Specific Surface Area Of Graphene Research Articles

Ultrahigh specific surface area of graphene for eliminating subcooling of water

Graphene is widely utilized because of its exceptional properties, such as strong mechanical strength, low weight, nearly optical transparency, and excellent conductivity of heat and electricity. In this study, we used the ultrahigh specific surface area of graphene due to its inherently two-dimensional nature to reduce the subcooling of freezing of a phase change material. The results enable graphene’s application in energy storage using the latent heat of phase transition. The need for subcooling to freeze water was eliminated completely with the suspension of a very low mass fraction (0.020±0.001wt%) or surface area concentration (0.070±0.003m2/ml) of graphene. Compared to nanoparticles of SiO2 and TiO2 with the same mass fraction suspended in water, flakes of graphene led to freeze water at a much smaller subcooling degree, and shorter total freezing time. The addition of surfactants can improve suspension stability and further reduce the degree of subcooling, but it also slightly increases the total freezing time. Graphene flakes are more suitable than spherical oxide nanoparticles for use as nucleating additives in water.

Manganese-incorporated iron(III) oxide–graphene magnetic nanocomposite: synthesis, characterization, and application for the arsenic(III)-sorption from aqueous solution

High specific surface area of graphene (GR) has gained special scientific attention in devel- oping magnetic GR nanocomposite aiming to apply for the remediation of diverse environmental problems like point-of-use water purification and simultaneous separation of contaminants applying low external magnetic field (\1.0 T) from ground water. Fabrica- tion of magnetic manganese-incorporated iron(III) oxide (Mnx 2? Fe2-x 3? O4 2- ) (IMBO)-GR nanocom- posite is reported by exfoliating the GR layers. Latest microscopic, spectroscopic, powder X-ray diffraction, BET surface area, and superconducting quantum interference device characterizations showed that the material is a magnetic nanocomposite with high specific surface area (280 m 2 g -1 ) and pore volume (0.3362 cm 3 g -1 ). Use of this composite for the immobilization of carcinogenic As(III) from water at 300 K and pH *7.0 showed that the nanocomposite has higher binding efficiency with As(III) than the IMBO owing to its high specific surface area. The composite showed almost complete ((99.9 %) As(III) removal (B10 l gL -1 ) from water. External magnetic field of 0.3 T efficiently separated the water dispersed composite (0.01 g/10 mL) at room temperature (300 K). Thus, this composite is a promising material which can be used effectively as a potent As(III) immobilizer from the contaminated groundwater ((10 l gL -1 ) to improve drinking water quality.

The electrical properties of a sandwich of electrodeposited polypyrrole nanofibers between two layers of reduced graphene oxide nanosheets

A sandwich of polypyrrole (PPy) nanofibers between two electrodeposited reduced graphene oxide (RGO) layers was prepared by an electrochemical method. The structure and compositions were characterised by field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. The electrical properties were studied by electrochemical impedance spectroscopy (EIS). The FESEM results confirmed synthesis of a sandwich structure with PPy nanofibers between two electrodeposited RGO layers (RGO/PPy/RGO). The mean width of PPy nanofibers was approximately 76±16nm. The EIS results showed that the charge transfer resistance of the coated glassy carbon electrode (GCE) with a sandwich structure of RGO/PPy/RGO was significantly decreased in comparison with coated GCE with PPy nanofibers. This was because the RGO with many small band gaps is more favourable for electron conduction. The comparison of EIS results shows that diffusion of active species through the RGO layers is increased in the presence of the second layer of RGO. The simulation results indicate a high interfacial capacitance (Cdl) of 2170.60μFcm−2 for the coated GCE with RGO/PPy/RGO compared with 360.77μFcm−2 for coated GCE with PPy/RGO. This difference in capacitance can be attributed to the highly accessible specific surface area of graphene and its high efficiency towards electrolyte ion absorption.

