Graphene Powder Research Articles

Compact graphene powders with high volumetric capacitance: Microspherical assembly of graphene via surface modification using cyanamide

Graphene has received increasing attention as an electrode material for electrical double-layer capacitors (EDLCs) due to its high specific surface area and high intrinsic electrical conductivity. Recently, there have been tremendous achievements for improving the gravimetric capacitance of graphene. However, graphene’s low density limits its practical applications as electrode material for EDLCs because of the unacceptably poor volumetric capacitance. To take full advantage of graphene’s superior properties, it preferably needs to be assembled into microspherical powder form with low ion transport resistance as well as high packing density. Herein, we demonstrate novel spray-drying strategy for the facile and scalable assembly of graphene into a compact microspherical powder via surface modification using cyanamide, which plays very important roles in the assembly process: preventing graphene oxide from interacting with water and restacking, polymerization into graphitic carbon nitride, and its thermal decomposition. The key challenges are the assembly of graphene in the form of microspherical particles, the densification of graphene microspheres with a high packing density and compressive strength, and the generation of mesopores in the graphene microspheres. Notably, N doped graphene microspheres exhibit an outstanding volumetric capacitance (259 F cm−3 at 0.1 A g−1) in 1 M tetraethylammonium tetrafluoroborate (TEABF4)/acetonitrile (ACN) electrolyte with excellent cycle stability (93.8% of the initial capacitance after 100,000 cycles at 2 A g−1). The graphene microspheres exhibit an excellent rate capability with a time constant of 0.92 s owing to the favorable formation of mesopores.

Mesoporous graphene adsorbents for the removal of toluene and xylene at various concentrations and its reusability

As novel technologies have been developed, emissions of gases of volatile organic compounds (VOCs) have increased. These affect human health and are destructive to the environment, contributing to global warming. Hence, regulations on the use of volatile organic compounds have been strengthened. Therefore, powerful adsorbents are required for volatile organic compounds gases. In this study, we used graphene powder with a mesoporous structure to adsorb aromatic compounds such as toluene and xylene at various concentrations (30, 50, 100 ppm). The configuration and chemical composition of the adsorbents were characterized using scanning electron microscopy (SEM), N2 adsorption-desorption isotherm measurements, and X-ray photoelectron spectroscopy (XPS). The adsorption test was carried out using a polypropylene filter, which contained the adsorbents (0.25 g), with analysis performed using a gas detector. Compared to graphite oxide (GO) powder, the specific surface area of thermally expanded graphene powder (TEGP800) increased significantly, to 542 m2 g−1, and its chemical properties transformed from polar to non-polar. Thermally expanded graphene powder exhibits high adsorption efficiency for toluene (92.7–98.3%) and xylene (96.7–98%) and its reusability is remarkable, being at least 91%.

Preparation of graphene coated aluminum composite powders by high-energy ball milling

The preparation of composite powders has an important impact on the properties of the synthesized bulk materials. In this work, graphene coated aluminum composite powders were successfully prepared by high-energy ball milling. The microstructure of graphene/aluminum mixed powders was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The effects of the micro-morphology of the composite powders and the ratio of the ball to the particle size of the graphene-coated aluminum composite powders were analyzed in detail. The results show that graphene can be uniformly dispersed in aluminum powder without significant agglomeration in the case of ball milling parameters with a ball-to-powder ratio of 5:1. When the ratio of ball to material is 6:1, the dispersion effect was not so obvious. However, the level of agglomeration in the composite powders at ratios 7:1 and 8:1 differed respectively; some particles were deformed and the dispersion effect was reduced. The particle size of the graphene coated aluminum composite powder increased with the increase of ball to material ratio. Thermodynamic analysis of the interface reaction between graphene and aluminum composite powders shows that the maximum content of graphene microflakes on the surface of aluminum powder is 0.3wt%.

