Graphene Particles Research Articles

Цепочечная модель декорирования зигзагообразной кромки графена

AbstractFor a brick-wall-like lattice topologically equivalent to the graphene lattice, a simple structural model of a zigzag edge decorated with particles is constructed. Analytical expressions for the energy band spectrum, densities of states, and occupation numbers of the graphene–particles system are derived for a system in the free state and for a system formed on a metal substrate.

Highly Stable Aqueous Dispersion of CTAB- Intercalated Reduced Graphene Oxide

Abstract A highly stable aqueous dispersion of reduced graphene oxide is obtained through the chemical reduction of graphene oxide by hydrazine hydrate in presence of cetyltrimethyl ammonium bromide (CTAB). Herein we report the preparation of reduced graphene particles which can be stably dispersed in water. The surfactant serves an effective role in graphene layer exfoliation. The dispersion in aqueous media has been observed over a week period. The reduced graphene particles were characterized by X -ray Diffraction (XRD), Fourier Transformed Infra-red (FTIR) spectroscopy. The morphology of prepared particles was studied by High Resolution Transmission Electron Microscopy (HRTEM).

A Chainlike Model of the Zigzag Edge Decoration of Graphene

For a brick-wall-like lattice topologically equivalent to the graphene lattice, a simple structural model of a zigzag edge decorated with particles is constructed. Analytical expressions for the energy band spectrum, densities of states, and occupation numbers of the graphene–particles system are derived for a system in the free state and for a system formed on a metal substrate.

Freestanding sulfur-graphene oxide/carbon composite paper as a stable cathode for high performance lithium-sulfur batteries

The structural design and synthesis of sulfur-carbon composite materials with high performance is still a major challenge for rechargeable lithium-sulfur batteries. Interconnected three-dimensional frameworks comprising multi-walled carbon nanotubes, graphene, or carbon particles offer a combination of constituent advantages and can thus be used to achieve superior energy conversion and storage properties. Herein, we designed and prepared free-standing three-dimensional sulfur papers containing interconnected highly conductive carbon materials, which enable to be flexible binder-free cathodes for Li-S batteries. The resultant sulfur-carbon composite paper cathode exhibited high reversible specific capacity of 1386 mAhg−1, good rate capability up to 5C, and excellent cycling performance (a capacity retention 68% after 400 cycles), all of which are significantly improved from those of bare sulfur cathode or sulfur-GO composite only. Rational design of cathode composition, structure, and a simple fabrication process can give insight into the development of various advanced cathode materials for high-performance Li-S batteries.

Effect of graphene treated with cyclohexyl diamine by diazonium reaction on cure kinetics, mechanical, thermal, and physical properties of natural rubber/graphene nanocomposite foam

The influence of functionalization of cyclohexyl diamine onto the graphene surface via diazonium reaction on the cure kinetics as well as morphology, mechanical, thermal and physical properties of natural rubber (NR)/graphene nanocomposite foam was investigated. The surface functionalization of graphene was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). Without an addition of blowing agent, the vulcanized NR composites containing cyclohexyl amine‐treated graphene showed not obvious different dispersion of graphene nanoplatelets than those containing untreated graphene as confirmed by transmission electron microscopy micrographs. Although the addition of untreated graphene could accelerate the sulfur vulcanization rate of NR nanocomposite foam due to the high thermal conductivity of graphene particle, and the remaining oxygen functional groups on the surface of graphene, the amines from cyclohexyl diamine on the treated graphene could react with carboxylic and epoxide group on the surface of graphene leading to a reduction of reactive oxygen functional groups on graphene surface and in turn slowed vulcanization rate. The fast vulcanization rate in untreated graphene system led to small bubble size in the NR nanocomposite foams. In contrast, the treated graphene system showed high tensile strength and low thermal expansion coefficient owing to low cell density. Finally, the defect on the graphene surface after functionalization was detected by Raman spectroscopy; this resulted in poor thermal conductivity for the treated graphene composite system. POLYM. COMPOS., 40:E1766–E1776, 2019. © 2018 Society of Plastics Engineers

A new enzyme-free biosensor based on nitrogen-doped graphene with high sensing performance for electrochemical detection of glucose at biological pH value

