Preparation Of Graphene Nanosheets Research Articles

Durable, highly sensitive conductive elastomeric nanocomposite films containing various graphene nanoplatelets and their derivatives

AbstractIn recent years, the use of nano‐fillers in flexible polymer matrix to prepare highly flexible, stretchable, and multifunctional product has been widely studied. However, the uneven dispersion of nano‐fillers in polymer matrix is an important factor hindering their performance. In this study, a method to prepare graphene nanosheets by ball milling and modification with the silane coupling agent APTES is reported, and this method can reduce the thickness of the nanosheets, improving the dispersion effect and compatibility of the nanosheets in the PDMS matrix. The mechanical and conductive properties of the prepared composite films were further analyzed. The morphology showed that our modified graphene (MGE and BMGE) are more evenly dispersed in the PDMS matrix compared to the unmodified graphene (GNP). The MGE/PDMS composite film has significantly improved electrical conductivity. It has a wide sensing range (up to 48%), high sensitivity (GF of 152 in the 20%–40% strain range) and reliable cycle repeatability (>10,000 cycles) with a response time of 0.12 s. The results show that the modified graphene/PDMS conductive elastic nanocomposite film is an ideal material for making flexible electronic products.

Preparation of Graphene Nanosheets from Graphite Flakes via Shear Assisted Exfoliation

Graphene is one of the most important forms of carbon. Due to its exceptional physical, chemical, and mechanical properties, it’s used in different fields such as electronic, energy storage, and medical applications. Therefore, the production of graphene in large quantities, at a low cost, and high quality, has become critical. Using graphite powder, a few layers of graphene sheets were prepared via a series of mechanical exfoliation methods. the dry ball milling process by the planetary mill was used. Thereafter, the milling was followed by shear force and then supported by ultra-sonication to reach the lowest level of the graphene layers. Morphological properties were examined using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Also, structural characterizations were investigated using Raman spectra and X-ray diffraction measurements (XRD) and (FTIR). Findings presented in this research highlighted that the synthesis method followed was found to have several advantages, including low cost and the ease of producing a few layers of graphene nanosheets. Subsequently, the promising efficiency of the used methodology is important.

Microstructure and Mechanical Properties of Zinc Matrix Biodegradable Composites Reinforced by Graphene.

This work used spark plasma sintering (SPS) to prepare graphene nanosheets (GNS) reinforced zinc matrix composites. The influence of GNS on the microstructure and mechanical properties of zinc matrix composites was studied. The results show that the GNS/Zn composites prepared by SPS have a dense structure and good interface bonding, and GNS are uniformly distributed in the zinc matrix. Adding GNS can significantly improve the mechanical properties of the zinc matrix. When 0.7 wt% GNS are added, the comprehensive mechanical properties of the composite material are improved. The ultimate tensile strength is 254 MPa, and the Vickers hardness is 65 HV, which are 126 and 20.3% higher than those of pure zinc (112 MPa and 54 HV), respectively. The strengthening mechanisms of GNS/Zn composites are mainly load transfer of GNS and dislocation strengthening caused by coefficient of thermal expansion (CTE) mismatch. In addition, the biodegradability of GNS/Zn composites was evaluated by electrochemical measurement and immersion test. The results show that adding GNS to the zinc matrix will accelerate the degradation rate of the composite material. But the degradation rate can be controlled by the content of GNS. Its degradation rate is in the range of 69–301 μm/a, an ideal degradation rate as an orthopedic implant material.