High-strength graphene network reinforced copper matrix composites achieved by architecture design and grain structure regulation

Developing metallic materials with heterogenous nanostructures is one of the most promising strategies for obtaining excellent integrated mechanical properties towards structural applications. To explore the possibility of realizing intentional structural heterogeneities in graphene/metal composites, herein, we demonstrate a novel copper composite reinforced by three-dimensional network-like graphene powders, achieved by hot-pressing, cryo-rolling and low-temperature annealing. It was found that the structure of three-dimensional graphene could be well remained during the processing and thereby resulted in an alternated distribution of lath-like graphene-rich zones and graphene-free zones in the composites. The yield strength (380 ±5 MPa) and tensile strength (412 ± 7 MPa) of 1.5 vol % graphene/copper composite were 74% and 30% higher than that of pure Cu, respectively. Moreover, the ultimate tensile strength and fracture elongation of graphene/copper composite with heterogenous graphene distribution both exceeded those of a composite reinforced by homogeneously-distributed two-dimensional reduced graphene oxide nanosheets. The dominant strengthening mechanisms were verified as the Hall-Patch strengthening thanks to the highly refined matrix grain size of sub-micron level and the load transfer strengthening originated from the formation of ‘graphene-rich zones’ in the copper matrix. This study highlights the importance of architecture design in graphene reinforced metal matrix composites for actualizing their strengthening potential while retaining a balanced ductility.

Preparation of N‐doped graphene powders by cyclic voltammetry and a potential application of them: Anode materials of Li‐ion batteries

Preparation of N‐doped graphene powders by cyclic voltammetry and a potential application of them: Anode materials of Li‐ion batteries

Electrical resistivity and thermal conductivity properties of graphene‐coated woven fabrics

ABSTRACTIn this study, it was aimed to develop electrically and thermal conductive textiles surfaces. Pretreated polyester fabrics were coated with nano graphene powders at different concentration rates (50, 100, and 200 g/kg) by knife over roll technique. Electrical resistivity, thermal conductivity, thickness and mass per unit area measurements, bending rigidity, and abrasion resistance tests of coated fabrics were performed. Surface resistivity measurements of coated fabrics were made according to ASTM D 257 standard with Keithley 8009 Resistivity Test Fixture. Surface electrical resistivity values of coated fabrics decreased with increasing concentration rates. Of note, 2.53 × 104 Ω/sq surface resistivity value was obtained at 200 g/kg graphene concentration rate. Thermal conductivity measurements of coated fabrics were made according to JIS R 2618 standard with Quick Thermal Conductivity Meter (QTM‐710). Thermal conductivity property of fabrics improved depending on graphene concentration. The highest thermal conductivity value (0.4243 W/mK) was obtained at 200 g/kg graphene concentration rate. One of the most important results of the study was that a maximum weight loss of 0.40% was observed in the abrasion resistance test even after 100 000 cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48024.

Tribological performance of graphene/graphite filled phenolic composites - A comparative study

Abstract Tribological performance of Graphene in Phenolic based friction composite containing various ingredients such as fibers, fillers, tribo-modifiers was compared with the sample filled with Graphite. The Graphene powder was dry mixed with the Phenolic resin and characterized with fourier transform infrared spectroscopy . Two friction composites were fabricated with the Graphene/Graphite mix. The experimental results show that the Graphene filled Phenolic composite projects high friction stability, friction-fade performance, friction-recovery performance when compared to Graphite filled friction composite. Also, it is observed that the wear resistance of the Graphene composite is three times better than the Graphite based composite which is an essential characteristic of the friction material . The Graphene stabilizes the tribo film formation on the surface of the pad and the rotor which reduces the direct contact of the surface asperities of the pad and disc and reduces the wear of the composite.

X-Ray Diffraction Evaluation of the Average Number of Layers in Thermal Reduced Graphene Powder for Supercapacitor Nanomaterial

Graphene oxide (GO) can be partially reduced to graphene-like sheets by removing the oxygen-containing groups and recovering the conjugated structure. In this work, the thermal reduction of GO powder has been carried out using back pumping vacuum pressures and investigated employing X-ray diffraction analysis. The experimental results of estimating the number of graphene layers on the reduced powder at various temperatures (200 – 1000 °C) have been reported. Electrical changes have been produced in a graphene oxide with the vacuum reduction process. This study has shown that the ideal processing temperature for reducing graphene oxide nanomaterial was about 400 °C. It has also been shown that at 600 °C the number of layers in the reduced nanomaterial increased. The internal series equivalent resistance (ESR) has been improved substantially with the vacuum thermal treatment even at temperatures above 400 °C. ESR was reduced from 95.0 to about 13.8 Ω cm2 with this processing. These results showed that the process can be applied to the reduction of graphene oxide to produce supercapacitor nanomaterials. The advantage of employing this method is that the processing is a straightforward and low cost thermal treatment that might be used for large amount of nanocomposite material.

