Few-layer Graphene Research Articles

Selective conversion of carbon dioxide to formate using few-layer nitrogen-doped graphene on copper foam with enhanced suppression of the hydrogen evolution reaction

This research presents a novel electrocatalyst, a three-dimensional, few-layered nitrogen-doped graphene-coated copper foam (N-GP/Cu-foam), engineered for the selective electrochemical reduction of carbon dioxide (CO2) to formate.

Optically induced trion formation and its control in a MoS2/graphene van der Waals heterostructure.

Monolayer 2D transition metal dichalcogenides (TMDs) show high sensitivity to the local dielectric environment, leading to modulation of their optoelectronic properties. Here, we report on the formation of localized trions in a MoS2/few-layer graphene van der Waals heterostructure. We performed temperature-dependent photoluminescence and Raman studies down to 80 K, to understand the mechanism for localized charge excitation, which shows contrasting behaviour with MoS2/SiO2. We attribute trion formation to optically induced charge transfer from few-layer graphene to MoS2. Our theoretical analysis and simulations comparing the dielectric screening between MoS2/SiO2 and MoS2/few-layer graphene strongly suggest the dominance of excess charge carrier concentration over dielectric screening as the cause of trion formation. The concentration of charge carriers could be tuned actively with excitation power. Our findings provide an efficient approach for trion formation in MoS2 and explain the mechanism behind charge transfer in the MoS2/few-layer graphene heterostructure.

Functionalized graphene-based materials for cementitious applications.

Graphene-based materials (GBM) are promising cementitious composite additives that can significantly improve the mechanical characteristics and durability of concrete due to their unique properties, such as high surface area and aspect ratio and excellent tensile strength, to name a few. To display their full potential, GBM have to be homogeneously dispersed into the aqueous environment of cement-based matrices. The present study addresses the issue of limited dispersibility in the aqueous media of GBM through the chemical functionalization of mono- and few-layer graphene structures with hydrophilic aryl sulfonate groups and shows that a series of mortar samples containing modified GBM exhibit increased flexural and compressive strength by up to 17% and 30%, respectively, compared to mortar references without additives.

Direct localized growth of graphene on a substrate: a novel nickel-catalyzed CVD process assisted by H2 plasma.

An original metal catalyzed CVD methodology assisted by hydrogen plasma for the direct deposition of few-layer graphene on a substrate is presented. Graphene is grown at 900 °C directly on the surface of the substrate of technological interest by carbon diffusion through a nickel film by using methane (CH4) as the carbon precursor. Hydrogen atoms in the H2-plasma downstream are used to promote the solubilization of carbon atoms in Ni, thus favouring the growth of graphene at the Ni/substrate interface. Structural and transport properties of the as-grown multilayer graphene films on SiO2/Si and quartz substrates are provided. We demonstrate the peculiarity of this approach for controlling the thickness and transport properties of as-grown graphene films using process-step times. Finally, the potential of the proposed methodology for the bottom-up direct growth of patterned graphene is demonstrated.

2D diamond structures in multilayer graphene: Simulation and experimental observation

The presented paper investigates the formation of nanodiamond structures within multilayer graphene through irradiation with fast heavy ions. The study demonstrates that Xe26+ ions with energies ranging from 26 to 167 MeV can create diamond regions in graphene with lateral sizes ranging from 5 to 20 nm. The density of nanodiamonds formed in the few-layer graphene films is estimated to be approximately (5–30)% of the ion fluence. We show that the final structure of the diamond structures is influenced by factors such as surface orientation, number of graphene layers, and lateral size. Atomistic simulations predicted unusual mechanical properties of the formed 2D composite: its Young's modulus obtained by indentation can significantly exceed the stiffness of the original graphene film.