Syntheses, characterizationsna and water-electrolysis properties of 2D α- and β-PdSeO3 bulk and nanosheet semiconductors

In contrast to alkaline water electrolysis, water electrolysis in an acidic environment has higher energy efficiency, more compact cell design, higher gas purity, and less sensitivity to environmental impurity. Herein, the syntheses of the known 2D α- and β-PdSeO3 were improved. The bulk materials were exfoliated into nanosheets using an ultrasonic-assisted liquid-phase exfoliation similar to that of preparing graphene nanosheets. Their band-gaps, valence band maximums (VBMs) and conduction band minimums (CBMs) were determined using Mott-Schottky plots and the linear potential scan method in acidic aqueous solution, 0.2 ​M Na2SO4 aqueous solution and non-aqueous solution. Their transient photocurrent properties were also examined, along with their Electrochemical Impedance Spectra (EIS). The bulk materials are stable in pH ​= ​0–14 value water solution for at least 48 ​h. α- and β-PdSeO3 nanosheets exhibit moderate catalytic activities for hydrogen evolution reactions in 0.5 ​M ​H2SO4 (η10 (overpotential at 10 ​mA ​cm-2: 185 and 209 ​mV, respectively; catalyst loading: 0.28 ​mg ​cm-2), much better than the performances of the bulk materials. In addition, β-PdSeO3 bulk and nanosheets materials show good and similar OER catalytic activities in 0.5 ​M ​H2SO4 (η10: 381 and 405 ​mV, respectively; catalyst loading: 0.28 ​mg ​cm-2). Thus, β-PdSeO3 nanosheets were found to be a good overall water splitting catalyst in acidic solution. The above catalysts all show long-term stability. In contrast, α-PdSeO3 does not have OER catalytic property. To our knowledge, Pd-based acidic overall water splitting catalysts are very rare.

Screen-Printed High-Performance Flexible Electrothermal Films Based on Three-Dimensional Intercalation Graphene Nanosheets/MWCNT/Carbon Black Composite.

A liquid-phase stripping method was used to strip the graphite under the action of mechanical shear force to prepare graphene nanosheets (GNSs) on a large scale. Given the multicomponent composite conductive particles formed by GNSs with acid-treated MWCNTs (f-MWCNTs) and carbon black (CB), the three-dimensional (3D) intercalation electrothermal composite of GNSs/MWCNTs/CB with excellent conductivity and mechanical properties was prepared with water-based acrylic resin as a connector. Carbon particles (16.97 wt %) are found in the composite and the sheet resistance (Rs) is only 4 Ω sq-1 as f-MWCNTs and CB intercalations form a more stable 3D conducting medium between the GNSs. The flexible electrothermal film (2.5 cm × 2.5 cm) printed with the 3D intercalation GNSs/MWCNTs/CB composite had a saturation temperature (Ts) of 175 °C with an input of 3 V and lower power consumption (249.87 cm2 W-1). It only takes 10 s to reach Ts and the electrical performance is still intact under the pressure of 1 × 105 kPa. After being bent 2500 times (bending radius is 5 mm), the electrothermal performance of the flexible electrothermal film remained stable.

Preparation of graphene nano-sheets from graphite flakes via milling-ultrasonication promoted process

Abstract Graphene is a new wonder material that known as an atomic layer of graphite. Due to its exceptional mechanical, physical and chemical properties, it's used in different fields such as composites, medical, electronic, energy conversion, and for storage applications. So, preparation of graphene with high quality, low cost, large quantities became an important matter. In our study, planetary wet ball milling process used and modified to produce graphene from graphite flakes, preceded by annealing and sonication process that used as assistant factors to increase the cleavage and exfoliation rates on graphite structure. Morphological characteristics were investigated using scanning electron microscopy while the structural characterizations were studied using Raman spectroscopy. The exfoliated graphene sheets with fewest number of layers, some structural defects and small crystal size indicate the promising efficiency of the used methodology.

One-pot preparation of zwitterionic graphene nanosheets with exceptional redispersibility and its application in pickering emulsions

