As-prepared Graphene Nanosheets Research Articles

High-efficiency, self-grinding exfoliation of small graphene nanosheets from microcrystalline graphite driven by microbead milling as conductive additives

Direct mass exfoliation of graphene from bulk graphite with high yield and productivity for commercial applications is challenging. This work proposes self-grinding exfoliation using the mutual shear friction of graphite particles to fabricate graphene from microcrystalline graphite. The concept is implemented using microbeads as the grinding medium to drive the shear friction between graphite nanocrystals in a high-concentration paste. The proposed approach substantially improves graphene yield from 6.3% to 100% and simultaneously generates a record productivity of 7.5 g h−1 L−1, achieving total graphite-to-graphene conversion on the kilogram scale. The as-prepared graphene nanosheets have an average lateral size of 298 nm and the same C/O atomic ratio as the pristine graphite. In addition, the well-exfoliated, small nanosheets display good electrical conductivity and exhibit significant potential as conductive additives that improve the specific capacity and cyclic stability of Li-ion batteries better than commercial carbon-based conductive particles.

A novel approach to synthesize nitrogen-doped graphene in aspects of milling energy

Systematic report on the synthesis of Nitrogen-doped graphene (N-doped GNP) via solid-state ball milling of graphite with melamine powder is represented in the article. At the first time, the article briefs the mathematical representation for energy released at different speed of rotation of planetary ball mill using the various diameter of balls. It was observed that large diameter balls release more energy as compared to smaller balls. However, when combination of balls with different diameters were used, the energy released was much larger as compared with balls of individual diameter. Solid-state ball milling technique has successfully exfoliated the graphite into multilayer graphene and at the same time it has doped the nitrogen atoms onto the edge of graphene sheets. Field-emission scanning electron (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and particle size analyzer has confirmed the quality and final particle size of as-prepared graphene nanosheets (GNP). The particle size of 48 h milled graphene is observed to be double to that of 72 h graphene sample.

Electrochemical mass production of graphene nanosheets for arsenic removal from aqueous solutions

In this study, graphene nanosheets (GNS) produced from electrochemical exfoliation of graphite rods were directly employed for removing of arsenic (As(III)) from aqueous solution. The properties of GNS were characterized by scanning electron microscopy, tunneling electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. By applying Langmuir adsorption isotherm, the maximum adsorption capacity was calculated to be 25.84 mg/g, which is relatively high due to the effective interaction of As(III) and oxygenated functional groups available on the surface of as-prepared GNS.

Enhanced Comprehensive Performance of Polyethylene Glycol Based Phase Change Material with Hybrid Graphene Synthesized by Ball Milling

The stickiness of acacia gum was used to assist in the ball milling of graphite in aqueous media. Graphite is successfully exfoliated through a “sticky tape” mechanism, to give a 2.06 mg mL−1 aqueous dispersion of graphene. PEG6000 doped with 0.4 wt% of as-prepared graphene nanosheets (GN) exhibited obviously growing enthalpies and increasing thermal conductivity by 260% over pure PEG6000.

Amino-functionalization of graphene nanosheets by electrochemical exfoliation technique

An electrochemical exfoliation route to functionalize graphene nanosheets (GNs) directly from a graphite electrode exposed to N-containing electrolyte is explored under constant-voltage (5–12 V) model. The selection of electrolytes (i.e., (NH4)2HPO4, (NH4)2SO4, and NH4NO3) used herein turns out to be a crucial factor in affecting the amidation level and amino group distribution on as-prepared GNs. The low-potential exfoliation assists an in-situ amino-functionalization reaction, imparting high N-surface coverage on GNs. The electrochemical exfoliation in (NH4)2HPO4 is prone to the chemical doping of N element into sp2 domain, whereas using (NH4)2SO4 and NH4NO3 electrolyte takes parallel pathway: chemical N doping and decoration of amino and amide–carbonyl groups at edges of GNs. The N/C ratio on the GN sample can reach as high as 8.4 at%, confirmed by X-ray photon spectroscopy. The tunable photoluminescence response of GN dots due to the amino functionalization is investigated, using a band-gap structure model. Accordingly, the efficient approach exhibits a controllable processing method for producing GN product because of its well-defined amidation extent and one-step process without any surface modification treatment.