Preparation and assessment of ionic liquid and few-layered graphene composites to enhance heat and mass transfer in adsorption cooling and desalination systems

Adsorption systems can utilise low-temperature renewable and waste heat sources, which have emerged as a feasible alternative to conventional water desalination and cooling systems. However, the material of poor heat and mass transfer performance stall their widespread utilisation. This article presents the development and investigation of new composites employing few-layered graphene platelets and ionic liquids, namely ethyl-methylimidazolium methane sulfonate ([EMIM][CH3SO3]) and Ethyl-methylimidazolium-chloride ([EMIM][Cl]) to address such challenges. The impact of the few-layered graphene platelets, thermal properties, water adsorption properties of the developed composites and their thermal diffusivity were experimentally investigated. Besides, the overall cyclic performance was studied experimentally at the material level and computationally at the component level by employing a previously validated 2D dynamic heat and mass transfer model. The experimental investigation indicated that pristine few-layered graphene has a surface area of 56.8978 m2/g and a relatively high thermal diffusivity of 22.23 mm2/s. The developed composites showed higher thermal diffusivity than the baseline adsorbent silica gel. The highest thermal diffusivity was 11.84 mm2/s for GP-CH3SO3-10, 394 times higher than silica gel. Water adsorption characteristics of the composites were carried out, and the Dubinin–Astakhov (D-A) model was employed to model the experimental isotherms with good accuracy. The cumulative advanced adsorption and thermal characteristics of the developed composites resulted in higher cyclic performance by up to 82 % and 85 % than that of the baseline silica gel.

A Novel and Large-Scale Rapid Green Synthesis of Few-Layer and Multi-Layer Graphene

Mono-layer graphene has shown path-breaking potential in almost all areas that are useful to humankind. However, research in the last decade indicated that few-layer graphene (FLG) (3-10 layers) and multi-layer graphene (MLG) (>10 layers) could also be utilized for a wide range of applications. The synthesis of mono-layer graphene at a large scale is quite complex. Producing FLG and MLG at a kilogram scale is equally challenging. A vast amount of literature on different routes to prepare FLG and MLG is available. However, most of the preparation routes involve the use of hazardous chemicals, copious amounts of water, and thermal treatments and are time taking. Also, these processes need bigger machinery to convert the lab-scale methods into continuous large-scale production. On the contrary, in this work we report a novel process of producing FLG and MLG along with trace quantities of graphene (< 3 layers) developed using a kitchen mixer and a modified mixing jar (3 litres). The highlights of this process include the use of no hazardous chemicals/solvents, no washing or thermal treatment needed, much less time (30 minutes), and large quantity (250-500 grams) per batch. Our study successfully converted natural graphite flakes (NGF) into FLG and MLG by carrying out rapid liquid phase shear mixing using a green solvent. The shear mixing and the green solvent convert the NGF into FLG and MLG. The quantity of FLG and MLG getting produced is time-dependent. It has been optimized by thoroughly characterizing FLG and MLG using techniques like particle size analyser, X-ray diffraction, Raman spectroscopy, and electron microscopy. The conversion of NGF to FLG and MLG is also affirmed by studying changes in properties using tools like thermogravimetry, BET, and UV-visible spectroscopy. The developed process is rapid, efficient, economical, scalable, continuous, and, most importantly, chemical free.The graphenaceous powder produced unlike graphite can be easily coated on different substrates using appropriate binders and thus makes it useable for energy storage applications. Also the fine particle size of graphite makes is an ideal material to be used as lubricant, both in solid and liquid mediums. The developed material can be explored for its applications in several other areas which require FLG/MLG.

Elucidation of Electrochemical Performance of Few-Layered Graphene As Aluminium Battery Cathode Material: Effect of the Common O and S Impurities

Of late, few-layered graphene (FLG) is being tested as an efficient aluminum battery (AB) cathode material. FLG is typically prepared by reducing and exfoliating graphene oxide (GO), commonly prepared by wet-chemical methods. Therefore, FLG is bound to have impurities (commonly O and S). Consequently, it is crucial to study the influence of the S and O impurities in FLG on its performance as an AB cathode material. To conduct such a study, we considered FLG prepared by exfoliating GO using microwave irradiation. The considered FLG has O and S impurities (bonded to C atoms in FLG), collectively weighing 2.9 – 4.7 at.% (4.1 – 6.9 wt.%). The considered FLG as a cathode material in AB pouches delivered stable discharge capacities of around 100 mAh/g at 0.1 A/g current rate over 500 cycles and high irreversible capacities for the first few cycles. The effect of the O and S impurities was negligible when the FLG was cycled at 1.0 A/g, but initial energy storage capacities and cyclic behavior varied with the voltage window. However, the storage capacities at the end of 10000 cycles are similar, irrespective of the voltage window. Overall, the O and S impurities in FLG lead to initial high irreversible capacities, ruling out the commercial use of FLG. We therefore recommend careful characterization of O and S impurities (and any such impurities) before reporting FLG-related materials as AB cathode materials. Removing these impurities will help FLG outperform its class of materials because it shows excellent rate capability with excellent discharge capacities at a high current density of 5 A/g, even with O and S impurities.

