Multilayer Graphene Sheets Research Articles

Electromechanical response of multilayer graphene sheet/polypropylene nanocomposites and its relationship with the graphene sheet physicochemical properties

Abstract The mechanical, electrical, and piezoresistive responses of multilayer graphene sheet (GS)/polypropylene (PP) nanocomposites are investigated using four GSs of distinctive physicochemical properties. It is found that the morphology of the interconnected network of GS agglomerates at the mesoscale governs the mechanical, electrical, and electro-mechanical (piezoresistive) properties of the PP nanocomposites. The morphology of the mesoscale network of electroconductive fillers governs the effective properties of the nanocomposite. This network morphology strongly depends on the GS lateral size, dispersion, agglomeration, and, to a lesser extent, the specific surface area of the GSs. Within the range of lateral sizes investigated herein (1 - 21 m), larger GSs yields nanocomposites with higher electrical conductivity. On the other hand, GSs of moderate lateral size (~ 6.5 m) and specific surface area of ~ 141 m2/g render GS/PP nanocomposites with a more dispersed and more sparsely interconnected network. This better dispersed network with agglomerates of smaller dimensions is concomitant with improved stiffness and strength, and higher gauge factors (~ 18.2) for this GS/PP nanocomposites. Excellent capabilities for detection of human motion were proved for these nanocomposites.

Synthesis and structural analysis of graphene nanosheets via microwave atmospheric pressure plasma

This study reports the effective synthesis of multilayered graphene sheets via microwave atmospheric pressure plasma. This innovative approach streamlines and expedites graphene production and other carbon nanostructures, eliminating the need for catalysts, solvents, or complex processing conditions. Ethanol is directly injected into a microwave-generated argon plasma plume, leading to the formation of graphene. Raman spectroscopy revealed characteristic peaks (2D, G, and D bands) confirming graphene composition, with defects indicated by the D band. X-ray diffraction analysis supported these findings, indicating a broad peak at 25∘ corresponding to the (002) plane, affirming a multi-layered graphene structure. Scanning electron microscopy exhibited crumpled, randomly oriented graphene sheets, albeit with uneven structures suggesting impurity incorporation. The presence of defects was quantified through the intensity ratio of the D to G band (ID/IG) in Raman spectroscopy, revealing a value of 0.80, signifying the presence of defects in the synthesized graphene. The 2D to G band intensity ratio (I2D/IG) suggested the existence of 7–10 graphene layers, highlighting the need for further optimization for enhanced graphene quality and purity.

Enhanced physical and mechanical properties of Cu-based nanocomposites with bundled multi-layered carbon nanotubes incorporation: fabrication and comparative analysis via conventional sintering and SPS techniques

The current investigation delves into the influence of incorporating bundled multi-layered graphene sheets, specifically multiwalled carbon nanotubes (MWCNTs), on the microstructure, as well as the physical and mechanical attributes of Cu-based nanocomposites. Various weight percentages (1%, 2%, 3%, and 5%) of MWCNTs were infused into the Cu matrix, and the fabrication of these nanocomposites was conducted through the powder technology route. The fabrication process occurred under an argon atmosphere utilizing both conventional sintering and spark plasma sintering (SPS) techniques. The conventionally sintered Cu-based nanocomposite reinforced with 1% MWCNT exhibited the highest relative density (~86%), hardness (~551.12 MPa), compressive strength (~459 MPa), and outstanding resistance to wear. Conversely, the SPS-fabricated nanocomposite reinforced with the same MWCNT concentration demonstrated the highest relative density (approximately 94.25%) and compressive strength (~688 MPa), while the nanocomposite reinforced with 2% MWCNT displayed the highest hardness (~1178 MPa) and resistance to wear. Notably, a higher concentration of MWCNTs was observed to adversely affect the physical, mechanical, and wear properties of the Cu-MWCNT nanocomposites, irrespective of the chosen sintering technique for their production.

Evolution of the Surface Wettability of Vertically Oriented Multilayer Graphene Sheets Deposited by Plasma Technology.