Relationship between intrinsic capacitance and thickness of graphene nanosheets

A method to detect the intrinsic capacitance and thickness of graphene nanosheets (GNS) was developed. The ultrasonic-dispersed GNSs were separated by a kind of small-powder graphite (SG, 0.5–2 μm) with almost no capacitance to prevent the ultra-thin graphene layer from restacking face to face. In order to separate the GNSs as much as possible, we increased the mass ratio of SG in the GNS–SG composite gradually from 1 : 10 to 1 : 250. The electrochemical properties of different GNS–SG composites as electrode materials for an electric double-layer capacitor (EDLC) have been systematically investigated. It was found that, as the content of GNSs decreased from pure GNS to 1/100 of the GNS–SG composite, specific capacitance increased progressively from 171.8 F g−1 to 417.1 F g−1. As the ratio of GNSs in the GNS–SG electrodes was decreased further (1 : 200, 1 : 250 and 1 : 300), the specific capacitance held a stable value of ∼856.6 F g−1, revealing the intrinsic capacitance of these GNSs. Based on the theoretical specific surface area of graphene and capacitance of a common graphite electrode, the layer number of GNSs here was calculated to be 2–11. This strategy can not only calculate the average layer number but also preliminarily judge the aggregation of GNSs from the capacitance data.

Packing efficiency and accessible surface area of crumpled graphene

Graphene holds promise as an ultracapacitor due to its high specific surface area and intrinsic capacitance. To exploit both, a maximum surface area must be accessible while the two-dimensional (2D) graphene is deformed to fill volume. Here, we study stable crumpled graphene sheets of different lengths, $L$, using full atomistic molecular dynamics (MD) and determine a fractal dimension of $D\ensuremath{\cong}2.36\ifmmode\pm\else\textpm\fi{}0.12$, indicating efficient spatial packing. Introduction of defects inducing a transition from membrane-like to amorphous carbon further enhances packing efficiency. Further, variation of self-adhesion energy indicates a predominant role in randomly folded graphene. We determine that approximately 60% of the specific surface area of graphene is solvent accessible once crumpled and can be tuned with applied compression and crumpling. We analyze the solvent accessible surface area (SASA) and approximate the upper bound of free crumpled graphene capacitance to \ensuremath{\approx}329 F/g. Once crumpled, the achievable capacitance is highly dependent on the confined volume.

High sensitive simultaneous determination of hydroquinone and catechol based on graphene/BMIMPF 6 nanocomposite modified electrode

A novel nanocomposite, comprising of graphene sheet (GS) and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6), was developed on the glassy carbon electrode (GCE) for the simultaneous determination of hydroquinone and catechol in 0.10 M acetate buffer solution (pH 5.0). At the GS/BMIMPF 6/GCE, both hydroquinone and catechol can cause a pair of quasi-reversible and well-defined redox peaks. In comparison with bare GCE and GS modified electrode, GS/BMIMPF 6/GCE showed larger peak currents, which was related to the higher specific surface area of graphene and high ionic conductivity of BMIMPF 6. Under the optimized condition, the cathodic peak current were linear over ranges from 5.0 × 10 −7 M to 5.0 × 10 −5 M for hydroquinone and from 5.0 × 10 −7 M to 5.0 × 10 −5 M for catechol, with the detection limits of 1.0 × 10 −8 M and 2.0 × 10 −8 M, respectively. The proposed method was successfully applied to the simultaneous determination of hydroquinone and catechol in artificial sample, and the results are satisfactory.

Facile synthesis of α-MnO 2/graphene nanocomposites and their high performance as lithium-ion battery anode

α-MnO 2/graphene nanocomposites are synthesized via a facile wet-chemical route, and α-MnO 2 nanosheets are uniformly distributed on the surface of graphene. Their high performance as lithium ion battery anodes is obtained. Their reversible capacity at C/10 rate is up to 726.5 mA h/g, and maintains up to 635.5 mA h/g after 30 cycles. Such a performance can be partly attributed to high electron conductivity, excellent flexibility and high specific surface area of graphene. Also, α-MnO 2 nanostructures can play a role in preventing the pile of graphene nanosheets with the loss of their active surface area. The present results indicate that α-MnO 2/graphene nanocomposites have potential applications in lithium-ion battery anodes.