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.

Preparation, characterization, and physical properties of graphene nanosheets and films obtained from low-temperature expandable graphite

Graphene nanosheets have been prepared from low-temperature expandable graphite by ball milling and subsequent ultrasonication. The as-prepared graphene nanosheets were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, atomic force microscopy, differential thermal analysis, etc. The graphene concentration in the suspensions could be increased proportionally by simply extending the milling and ultrasonication duration. The graphene morphology changed from ribbons to single- and few-layer nanosheets with a porous nature. After milling for 40 h, the average number of stacking layers was estimated to be 3.5 for the graphene nanosheets. The lateral dimension of the defect-free crystallites decreased with the milling time, whereas the structural defects mainly from the graphene edges increased accordingly. The exfoliation process was interpreted in terms of complex factors, including weak interlayer attraction, shear-induced dislocation bands, and acoustic cavitation of ultrasonic irradiation. The sheet resistance of the graphene films dramatically decreased after the thermal treatments, especially in reducing atmospheres. This facile approach appears promising for its potential applications in functional composite materials.

Dielectric spectroscopy of high aspect ratio graphene-polyurethane nanocomposites

High aspect ratio graphene nanosheets (GNS), prepared via liquid exfoliation, are homogeneously dispersed in thermoplastic polyurethane (TPU). Dielectric spectroscopy results are reported for these nanocomposites (up to 0.55 vol. % GNS) in the frequency range of 100 Hz to 5 MHz. The as-prepared GNS increased the AC conductivity 10–1000 times across the given frequency range. The dielectric constant is increased 5–6 times at 100 Hz for the maximum loading of GNS when compared with the pristine TPU, with subsequently high dielectric loss making them a suitable candidate for high energy dissipation applications such as EMI shielding. The temperature effects on the dielectric characteristics of 0.55 vol. % GNS/TPU nanocomposites beyond 400 K are more pronounced due to the interfacial and orientation polarization. Mechanical characteristics evaluation of GNS/TPU composites shows a marked increase in the ultimate tensile strength without compromising their ductility and stiffness.

Pt–Co nanostructures electrodeposited on graphene nanosheets for methanol electrooxidation

Glassy carbon electrode modified by Pt–Co nanostructures decorated on graphene nanosheets (Pt–Co/G/GCE), is fabricated. Co nanostructures are electro-deposited on graphene modified GC electrode and then Pt nanostructures are loaded on the surface of modified electrode by galvanic replacement reaction between Co nanostructures and H2PtCl6. The physical and electrochemical properties of Pt–Co/G/GCE are investigated by scanning electron microscopy, energy dispersive X-ray, cyclic voltammetry and chronoamperometry. The morphology of as-prepared graphene nanosheets is investigated by transmission electron microscopy. The prepared Pt–Co/G is used as the anode electrocatalyst for methanol electrooxidation. The fabricated electrocatalyst exhibits an enhanced electrocatlytic performance for methanol electrooxidation.

Facile Synthesis of Graphene Nanosheets and their Anode Electrochemical Performances in Lithium Ion Batteries

In this work, graphene nanosheets (GNSs) were prepared by the thermal pyrolysis of graphene oxide (GO) at 900 °C for 3 h, and their electrochemical performances as anode materials for lithium ion batteries (LIBs) were also investigated. TEM and SEM images clearly showed that the as-prepared GNSs had a transparent two-dimensional (2D) structure with 5~10 multilayers. The other experimental results (XRD, Raman, TG and FT-IR) confirmed the successful synthesis of GNSs. Electrochemical measurements revealed that GNSs had an initial discharge capacity of 1276 mAh g-1 and still remained 723 mAh g-1 after 50 cycles, indicating that the as-prepared GNSs shows a great potential as anode materials for LIBs.