Carbon deposits consisting of vertically oriented multilayer graphene sheets on metallic foils represent an interesting alternative to activated carbon in electrical and electrochemical devices such as super-capacitors because of the superior electrical conductivity of graphene and huge surface-mass ratio. The graphene sheets were deposited on cobalt foils by plasma-enhanced chemical vapor deposition using propane as the carbon precursor. Plasma was sustained by an inductively coupled radiofrequency discharge in the H mode at a power of 500 W and a propane pressure of 17 Pa. The precursor effectively dissociated in plasma conditions and enabled the growth of porous films consisting of multilayer graphene sheets. The deposition rate varied with time and peaked at 100 nm/s. The evolution of surface wettability was determined by the sessile drop method. The untreated substrates were moderately hydrophobic at a water contact angle of about 110°. The contact angle dropped to about 50° after plasma treatment for less than a second and increased monotonously thereafter. The maximal contact angle of 130° appeared at a treatment time of about 30 s. Thereafter, it slowly decreased, with a prolonged deposition time. The evolution of the wettability was explained by surface composition and morphology. A brief treatment with oxygen plasma enabled a super-hydrophilic surface finish of the films consisting of multilayer graphene sheets.

A perspective of recent advances in PECVD-grown graphene thin films for scientific research and technological applications

The purpose of this review is to provide a perspective on some of the recent advances in applying graphene thin films, including monolayer and multilayer graphene sheets synthesized by a scalable approach based on plasma-enhanced chemical vapor deposition (PECVD), to scientific research and technologies. The technological applications present here include the use of graphene in flexible electronics, for anticorrosion of metals, and for Si-based technologies including superlubricity and optoelectronics. In the case of fundamental scientific research, we demonstrate that periodic patterns of nanoscale strain distributions in monolayer graphene can lead to local giant pseudomagnetic fields as well as global modifications to the electronic properties of monolayer graphene, including strain-induced valley Hall signals and quantized Landau levels in the absence of external magnetic fields, edge states, as well as increasing electronic correlation with increasing strain. These findings suggest new approaches towards developing emerging quantum states with tunable electronic correlation based on graphene straintronics.

Numerical investigation of non-local elasticity theory for free vibration of polymer embedded multi-layer graphene sheets

The present study investigates the free vibration behavior of multi-layered graphene sheets with various shapes embedded in a polymer matrix under different boundary conditions based on Eringen non local elasticity. The governing equations are obtained through the minimization of potential energy or Newton’s law which is not only equivalent to Hamilton’s principle and mutually can be derived from each other. Differential Quadrature and pb2 Rayleigh Ritz procedures are applied to Multi-layered Graphene sheets employing Eringen’s elasticity and classical plate theory. Results indicate that the resonant frequencies of the sheets are overestimated up to 60% using the classical elastic model. Depending on the shapes of Graphene sheets, small-scale parameters, boundary conditions, stiffness of polymer matrix, the number of layers and van der Waal’s interaction on the vibrational characteristics of graphene sheets are studied, and the results are tabulated. Conclusions are drawn and recommendations are provided for future work.

Peridynamics for the fracture study on multi-layer graphene sheets

Understanding the fracture properties of graphene sheets is a crucial step towards their practical applications. However, due to the limitations of experimental operations and all-atom (AA) methods, investigating the fracture of large-sized nano graphene sheets remains a formidable challenge. Especially, study on the layer-by-layer fracture of multi-layer graphene sheets (MLGS) is nearly impossible. To overcome this challenge, a peridynamic (PD) model is proposed in this study, which comprises the intra-layer part and the inter-layer part. The proposed PD model is validated by comparing the fracture toughness and the fracture forms of MLGS with existing experiments. It is found that the uniaxial tensile stress-strain curve of pre-cracked MLGS is closely related to the number of graphene layers in MLGS. The fracture property of MLGS can be enhanced by increasing the number of graphene layers, reducing the pre-crack length and blunting the pre-crack tip. Notably, asynchronous crack propagation with independent path observed in MLGS is a unique mechanism for strengthening the fracture property, which is distinct from monolayer graphene sheet. In this work, the PD theory is extended for the first time to investigate the in-plane fracture of large-sized nano MLGS.

