Few-layer Graphene Nanoflakes Research Articles

Adsorption of organic solvent vapours on carbon nanotubes, few-layer graphene nanoflakes and their nitrogen-doped counterparts

Adsorption of organic solvent vapours on carbon nanotubes, few-layer graphene nanoflakes and their nitrogen-doped counterparts

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

Abstract Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

Effect of Synthesis Conditions on Morphology, Structure, and Defectiveness of Few-Layer Graphene Nanoflakes

Effect of Synthesis Conditions on Morphology, Structure, and Defectiveness of Few-Layer Graphene Nanoflakes

The Discovery of Few-Layered Graphene Flakes in Paragenetic Association with Other Carbon Nano-sized Mineral Phases

Interstitial fibrous-matted micron-scale aggregates of few-layered graphene nano-flakes, multi-layered carbon nanotubes, fullerenes, and fullerenoids have been found between quartz and potassium feldspar grains of slag-like high temperature and shock-metamorphosed rocks (polymictous sandstones) of the Dzharakuduk area (Kyzyl-Kum Desert, Uzbekistan). This is the first finding of few-layered graphene nano-flakes as well as multi-layered carbon nanotubes (with ~10 A inner diameters) and their assemblages as mineral component of natural rocks. Amount of layers in natural few-layered graphene nano-flakes varied from 19 to 45. Mechanisms of few-layered graphene nano-flakes generation in natural rocks are discussed.

Synthesis of carbon nanoparticles in a non-thermal plasma process

A non-thermal plasma source based on magnetically stabilized gliding arc discharge (MSGAD) was used to prepare carbon nanoparticles via methane decomposition. Spherical carbon nanoparticles (SCNs), few-layer graphene nanoflakes (GNFs), and nitrogen-doped carbon nanoparticles were obtained. The results showed that the product microstructure was influenced by the buffer gas. In pure methane and argon, the products were a mixture of SCNs and GNFs. In helium and hydrogen, all products were highly crystalline GNFs with low defects, few layers, large BET surface areas, and excellent thermal stability. Under a nitrogen atmosphere, nitrogen-doped nanoparticles were formed, and the products were a mixture of GNFs, disordered graphitic layers, and tiny spots similar to carbon dots. The formation of GNFs was possibly related to the high input power and abundant hydrogen atoms, while the complex product morphology obtained under a nitrogen atmosphere was likely caused by the incorporation of nitrogen atoms.

Lightweight and Bulk Organic Thermoelectric Generators Employing Novel P-Type Few-Layered Graphene Nanoflakes.

Graphene exhibits both high electrical conductivity and large elastic modulus, which makes it an ideal material candidate for many electronic devices. At present not much work has been conducted on using graphene to construct thermoelectric devices, particularly due to its high thermal conductivity and lack of bulk fabrication. Films of graphene-based materials, however, and their nanocomposites have been shown to be promising candidates for thermoelectric energy generation. Exploring methods to enhance the thermoelectric performance of graphene and produce bulk samples can significantly widen its application in thermoelectrics. Realization of bulk organic materials in the thermoelectric community is highly desired to develop cheap, Earth-abundant, light, and nontoxic thermoelectric generators. In this context, this work reports a new approach using pressed pellets bars of few-layered graphene (FLG) nanoflakes employed in thermoelectric generators (TEGs). First, FLG nanoflakes were produced by a novel dry physical grinding technique followed by graphene nanoflake liberation using plasma treatment. The resultant material is highly pure with very low defects, possessing 3 to 5-layer stacks as proved by Raman spectroscopy, X-ray diffraction measurement, and scanning electron microscopy. The thermal and electronic properties confirm the anisotropy of the material and hence the varied performance characteristics parallel to and perpendicular to the pressing direction of the pellets. The full thermoelectric properties were characterized both parallel and perpendicular to the pressing direction, and the proof-of-concept thermoelectric generators were fabricated with variable amounts of legs.