Role of Curvature in Stabilizing Boron-Doped Nanocorrugated Graphene.

Boron-doped carbon nanostructures have attracted great interest recently because of their remarkable electrocatalytic performance comparable to or better than that of conventional metal catalysts. In a previous work (Carbon 123, 605 (2017)), we reported that along with significant performance improvement, B doping enhances the oxidation resistance of few-layer graphene (FLG) that provides increased structural stability for intermediate-temperature fuel-cell electrodes. In general, detailed characterization of the atomic and electronic structure transformations that occur in B-doped carbon nanostructures during fuel-cell operation is lacking. In this work, we use aberration-corrected scanning transmission electron microscopy, nanobeam electron diffraction, and electron energy-loss spectroscopy (EELS) to characterize the atomic and electronic structures of B-doped FLG before and after fuel-cell operation. These data point to the nanoscale corrugation of B-doped FLGs as the key factor responsible for increased stability and high corrosion resistance. The similarity of the 1s to π* and σ* transition features in the B K-edge EELS to those in B-doped carbon nanotubes provides an estimate for the curvature of nanocorrugation in B-FLG.

Graphene self-folding: Evolution of free-standing few-layer graphene in plasma synthesis

Substrate and catalyst free gas-phase plasma synthesis of freestanding few-layer graphene (FLG) flakes leads to crumpled FLG structures. In this paper, we elucidate a folding-based mechanism and structure-formation process in accordance with literature on the stability of graphene sheets. Transmission electron microscopy is applied to thermophoretically-sampled FLG at various distances from the plasma zone. Single-layer and few-layer graphene were observed, and a morphology pattern evolution could be discerned. A conceptual model of graphene formation and growth is derived, starting from initial rounded single-layer graphene of a few hundred nanometer in diameter to, eventually, self-folded and strongly crumpled FLG.

Few-layer graphene as an ‘active’ conductive additive for flexible aqueous supercapacitor electrodes

We demonstrate that few layer graphene (FLG), formed by high-shear exfoliation into an aqueous suspension, can be successfully employed as an ‘active’ conductive additive in flexible activated carbon-based aqueous electric double layer capacitor (supercapacitor) electrodes if introduced by a novel ‘vacuum infiltration’ technique. The effectiveness of the FLG can be optimised by tailoring its size distribution and loading. It is found that best performance is achieved using FLG with the broadest size distribution and, moreover, that the larger size distribution is effective over the broadest range of loading. With optimum size distribution and loading, FLG is shown to outperform a commercial carbon black conductive additive (Timcal C65). Electrodes containing 8 wt% infiltrated FLG have an equivalent series resistance (ESR) of 1.3±0.4Ω, and a specific capacitance of 142.3±0.1 F g−1 over a voltage window of 1.2 V, compared with an ESR of 3±1Ω and a specific capacitance of 96.81±0.02 F g−1 for equivalent electrodes produced with an optimal loading of carbon black additive. As a result, the specific energy density of electric double layer capacitors (EDLCs) produced with a vacuum infused FLG additive is demonstrated to be an average of 47±3% superior to those containing carbon black measured at similar power densities. In contrast to vacuum infiltration, direct mixing of FLG suspension into the electrodes is found to be ineffective, resulting in limited improvement relative to electrodes without conductive additive, the reasons for which are discussed.

Adsorption of Rhodamine G from Aqueous Solutions onto Particles of Few-Layer Graphene Prepared by Self-Propagating High-Temperature Synthesis

The ability of few-layer graphene prepared by self-propagating high-temperature synthesis to adsorb Rhodamine G was studied. The dependences of the sorption capacity of few-layer graphene particles on the Rhodamine G concentration in aqueous solution, solution temperature, and adsorption time were determined. The adsorption of Rhodamine G on the surface of few-layer graphene is satisfactorily described by the Langmuir and Freundlich models. The process occurs under mixed diffusion control and can be described by a pseudo-second-order rate equation.

