Few-layer Graphene Nanosheets Research Articles

Two-photon absorption and negative nonlinear refraction in few-layer graphene nanosheets suspensions via liquid-phase exfoliation

Two-photon absorption and negative nonlinear refraction in few-layer graphene nanosheets suspensions via liquid-phase exfoliation

Recent Progress of Vertical Graphene: Preparation, Structure Engineering, and Emerging Energy Applications.

Vertical graphene (VG) nanosheets have garnered significant attention in the field of electrochemical energy applications, such as supercapacitors, electro-catalysis, and metal-ion batteries. The distinctive structures of VG, including vertically oriented morphology, exposed, and extended edges, and separated few-layer graphene nanosheets, have endowed VG with superior electrode reaction kinetics and mass/electron transportation compared to other graphene-based nanostructures. Therefore, gaining insight into the structure-activity relationship of VG and VG-based materials is crucial for enhancing device performance and expanding their applications in the energy field. In this review, the authors first summarize the fabrication methods of VG structures, including solution-based, and vacuum-based techniques. The study then focuses on structural modulations through plasma-enhanced chemical vapor deposition (PECVD) to tailor defects and morphology, aiming to obtain desirable architectures. Additionally, a comprehensive overview of the applications of VG and VG-based hybrids d in the energy field is provided, considering the arrangement and optimization of their structures. Finally, the challenges and future prospects of VG-based energy-related applications are discussed.

Biomass-Derived Carbonaceous Materials with Graphene/Graphene-Like Structures: Definition, Classification, and Environmental Applications.

Biomass-derived carbonaceous materials with graphene/graphene-like structures (BGS) have attracted tremendous attention in the field of environmental remediation. The introduction of graphene/graphene-like structures into raw biochars can effectively improve their properties, such as electrical conductivity, surface functional groups, and catalytic activity. In 2021, the International Organization for Standardization defined graphene as a "single layer of carbon atoms with each atom bound to three neighbours in a honeycomb structure". Considering this definition, several studies have incorrectly referred to BGS (e.g., biomass-derived few-layer graphene or porous graphene-like nanosheets) as "graphene". The definitions and classifications of BGS and their applications in environmental remediation have not been assessed critically thus far. Comprehensive analysis and sufficient and robust evidence are highly desired to accurately determine the specific structures of BGS. In this perspective, we provide a systematic framework to define and classify the BGS. The state-of-the-art methods currently used to determine the structural properties of BGS are scrutinized. We then discuss the design and fabrication of BGS and how their distinctive features could improve the applicability of biomass-derived carbonaceous materials, particularly in environmental remediation. The environmental applications of these BGS are highlighted, and future research opportunities and needs are identified. The fundamental insights in this perspective provide critical guidance for the further development of BGS for a wide range of environmental applications.

Synthesis and characterization of graphene via electrochemical exfoliation technique and study its electrochemical properties

In this study, we present a one-pot approach for the large-scale synthesis of multilayer to few-layer graphene nanosheets in an aqueous medium that is cost-effective, environmentally friendly, high-yielding, and simple. This electrochemical exfoliation method produces low defect and high yield graphene nanosheet products and is more efficient than chemical exfoliation methods. Two highly oriented pyrolytic graphite plates (HOPG) are utilized as the anode and cathode in this method, which also incorporates two electrode geometry configurations. XRD, HRTEM, AFM, XPS, and Raman spectroscopy are used to describe graphene nano-sheets. Raman characterization supports graphene’s inherent qualities. By using cyclic voltammetry, the electrochemical performance of the produced nano-sheets is evaluated.