Abstract Using biomass materials as exfoliating agents to produce graphene is a promising strategy due to their biocompatibility, reproducibility and sustainability. However, it’s still a challenge to prepare high-concentration graphene dispersion using biomass exfoliating agents. Here, we present a green and facile method to prepare few layered graphene nanosheets in aqueous solution by one-pot ball milling in the presence of protein, casein (CN). The results show that CN protein could be acted as an efficient exfoliating and stabilizing agent, producing water-soluble graphene nanosheets with a concentration up to 2.14 mg ml−1. As CN protein contains both amino and carboxyl groups, thus the prepared graphene nanosheets decorated with CN protein (GN-CN) show zwitterionically charged character and thereby can be stably dispersed under both acidic and alkaline conditions. Moreover, the oven-dried GN-CN hybrid exhibits exceptional redispersibility in water with a concentration as high as 100 mg ml−1 and even more. Benefiting from the zwitterionic character, GN-CN shows the Pickering emulsion effect over a wide pH range. As a proof of concept, the application of the zwitterionic GN-CN as a Pickering emulsifier to prepare microcapsule phase change composite material has been successfully demonstrated.

On the difference of characterization and supercapacitive performance of graphene nanosheets from precursors of inertinite- and vitrinite-rich coal

Being an interesting carbon material, graphene has gained a lot of attention. Graphene nanosheets (GNs) can be produced from coal-based graphite, which is metamorphosed from coal. In this paper, inertinite- and vitrinite-rich coals were used as precursors for preparing graphene nanosheets, and the characterization and supercapacitive performance of GNs were studied. The results show that GNs from inertinite-rich coal (GNs-I) are relatively larger and more disordered than GNs from vitrinite-rich coal (GNs-V). The electrochemical experiments indicate that the capacitance and the resistance of GNs-I is both larger and higher than GNs-V.

Preparation of graphene nanosheets by electrochemical exfoliation of a graphite-nanoclay composite electrode: Application for the adsorption of organic dyes

A simple and cost-effective approach to get a few layers of graphene nanosheets is reported in this work. The electrochemical exfoliation of a graphite-nanoclay composite electrode, a pencil core, was carried out in the presence of Mohr's salt (ammonium ferrous sulfate solution) as an electrolyte and aluminum foil as a counter electrode. The unique property behind using this method was that the produced graphene colloid does not require any secondary physical processing or ultra-sonication for separation, as it raised over the electrolyte solution during the exfoliation process. To optimize the exfoliation conditions, different electrolyte concentrations (0.1, 0.5 and 1 M) and D.C bias voltages (7.5, 9 and 12 V) were investigated. The as-produced graphene nanosheets were filtrated, washed and characterized using Raman spectrometer, FT-IR, XRD, SEM and TEM, UV–vis spectrophotometer. The electrochemical exfoliation process was found to produce a few layers of graphene nanosheets with a lateral size ranged from 60 to 210 nm. Based on characterization results, especially Raman and TEM analysis, highly pure graphene nanosheets were obtained at 7.5 V and 0.5 M of electrolyte solution concentration. A promising application of the produced graphene sheets for cationic and anionic dye removal has been investigated. The removal efficiency of the prepared graphene against MO and MB was 22% and 77%, respectively.

Oxalic acid assisted expansion–reduction exfoliation of graphene oxide into graphene nanosheets

A novel approach to prepare graphene nanosheets was developed by exfoliating graphene oxide (GO) assisted with oxalic acid (H2C2O4). The expansion and reduction of GO were synchronously fulfilled through the decomposition of H2C2O4 impregnated into the interlayer of GO. The structure of the as-exfoliated graphene nanosheets were determined by a series of characterizations. The results showed that the as-exfoliated graphene nanosheets possessed ca. 10-layered thickness and the lower oxygen content. The mechanism was proposed that H2C2O4 played a role of the expansion–reduction associated effect in exfoliation.

Simultaneous Surface Modification and Chemical Reduction of Graphene Oxide Using Glucose.

In this paper, we develop a simple and facile approach to prepare graphene nanosheets through chemical reduction with glucose as reducing agent and modification agent. The reduced and modified graphene by glucose (denoted as g-rGO) was characterized with techniques of Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), etc. It is found that, besides the desired reduction capability to graphene oxide (denoted as GO), glucose plays an important role as a modifying reagent in stabilizing the as-prepared graphene nanosheets simultaneously and the g-rGO exhibits good dispersibility and stability in water and waterborne polyurethane matrix (denoted as WPU). Moreover, the g-rGO can improve evidently the mechanical properties, weather ability and water resistance of WPU.