Recyclable waste derived green triboelectric nanogenerator for Self-Powered synthesis of Defect-Free graphene via Mechano-Electrochemical exfoliation

With an upsurge in global waste generation per capita, and energy consumption, there is a simultaneous need for new strategies that can reuse plastic waste and harvest energy for practical applications. Hence, we propose a green triboelectric nanogenerator derived from waste (W-TENG), which was used to demonstrate a novel self-powered application of mechano-electrochemical exfoliation process for graphene synthesis. The W-TENG comprised of discarded plastic banner as tribo-negative material and chocolate wrapper as tribo-positive material, which were confirmed to be polyvinyl chloride (PVC) and aluminium, respectively by using different characterization techniques. The as-fabricated W-TENG exhibited an output VOC of 35 V and ISC of 0.4 µA. The instantaneous power output of the W-TENG was calculated as 0.0217 W/m2 at 45 MΩ external resistance load. The force-dependency behaviour of W-TENG demonstrated that the voltage and current output increased from 20 V to 58 V, and 0.2 to 0.4 µA, upon changing the applied force from 9 N to 30 N. Further, we have demonstrated a novel application, wherein 2D graphene nanosheets were synthesized via mechano-electrochemical exfoliation under highly conductive acidic solution, powered by the W-TENG. Various physico-chemical characterization techniques confirmed it to be defect free few-layered graphene. This work demonstrates a promising “waste to wealth” strategy of using discarded plastic waste to develop a robust mechanical energy harvester to power various applications.

Synthesis of nanoscale LiCoPO4/C between few-layer graphene and its influence on electrochemical performance for lithium-ion batteries

In this study, the composite cathode material of LiCoPO4/C and graphene is synthesized using solvothermal method assisted by oleylamine. The effect of graphene addition on the material properties is fully investigated, and the synergistic effect of amorphous carbon and graphene is also studied. Graphene serves as a conductive skeleton and provides abundant diffusion paths for electrons. The nanoscale LiCoPO4 material synthesized by solvothermal method is evenly distributed around the few-layer graphene with the assistance of oleylamine, and the amorphous carbon formed after the pyrolysis of oleylamine at high temperature tightly connects LiCoPO4 to the graphene, which improves the conductivity and electrochemical performance of the sample. The results of characterization reveal that adding graphene can prepare LiCoPO4 materials with good crystallization and improve the specific surface area and pore size of the material. At the same time, the amorphous carbon and graphene inside the material also show a good degree of graphitization. Electrochemical test results show that doping graphene with a mass ratio of 6% can enhance the electrochemical performance and cycle stability of LCPC-6%G sample. The initial discharge capacity of LCPC-6%G sample reaches 157.2 mA h g−1 at 0.1 C. In this study, nanoscale LiCoPO4 samples are successfully synthesized on the surface of graphene, which provides a new idea for the preparation of nanoelectrode materials and conductive skeleton composite samples.

Production of few-layered graphene reinforced copper by powder metallurgy

Powder metallurgy (P/M) was utilized to produce copper (Cu) matrix composites reinforced with few-layered graphene (FLG), which was produced by electric arc discharge (EAD). The structural and mechanical properties of the composites were investigated depending on the milling time and the graphene content. It was determined in SEM and TEM analyses that FLG was uniformly dispersed in the Cu matrix. Compared to pure Cu, an increase in hardness of approximately 31.8% was provided for 0.3 wt% FLG/Cu composite sintered after 5h of milling. Furthermore, with the addition of FLG, a decrease was observed in the COF values of the composites obtained by 7h milling. Grain refinement is considered a relevant strengthening mechanism for FLG/Cu composites.

Graphene and Its Derivatives: Properties, Synthesis, and Applications in Wearable and Transparent Sensors

Graphene is a 2-D carbon-based material consisting of a single layer or few layers that has revolutionized the scientific world with its potential applications in various types of sensors, especially wearable and transparent devices. This material possesses astonishing thermal, electrical/electronic, optical, and excellent mechanical properties. It has the potential to replace carbon nanotubes (CNTs) due to its low cost and relatively similar properties. There is a need to work on different graphene synthesis methods, optimize various parameters, reduce costs, and achieve large-scale production. This study discusses in detail graphene, graphene oxide, reduced graphene oxide, their properties, various synthesis methods, and potential applications. Among these methods, we have found that Hummer’s method is relatively better for producing low-cost graphene on an industrial scale. However, there is a need to optimize Hummer’s method parameters, such as finding the right chemical to reduce graphene oxide and synthesizing few layers of graphene with high conductivity.

