, disposable graphene-based electrode for low-cost sensor application. Herein, we aimed to report the synthesis of high-quality graphene nanosheets obtained by electrochemical exfoliation of biomass-derived from corn cob. The conductive ink was prepared from this exfoliated graphene and was utilized for the preparation of paper-based graphene electrode towards double stranded DNA (dsDNA) sensor application. This paper, based graphene electrode opens the possibility of direct electrochemical analysis of analyte without any sample preparation. In this study, two irreversible oxide peaks were obtained from paper-based printed graphene electrode, corresponds to oxidation of guanine (G) and adenine (A) of dsDNA in the linear range of 0.2 pg mL−1 to 5 pg mL−1 with the detection limit of 0.68 pg mL−1 and the sensitivity of 0.00656 mA pg−1 cm−2. Further, a small-scale printable circuit is fabricated using this graphene shows good conductivity of 1.145x103(S/m).

Tailored and highly efficient oxidation of various-sized graphite by kneading for high-quality graphene nanosheets

Abstract Graphene oxide (GO) exfoliated from graphite oxide is a precursor of graphene, which is a highly promising two-dimensional material for energy storage, printing electronics, composites, conducting fibers, etc. However, during the fabrication of GO by chemical oxidation, large amounts of oxidants and acid are used, which lead to many concerns, such as severe environmental pollution and high processing cost. In this study, we propose a highly efficient and rational oxidation of various-sized graphite powder by minimizing the amount of acid used (reducing 1/10 times) through kneading, inspired by the concept of kneading dough. First, NaClO3 and graphite were mixed together. Then, a small amount of fuming nitric acid was added, and the mixture was kneaded for several minutes. The ratio of oxidant to graphite and the reaction time, with and without kneading, were investigated based on the lateral size of graphite, because large-sized graphite requires more diffusion time for oxidizing the species through the graphitic layers. The chemically-reduced GO nanosheets exhibit highly crystalline structures based on the Raman spectroscopy and transmission electron microscopy studies, and their films exhibit a high electrical conductivity of over 45,000 S/m from large graphite, which is promising for electrical and electrochemical applications.

Water-Dispersed High-Quality Graphene: A Green Solution for Efficient Energy Storage Applications.

Graphene has been the subject of widespread research during the past decade because of its outstanding physical properties which make it an ideal nanoscale material to investigate fundamental properties. Such characteristics promote graphene as a functional material for the emergence of disruptive technologies. However, to impact daily life products and devices, high-quality graphene needs to be produced in large quantities using an environmentally friendly protocol. In this context, the production of graphene which preserves its outstanding electronic properties using a green chemistry approach remains a key challenge. Herein, we report the efficient production of electrode material for micro-supercapacitors obtained by functionalization of water-dispersed high-quality graphene nanosheets with polydopamine. High-frequency (terahertz) conductivity measurements of the graphene nanosheets reveal high charge carrier mobility up to 1000 cm-2 V-1 s-1. The fine water dispersibility enables versatile functionalization of graphene, as demonstrated by the pseudocapacitive polydopamine coating of graphene nanosheets. The polydopamine functionalization causes a modest, i.e., 20%, reduction of charge carrier mobility. Thin film electrodes based on such hybrid materials for micro-supercapacitors exhibit excellent electrochemical performance, namely a volumetric capacitance of 340 F cm-3 and a power density of 1000 W cm-3, thus outperforming most of the reported graphene-based micro-supercapacitors. These results highlight the potential for water-dispersed, high-quality graphene nanosheets as a platform material for energy-storage applications.

Graphene nanosheets production using liquid-phase exfoliation of pre-milled graphite in dimethylformamide and structural defects evaluation

The non-oxidation-based procedure is proposed for the production of high-quality graphene nanosheets using graphite as the raw materials. This research demonstrated a hybrid two-step production method by liquid-phase exfoliation (LPE) of Premilled graphite in Dimethylformamide (DMF) and compared it with the purely milled and just sonicated samples. However, a simple physical separation procedure composed of two centrifuge processes also designed for the separation of the products in each step. By this process, the exfoliated graphite, less-exfoliated ones and produced nanoparticles are separated, and the less-exfoliated ones are reused again in moderate sonication process. Two grades of graphene nanosheets and a grade of graphitic nanoparticles result at the end. The quality and the nature of defects in all graphene samples produced from LPE, wet milling of graphite and a combination of both, was investigated and discussed by Raman spectroscopy related indices. Raman spectra analysis indicates the adverse effect of sonication power on the in-plane defects formation in the graphene nanosheets which could be hindered by the reduction in power of sonication along with the pre-milling of the graphite. Also inductively-coupled plasma (ICP) and field emission scanning electron microscopy (FE-SEM) analysis used for further characterization of the milled-sonicated sample.