Effects of functionally graded graphene reinforcements on nonlinear post-local buckling and axial stiffness of laminated channel section struts

The role of local buckling on the behavior of slender members under compression has received considerable attention in structural engineering. For thin-walled sections, in particular, there is a noticeable decrease in the axial compressive stiffness, resulting in a substantial reduction in their load-bearing capacity due to the occurrence of local buckling. The principal purpose of this article is to explore the potential improvements in the postbuckling characteristics of polymeric composite channel section struts subjected to a progressive end-shortening by employing multi-layer graphene sheets reinforcements. The solution methodology incorporates the von Karman geometrical nonlinearity and is based on the layerwise third-order shear deformation theory (LW-TSDT). To verify the accuracy of the results obtained based on LW-TSDT and to evaluate its computational efficiency, a three-dimensional (3D) finite element model is also developed using ABAQUS for the comparative analysis. A thorough examination of nonlinear instability is conducted on composite laminated channel section struts, featuring distinctive graphene distribution patterns through the thickness directions of the flanges and webs to identify the most effective material distribution with the objective of a significant increase in critical end-shortening and axial compressive stiffness. The influence of the geometrical parameters on the critical end-shortening, postbuckling equilibrium paths, and load-bearing capacity of functionally graded graphene reinforced composite (FG-GRC) laminated channel section struts are elicited. The conducted parametric analyses emphasize that altering the distribution patterns of graphene reinforcement across the flanges and web can enhance the critical end-shortening and load-bearing capacity by 80% and 25%, respectively.

Highly Selective NO2 Sensors Based on Electrolytically Exfoliated Graphene/Flame-made WO3 Composite Films

Gas sensors based on flame-synthesized WO3 nanoparticles loaded with 0.2-5 wt% electrochemically exfoliated graphene were evaluated for NO2 detection at ppb levels. The characterizations by X-Ray diffraction, nitrogen adsorption, electron microscopy and Raman spectrometry verified that multi-layer graphene sheets were well dispersed within spheroidal WO3 nanoparticles. Sensing layers fabricated with different graphene loading levels were tested towards 50-5000 ppb NO2 with varying operating temperatures from 100 to 350 °C in dry air. From the test results, the graphene-loaded WO3 nanoparticles with the optimal graphene content of 2 wt% exhibited the highest sensor response of ~ 5061 to 5000 ppb NO2 at the optimum working temperature of 150 °C. Furthermore, the sensor based on graphene/WO3 composites displayed high NO2 selectivity against various environmental gases and volatile organic compounds at 150 °C. The mechanistic roles of graphene on NO2 gas-sensing performances were described based on reactive ohmic M-S heterointerfaces. Therefore, the combination of electrochemically exfoliated graphene and flame-made WO3 nanoparticles could be an attractive mean to achieve highly sensitive and selective NO2 sensors.

Structure-property relationships in the electrical conductivity of multilayer graphene sheet/epoxy nanocomposites

The relationship between the physicochemical properties of multilayer graphene sheets (GSs), their resulting state of dispersion, and the effective electrical conductivity of GS/epoxy nanocomposites is investigated. To construct such relationship, four types of GSs with dissimilar properties were physicochemically, structurally, and morphologically characterized, and correlated with the direct current and alternating current (AC) electrical responses of their polymeric nanocomposites. It was found that the most influential parameters that affect the electrical conductivity of the nanocomposites are the size and density of agglomerates formed at the mesoscale. Both parameters, in turn, are governed by the physicochemical properties of the individual GSs. At the nanostructure level, the lateral size of the GS arises as the most influential parameter, with larger GSs yielding higher conductivities and lower percolation thresholds. The carbon/oxygen ratio of the GSs also showed moderate influence. The nanocomposites showed a resistive (R)-capacitive (C) electrical response in AC, which fits to a two-element parallel RC model. Both, the power law and general effective media (GEM) models predict similar percolation thresholds, but the GEM model is more general and adequately reproduces the whole electrical curve for all filler concentrations.