Modified Unzipping Technique to Prepare Graphene Nano-Sheets

Graphene nano-sheets have been prepared via unzipping approach of multiwall carbon nanotubes (MWCNTs). The method includes two chemical-steps, in which a multi-parameter oxidation step is performed to achieve unzipping the carbon nanotubes. Then, a reduction step is carried out to achieve the final graphene nano-sheets. In the oxidation step, the oxidant material was minimized and balanced with longer curing time. This modification is made in order to reduce the oxygen-functional groups at the ends of graphene basal planes, which reduce its electrical conductivity. In addition, a similar adjustment is achieved in the reduction step, i.e. the consumed chemicals is reduced which make the overall process more economic and eco-friendly. The prepared nano-sheets were characterized by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The average thickness of the prepared graphene was about 5.23 nm.

Mechanochemical Reinforcement of Graphene Sheets into Alkyd Resin Matrix for the Development of Electrically Conductive Paints

AbstractIn this work, we are reporting the preparation of graphene‐based conductive paints using mechanochemically prepared graphene nanosheets as a conductive pigment and alkyd resin as the binder with non‐toxic additives. The surface morphology and intermolecular interactions between the graphene pigments and alkyd resin in the prepared graphene nanopaint are studied using field emission scanning electron microscope, X‐ray photoelectron spectroscopy, and Raman spectroscopic analysis, respectively. The formation of percolation pathways owing to the interconnected graphene sheets in the paint matrix resulted in an excellent conductive behavior of the as‐prepared graphene paint, thus ensuring its applications in conductive paint technology. Furthermore, Raman mapping analysis (including intensity maps and peak position maps) was used to understand the spatial distribution of graphene sheets in the alkyd resin matrix of the paint.

Facile enhancement of the active catalytic sites of N-doped graphene as a high performance metal-free electrocatalyst for oxygen reduction reaction

A simple and facile N-doping process has been developed to prepare graphene nanosheets with a high loading of active catalytic sites through the combination of hydrothermal and microwave processes. High resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Raman analysis have been used to characterize the morphology and composition of the prepared materials. Also, linear sweep voltammetry (LSV) was conducted to investigate the electrocatalytic performance of the N-doped specimens toward oxygen reduction reaction (ORR). It was revealed that post-treatment of hydrothermally-treated N-doped graphenes under microwave irradiation in the presence of nitrogen precursor can result in the formation of a large content of quaternary nitrogen functionalities. Also, the LSV analysis revealed that fabrication of the graphene nanosheets under the proposed N-doping strategy resulted in potent electrocatalytic activity of graphene nanosheets toward ORR through a four electron pathway.

Facile synthesis of an all-in-one graphene nanosheets@nickel electrode for high-power performance supercapacitor application.

We report a facile and novel approach for the fabrication of all-in-one supercapacitor electrodes by in situ electrochemical exfoliation of flexible graphite paper (FGP) on a nickel collector. The binder-free three dimensional (3D) graphene nanosheets@Ni (GNSs@Ni) supercapacitor electrodes exhibit a high specific capacitance of 196.4 F g−1 and 36.2 mF cm−2, respectively, at a scan rate of 50 mV s−1. Even at the high scan rate of 2500 mV s−1 the specific capacitance of the capacitor still shows a retention of 85.6% (168 F g−1, 31 mF cm−2). Meanwhile, the as-prepared electrode offers excellent cycling performance with 91.5% capacitance retention after 100 000 charging–discharging cycles even at the high current density of 11 A g−1. Such high rate capability, specific capacitance and exceptional cycling ability of the GNSs@Ni electrode are attributed to the all-in-one architecture which provides unique properties including high electrical conductivity, large specific surface area and excellent electrochemical stability. We anticipate that these results will shed light on new strategies to synthesize high-performance hybrid nanoarchitectures electrodes using the prepared graphene nanosheets as the support, which offers great potential in energy storage devices and electrochemical catalysis applications.

