Exfoliated Graphene Nanosheets Research Articles

Adsorption of cadmium(II) ions from aqueous solution on exfoliated graphene nanosheets and its determination by flame atomic absorption spectrometry

In this study, we investigated the enrichment ability of exfoliated graphene nanosheets for determination of trace cadmium in water and vegetable samples with flame atomic absorption spectrometry. Various experimental parameters that could affect the extraction efficiency have been investigated. Under the optimum conditions, the enrichment factor of the method for the target analyte was 100. A liner response was achieved in the concentration range of 0.3–28.8 ng mL−1. The detection limit and precision of the method were 0.2 ng mL−1 and 0.8%, respectively. The proposed method was applied to determine the cadmium in water, onion, and tomato samples and recoveries of target analyte were in the range 97.6%–98.5%. All of these experimental results indicated that this new procedure could be applied for the determination of trace cadmium in real samples.

Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18wt% IFR, 1wt% CNTs and 1wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40s compared with neat PP.

An FAAS assay utilizing graphene nanosheets-based solid-phase extraction for preconcentration and determination of trace amounts of palladium

A solid-phase extraction procedure is presented for the separation and preconcentration of trace levels of Pd(II) ion by using exfoliated graphene nanosheets (GNs). Experimental parameters such as extraction time, pH, type of eluent, sample volume and temperature were studied in detail. The Pd(II) adsorbed on the GNs was eluted with 1.5 mol L−1 sodium thiosulfite and then determined by flame atomic absorption spectrometry. The effects of potentially interfering ions on the recovery of Pd(II) were also examined. Under optimized conditions, the method provided a preconcentration factor of 100, had a linear range from 5.0 to 100 ng mL−1 of Pd(II), a limit of detection 2.1 ng mL−1, and a relative standard deviation 1.1 % at 20 ng mL−1 of Pd(II). The method was validated by the extraction and determination of Pd(II) in water, tea, lentil and bovine liver samples.

In situ processing of epoxy composites reinforced with graphene nanoplatelets

Abstract Several conventional techniques for nanofiller dispersion (high shear mixing, calendering, or a combination of the two) based on applying shear mechanical forces were studied in order to analyze their efficiency in manufacturing epoxy resin reinforced with graphene nanoplatelets (GNPs). Both provide composites with uniform GNP distributions although the calendering process also induces partial exfoliation of graphene. High-shear mixing could induce the reduction of flakes’ lateral size due to breakage and the rolling of nanoplatelets. Several physical properties of manufactured composites were measured. The density and glass transition temperature increase for composites manufactured by the calendering method due to the steric hindrance of exfoliated graphene nanosheets. Finally, the thermal stability of resin is increased by the addition of GNPs. The degradation temperature is increased up to 20 °C for composites manufactured by the calendering method.

Alkali doped polyvinyl alcohol/graphene electrolyte for direct methanol alkaline fuel cells

Despite the intensive effort directed at the synthesis of anion exchange membranes (AEMs) only a few studies show enhanced ionic conductivity with simultaneous suppression of unfavourable mass transport and improved thermal and mechanical properties. Here we report an alkaline nanocomposite membrane based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) prepared by a simple blending process. The composite membrane shows improved ionic transport due to the homogeneous distribution of the graphene nanosheets which are able to form continuous, well-connected ionic channels. Significant enhancement of the ionic conductivity for the prepared graphene/PVA composite membranes is observed with a 0.7 wt% graphene loading resulting in a ∼126% improvement in ionic conductivity and a ∼55% reduction in methanol permeability. The resulting maximum power density obtained by incorporating the membrane in a cell is increased by ∼148%. A higher graphene loading (1.4 wt%) enhances the adhesion of the nanofiller–matrix, giving a ∼73% improvement in the tensile strength. This study provides a simple route to designing and fabricating advanced AEMs.

An Improved Technique for the Exfoliation of Graphene Nanosheets and Utilization of their Nanocomposites as Fuel Cell Electrodes

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional 2D honeycomb lattice. The graphene sheets in graphite interact with each other through van der Waals forces to form layered structure. The first graphene sheets were obtained by extracting monolayer sheets from the three-dimensional graphite using a technique called micromechanical cleavage in 2004 [. There are numerous attempts in the literature to produce monolayer graphene sheets by the treatment of graphite. The first work was conducted by Brodie in 1859 and GO was prepared by repeated treatment of Ceylon graphite with an oxidation mixture consisting of potassium chlorate and fuming nitric acid [. Then, in 1898, Staudenmaier produced graphite oxide (GO) by the oxidation of graphite in concentrated sulfuric acid and nitric acid with potassium chlorate [. However, this method was time consuming and hazardous. Hummers and Offeman found a rapid and safer method for the preparation of GO and in this method graphite was oxidized in water free mixture of sulfuric acid, sodium nitrate and potassium permanganate [.