Advances in Microwave-Assisted Production of Reduced Graphene Oxide

Efficient reduction of graphene oxide to obtain high-quality graphene nanosheets is desirable for energy storage, catalysis, electronics and environmental remediation. In this brief review, we mainly focus on the microwave-assisted production of reduced graphene oxide in three categories: (1) microwave-assisted chemical reduction of graphene oxide; (2) microwave-assisted thermal reduction of graphene oxide; (3) microwave-assisted simultaneous thermal exfoliation & thermal reduction of graphite oxide. We also summarize common techniques for characterizing reduction efficiency and quality of as-obtained rGO.

High-quality liquid phase-pulsed laser ablation graphene synthesis by flexible graphite exfoliation

This work reports a one-pot procedure of laser ablation on a graphite target in a liquid medium, based on the variation of different parameters such as target type, laser wavelength, and ablation medium, to obtain high-quality graphene nanosheets. The morphology of derived products was characterized by the field emission scanning electron microscopy (FE-SEM). Then, the morphology and structure of the optimized sample were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible-near infrared (UV–vis-NIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). By controlling the laser ablation parameters, we were able to prepare micrometer-sized few-layer graphene nanosheets with mainly less than ten layers. Such synthesized graphene nanosheets were grown at the surface of a flexible graphite target, indicating many potential applications in fundamental research, electrochemical and as hydrophobic surfaces.

Hydrothermal synthesis of high quality graphene nanosheets anchored by uniform and well distributed silicon nanoparticles

Synthesis of graphene doped silicon nanoparticles is important for many applications such as energy storage materials for lithium ion batteries and super capacitors. In this letter, we provide a simple, cost effective, and scalable thermal method to get a uniformly distributed spherical silicon nanoparticles within reduced graphene oxide. The distribution and morphology of the composites were investigated using field emission scanning electron microscopy (FE-SEM), and high resolution transmission electron microscopy (HR-TEM) measurements. Different concentrations (0.025%, 0.05% and 0.1%) of silicon/reduced graphene oxide (RGO) have been synthesized using hydrothermal technique. C8H20O4Si was used as Si aqueous source which dispersed in graphene oxide solution. Si nanoparticles act as a spacer that prevent the stacking of graphene sheets, and the generated volumetric strain of silicon can be accommodated by graphene. The structure was evaluated by X-ray diffraction (XRD). Meanwhile, the existed function groups were assigned using Fourier transform infra-red (FTIR) spectra. Raman measurement confirmed the successful formation of graphene doped silicon nanocomposite. The increment in the generated defects within the graphene sheets as the silicon contents increase, provides a clear indication that silicon nanoparticles were anchored in the graphene nano sheets.

Quantification of Chloroxylenol, a Potent Antimicrobial Agent in Various Formulations and Water Samples: Environmental Friendly Electrochemical Sensor Based on Microwave Synthesis of Graphene

A green method was applied for synthesis of high quality graphene nano-sheets (GR) by simultaneous reduction and exfoliation of as-prepared graphite oxide via microwave irradiation for only 30 s. The highlighted superiority of this developed method over those depicted in the literature is the absence of any hazard reducing, intercalation or chemical activating agents. TEM, FTIR, TGA and XRD analysis confirmed the formation of graphene nanosheets. TEM image reveals a typical wrinkled and crumpled GR structure. A number of graphene layers of 3.0 and interlayer spacing of 0.38 nm were calculated from XRD pattern. Graphene carbon paste modified electrode (GR/CPE) was then fabricated, characterized using SEM, EIS and CV techniques and applied for detection of a potent antimicrobial agent “Chloroxylenol”. This developed sensor exhibited excellent performance for detecting bulk Chloroxylenol (LOD of 1.37 × 10−9 M). Due to the high toxicity of such chlorinated phenolic compound as it can release to the environment through various waste streams and persistent in nature, GR/CPE was also employed for detecting Chloroxylenol in real samples such as its formulation products and water samples. This promising sensor based on ultrafast and cost-effective production of graphene can be employed for quality control analysis of pharmaceutical and environmental samples.

Large scale green production of ultra-high capacity anode consisting of graphene encapsulated silicon nanoparticles

High quality graphene nanosheets produced in molten salts were found to be capable of wrapping silicon nanoparticles, leading to the fabrication of graphene encapsulated silicon nanoparticles with an excellent stable electrochemical performance as anode material for Li-ion batteries.

Efficient strategy of chlorine-assisted liquid-phase exfoliation of graphite

A large-scale, inexpensive, and facile strategy has been successfully developed for preparation of high-quality graphene nanosheets by combining electron-absorbing materials and chorine in N-methyl-2-pyrrolidone. The as-obtained graphene sheets were proven to contain low levels of naturally absorbed oxygen inherited from the starting graphite by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and X-ray diffraction. Meanwhile, the structure of produced graphene sheets was further characterized using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Compared to the previous techniques, this eco-friendly approach demonstrates obvious advantages, such as low cost and simplicity, which could be an alternative method to prepare graphene-based composites for the potential applications in the near future.