Recent Developments in Graphene‐Based Tactile Sensors and E‐Skins

AbstractHuman skin, the largest organ of human body, can perceive tactile sensations, temperature, humidity, and other complex environmental stimulations. To mimic the capabilities of human skin, graphene provides great potential in building wearable electronic skins (E‐skins), which hold broad applications in advanced robotics, healthcare monitoring, artificial intelligence, human–machine interfaces, etc. Herein, the recent progress in flexible tactile sensors and E‐skins based on graphene material is presented. A brief introduction of the main approaches to prepare graphene nanosheets is provided. The main developments on the functions and mechanisms of bionic functional devices in E‐skins including tactile sensors, temperature sensors, and humidity sensors are then highlighted. The current and future applications for graphene‐based E‐skins, such as multifunctional biomimetic E‐skins, healthcare monitoring, and interactive human–machine interface, are also described. Finally, the existing challenges and future development trends for graphene‐based E‐skins are discussed.

Facile synthesis of graphene nanosheets via barium ferrite assisted intercalation and secondary expansion of graphite

In this work, we proposed a new method to prepare graphene nanosheets. Expand graphite has large sheet spacing and oil absorption, and the self-combustion precursor of BaFe12O19 is oily gel. It means that the BaFe12O19 oily gel can enter between the layers of expand graphite. When BaFe12O19 oily gel is self-combusted to form BaFe12O19 particles, it has a significant increase in volume. Expand graphite will occur secondary expansion and be peeled into graphene nanosheets. We characterized it by several ways and this is a time-saving, convenient, and low-cost method.

One-step synthesis of graphene nanosheets through explosive process

ABSTRACTHerein, we report a facile process to prepare graphene nanosheets through explosive method. The explosive products were characterized by using XRD, TEM, AFM, Raman and XPS. The results show that the obtained materials have a perfect sheet-like structure, and vary in the two-dimensional plane at the macron scale and in thickness at the nanoscale. This technique may offer a low-cost, energy-saving, and efficient way to prepare graphene materials.

One-step preparation of graphene nanosheets via deflagration of obsoleted energetic materials

Herein, we report the large-scale preparation of graphene nanosheets via the deflagration of an obsoleted single base propellant in the presence of dibutyl phthalate (DBP) aiming at decreasing the oxygen balance. The high ambient pressure and high temperature generated during the deflagration process provided sufficient conditions for the efficient formation of carbon atoms and the subsequent shaping of graphene nanosheets. The prepared graphene nanosheets were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD). This simple method is promising for future large-scale and cost-effective production of graphene nanosheets, as well as for the disposal of obsoleted energetic materials.

Graphene nanosheets prepared by low-temperature exfoliation and reduction technique toward fabrication of high-performance poly(1-butene)/graphene films

Thermal exfoliation and reduction of graphene oxide (GO) were performed to prepare graphene nanosheets at 300 °C under the ambient atmosphere without any supplementary conditions. The microstructure and morphology of the resulting graphene nanosheets were characterized with scanning electron microscopy, transmission electric microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The composite films based on poly(1-butene) (PB) and graphene nanosheets were prepared successfully through solution blending and compression molding. The morphological investigation suggested that the graphene nanosheets with nanoscale thickness achieved a homogeneous dispersion in the PB matrix. The composite films exhibited a sharp transition from insulating state to the conducting one with a low percolation threshold, followed by a high electrical conductivity at graphene content higher than 1.6 vol %. The composite films also achieved high dielectric constant with low dielectric loss due to the effective electrical conductive path established by graphene nanosheets in a local range. Moreover, the mechanical evaluation demonstrated that a considerable reinforcement was achieved for the composite films due to the strong interfaces between the graphene nanosheets and PB matrix. The introduction of graphene nanosheets not only enhanced the nucleation capability and crystallinity of PB domain but also improved the thermal stability of the composite films. In addition, the composite films showed an increase in storage modulus and a decrease in loss factors due to the incorporation of graphene nanosheets.