A new enzyme-free glucose biosensor with high sensing performance was developed based on N-doped graphene for glucose detection at biological pH value. The impact of various N functionalities on glucose sensing performance was investigated. In this regard, three N-doped graphene specimens with various amounts of pyridinic, pyrrolic and quaternary nitrogen functionalities were synthesized and thoroughly characterized for enzyme-free glucose detection. Accordingly, the microwave-treated N-doped sample with large pyridinic nitrogen content exhibited the best glucose sensing performance in terms of a proper limit of detection of 0.13 μM and a high sensitivity of 774.23 μA mM−1 cm−2 in a wide linear range of glucose concentration from 0.13 μM to 14 mM at pH 13. Also, it provided a superior sensitivity of 122.336 μA mM−1 cm−2, an appropriate detection limit of 14.52 μM and a fast linear response within the concentration range of 14.52 μM to 10 mM at biological pH (7.4) value. In addition, no interference was observed with addition of dopamine, ascorbic acid, uric acid, maltose, sucrose and fructose. The results of XPS analysis indicate that the pyridinic N dopants activate the electrocatalytic sites of graphene particles for glucose oxidation reaction.

Tunable broadband terahertz absorber based on multilayer graphene-sandwiched plasmonic structure.

We numerically demonstrate a tunable broadband terahertz absorber with near-unity absorption by using multilayer graphene ribbons sandwiched in a plasmonic integrated structure. By stacking slightly different widths of graphene ribbons in a sandwiched configuration, the absorption bandwidth can be increased because of the different resonant modes closely positioned together. The absorption spectrum's center frequency can be manipulated by varying the graphene's chemical potential, which provides a flexible way to design and optimize absorption property after fabrication. Furthermore, the structure can tolerate a wide range of incident angles, while the improved structure with graphene nanoparticles also shows polarization-independent feature. In this routine, stacking more graphene ribbons or particles with well-designed dimensions can further increase the bandwidth, as long as the metamaterial dimension satisfies the sub-wavelength condition. Therefore, our research provides an important theoretical guide for designing various graphene-based tunable broadband absorbers at terahertz, infrared, and microwave frequencies. This may have promising applications in imaging, sensing, and novel optoelectronic devices.

Microstructure and wear resistance of graphene-reinforced aluminum matrix composites

Graphene has excellent mechanical and physical properties that make it ideal for use as reinforcement nanofillers in aluminum matrix nanocomposites. This paper reports on the preparation of graphene-reinforced Al matrix composites by hot-press sintering at different temperatures using graphene uniformly dispersed into Al powder by ball milling. The as-prepared composite samples were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy. In addition, the mechanical properties of composite samples were evaluated by microhardness and wear testing at room temperature. The results demonstrate that interfacial reactions do not occur between Al and graphene particles during the hot-press sintering process. The composite obtained at a sintering temperature of 600 °C was dense, the graphene was uniformly distributed, and the composite exhibited good hardness and wear resistance at room temperature. The wear loss of the composite is mainly caused by microcutting abrasion.

Formation Mechanism and Cohesive Energy Analysis of Metal-Coated Graphene Nanocomposites Using In-Situ Co-Reduction Method.

Nanocomposite powders based on metal-coated graphene were synthesized using an in-situ co-reduction method in order to improve wettability and interfacial bonding between graphene and metal. Graphene oxide (GO) of 2~3 atomic layers was synthesized using the Hummer’s method with graphite as a raw material and then dispersed into a dispersing agent solution mixed with N-Methyl pyrrolidone and deionized water to form a homogeneous GO suspension, which was finally added into electroless plating solutions for the reduction process. Copper-coated graphene (Cu@graphene) and nickel-coated graphene (Ni@graphene) were synthesized using this one-step and co-reduction method by mixing salt solutions containing metal ions and GOs into the plating solution. The Cu ions or Ni ions were adsorbed and bonded onto the edges and surfaces of graphene, which was reduced from the GOs using a strong reducing agent of ascorbic acid or sodium borohydride. Crystalline Cu particles with an average size of about 200 nm were formed on the surface of graphene, whereas amorphous or nanocrystalline Ni particles with an average size of 55 nm were formed on the surface of graphene. Distribution of these metal particles on the graphene is homogeneous and highly dispersed, which can effectively improve the sinterability of composite powders. Cohesive energy distribution between graphene and metal interface was analyzed using first-principle calculation method. Formation mechanism of metal coated graphene was identified to be that both the GO and metal ions were simultaneously reduced in the reducing agents and thus a chemical bonding of graphene/metal was formed between the metal particles and graphene.