Enhancement of corrosion resistance by electrophoresed graphene obtained through ionic solution based electrochemical exfoliation

The present work describes the electrochemical synthesis of few layer graphene nanosheets (FLGNs) through a green, non-toxic route in an ionic solution having four different stoichiometric solutions. The FLGNs have been characterized by X-ray diffraction, UV, RAMAN and FTIR to understand the chemical structure. UV, FTIR and EDS exhibited the presence of functional groups. The average particle size of FLGNs measured through DLS was in the range of 300–450 nm with good stability behaviour as seen through zeta potential measurements. SEM, TEM and AFM depict a layered morphology of the FLGNs. The synthesized graphene was electrophoretically deposited onto copper with different iterations i.e. time and number of layers and corrosion tests as well as EIS analysis of the coated copper was conducted in 0.6 M NaCl solution. SEM micrographs show layer-upon-layer deposition of graphene on copper substrate. Polarization tests and impedance measurements highlighted the efficiency of graphene as a barrier against corrosion in comparison to uncoated substrate. Authors also made an attempt to understand the effect of different layers of the coating on the substrate and its protection ability. It was found that 2 layered coatings offered better resistance in comparison to others. On an overall note, it can be stated that the choice of graphene for corrosion prevention is justified with the need for further exploration.

Continuous Production of Functionalized Graphene Inks by Soft Solution Processing.

The continuous production of high-quality, few-layer graphene nanosheets (GNSs) functionalized with nitrogen-containing groups was achieved via a two-stage reaction method. The initial stage produces few-layer GNSs by utilizing our recently developed glycine-bisulfate ionic complex-assisted electrochemical exfoliation of graphite. The second stage, developed here, uses a radical initiator and nitrogen precursor (azobisisobutyronitrile) under microwave conditions in an aqueous solution for the efficient nitrogen functionalization of the initially formed GNSs. These nitrile radical reactions have great advantages in green chemistry and soft processing. Raman spectra confirm the insertion of nitrogen functional groups into nitrogen-functionalized graphene (N-FG), whose disorder is higher than that of GNSs. X-ray photoelectron spectra confirm the insertion of edge/surface nitrogen functional groups. The insertion of nitrogen functional groups is further confirmed by the enhanced dispersibility of N-FG in dimethyl formamide, ethylene glycol, acetonitrile, and water. Indeed, after the synthesis of N-FG in solution, it is possible to disperse N-FG in these liquid dispersants just by a simple washing-centrifugation separation-dispersion sequence. Therefore, without any drying, milling, and redispersion into liquid again, we can produce N-FG ink with only solution processing. Thus, the present work demonstrates the 'continuous solution processing' of N-FG inks without complicated post-processing conditions. Furthermore, the formation mechanism of N-FG is presented.

Nonstationary thermophysical characterization of exfoliated graphite with carbon nanotubes composites

The sheet samples of thermally exfoliated graphite (TEG)–carbon nanotubes (CNT) composites (TEG-CNT-cs) were obtained by persulphate oxidation using chemical (CO) and electrochemical (anode) oxidation (ECAO). Electron microscopy reveals multi-layered structures of few-layer graphene nanosheets with folded and tubular-like fragments. The effective thermal diffusivity values were estimated by nonstationary photo-pyroelectric thermophysical characterization using the heat pulse and thermowave modulation methods. Comparison with other carbon (C-) based thermal management materials shows that TEG-CNT-cs exhibit thermal diffusivity, effusivity, and conductivity comparable with those of actual C–polymer- and C–C-composites. For TEG-CNT-cs, evaluated values of phonon mean free path (MFP) and relaxation time (RT) are in the ranges estimated for defective graphene. The values of diffusivity and effusivity, MFP, and RT are lower for denser TEG-CNT-cs obtained by ECAO and are higher for less dense TEG-CNT-cs obtained by CO. The obtained diffusivity and effusivity values designate TEG-CNT-cs as suitable thermal management materials.

Preparation and optical-electronic properties of thin films comprising P3HT and few-layer graphene nanosheets

The present work investigates the production of thin films from nanocomposites obtained by solution mixing a synthesized P3HT with different proportions of few-layered graphene (FLG) in chloroform and its influence on crystallography and light absorption in the visible region. Commercial FLG produced through exfoliation in the liquid phase assisted by a non-anionic surfactant was employed, being a material not yet tested for the production of nanocomposites, let alone to be applied in photovoltaic cells. The deposition of thin films was evaluated at low (1000 rpm) and high (2500 rpm) rotation speeds in a dynamic and static deposition process. In addition, the annealing heat treatment in the optimized thin films was evaluated. The results showed that the P3HT was synthesized with suitable molar mass, regioregularity, and thermal resistance as characterized by the analyses of gel permeation chromatography (GPC), 1H-nuclear magnetic resonance (1H NMR), and thermogravimetric analysis (TGA). The thin films produced showed that the FLG enlarged and strengthened the P3HT absorption, increasing the absorption region by up to 34 % in addition to improving the resolution of the absorption peaks favoring the π-π* transition, which is important for the photovoltaic effect. By the X-ray diffraction analysis, it can be suggested that incorporating the FLG improves the charge mobility as there was an increase in the crystallite size without changing the interplanar distance. Based on these results, it can be suggested that P3HT/FLG nanocomposites are promising for application in both the active and hole transport layers of solar cells.