Electrodeposition of platinum nanoparticles on polypyrrole-functionalized graphene

In this study, the new electrocatalyst of platinum support on polypyrrole-functionalized graphene (GNS–PPy/PtNPs) is reported. The polypyrrole-functionalized graphene (GNS–PPy) is constructed first with graphene nanosheets (GNS) and polypyrrole (PPy) particles by constant potential deposition. And then PtNPs are deposited on the surface of GNS–PPy by cyclic voltammetry. The as-prepared GNS–PPy/PtNPs is characterized by scanning electron microscopy, energy-dispersive spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The prepared GNS–PPy/PtNPs catalyst is employed for methanol oxidation reactions. Compared with GNS/PtNPs and PPy/PtNPs, the GNS–PPy/PtNPs has higher catalytic activity (508 mA/mg), better stability, and stronger poisoning-tolerance (I f/I b = 4.18) due to high dispersion of PtNPs on large surface of GNS–PPy as well as synergic effect among the GNS, PPy particles, and PtNPs. The experimental results indicate that GNS–PPy/PtNPs may be an ideal candidate catalyst for direct methanol fuel cell.

LiAlH4 and PBr3 assisted high quality synthesis of graphene with excellent performances for lithium ion batteries

An easy novel approach which offers a fast pathway of macroscopic quantity preparation of graphene nanosheets (GS) at room temperature has been firstly proposed via lithium aluminum tetrahydride (LiAlH4) and phosphorus tribromide (PBr3) as the deoxidizer based on graphite oxide (GO). The structure of the graphene was investigated by high-resolution transmission electron microscopy (HR-TEM) indicating the GS with few layers (~3 layers). It is found that the GS as anode material used for lithium ion battery (LIB) has high initial coulombic efficiency (83.1%). The first discharge and charge capacity of the prepared GS were 1029.4mAh·g−1 and 855.1mAh·g−1 at a current density of 100mA·g−1, respectively. After 21cycles, the reversible capacity is still kept at 760.7mAh·g−1. The as-prepared GS with few layers and defects could be optimized for excellent electrochemical performance as lithium ion battery anode material.

Graphene nanosheets as cathode catalysts for lithium-air batteries with an enhanced electrochemical performance

Graphene nanosheets have been investigated as cathode catalysts for lithium-air batteries with alkyl carbonate electrolyte. Field emission scanning electron microscopy, transmission electron microscope and Raman spectroscopy have confirmed the high quality of the as-prepared graphene nanosheets and the surface analysis has identified the mesoporous characteristic of graphene nanosheets. The electrochemical properties of graphene nanosheets as cathode catalysts in lithium-air batteries were evaluated by a galvanostatic charge/discharge testing. The reaction products on the graphene nanosheets cathode were analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. The graphene nanosheet electrodes exhibited a much better cycling stability and lower overpotential than that of the Vulcan XC-72 carbon. This work demonstrated that graphene nanosheets could be an efficient catalyst for lithium-air batteries.

Graphene nanosheets based on controlled exfoliation process for enhanced lithium storage in lithium-ion battery

A facile and rapid approach was used for the fabrication of chemically derived graphene nanosheets based on the reduction of graphite oxide (GO) in tube furnace assembly at different temperatures. The morphologies, microstructures, specific surface areas and other features of GO and graphene nanosheets were characterized. Structure characterization indicates that the platelet thickness of graphene nanosheets obtained at 300 °C was 1.62 nm, which corresponds to an approximately 5 layers stacking of the monoatomic graphene nanosheets. Electrochemical performances of the as-prepared graphene nanosheets were performed, the result of which could prove the above observation that graphene nanosheets (5 layers) obtained at 300 °C actually displayed the most remarkable electrochemical performances: the first discharge and charge capacities of graphene nanosheets were as high as 2137 mAh/g and 994 mAh/g, respectively, and after 100 cycles graphene nanosheets still possessed a high capacity of 478 mAh/g.