Scalable Salt-Templated Synthesis of Nitrogen-Doped Graphene Nanosheets toward Printable Energy Storage.

Mass production of graphene powders affording high quality and environmental benignancy serves as a prerequisite for the practical usage of graphene in multiple energy storage applications. Herein, we exploit a salt-templated CVD approach to harness the direct synthesis of nitrogen-doped graphene (NG) nanosheets and related ink dispersions in a scalable, safe, efficient, and green fashion. Thus-fabricated NG accompanying large productivity, excellent electrical conductivity, and favorable solution processability possesses implications in printable energy storage devices. With the NG-based ink in hand, self-standing 3D architectures with programmable patterns can be directly printed over a myriad of substrates. Accordingly, both electrode preparation for flexible supercapacitors and separator modification in Li-S batteries can be enabled via printing by employing our NG-based composite inks. This work thus represents a practical route for mass production of graphene inks with cost-effectiveness and eco-friendliness for emerging energy storage technology.

Effect of double-layer composite absorbing coating on shielding effectiveness of electromagnetic shielding fabric

In order to meet the demand for high-performance electromagnetic shielding fabrics, using absorbing coatings to improve the shielding effectiveness has become an research object increasingly. The effect of double-layer mixed material’s absorbing coatings on electromagnetic shielding fabrics has not been clarified currently. At the same time, it is difficult to satisfy the broadband requirement for a single type of absorption layer. Carbon nanotubes, graphene, ferrite and nano-nickel powder are used in this paper. Which made it content at 15%, 25% and 35% respectively. The shielding effectiveness test of the stainless steel electromagnetic shielding fabric coating was carried out by the DR-SO4 electromagnetic shielding test system. Through the experiment, some findings are summarized as followed. Regardless of the same mixed materials, different content of shielding effectiveness comparison experiments, or the comparison of the performance of different kinds of materials mixed with the same content of screen combination, when the content is 15%, the best shielding effectiveness is the double-layer combination of Graphene + Ferrite and Graphene + Nickel. Which peak value is 68 dB respectively. In the analysis of the influence factors of the test coating, the larger the thickness and the corresponding resistance value smaller, the higher the combined shielding effect value. The optimal combination order of shielding effectiveness is: reflective layer + absorbing layer + absorbing layer + reflective layer. This paper revealed the influence of double-layer hybrid coating on the shielding effectiveness of electromagnetic shielding fabrics. It has important academic significance for the design, production and evaluation of high performance electromagnetic shielding fabrics.

Biofilms By E.coli & S.Epidermidis and Its Sensing Possibility By Graphene-Dispersed Silane Coating

We already found that graphene is very sensitive to biofilm formation by bacterial activities. The problem is how to constitute proper sensing systems to detect biofilms in various cases. In this study, we focussed on the silane compound coating in which nano graphene powder would be dispersed in its free volume. The concentration of graphene powders in silane compound coating was changed from 0.1 wt % to 30 wt% and the graphene dispersed silane compounds were coated on glass and pure copper substrates. And biofilms were formed on those specimens in the well plates filled with liquid cultures containing Staphylococcus epidermis (S.epidermidis) as gram-positive bacteria and Escherichia coli (E.coli) as gram-negative ones. And the formation process was checked by the specimens' potential change in liquid cultures, color changes by staining with Crystal violet and some electrical measurement (capacitance etc.). Finally, we compared all of them each other and discussed about the advantage and disadvantage among the methods for the application as sensing method.