In situ deposition of hydroxyapatite on graphene nanosheets

Graphene nanosheets were effectively functionalized by in situ deposition of hydroxyapatite through a facile chemical precipitation method. Prior to grafting of hydroxyapatite, chemically modified graphene nanosheets were obtained by the reduction of graphene oxide in presence of ethylenediamine. The resulting hydroxyapatite functionalized graphene nanosheets were characterized by attenuated total reflection IR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray energy dispersive spectroscopy, Raman spectroscopy and thermogravimetric analysis. These characterization techniques revealed the successful grafting of hydroxyapatite over well exfoliated graphene nanosheets without destroying their structure.

Water vapor adsorption on low-temperature exfoliated graphene nanosheets

Adsorption of water vapor on graphene nanosheets (GNS) derived by vacuum-promoted low-temperature exfoliation method was investigated using a volumetric system. The pristine and thermally modified GNS were characterized with scanning electron microscopy (SEM) observation, Fourier transform infrared (FT-IR) analysis and nitrogen adsorption–desorption. The results show that the absorbed amount of water vapor against the pristine GNS can reach 249cm3/g at 20°C, and the capability of water vapor adsorption was weakened by heat treatment at 500°C and 700°C, the isosteric heat of water vapor adsorption against GNS is 42.6kJ/mol based on the adsorption isotherms at 10°C and 30°C.

Adsorption of Lead(II) Ions from Aqueous Solution on Low-Temperature Exfoliated Graphene Nanosheets

Graphene nanosheets (GNSs) that were obtained by vacuum-promoted low-temperature exfoliation were used to adsorb lead ions from an aqueous system. The pristine and thermally modified GNSs were characterized with scanning electron microscopy observation and X-ray photoelectron spectroscopy analysis. It was interestingly found that the adsorption against lead ions was enhanced by heat treatment, although the oxygen complexes of GNSs showed a significant decrease. In addition, lead ion uptake resulted in an increase in the pH value of the solution. It is supposed that the Lewis basicity of GNSs is improved by heat treatment under a high vacuum, in favor of simultaneous adsorption of lead ions and protons onto GNSs.

Conductive graphene-based macroscopic membrane self-assembled at a liquid–air interface

Free-standing graphene-based macroscopic membranes, which are characterized by a layered structure and tunable conductivity, are prepared by a self-assembly process at a liquid–air interface. Since the preliminary results indicate that it is hard to construct macroscopic graphene membranes solely by low-temperature exfoliated graphene nanosheets (LGNs) at the liquid–air interface, graphene oxide nanosheets (GONs), as the stacking template and sticking component, are introduced into the assembly process of graphene layers to promote the formation of layer-by-layer stacking structure and help form a conductive macroscopic membrane. The conductivity of such a graphene-based membrane can be tuned by changing the GON fraction in the LGN/GON hybrid membrane.

A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets

We demonstrate a highly efficient and large area synthesis of 2-D graphene nanosheets on the surface of flexible graphite foils by electrochemical exfoliation of graphite in an effective electrolyte, poly(sodium-4-styrenesulfonate) solution. A constant current of 150 mA/cm was applied to the vertically aligned graphite (anode) and copper (cathode) sheet in the PSS electrolyte solution during a preset time for electrolytic surface exfoliation of the graphite sheet; uniform expansion of the graphite foil was observed. This expanded foil was characterized using scanning electron microscopy, confocal laser scanning microscopy, and high-resolution transmission electron microscopy. Furthermore, we demonstrate the ability of this high surface area foil, covered with uniform graphene, to enable improved electrolyte permeability and Li ion transfer, thereby enhancing electrochemical performance of Li ion battery electrodes.

Enhanced Mechanical Properties of Graphene-Based Poly(vinyl alcohol) Composites

Graphene, flat carbon nanosheets, has generated huge activity in many areas of science and engineering due to its unprecedented physical and chemical properties. With the development of wide-scale applicability including facile synthesis and high yield, this exciting material is ready for its practical application in the preparation of polymer nanocomposites. Here we report that nanocomposites based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) are prepared via a facial aqueous solution. A significant enhancement of mechanical properties of the graphene/PVA composites is obtained at low graphene loading; that is, a 150% improvement of tensile strength and a nearly 10 times increase of Young’s modulus are achieved at a graphene loading of 1.8 vol %. The comparison between the experimental results and theoretical simulation for Young’s modulus indicates that the graphene nanosheets in polymer matrix are mostly dispersed randomly in the nanocomposite films.