Highly effective electromagnetic interference shielding composites with solvent-dispersed uniformly aligned graphene nanosheets enabled by strong intrinsic diamagnetism under magnetic field

Graphene nanosheets (GNS) have been regarded as one of the best fillers in polymers for electromagnetic interference (EMI) shielding composites, but it remains a challenge to prepare well-dispersed and highly aligned GNS for optimal EMI shielding despite many recently developed methods. Here we demonstrate a new technology that not only enables uniform alignment of GNS in polymer composites in any direction but also allows us to systematically tune the composites for optimal EMI performance. The technique makes use of graphene's strong intrinsic and anisotropic diamagnetic susceptibility. Unlike paramagnetism and ferromagnetism, diamagnetism allows us to fully control the orientation of GNS by a rotating magnetic field without causing any aggregation or introducing unwanted magnetic particles due to the repulsive force between GNS. This process for GNS composites further enables us to systematically modify GNS concentration and polymer matrix besides GNS orientations. A record-high shielding effectiveness (SE) of 95 dB is achieved with industrially mass-produced multilayer GNS aligned parallel to the surface of a mixed polyvinylidene fluoride-epoxy composite, and a 50% higher SE is further achieved with few-layer GNS. This technique is scalable, thus opening the practical applications of graphene in EMI shielding.

ZnO/Graphene Composite from Solvent-Exfoliated Few-Layer Graphene Nanosheets for Photocatalytic Dye Degradation under Sunlight Irradiation.

ZnO/graphene nanocomposites were prepared using a facile approach. Graphene nanosheets were prepared by ultrasonication-based liquid phase exfoliation of graphite powder in a low boiling point organic solvent, 1,2-Dichloroethane, for the preparation of ZnO/graphene nanocomposites. Structural properties of the synthesized ZnO/graphene nanocomposites were studied through powder XRD and micro-Raman analysis. The characteristic Raman active modes of ZnO and graphene present in the micro-Raman spectra ensured the formation of ZnO/graphene nanocomposite and it is inferred that the graphene sheets in the composites were few layers in nature. Increasing the concentration of graphene influenced the surface morphology of the ZnO nanoparticles and a flower shape ZnO was formed on the graphene nanosheets of the composite with high graphene concentration. The efficiencies of the samples for the photocatalytic degradation of Methylene Blue dye under sunlight irradiation were investigated and 97% degradation efficiency was observed. The stability of the nanocomposites was evaluated by performing five cycles, and 92% degradation efficiency was maintained. The observed results were compared with that of ZnO/graphene composite derived from other methods.

On the gas-phase graphene nanosheet synthesis in atmospheric microwave plasma torch: Upscaling potential and graphene nanosheet‑copper nanocomposite oxidation resistance

Efficient gas-phase synthesis of few-layer graphene nanosheets (GNS) is based on the controlled formation of the high-temperature environment and the reaction pathway of gas-phase species formed by the decomposition of organic precursors. Such a process results in the formation of high-quality carbon nanomaterial and hydrogen while the concentration of other gaseous by-products is minimized. In this work, the main factors affecting the efficiency of such processes in the TIAGO microwave plasma torch were investigated using detailed material analysis and mass spectrometry of the gas-phase products during the synthesis process. The results showed a limiting effect of increasing the microwave power (MW) on both the product yield as well as material quality, as shown by Raman and x-Ray photoelectron spectroscopy. The change in the reaction pathway increased the formation of C2H4, resulting in the upper limit of the achievable nanopowder yield. The prepared material showed a decrease in its high oxidation resistance, with increasing the delivered MW power as determined by thermogravimetry analysis. This behavior was related to the formation of GNS-Cu nanoparticles composite due to the presence of copper nanoparticles originating from erosion of the electrode of the TIAGO torch during the synthesis process at high MW powers.