Encapsulated Phase Change Material Embedded by Graphene Powders for Smart and Flexible Thermal Response

Flexible responsive materials, such as graphene embedded phase change material (PCM), can exhibit a smart response to the heating and cooling steps and be utilized for the thermal sensing applications. The electrical conductivity is varied during the phase transition due to volume change of the working material. However, the leakage is one of the serious problems and restricts the PCM from applications. Phase change material was encapsulated in the present work to prevent the leakage problem. Polyaniline (PANI) was selected as the supporting material to surround the pure phase change material and thus the fabricated PCM composite could sustain the shape under the phase transition process. Herein, the polyaniline encapsulated phase change material was produced and the graphene powder was added to increase the electrical property of the PCM composite. The graphene embedded PCM composite showed excellent electrical performance when the temperature was increased to the isothermal phase transition state. The pure PCM inside the microcapsule began to melt and the liquid state lead to the volume expansion of the PCM composite. Therefore, the reversible form stable phase transition was achieved and the electrical conductivity was increased as the distance between conductive graphene fillers was reduced with volume expansion of the PCM. This study suggests that the microencapsulated PCM composite should provide new applications for thermal sensing and flexible thermo-electric devices like smart photodetectors.

Graphene/Polyaniline flexible supercapacitors using non-metalic electrodes

Flexible supercapacitors are attractive devices for portable applications including those integrated in clothes. Highly conducting flexible electrodes can easily be fabricated by graphene powder and PE polymer foil but reliable fabrication of supercapacitor structure is still a challenge. A promising solution could be the incorporation of conducting polymer as polyaniline (PANI) intended to stabilize the mesoporous carbon and graphene plates, to form a conductive porous composite and to increase the capacitance. Low-cost aqueous electrolyte (1V) supercapacitor devices based on graphene/PANI composite were developed, tested in series configurations and compared in electrical performance. Preliminary applications in portable solar chargers are discussed.

Direct Printing of a Multi-Layer Sensor on Pet Substrate for CO2 Detection

The use of inexpensive gas sensors is a real need for many applications requiring the use of disposable sensors. This work deals with the realization and characterization of a low cost CO2 sensor realized by rapid prototyping techniques. In particular, the sensor consists of a set of InterDigiTed electrodes, over which a double sensing layer made of PEDOT/PSS (CLEVIOS™ PHCV4, by H.C.Starck) and a solution of pristine graphene powder has been deposited. A silver nano-particle solution is used for inkjet printing the electrodes onto the PET (PolyEthylene Terephthalate) substrate, through a commercial inkjet printer. The sensing strategy is based on the variation of the electrical conductance of graphene due to gas molecules adsorption. The device responsivity observed in two different operating conditions (50 °C and 60 °C), is 4.0 µΩ/Ω/ppm and 4.7 µΩ/Ω/ppm. The corresponding values of the resolution are 400 ppm and 420 ppm. Main advantages of the developed sensor consist in the cost-effective fabrication techniques and the device flexibility, which are strategic for applications requiring disposable and shapeable devices to be installed into irregular surfaces.

Molecular group system as one energy unit

In view of the various qualifications required of materials nowadays, efforts to change the characteristics of inherent materials have continued. However, most material conversion techniques that have been used in the past, such as alloy design and doping effect, cannot overcome the limitation that properties are only added to the original characteristics of pristine materials. Therefore, herein, we introduced a new material design technique, a so-called “Molecular Group System”, which is completely different from existing methods. Since whole-set-systems are considered one-energetic-unit-system, either only the merits of the constituent elements can be emphasized or new materials completely different from the raw ones can be synthesized. In this study, block-stacking bottom-up approach was employed to form a one group system from SnO2, SnOx, Sn, and graphene powders, and a binder, using high-energy irradiation. Then, we discussed theoretical verifications such as SnO2-reduction and Sn-channeling.

Influence of the synthesis method on electrical storage capacity of graphene-related materials

ABSTRACTThe electrochemical properties and their relationship with the physico-chemical properties of graphene-based materials have been studied. Graphite was used as the raw material and it was oxidised and then reduced by two alternative approaches, namely thermal and multi-step reduction using ascorbic acid. It was demonstrated that the physico-chemical characteristics of the material are directly related to the synthesis method and greatly influence the major capacitance of the material. It was observed that the materials with lower levels of functional oxygen groups and with a more ordered structure, i.e. similar to graphene powder, are the ideal candidates for use in electrochemical applications as these materials have better capacitance and specific capacitances.