Electroactive graphene composite scaffolds for cardiac tissue engineering.

Contractile behavior of cardiomyocytes relies on directed signal propagation through the electroconductive networks that exist within the native myocardium. Due to their unique electrical properties, electroactive materials, such as graphene, have recently emerged as promising candidate materials for cardiac tissue engineering applications. In this work, the potential of three-dimensional (3D) nanofibrous graphene and poly(caprolactone) (PCL + G) composite scaffold for cardiac tissue engineering has been explored for the first time. The addition of graphene into PCL led to an increased volume conductivity of scaffolds with an even distribution of graphene particles throughout the matrix. Graphene particles provided local conductive sites within the PCL matrix, which enabled application of external electrical stimulation throughout the scaffold using a custom point stimulation device. When mouse embryonic stem cell derived cardiomyocytes (mES-CM) were seeded on PCL + G scaffolds, cells adhered well, contracted spontaneously, and exhibited classical cardiomyocyte phenotype confirming the biocompatibility of electroactive PCL + G scaffolds. Further functional characterization demonstrated that graphene especially affected Ca2+ handling properties of mES-CM compared to that of cardiomyocytes cultured in 2D culture, highlighting the potential of PCL + G for in vitro cardiac tissue engineering. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part A: 106A: 2923-2933, 2018.

Chemical synthesis of single‐layer graphene by using ball milling compared with NaBH 4 and hydroquinone reductants

Graphene materials especially single-layer graphene have been identified as a new generation of nanomaterials having various potential applications in material industries. However, the synthesis procedure of single-layer graphene to improve its quality, size and amount has been still under research for commercial applications. The graphene oxide (GO) is synthesised from graphite by Hummer's spontaneous approach which is the most suitable reaction for a large-scale production. For the single-layer graphene, in this work, GO was exfoliated by using a ball milling in an inert atmosphere. Owing to using ball milling as intermediate treatment degreased oxygen functional groups and number of layers, it facilitates to synthesise graphene. Sodium borohydride (NaBH4) and hydroquinone were used as a reductant for the chemical conversion of the exfoliated GO to graphene. The results showed that due to the strong reduction feature, both reducing agents can be applied in the graphene production. As a preferred reductant, hydroquinone can be successfully applied for the synthesis of the single-layer graphene compared to NaBH4. The obtained graphene particles by two different chemicals were characterised by various analytical techniques. The big difference in the structure of GO and graphene was observed in transmission electron microscope analysis.

Fabrication of highly conductive graphene particle‐coated fiber yarns using polymeric binders through efficient coating techniques

AbstractElectrically conductive yarns have been produced by fabricating graphene particles (both graphene nanoplatelets and reduced graphene oxide) on glass, flax, and polypropylene yarns using binding materials (epoxy resin and thermoplastic starch solution) and a dip coating process. Three different dip coating processes have been developed to identify an efficient method of coating in terms of improving electrical conductivity. Morphological study has been carried out to understand the mechanism at the interphase between binder and conductive particles, and it has been found that Van der Waals force and adhesive bonding are higher with epoxy‐based samples than those of starch‐based. Glass fiber yarns (with epoxy binder and rGO/GNP) have been identified as having the highest electrical conductivity of 0.1 S/cm.

Manufacturing Transparent Conducting Films Based on Directly Exfoliated Graphene Particles via Langmuir–Blodgett Technique

Transparent conducting films based on graphene particles are obtained via ultrasonic-assisted liquid-phase exfoliation of natural graphite. For the first time, the Langmuir–Blodgett technique is reported to be utilized for the deposition of transparent conducting thin films based on directly exfoliated graphene on dielectric substrates (glass and lithium niobate). It is shown that centrifugation of graphene suspensions prior to the film deposition enables the formation of conducting coatings with high transparency (higher than 90%). A number of film parameters (sheet conductance, transmission coefficient in the optical domain) are investigated; the achieved level of properties (the sheet resistance of 143 Ω/sq at the optical transmission coefficient of 90% and the weak dependence of absorption on the wavelength) makes these films an attractive material for transparent electrodes in photovoltaic devices, light emitting diodes, and advanced sensor technologies. The samples of graphene-based films deposited on a transparent piezoelectric substrate (lithium niobate) showed themselves as candidates for application as a part of primary transducers for electronic devices and sensing technologies as a possible substitute for ceramic materials based on indium-tin oxide.