Few layer graphene nanosheets from kinnow peel waste for high-performance supercapacitors: A comparative study with three different electrolytes

Utilization of carbonaceous waste into energy storage applications not only solves the problem of waste management but also promotes the circular economy. Any carbonaceous material with a high surface area and sheet-like nanostructure facilitates fast-ion transport due to which it can act as a suitable candidate for the electrode material in Supercapacitors. This work reports the preparation of few-layer graphene nanosheets from fruit waste: kinnow peel waste (KPW) for the first time, via two-step pyrolysis with activation using KCl as the activating agent followed by probe sonication. The confirmation of few-layer graphene (FLG) nanosheets from KPW was done with the help of RAMAN, XRD, FT-IR, SEM, and TEM. The high surface area with the presence of both the meso and micropores in synthesized FLG nanosheets was confirmed with the help of BET. The KPW-derived few-layer graphene (KPW-FLG) nanosheets were further investigated for high-performance supercapacitors by fabricating three different supercapacitor devices (SCs); SC-1, SC-2, and SC-3 corresponded to 6 M KOH, 1 M H2SO4 and 1 M H3PO4 respectively. The ideal and reversible capacitive behavior of the fabricated SC devices was analyzed with the help of Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. The SC-2 displayed the highest gravimetric specific capacitance (Cs) value of 642 F/g at a scan rate of 5 mV/s in a 1 M H2SO4 electrolyte with the highest energy density of 48.9 Wh/Kg and better power density of 629.5 W/Kg. Our study revealed that the KPW-FLG can be used as the potential candidate for electrode material in fabricating the high-performance supercapacitor which showed the best results in capacitance, charge-discharge, cyclic stability, and energy density with 1 M H2SO4 electrolyte.

Investigation on the In Situ Ti2AlC/TiAl Composite with a Homogenous Architecture by Adding Graphene Nanosheets.

The Ti2AlC/TiAl composite with a homogenous architecture was fabricated via spark plasma sintering (SPS) using Ti/Al/GNSs composite powders, after ultrasonic mechanical stirring, as raw materials. The phases, microstructure, compressive properties and Vickers hardness of the composite were methodically characterized. We observed the transformation of graphene nanosheets from multi-layer to few-layer by the ultrasonic dispersion and the uniform distribution of few-layer graphene nanosheets in composite powders by ultrasonic mechanical stirring. The composite is mainly composed of rod-shaped Ti2AlC particles and a TiAl matrix, and the formation of rod-shaped morphology with the long axis along the (0001) plane is due to the fact that the growth rate of Ti2AlC parallel to the (0001) plane is much higher than the growth rate along the [0001] direction. The compressive stress and strain of the as-prepared Ti2AlC/TiAl composite reach 1451.2 MPa and 19.7%, respectively, which are better than some Ti2AlC/TiAl composites using graphite as the carbon source, and the Vickers hardness remains between 400~500 HV. The fracture morphologies show the deformation and fracture features of Ti2AlC particles, i.e., lamellae kinking and laminated tearing, which could increase the toughness of TiAl alloys.

Cost-Effective Fabrication of High-Density Polyethylene/Graphene Nanocomposites by an In Situ Exfoliation Method Based on a Series Explosion Effect

As ideal nanofillers, graphene nanosheets (GNS) are widely used to prepare high-performance graphene-reinforced nanocomposites owing to their excellent properties. However, the high manufacturing cost and low production efficiency of GNS severely restrict their large-scale application. Herein, a cost-effective melt blending approach was demonstrated for facilely preparing high-density polyethylene (HDPE)/GNS nanocomposites by using industrial-grade expanded graphite (EG). The exfoliation and dispersion of GNS in the matrix under different processing temperatures and times have been studied. A series explosion effect generated by the synergy of volumetric extensional rheology and free water can violently and fastly exfoliate pristine EG into few-layer GNS. The in situ exfoliation mechanism revealed that the synergistic effect of the explosive forces of free water and the adhesion between HDPE and GNS can destroy the van der Waals forces between the EG sheets during melt blending, thereby realizing ultrafast exfoliation and uniform dispersion of EG in the HDPE matrix. As expected, the HDPE/GNS nanocomposites showed high crystallinity, excellent thermal conductivity, high dielectric constant, and extremely low dielectric loss. This work provides a new idea for facilely fabricating high-performance polymer-based two-dimensional layered nanocomposites.