High yield production of graphene and its improved property in detecting heavy metal ions

A simple and economical approach to produce graphene nanosheets (GNSs) in quantity based on the thermal expansion of graphite oxide (GO) powder has been developed, and the as-prepared GNS was further used for the detection of different trace heavy metal ions including Cu 2+, Pb 2+, and Cd 2+. The few-layer GNSs with defects and residual –OH groups were shown to be particularly well suited for the determination of metal ions in the liquid phase using an electrochemical method, in which a remarkably low detection limit of 10 −11M for Pb 2+ was achieved. The high-yield production technique of GNSs combined with the high sensitivity for the detection of metal ions could promote the development of the industrial manufacture of graphene-based nanosensors.

A green and ultrafast approach to the synthesis of scalable graphene nanosheets with Zn powder for electrochemical energy storage

We developed a novel and ultrafast method to reduce graphene oxide (GO) with Zn powder in mild alkaline conditions under ultrasonication only for 10 min at room temperature. The as-prepared graphene nanosheets (GNs) are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and so on. Moreover, we proposed the reducing mechanism under which Zn powder and GO formed numerous Zn-GO primary batteries in the presence of ammonia solution, which can effectively remove a significant fraction of the oxygen-containing functional groups and yield a C/O ratio as high as 8.09 and 8.58 reduced by ultrasonication for 10 min and 60 min, respectively. A maximum specific capacitance of 116 F g−1 in an aqueous KOH electrolyte solution has been obtained. This approach presents us with a possibility for an environmentally friendly, ultrafast, low-cost and large-scale production of GNs and great potentials in electrochemical energy storage applications of graphene-based materials.

Microwave-assisted covalent modification of graphene nanosheets with chitosan and its electrorheological characteristics

Biofunctionalization and manipulating of graphene nanosheets (GNS) are important for biomedical research and application. Chitosan (CS) modified graphene nanosheets have been successfully prepared under microwave irradiation in N,N-dimethylformamide medium, which involved the reaction between the carboxyl groups of graphene oxide nanosheets (GONS) and the amido groups of chitosan followed by the reduction of graphene oxide nanosheets into graphene nanosheets using hydrazine hydrate. The as-prepared graphene nanosheets–chitosan (GNS–CS) nanocomposites have been characterized by FTIR, TEM, FESEM, XRD and TG. The results showed that chitosan was covalently grafted onto the surface of graphene nanosheets via amido bonds. Solubility measurements indicated that the resultant nanocomposites dispersed well in aqueous acetic acid. Especially, the electrorheological (ER) properties of the GNS–CS nanocomposites have been investigated. It is believed that this new nanocomposites may be promising for biomedical applications.

Reducing Sugar: New Functional Molecules for the Green Synthesis of Graphene Nanosheets

In this paper, we developed a green and facile approach to the synthesis of chemically converted graphene nanosheets (GNS) based on reducing sugars, such as glucose, fructose and sucrose using exfoliated graphite oxide (GO) as precursor. The obtained GNS is characterized with atomic force microscopy, UV-visible absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and so on. The merit of this method is that both the reducing agents themselves and the oxidized products are environmentally friendly. It should be noted that, besides the mild reduction capability to GO, the oxidized products of reducing sugars could also play an important role as a capping reagent in stabilizing as-prepared GNS simultaneously, which exhibited good stability in water. This approach can open up the new possibility for preparing GNS in large-scale production alternatively. Moreover, it is found that GNS-based materials could be of great value for applications in various fields, such as good electrocatalytic activity toward catecholamines (dopamine, epinephrine, and norepinephrine).

A dehydration and stabilizer-free approach to production of stable water dispersions of graphene nanosheets

Graphene has received great attention because of its exceptional properties and formidable potential in various applications. A practical approach to the production of processable graphene sheets in large quantities at low cost is the key to exploiting most proposed applications. Here we show a dehydration and stabilizer-free method for facile and cost-effective production of water dispersions of graphene nanosheets with concentrations up to 0.05 mg mL−1 using concentrated sulfuric acid or phosphoric acid as the dehydrating and intercalating reagent. The unique opto-electronic properties of graphene could be chemically engineered without losing the macroscopic structure integrity. The self-assembly properties of as-prepared graphene nanosheets in aqueous solution and at the air/water interface offer great flexibility for a wide range of applications.