Effects of hydrogen/carbon molar ratio on graphene nano-flakes synthesis by a non-thermal plasma process

Few-layer graphene nano-flakes (GNFs) are successfully prepared via hydrocarbon pyrolysis using a non-thermal plasma process based on a magnetically stabilized gliding arc discharge (MSGAD) at atmospheric pressure. The effects of feedstock gas type and hydrogen flow rate on the morphology of carbon nanomaterials are investigated. When the hydrogen/carbon (H/C) molar ratio is 4, the synthesized GNFs consist of 10 layers per stack with dimensions between 100 and 300 nm in a 4.57.2% yield. The energy cost is 0.1–0.2 kWh/g, which makes this process feasible for large-scale GNFs production. The results show that appropriately increasing the H/C molar ratio promotes the morphological transformation of carbon nanomaterials from spherical carbon nanoparticles (SCNs) to GNFs, improve the quality of GNFs and reduce the stacking of graphite layers. However, increasing the H/C ratio reduces the yields of carbon nanomaterials, so as to increase the energy cost. Analysis suggests that increasing the H/C ratio reduces the concentration of polycyclic aromatic hydrocarbon (PAH) and generates more H atoms, which helps form a two-dimensional nucleation and promotes planar growth. However, an excessive H/C ratio may introduce some defects due to an etching effect.

Graphene nanoflakes as effective dopant to Li-based greases

Lithium and complex lithium greases were modified by few-layer graphene nanoflakes. Tribological tests demonstrate improvement of the lubricating characteristics, e.g. increase of the welding load and decrease of the wear scar diameter after the modification. XPS method showed occurrence tribochemical reaction between lithium 12-hydroxystearate molecules and graphene nanoflakes surface during exploitation of the grease. It was shown that graphene nanoflakes are corrosion-inactive in lubricating compositions and compatible with modern additive packages.

Mechanism and kinetics of decomposition of N-containing functional groups in few-layer graphene nanoflakes

Doping of graphene-based nanomaterials with heteroatoms is a flexible and widely used approach to modify their electronic structure and chemical properties. Applications of these doped materials may imply thermal treatment, so this work was devoted to the transformations of nitrogen-containing functional groups during heating. Jellyfish-like few-layer graphene nanoflakes with the bulk and surface localization of N-groups were synthesized by different techniques: CVD growth, post-doping, CVD growth followed by oxidation, and nitric acid treatment. Synthesized materials contained a wide range of N-functionalities. The mechanism of their thermal transformations and decomposition was studied using XPS and TGA–MS. The activation energies for the decomposition of different nitrogen-containing groups were estimated by the Kissinger method.

Continuous synthesis of graphene nano-flakes by a magnetically rotating arc at atmospheric pressure

A novel approach for the preparation of few-layer graphene nano-flakes (GNFs) is presented in this paper. The GNFs are continuously synthesized by thermal decomposition of hydrocarbons using a magnetically rotating arc at atmospheric pressure. The effects of magnetic field, arc current, feedstock gas flow rate, and feedstock gas type on the morphologies and microstructures of pyrolysis products are investigated and discussed. Results show that the microscopic characteristics of pyrolysis products are affected by the operating parameters. High temperature and high hydrogen concentration are considered the essential condition for the formation of GNFs. The synthesized GNFs are agglomerative flakes, where each flake is between 50 and 300 nm. Material analyses indicates that the GNFs have excellent properties such as a good crystalline structure, a low number of layers, and a large specific surface area. This indicates that the GNFs could be applied in fuel cells and energy storages. This method is suitable for mass production of few-layer GNFs since it is a continuous process with a relatively high yield (∼14%) and a relatively low energy cost (∼0.4 kWh/g).

Photocatalytic performance of few-layer Graphene/WO3 thin films prepared by a nano-particle deposition system

Abstract The nano-particle deposition system (NPDS) is an environmentally friendly, room temperature, dry particle deposition technique to impart thin films of metal or ceramic particles onto different substrates without any additional chemicals. In this work, graphite and WO3 powders with different graphite contents (0–30 wt%) were successfully deposited on a polypropylene substrate by an NPDS without generating any thermal damage of the substrate. The graphite particles can easily be fragmented into small few-layer graphene nano-flakes along with WO3 utilizing the high kinetic energy during NPDS. With field emission scanning electron microscopy, fragmentation of particles due to the high impact velocity of the powders during deposition was observed. X-ray diffraction showed the absence of any graphite peak in the composite thin film. Finally, the existence of few-layer graphene in the fabricated thin film was confirmed by Raman spectroscopy. To evaluate the photocatalytic activity of the fabricated thin films, degradation of methylene blue dye under illumination of light for 2 h was observed. Degradation of the dye was evaluated using absorbance values measured by UV/Vis spectroscopy before and after the test. The results showed that the photocatalytic performance was significantly enhanced when the WO3 contained added graphite and suggested that 15 wt% of graphite was the optimal level in the composite thin film. The photocatalytic reaction followed pseudo-first-order kinetics. Repeatability determines the feasibility of thin films in using real applications. Here, all the thin films showed good stability up to five cycles. The few-layer graphene/WO3 composite thin films were easily prepared for the photocatalytic application using NPDS.