New Way of Synthesis of Few-Layer Graphene Nanosheets by the Self Propagating High-Temperature Synthesis Method from Biopolymers.

For the first time, few-layer graphene (FLG) nanosheets were synthesized by the method of self-propagating high-temperature synthesis (SHS) from biopolymers (glucose, starch, and cellulose). We suggest that biopolymers and polysaccharides, particularly starch, could be an acceptable source of native cycles for the SHS process. The carbonization of biopolymers under the conditions of the SHS process was chosen as the basic method of synthesis. Under the conditions of the SHS process, chemical reactions proceed according to a specific mechanism of nonisothermal branched-chain processes, which are characterized by the joint action of two fundamentally different process-accelerating factors—avalanche reproduction of active intermediate particles and self-heating. The method of obtaining FLG nanosheets included the thermal destruction of hydrocarbons in a mixture with an oxidizing agent. We used biopolymers as hydrocarbons and ammonium nitrate as an oxidizing agent. Thermal destruction was carried out in SHS mode, heating the mixture in a vessel up to 150–200 °C at a heating speed of 20–30 °C/min and keeping at this temperature for 15–20 min with the discharge of excess gases into the atmosphere. A combination of spectrometric research methods, supplemented by electron microscopy data, has shown that the particles of the carbonated product powder in their morphometric and physical parameters correspond to FLG nanosheets. An X-ray diffraction analysis of the indicated FLG nanosheets was carried out, which showed the absence of formations with a graphite crystal structure in the final material. The surface morphology was also studied, and the IR absorption features of FLG nanosheets were analyzed. It is shown that the developed SHS method makes it possible to obtain FLG nanosheets with linear dimensions of tens of microns and a thickness of not more than 1–5 graphene layers (several graphene layers).

Decoration of graphene sheets with silver nanoparticles and their characterization

Graphene has been an emerging area of research since last decade. This fantastic material promises a wide variety of applications starting from electronics to biomedical fields. The properties of graphene can be enhanced by conjugating it with various other elements. The present work describes about the deposition of silver nano-particles via chemical synthesis onto in-house synthesized graphene nanosheets. It can be pointed out that application of infrared accelerates the synthesis process. Few layered graphene nanosheets (FLGNs) has been synthesized through electrochemical exfoliation technique. The colloidal graphene solution stabilized by citrate ions helps in the chemical reduction of AgNO3, which is essential in the formation of a nano-sized silver particulate layer (Ag NPs) over the graphene sheets. The presence of Ag NPs over the as-synthesized graphene was established by XRD, UV–VIS, FE-SEM and STM studies. The change in colloidal stability for the as-synthesized graphene and Ag NPs coated graphene was explained by the dynamic light scattering studies. The electronic characteristics of graphene coated Ag NPs was studied by scanning tunneling spectroscopy (STS) technique. The STS studies revealed that graphene with various numbers of coupled layers is responsible for the variations in the density of states (DOS) pattern. For Ag NPs-FLGNs, the spatial variations in the DOS spectra can be correlated to the size effects of the Ag NPs over the FLGNs. The local density of states (LDOS) spectra originates from the quantized electronic structure of the Ag NPs–FLGs system.

Phenomenological model of synthesis of few-layer graphene (FLG) by the selfpropagating high-temperature synthesis (SHS) method from biopolymers

A phenomenological model for the synthesis of few-layer graphene (FLG) nanosheets by the method of self-propagating high-temperature synthesis (SHS) from starch, lignin, and other biopolymers is considered. We suggested that polysaccharides, in particular starch, could be an acceptable source of native cycles for the SHS process. The carbonization of biopolymers under the conditions of the SHS process was chosen as the basic method of synthesis. Chemical reactions, under the conditions of the SHS process, proceed according to a specific mechanism of nonisothermal branched-chain processes, which are characterized by the joint action of two fundamentally different process-accelerating factors - avalanche reproduction of active intermediate particles and self-heating. It is shown that the proposed model can explain the production of few-layer graphene nanosheets with linear dimensions of tens of microns and a thickness of several graphene layers.