Electrically Conductive Composites Based on Chitosan and Graphene Stabilized by Pluronic F-108

Highly concentrated dispersions of few-layer graphene stabilized by amphiphilic block copolymer Pluronic F-108 are obtained. According to transmission electron and atomic force microscopy, the thickness of the graphene particles is on average from one to ten layers and their lateral sizes vary from 150 nm to 1 μm. Using these dispersions, new chitosan-based film composites with the filler content up to 5 wt % are obtained; the electrical conductivity of these composites reaches 4.3 × 10–1 S/cm.

Unsteady nonlinear convection on Eyring–Powell radiated flow with suspended graphene and dust particles

This research contemplates the flow and heat transport of MHD rheological Eyring–Powell fluid embedded with dust and graphene nanoparticles (GP) in an ethylene–glycol (EG) mixture in the presence of nonlinear convection, Cattaneo–Christov heat flux, and thermal radiation. Primarily existing PDEs (fluid and dust phase) are transferred to non-dimensional form by invoking similarity transformations then solved numerically through RKF-45 method. The graphene particles are significantly used in energy transmission in aerospace, power and propulsion generation etc. Through graphical illustrations, velocity and temperature profiles (fluid and dust phases) converse for various prominent parameters. The results of friction factor and heat transfer rate are presented and analyzed. Validation of the present result is made with the existing data. Results demonstrate that increasing nonlinear convection parameter has an inverse relationship with the Nusselt number and the velocity in the dust and fluid phases. This may happen due to the domination of unsteadiness in the flow.

Synergistic Effect of Irregular Shaped Particles and Graphene on the Thermal Conductivity of Epoxy Composites

Improving the heat transfer properties of the thermal interface materials (TIMs) is the basic way to solve heat dissipation problem of electronic products with high energy density. In this study, the synergistic heat transfer between graphene and irregular particles at low loading is systematically studied; these irregular shaped particles include Ag, Cu, and MgO. When the mass fraction of the irregular shaped particles is <20%, the heat transfer network chain is mainly formed by the fully dispersed graphene. However, when the irregular shaped particle mass fraction reaches 30%, more heat transfer network chain will form between particles. In addition, the interfacial thermal resistance between fillers and matrix is the most crucial factor, and the intrinsic thermal conductivity of irregular particles is a relatively minor factor for the synergistic heat transfer between graphene and irregular particles at low loading. POLYM. COMPOS., 40:E1294–E1300, 2019. © 2018 Society of Plastics Engineers

Friction and wear of nanocomposite Al2O3 + G processed by spark plasma sintering

The effect of allotropic carbon modification content, graphene (G), in the range of 0.5 – 2.0 wt.% on tribological, strength and structural characteristics of Al2O3/G nanocomposite processed by 10-min plasma spark sintering (pressure 50 MPa, temperature 1550 °C) of nanopowder mixture previously subjected to ultrasonic dispersion in organic solvent is studied. The results of tests for friction and wear without lubricant on a tribometer under a load of 20 N at room temperature and roundabout motion of a ruby ball penetrator on a disk are presented along with data on kinetic indentation with determination of the nanohardness and elastic module and observations of the fracture surface structure and friction track using a scanning microscope. Methods of the transmission electron microscopy of thin foils in dark and bright fields and Raman spectroscopy, respectively, were used to determine the microstructure in the bulk of a nanocomposite and prove the graphene thermal stability during plasma spark sintering. It is shown that introduction of graphene contributes to the increase of micro- and nanohardness, elastic modulus, wear resistance by two or three orders of magnitude and a slight decrease in the coefficient of friction. Increase in graphene content to 2 wt.% changes the wear mechanism from brittle breakage to viscous shear due to strengthening in coupling of matrix grains and presnrce of agglomerates. Lack of degradation and retention of graphene thermal stability are proved. The morphology of graphene particles indicates to their preferential arrangement inside the corundum grains and more rarely — on the grain boundaries.