Pell-Shear-Exfoliation of few-layer graphene nanoflakes as an electrode in supercapacitors

Introduction: The graphene has received a great attention becauseof its extraordinary characteristics of high carrier mobility, excellent thermal conductivity, high optical transmittance, and superiormechanical strength. Developing a simple methods with the property of producing large quantities of high-quality graphene havebecome essential for electronics, optoelectronics, composite materials, and energy-storage applications. Materials and Methods: Inthis study, the simple one step and efficient method of grindingwas used to produce few-layers graphene nanoflakes from graphite.Different microscopic (TEM, SEM, and AFM) and spectroscopics(XRD, XPS, and Raman) charactrization tools were used to testthe quality of the resultant graphene nanoflakes. Results: The produced nanoflakes showed no traces of oxidation due to the grindingprocess. In addition, the applicability of the obtained nanoflakes aspotential supercapacitor electrodes was investigated. For that purpose, thin films of the few-layer graphene nanoflakes were developed using spray coating technique. In terms of both transparencyand conductivity, the prepared films showed equivalent propertiescompared to those prepared by more complex methods. The electrochemical properties of the prepared electrodes showed highspecific capacitance of 86 F g_1 at 10 A g_1 with excellent stability.The electrodes sustained their original capacity for more than 7000cycles and started reducing to 72 F g-1 after 10000 cycles. Conclussions: The method provides a simple, efficient, versatile, andeco-friendly approach to low-cost mass production of high-qualitygraphene few-layers. The electrochemical stability and flexibility ofthe developed thin films indicated that the films could be used aselectrodes in a wide range of electronic applications.

Electrochemical Performance of Few-Layer Graphene Nano-Flake Supercapacitors Prepared by the Vacuum Kinetic Spray Method

A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene nano-flakes using a nanoparticle deposition system (NPDS). The NPDS allows for a large area deposition at a low cost and can deposit various metal oxides at room temperature and low vacuum conditions. The morphology and structure of the deposited thin films are alterable by changing the scan speed of the deposition. These changes were verified by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electrochemical performances of the supercapacitors, fabricated using the deposited films and H3PO4–PVA gel electrolytes with different concentrations, were measured using a 2-electrode cell. The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic Charge–discharge, and electrochemical impedance spectroscopy. The proposed affordable fabricated supercapacitors show a high areal capacitance and a small equivalent series resistance.

High surface graphene nanoflakes as sensitive sensing platform for simultaneous electrochemical detection of metronidazole and chloramphenicol

We demonstrate a mediator-free electrochemical sensitive sensing for detection of metronidazole (MNZ) and chloramphenicol (CAP) in real samples. A few-layered defect-free graphene nanoflakes (GNFs) were synthesized by surfactant-assisted exfoliation method, which was characterized by several methods like XRD, Raman spectroscopy, FE-SEM and TEM images. Cyclic voltammetry and electrochemical impedance spectroscopy were studied to understand the electron transfer behavior of GNFs modified glassy carbon electrode (GCE). Electrochemical behavior of MNZ and CAP was investigated at GNFs/GCE in PBS and observed peak potentials at −0.32 V and − 0.51 V vs. Ag/AgCl. A wider reduction potential window of MNZ and CAP were observed by differential pulse voltammetry which was found to be 280 mV at GNFs/GCE. Amperometry method was employed for detection of the unknown concentration of analytes under hydrodynamic condition. A linear calibration plot was obtained by plotting the concentrations of MNZ and CAP in ranging from 0.5 to 5.5 nM with R2 of 0.9983 and 0.9980, respectively. The detection limit of MNZ and CAP were found to be 0.15 nM and 0.38 nM, this system have shown good stability, excellent reproducibility and free interference from GNFs/GCE. The present method was successfully applied for the determination of MNZ and CAP in drugs and urine samples.