Water transport through a multilayer graphene pore in electric fields: Effect of pore size arrangement

In recent experiments, multilayer graphene sheets can be fabricated through van der Waals assembly, where the pore size could have different distributions and arrangements; however, our understanding on how this affects water transport is still rather poor. In this work, we use molecular dynamics (MD) simulations to study the transport of water through a multilayer graphene pore in electric fields, focusing on the effect of pore size arrangement. We consider the arrangement of two pore sizes, namely S1212 (uniform) and S1122 (concentrated), respectively. Notably, because of different friction environment, the water dynamics exhibit a bifurcation for S1212 and S1122. For example, with the increase in electric field, the water flux and flow both exhibit a monotonous decrease for S1212; while for S1122 the water flux increases monotonously and the water flow displays a minimum behavior. For the change of electric fields and pore length (graphene layer number), S1122 always has a larger water flux, water flow and unidirectional transport efficiency, as well as a smaller translocation time. Consequently, we can conclude that a more concentrated pore size arrangement facilitates the water transport, providing a new direction for the design of high flux nanofluidic devices.

Quantum size effects in stacked multilayer graphene

In this paper,we study the quantum size effects in multilayer graphene sheets using first principles methods within the framework of density functional theory. Four different types of functionals are adopted respectively to describe the van der Waals interactions between graphene layer sheets: the DFT-GGA(PBE), the DFT-D2, the vdW-DF and the optPBE-vdW. By inspecting the binding energy as a function of increasing graphene layers, we find that the PBE functional can not well describe the van der Waals interactions between different layers of graphene sheets. In contrast, the other three methods exhibit similar results with monotonic increasing binding energy as a function of graphene layers towards the bulk limit, concluding that the layered graphene structure is stabilized by van der Waals interactions. The density of states at zero temperature indicate that the multilayer graphene sheets is a semi-metal, which is independent of sheet layers number. The finite temperature (about 200 K) density of states at Fermi surface are studied as a function of the number of stacking graphene layers. The systematic oscillating behavior of finite temperature density of states between odd and even number of layers is a demonstration of quantum size effects. The Fermi wavelength will converge to two times the inter-layer distance of graphite, which is consistent with the theory describing the motion of particles in a quantum well. Finally, we study the adsorption of single H atom on multilayer graphene sheets to test the role of quantum size effects. The adsorption energies and the vibration frequencies are calculated for comparison with experiments. Our results shed light on understanding the stacking process of multilayer graphene in vacuum both theoretically and experimentally.

Perforated Turbostratic Graphene As Active Layer in a Nonvolatile Resistive Switching Memory Device

Perforated turbostratic graphene (PTG) sheets have been synthesized from a natural waste material, dead bougainvillea bracts, using a single-step pyrolysis method, and a resistive switching (RS) memory device has been constructed with it for the very first time. Herein, the edges of these large-area multilayer graphene sheets are highly conducting due to the turbostratic stacking between the adjacent layers of the graphene sheets. These highly conducting PTG sheets embedded inside an insulating polymer matrix can act as an active layer for resistive switching memory devices. This hybrid structure shows nonlinear resistance change between two distinct resistance states by simple bias voltage variation. The trap-assisted space-charge-limited conduction can realize the high resistive state (HRS), whereas the low resistive state (LRS) takes place through direct conduction. To achieve the best performing device, a number of optimizations have been performed, like the variation of polymer matrices, variation of PTG and polymer concentration, active layer thickness variation, and top electrode area variation. The best performing device showed reproducibility of current–voltage data (>200 cycles), low power consumption (SET voltage <1 V), a high ON/OFF ratio (>104), a long retention time (>104 s), and a large number of endurance cycles (>103). High writing-read-erase-read speed and flexibility/bending cycle tests were also carried out on the best-performing device to examine its tenacity. The current PTG-based flexible RS memory device derived from a biowaste, dead bougainvillea bracts, can provide an important step toward developing green electronics.

Transient thermal behaviour of high thermal conductivity graphene based composite materials: Experiments and theoretical models

High thermal conductivity composites could be a valid alternative to traditional materials in many engineering applications. This work presents the realization of high thermal conductivity composites based on multilayer graphene sheets (GS) impregnated with polydimethylsiloxane (PDMS). Three composite configurations were prepared: discs, slab, and roll. The in-plane and out-of-plane effective thermophysical properties of GS/PDMS composites have been measured. Thermal diffusivity has been measured by a homemade Flash Method (FM) and the density by a gravimetric method. Specific heat and thermal conductivity have been calculated. The experiment results showed that the GS/PDMS composite has an in-plane thermal conductivity up to 430 W m−1K−1 with a GS loading of 70 wt%, higher than standard metals used in heat exchangers (e.g. copper, aluminum). The out-of-plane effective thermal conductivity reached up to 1 W m−1K−1 with a GS loading of 95 wt%, comparable with other high thermal conductivity composites that work as thermal interface materials in electronic applications. Two analytical models to predict the effective thermophysical properties of the multiphase composites were developed and presented.