Direct growth of few-layered graphene on boron doped diamond surface with varying boron doping concentration

The diamond-graphene heterostructure is a promising all‑carbon composite structure, which can take advantages of excellent properties of these two materials. At present, the diamond-graphene heterojunction were mostly synthesized by chemical vapor deposition (CVD) method with intrinsic diamond substrate. In this study, the few-layered graphene is synthesized on boron-doped-diamond (BDD) surface through a simple thermal treatment method with Ni catalyst. The effects of boron doping concentration of substrate on the synthesis of diamond-graphene heterojunctions is studied. It demonstrates that the surface morphology and roughness are improved with the increasing of substrate doping concentration. Compared with the light doped and un-doped diamond, the number of graphene layers and quality decreases and increases, respectively.

Few-Layer Graphene Structures as a Promising Mycotoxin Sorbent

Few-Layer Graphene Structures as a Promising Mycotoxin Sorbent

Graphene-Based Electrochemical Sensing Platform for Rapid and Selective Ferulic Acid Quantification

Due to the multitude of physiological functions, ferulic acid (FA) has a wide range of applications in the food, cosmetic, and pharmaceutical industries. Thus, the development of rapid, sensitive, and selective detection tools for its assay is of great interest. This study reports a new electroanalytical approach for the quantification of ferulic acid in commercial pharmaceutical samples using a sulphur-doped graphene-based electrochemical sensing platform. The few-layer graphene material (exf-SGR) was prepared by the electrochemical oxidation of graphite, at a low applied bias (5 V), in an inorganic salt mixture of Na2S2O3/(NH4)2SO4 (0.3 M each). According to the morpho-structural characterization of the material, it appears to have a high heteroatom doping degree, as proved by the presence of sulphur lines in the XRD pattern, and the C/S ratio was determined by XPS investigations to be 11.57. The electrochemical performances of a glassy carbon electrode modified with the exf-SGR toward FA detection were tested by cyclic voltammetry in both standard laboratory solutions and real sample analysis. The developed modified electrode showed a low limit of detection (30.3 nM) and excellent stability and reproducibility, proving its potential applicability as a viable solution in FA qualitative and quantitative analysis.

Piezoelectric, mechanical, and crystallographic properties of polyvinylidene fluoride‐hexafluoropropylene based composites reinforced by different dimensional carbon nanomaterials

AbstractPolymer based piezoelectric materials are increasingly used because of their lightweight and flexibility. To understand the effects of different dimensional carbon nanomaterials on the properties of polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) based composites, carbon black (CB), carbon nanotube (CNT), and few‐layer graphene (FLG) were used to reinforce PVDF‐HFP for preparing different composites, respectively. Their piezoelectric, mechanical, and crystallographic properties were tested. The results show that CB/PVDF‐HFP composite film has the best piezoelectric property, successively followed by FLG/PVDF‐HFP and CNT/PVDF‐HFP at 0.5%, 0.05%, and 0.1% contents of CB, FLG, and CNT, respectively. In the initial crystallization stage, CB better plays the best role of crystallization core, increasing the electroactive crystalline phase content and crystallization rate. The appropriate contents of CNT and FLG promote the formation of β crystalline phase. In the polarization stage, CB forms a uniform nonconductive network in the composite film and shows the best polarization effect. CNT tends to form connections and has the worst polarization effect. FLG forms a “microcapacitor” structure to enhance the local polarization effect. The effects of CB, CNT, and FLG on crystalline phase changes and piezoelectric property enhancements of PVDF‐HFP based composites are mainly due to their differences in size, morphology, and quantity.Highlights Effects of CB, CNT, and FLG on the piezoelectricity of PVDF‐HFP are investigated; CB more obviously increases the piezoelectricity of PVDF‐HFP than CNT and FLG; α, β, and γ crystalline phase changes in PVDF‐HFP based composites are understood; CB forms smaller and more uniform crystal cores in PVDF‐HFP than CNT and FLG; CB markedly increases the contents of electroactive crystalline phases in PVDF‐HFP.