Biological recognition of graphene nanoflakes

The systematic study of nanoparticle–biological interactions requires particles to be reproducibly dispersed in relevant fluids along with further development in the identification of biologically relevant structural details at the materials–biology interface. Here, we develop a biocompatible long-term colloidally stable water dispersion of few-layered graphene nanoflakes in the biological exposure medium in which it will be studied. We also report the study of the orientation and functionality of key proteins of interest in the biolayer (corona) that are believed to mediate most of the early biological interactions. The evidence accumulated shows that graphene nanoflakes are rich in effective apolipoprotein A-I presentation, and we are able to map specific functional epitopes located in the C-terminal portion that are known to mediate the binding of high-density lipoprotein to binding sites in receptors that are abundant in the liver. This could suggest a way of connecting the materials' properties to the biological outcomes.

Jellyfish-like few-layer graphene nanoflakes: Synthesis, oxidation, and hydrothermal N-doping

Few-layer graphene nanoflakes with the bent edges, diameter of 15–40 nm and thickness of 6–7 graphene layers have been synthesized using MgO-templated CVD growth. Their oxidation by nitric acid led to the high oxygen content of 18 at.%, a third of which was attributed to carboxylic groups. Oxidized nanoflakes were post-doped by nitrogen groups using hydrothermal treatment at 220 °C with ammonia and urea water solutions resulting in corresponding nitrogen content of 7 and 5 at.%. Synthesized and treated materials were characterized by XPS, Raman spectroscopy and electron microscopy.

Kinetics of the defunctionalization of oxidized few-layer graphene nanoflakes

Thermal defunctionalization of oxidized jellyfish-like few-layer graphene nanoflakes was studied under non-isothermal conditions by simultaneous thermal analysis. Activation energies for thermal decomposition of different oxygen functional groups were calculated by the Kissinger method and compared with those for oxidized carbon nanotubes. Oxygen content in graphene nanoflakes was found to significantly affect the decomposition activation energies of carboxylic and keto/hydroxy acids because of their acceptor properties and strong distortion of the graphene layers at the edges of the nanoflakes. The structure of the carbon material and the oxygen chemical state significantly influence the decomposition kinetics of thermally stable oxygen-containing groups. The activation energy for thermal decomposition of phenol groups (110-150 kJ mol-1) is close to that for graphene oxide reduction.

Tuning the Electronic and Magnetic Properties of Nitrogen-Functionalized Few-Layered Graphene Nanoflakes

In this article, we report the modification of the electronic and magnetic properties of few-layered graphene (FLG) nanoflakes by nitrogen functionalization carried out using radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) and electron cyclotron resonance (ECR) plasma processes. Even though the rf-PECVD N2 treatment led to higher N-doping levels in the FLG (4.06 atomic %) as compared to the ECR process (2.18 atomic %), the ferromagnetic behavior of the ECR FLG (118.62 × 10–4 emu/g) was significantly higher than that of the rf-PECVD FLG (0.39 × 10–4 emu/g) and pristine graphene (3.47 × 10–4 emu/g). Although both plasma processes introduce electron-donating N atoms into the graphene structure, distinct dominant nitrogen bonding configurations (pyridinic, pyrrolic) were observed for the two FLG types. Whereas the ECR plasma introduced more sp2-type nitrogen moieties, the rf-PECVD process led to the formation of sp3-coordinated nitrogen functionalities, as confirmed through Raman measurem...

Enhanced and Stable Field Emission from in Situ Nitrogen-Doped Few-Layered Graphene Nanoflakes

Vertically aligned few-layered graphene (FLG) nanoflakes were synthesized on bare silicon (Si) substrates by a microwave plasma enhanced chemical vapor deposition method. In situ nitrogen (N2) plasma treatment was carried out using electron cyclotron resonance plasma, resulting in various nitrogen functionalities being grafted to the FLG surface. Compared with pristine FLGs, the N2 plasma-treated FLGs showed significant improvement in field emission characteristics by lowering the turn-on field (defined at 10 μA/cm2) from 1.94 to 1.0 V/μm. Accordingly, the field emission current increased from 17 μA/cm2 at 2.16 V/μm for pristine FLGs to about 103 μA/cm2 at 1.45 V/μm for N-doped FLGs. Furthermore, N-doped FLG samples retained 94% of the starting current over a period of 10 000 s, during which the fluctuations were of the order of ±10.7% only. The field emission behavior of pristine and N2 plasma-treated FLGs is explained in terms of change in the effective microstructure as well as a reduction in the work function as probed by X-ray photoelectron valence band spectroscopy.