Rational Design of Layered MnO2@Graphene with Hierarchical Structure for Flexible Quasisolid‐State Aqueous Zinc‐Ion Battery via Laser Activation

AbstractAqueous zinc‐ion battery (AZIB) based on Zn//MnO2 is considered as one of the most promising energy storage devices. However, the poor Zn2+ storage kinetics and structural integrity of MnO2 affect its electrochemical performance. In this work, the vertically aligned multilayer graphene sheets (VGS) are in situ formed on the graphite paper via laser activation, and then MnO2 nanoflakes are coated on the VGS by electrochemical deposition, leading to the layered MnO2@graphene with hierarchical structure. The MnO2 nanoflakes coated on the VGS not only have improved charges transfer and structural integrity owing to the conductive skeleton, but also expose more accessible area to the electrolyte. In addition, the inner layer of graphite paper maintains its original structure, which can serve as current collector and endow the composite materials with good flexibility. In light of this rational design, the coin‐type AZIB assembled with layered MnO2@graphene as cathode shows a maximum capacity of 363.6 mAh g−1. Furthermore, a flexible quasisolid‐state AZIB is fabricated, which also exhibits superior electrochemical performance and flexibility (97.0% capacity retention after 1000 bending cycles). This work provides a feasible and effective strategy to develop flexible MnO2@graphene as cathode for high‐performance rechargeable Zn//MnO2 AZIB by rational design of the structure.

Eco-Friendly Synthesis of Wrinkle-Free Ultra-Flat Multi-Layer Graphene by Femtosecond Laser Irradiation of Graphite Under Ambient Conditions

Here, we report a single-step, high-yield technique for producing planar sheets of wrinkle-free multi-layer graphene (MLG) under ambient conditions by ablation of graphite powder dispersed in ethanol using a femtosecond laser. The parameters for the synthesis of MLG have been optimized and established. The number of layers and quality of MLG produced at several laser fluences (39.4 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 98.72 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 197.45 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 296.16 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) was established based on detailed characterization using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Wrinkle-free, ultra-flat crystalline MLG sheets with 2-12 layers were produced in each case with an average lateral dimension of ∼1-3 μm. The associated oxy- functional groups were characterized and quantified using FTIR and XPS. The highest percentage of sp <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C atoms and C/O ratio for MLG was achievedat the lowest laser fluence. The higher the laser fluence higher the defects produced in the MLG sheets. The technique produces zero chemical waste, has a very high yield of ∼ 95%, and is promising for bulk-scale production of MLG.

Extraction of Novel Effective Nanocomposite Photocatalyst from Corn Stalk for Water Photo Splitting under Visible Light Radiation

Novel (Ca, Mg)CO3&SiO2 NPs-decorated multilayer graphene sheets could be successfully prepared from corn stalk pith using a simple alkaline hydrothermal treatment process followed by calcination in an inert atmosphere. The produced nanocomposite was characterized by SEM, EDX, TEM, FTIR, and XRD analytical techniques, which confirm the formation of multilayer graphene sheets decorated by inorganic nanoparticles. The nanocomposite shows efficient activity as a photocatalyst for water-splitting reactions under visible light. The influence of preparation parameter variations, including the alkaline solution concentration, hydrothermal temperature, reaction time, and calcination temperature, on the hydrogen evolution rate was investigated by preparing many samples at different conditions. The experimental work indicated that treatment of the corn stalk pith hydrothermally by 1.0 M KOH solution at 170 °C for 3 h and calcinating the obtained solid at 600 °C results in the maximum hydrogen production rate. A value of 43.35 mmol H2/gcat.min has been obtained associated with the energy-to-hydrogen conversion efficiency of 9%. Overall, this study opens a new avenue for extracting valuable nanocatalysts from biomass wastes to be exploited in hot applications such as hydrogen generation from water photo-splitting under visible light radiation.

Preparation of Nitrogen-doped Holey Multilayer Graphene Using High-Energy Ball Milling of Graphite in Presence of Melamine.