Green Synthesis of Clean Edge Graphene Nanosheets Using Natural Precursor

Graphene, a two-dimensional crystalline allotrope of carbon, has received greater attention from numerous researchers due to its excellent properties. Graphene could be produced by various techniques, each method has its advantages and disadvantages. In this research article, a novel method using agricultural waste rice husk as a precursor and chemical activation to produce few-layer graphene nanosheets was developed. Traditional approaches significant shortcomings and the environmental concern of agricultural waste have been eliminated. The synthesized material was characterized using FESEM, Raman Spectroscopy, X-Ray diffractometer, UV-Vis absorbance and FTIR analysis. FESEM analysis of the surface morphology revealed smooth edge few-layer graphene. The formation of sp2 hybridized atoms can be seen in XRD spectra at 26.3 degrees. The C=C stretching bonds detected at 1612 cm-1 wavelength are responsible for the graphitic structure.

Hydrodynamic cavitation for scalable exfoliation of few-layered graphene nanosheets

A scalable manufacturing method for the production of biocompatible fewlayered graphene nanosheets is developed using hydrodynamic cavitation. Scalable exfoliation is induced by employing hydrodynamic cavitation and a serum albumin protein. Unlike acoustic cavitation, the primary means of bubble collapse in hydrodynamic cavitation is caused laterally, thereby separating two adjacent flakes through a shear effect. In this process, bovine serum albumin, a known protein, was employed to act as an effective exfoliation agent and provide desired stability by preventing restacking of the graphene layers. This method was used to study the effect of time of graphene exfoliation in a novel hydrodynamic cavitation system. The fabricated products were characterized using Raman spectroscopy, Transmission electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. The results showed that with increasing the time of exfoliation, the number of graphene layers decreased based on the I 2D/I G ratio but disorder increased based on the I D/I G ratio. At 3 h, the I 2D/I G ratio was at 0.39 and the I D/I G ratio was 0.25, while at 6 h the I 2D/I G ratio was 0.35 and I D/I G ratio was 0.29. The results of the theoretical and computational analysis this research outlines are needed to obtain an effective cavitation model that can be used to potentially improve graphene synthesis and quality. The captured images of bubble propagation in the solution imply that this fluidic phenomenon could assist the graphene exfoliation. To prove this, a simple cavitation model using a needle valve was designed. The needle valve cavitation setup was able to identify that cavitation assists in graphene exfoliation and this was proved using the graphene characterization data. Based on these findings, the simulation models were designed in ANSYS and COMSOL. Specifically, through the ANSYS simulation, we were able to calculate cavitation numbers for specific flow rates and fluid temperatures.

Graphene nanosheets from hazardous/solid wastes: An efficient CO2 capture material

Highly efficient CO2 capture at elevated temperatures has been achieved with a few-layered graphene nanosheets (GNS) prepared from solid waste generated from high energy explosive materials manufacturing industry. These materials were used to adsorb CO2 from simulated industrial flue gases with an aim to reduce CO2 concentration in the atmosphere. The GNS is a microporous material with pore volume of 0.59 cm3 g−1 and 70% of pores were of average size of 0.55 nm. The surface area of GNS was 964 m2 g−1 which was reduced to 268 m2 g−1 when the number of layers in GNS increased to >50. The adsorption capacity of 3.89 mmol g−1 was achieved at 303 K/0.5 bar and this adsorption capacity was further increased to 23.63 mmol g−1 at 303 K/20 bar. The Sips adsorption model was used for evaluating the relationship between surface heterogeneity of GNS and adsorption capacity at temperature. The GNS materials selectively captured CO2 in the presence of gases mixtures (CO2/N2 and CO2/CH4). The fast adsorption kinetics and recycling stability of GNS for about 20 cycles suggests that the solid adsorbents prepared in this study are efficient and technically feasible to capture CO2 from industrial stacks and other real-life situations.