In-line monitoring of carbon nanoparticle epoxy dispersion processes

The new generation of three roll mills is able to monitor occurring process loads while dispersion. This paper focuses on the interpretation of the gathered data to find criteria quantifying the dispersion state online. The aim is process time reduction. We used impedance spectroscopy to identify the dispersion state and correlated it with the occurring process loads. The dispersion process of a wide spectrum of carbon based nano particles, namely carbon black, single walled carbon nanotubes, multi walled carbon nanotubes, a few-layer graphene powder, electrochemically exfoliated graphite and a functionalized electrochemically exfoliated graphite was investigated. The filler content was varied along the material’s electrical percolation threshold. The criteria found led to a reduction of processing time and revealed the prevalent mechanisms during dispersion.

Sorption behavior of Co-radionuclides from radioactive waste solution on graphene enhanced by immobilized sugarcane and carboxy methyl cellulose

Abstract Novel graphene-sugarcane bagasse-carboxy methyl cellulose (GSCCMC) nanocomposite have been synthesized via freeze-drying technique after preparation of graphene from natural graphite by modified Hummer method and evaluated as adsorbent for sorption of 60Co(II)-radionuclides from radioactive waste solution and real wastewater samples using a series of batch adsorption experiments and compared with graphene. The synthesized (GSCCMC) nanocomposite was characterized using Fourier transformer infrared (FT-IR), Transmission electron microscope (TEM), Thermal analysis, Elemental analysis, Specific Surface area (SBET) and X-ray diffraction (XRD), which confirmed the successful formation of graphene-sugarcane bagasse-carboxy methyl cellulose (GSCCMC) nanocomposite. Different parameters affecting the removal process including pH, contact time and metal ion concentration were investigated. Isotherm and kinetic models were studied. Adsorption kinetics described well by pseudo-second-order. The Langmuir model provides a better fitting than the Freundlich and Temkin models and the maximum adsorption capacity from Langmuir model were found to be 0.4186 and 0.2424 mol/g for (GSCCMC) nanocomposite and graphene (G), respectively. From Dubinin–Radushkevich (D–R) isotherm model, the sorption energy (E)-values of graphene (G) and (GSCCMC) are 10.16 and 10.564 kJ/mol, respectively and this mean the adsorption of 60Co(II)-radionuclides can be explained by chemisorption process, which is characteristic of ion exchange. Desorption of 60Co(II)-radionuclides from loaded (GSCCMC) nanocomposite was studied using different eluents (0.1 M HCl, 0.1 M NaOH and H2O). The data illustrated that 0.1 M HCl solution showed maximum desorption percent (D%) than other eluents. The economic viability of the adsorption process for the removal of 60Co(II) from wastewater samples was studied. The result indicated that the cost for preparation of (GSCCMC) nanocomposite is lower than for (GSCCMC) nanocomposite that prepared from purchase the graphene powder. Therefore, the synthesized (GSCCMC) nanocomposite was used as regenerated material for sorption of 60Co(II)-radionuclides from aqueous solutions and can be used for many times as a cost-effective and environmental friendly material in wastewater treatment.

Determination of the graphene–graphite ratio of graphene powder by Raman 2D band symmetry analysis

This paper presents a method to distinguish graphene from graphite in powdered samples by analysing the Raman 2D band symmetry.

Preparation of high concentration graphene dispersion with low boiling point solvents

Exploring the graphene material is premised on the graphene sheets being single-layer graphene (SG) or bi-layer graphene (BG) state, and graphene suspension keeps stably disperse are critical. Since graphene has a highly conjugated system, it is easy to conduct strong π-π interaction with conjugated structure. In this paper, by dispersing graphene powder at low boiling point solvent water or ethanol, ensuring the excellent properties of graphene are not affected by the solvent, which simultaneously solves the difficulty of removing organic solvents. On the basis the concentration of graphene suspension can be greatly improved and no damage to the graphene sheets in the presence of dispersant. This method allows us to prepare a large amount of excellent graphene dispersion, making it possible to obtain graphene-based materials through the low-cost technology, as well as opening up the opportunity for exploiting the application of this nanocarbon material with unique structure.