Preparation of n-MoS2 for HER Using a High Voltage Electrochemical Deposition Method

Recently, MoS2 has attracted attention as a HER (hydrogen evolution reaction) catalyst for replacing Pt, because it has similar hydrogen bonidng energy to Pt. Here, a HVER (high-voltage electrochemical reduction) method in a H-cell was attempted to prepare nanosized MoS2 on graphene. A Pt wire was used as a cathode to reduce (NH4)2MoS4 to MoS2 on the graphene particles dispersed in water and a potential of 60 V was applied to the cell and a varible resistor was adjusted to allow a current of 50 mA to flow. During the electrochemical reduction, no Mo deposition on the Pt cathode was observed and MoS2/graphene particles were simply obtained with a short preparation time of less than 15 min. Fig.1 shows LSV of MoS2/rGO synthesized at the diffierent reduction time with a RDE and EIS Nyquist plots corresponding to the LSV. The MoS2/rGO sample prepared at the reduction time of 10 min exhibited the highest current density of 37.6 mA/cm2 at the overpotential of 200 mV. EIS analysis showed that the MoS2/rGO sample (10 min) has the lowest charge transfer resistance of 25 Ω. Particle sizes of the prepared MoS2 were observed with TEM analysis. The particle size of MoS2 (10 min) was in the range of 4-10 nm. The particle size of MoS2 increased with increasing the electroreduction time. It was reported that the smaller the particle size of MoS2, the higher the HER activity.1) So, one reason for the decrease in the activity of the sample prepared at a reduction time of more than 10 minutes is because the particle size of MoS2 increases as the electrochemical reduction time increases. XRD diffraction patterns of the prepared samples showed that the prepared MoS2 samples had three phase of 1T (tegragonal), 2H (hexagonal) and 3R (rhombohedral) and the 3R phase was mainly observed. The MoS2 has been prepared in a hydrothermal method for HER, which shows mainly 2H phase. Recently, it was suggested that 3R phase of MoS2 outperformed the corresponding 2H phase for hydrogen evolution.2) In that aspect, it is proposed that the HVER method is a promising technique for producing high activity MoS2 catalysts.

Electrical conductivity of unidirectional carbon fiber composites with epoxy-graphene matrix

This paper aims at establishing connections between electrical resistivity and stresses in carbon fiber reinforced epoxy-graphene composites. To avoid the interconnection of multiple parameters, we examined composite specimens consisting of a single strand or tow (12,000 carbon fiber filaments) embedded in an epoxy matrix containing up to 1.0 wt% of graphene (TG679) particles. The specimens show resistance increase with the tensile stress. The characteristic of the dependence varies with the content of graphene particles, tending to be linear as the percentage of graphene content increases. We did not observe any significant changes in the ultimate strength of the composite with an increase of the graphene particles concentration.

Effects of nano graphene particles on surface roughness and cutting temperature during MQL milling of AISI 430 stainless steel

Abstract Stainless steel is hard-to-cut due to its material specifications and many problems are encountered machining it. Nevertheless, stainless steel is frequently preferred in industry and its use increases. In this experimental study, the machining of AISI 430 ferritic stainless steel under dry, MQL (minimum quantity lubrication) and nanofluid MQL milling conditions was investigated. Nanofluids were prepared by adding 1 wt.-% and 2 wt.-% nano graphene to commercial vegetable cutting fluid. In these experiments, uncoated WC (tungsten carbide) and TiN (titanium nitride) coated WC cutting tools were used and MQL flow rates were selected as 20 ml × h−1 and 40 ml × h−1. Surface roughness and cutting temperatures were measured and the effects of using nanofluid, MQL flow rate, and TiN coated cutting tools were specified. According to the experimental results, the MQL method was shown to be beneficial for reducing cutting temperature and surface roughness values and the nanofluid MQL yielded minimum values. Moreover, TiN coating and an increased MQL flow rate decreased cutting temperature and surface roughness.