Holey graphene, consisting of graphene sheets with in-plane nanopores, has recently attracted more attention as it expands graphene applications to other fields inaccessible by the pristine graphene. To ensure an effective implementation of holey graphene in the market, it is crucial to explore new preparation methods that are simple, cost effective, eco-friendly, versatile, and scalable. While ball milling of graphite in presence of exfoliating agents was found very effective in the preparation of graphene (doped and undoped) and graphene-composites, this technique remains unexplored for the preparation of holey graphene. In the present work, Nitrogen-doped multilayer holey graphene sheets were prepared by an all-solid, one-step procedure based on high-energy ball milling of graphite as the starting material in presence of melamine in a shaker-type mill for 1 hour under ambient conditions. Melamine acted simultaneously as an exfoliating agent to enhance the exfoliation of graphene layers and a diluent to protect graphite against the continuous fragmentation into amorphous carbon during the high-energy "shock" mode of ball milling. The high-energy "shock" mode of ball milling of graphite in presence of melamine induced the formation of multilayer defective graphene as an intermediate product before being converted into N-doped multilayer holey graphene after the removal of the in-plane defects during the milling process. The characterization of the final product confirmed the formation of N-doped multilayer holey graphene with a content in nitrogen as high as 12.96 at.%, making it promising for energy storage and energy conversion applications.

Electrically driven on-chip transferrable micro-LEDs

In this study, we report the experimental demonstration of electrically driven on-chip transferrable microdisk light-emitting diodes (LEDs). A vertical p–i–n doped AlGaInP microdisk, including multi-quantum-well structures, is top-down-fabricated, on-chip micro-transferred, and converted into single micro-LEDs. Optically transparent and mechanically flexible multilayered graphene sheets are judiciously designed and introduced to the top and bottom surfaces of a single microdisk, thereby forming the top and bottom contacts. Using electroluminescence measurements, the fabricated micro-LEDs are characterized; they exhibit diode-like transport behaviors, spectroscopic light-out vs current (L–I) characteristics, and polarization-resolved emission properties. We believe that the proposed all-graphene-contact approach offers a direct and easy current injection scheme and further helps electrify various on-chip transferrable microarchitectures.

Synthesis of high-quality graphene sheets via decomposition of non-condensable gases from pyrolysis of polypropylene waste using unsupported Fe, Co, and Fe–Co catalysts

Producing high-quality graphene sheets from plastic waste is regarded as a significant economic and environmental challenge. In the present study, unsupported Fe, Co, and Fe–Co oxide catalysts were prepared by the combustion method and examined for the production of graphene via a dual-stage process using polypropylene (PP) waste as a source of carbon. The prepared catalysts and the as-produced graphene sheets were fully characterized by several techniques, including XRD, H2-TPR, FT-IR, FESEM, TEM, and Raman spectroscopy. XRD, TPR, and FT-IR analyses revealed the formation of high purity and crystallinity of Fe2O3 and Co3O4 nanoparticles as well as cobalt ferrite (CoFe2O4) species after calcining Fe, Co, and Fe–Co catalysts, respectively. The Fe–Co catalyst was completely changed into Fe–Co alloy after pre-reduction at 800 °C for 1 h. TEM and XRD results revealed the formation of multi-layered graphene sheets on the surface of all catalysts. Raman spectra of the as-deposited carbon showed the appearance of D, G, and 2D bands at 1350, 1580, and 2700 cm−1, respectively, confirming the formation of graphene sheets. Fe, Co, and Fe–Co catalysts produced quasi-identical graphene yields of 2.8, 3.04, and 2.17 gC/gcat, respectively. The graphene yield in terms of mass PP was found to be 9.3, 10.1, and 7.2 gC/100gPP with the same order of catalysts. Monometallic Fe and Co catalysts produced a mix of small and large-area graphene nanosheets, whereas the bimetallic Fe–Co catalyst yielded exclusively large-area graphene sheets with remarkable quality. The higher stability of Fe–Co alloy and its carbide phase during the growth reaction compared to the Fe and Co catalysts was the primary reason for the generation of extra-large graphene sheets with relatively low yield. In contrast, the segregation of some metallic Fe or Co particles through the growth time was responsible for the growth small-area graphene sheets.