Graphene Nanopowder Research Articles

Effect of Filler Loading on the Tensile Properties of Multi-walled Carbon Nanotube and Graphene Nanopowder filled Epoxy Composites

At present, carbon nanotube (CNT) and graphene are attracting a great deal of attention due to their superior structural and functional properties as well as its suitability for engineering applications. In this work, multi-walled carbon nanotube (MWCNT) and graphene nanopowders (GNP) filled epoxy composites were fabricated via ultrasonication and casting method. The effect of MWCNT and GNP loadings (0-1 vol%) on tensile properties of filled epoxy composites were investigated. The experimental results prove that the strength and modulus of filler (MWCNT and GNP) filled epoxy composites are lower as compared to pristine epoxy. However, the addition of GNP at 0.8 vol% had slightly increased the composite tensile modulus which was approximately 3.4% in comparison with pristine epoxy. Thus, in general it indicates that the addition of filler (MWCNT and GNP) had reduced the mechanical properties of epoxy composites. The reason for this is due to the high aspect ratio and high van der Waals attraction of the MWCNT causes entanglement among nanotube. Subsequently, this leads to aggregations and agglomerations which limit the load transfer from the matrix to nanotubes. Similarly, agglomeration in GNP composites is due to the stacking of flaky-shaped GNP particles and the sharp edges of GNP cause cracks to initiate and resulting in lower mechanical properties.

Wear and friction behaviour of poly-ether-ether-ketone (PEEK) filled with graphene, WS2 and CNT nanoparticles

High-performance polymers show a great potential to replace machined metal components in a wide variety of applications owing to their promising mechanical, thermal and tribological properties. However, further improvements in their properties are still needed. The aim of this study was to evaluate and compare the effect of the material type and the morphology of well-known solid lubricant nanoparticles on the tribological properties of poly-ether-ether-ketone (PEEK) composites. Different nanoparticles were added to the PEEK matrix: WS2 fullerene-like (WS2F), WS2 needle-like (WS2N), carbon nanotubes (CNT) and graphene nanopowder (GNP). The results of dry-sliding tribological tests show that the material and the morphology of the nanoparticles have a crucial effect on both the wear and the coefficient of friction, primarily by affecting their macroscopic hardness, as well as the thickness and the surface coverage of their transfer films. The WS2-based nanoparticles outperformed the carbon-based nanoparticles in terms of wear performance; compared to PEEK, WS2F improved the wear rate by 10% and the WS2N by 60%, while the carbon-based particles deteriorated the wear behaviour by 20% (CNT) and as much as three times in the case of the GNP. The addition of WS2F nanoparticles and the CNT resulted in a lower coefficient of friction compared to the WS2N particles and the GNP.

The Electrochemical Performance of Li3V2(PO4)3/Graphene Nano-powder Composites as Cathode Material for Li-ion Batteries

The Li3V2(PO4)3/graphene nano-particles composite was successfully synthesized by a facile sol-gel method. The addition of a graphene in Li3V2(PO4)3(LVP) showed the high crystallinity and influenced the morphology of the Li3V2(PO4)3 particles observed in X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LVP/graphene samples were well connected, resulting in fast charge transfer. The effect of the addition graphene nano-particles on electrochemical performance of the materials was investigated. Compared with the pristine LVP, the LVP/graphene composite delivered a higher discharge capacity of 122 mAh g �1 at 0.1 C-rate, better rate capability and cyclability in the potential range of 3.04.3 V. The electrochemical impedance spectra (EIS) measurement showed the improved electronic conductivity for the LVP/graphene composite, which can ensure the high specific capacity and rate capability.

The seeded growth of graphene.

In this paper, we demonstrate the seeded growth of graphene under a plasma chemical vapor deposition condition. First, we fabricate graphene nanopowders (~5 nm) by ball-milling commercial multi-wall carbon nanotubes. The graphene nanoparticles were subsequently subject to a direct current plasma generated in a 100 Torr 10%CH4 - 90%H2 gas mixture. The plasma growth enlarged, over one hour, the nuclei to graphene sheets larger than one hundred nm2 in area. Characterization by electron and X-ray diffraction, high-resolution transmission electron microscopy images provide evidence for the presence of monolayer graphene sheets.

Multiwalled Carbon Nanotube@Reduced Graphene Oxide Nanoribbon as the Counter Electrode for Dye-Sensitized Solar Cells

In this study, a new core–shell heterostructure of multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) was prepared by modified microwave-assisted synthesis step and a chemical reduction. The core–shell heterostructure of MWCNT@rGONR was used as the catalytic film of the counter electrode (CE) of a dye-sensitized solar cell (DSSC). The chemical state and the degree of defects on the surface of MWCNT@rGONR were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectra, respectively. Transmission electron microscopy (TEM) image of the film of MWCNT@rGONR shows graphene sheet, covering on a MWCNT, indicating a core of the carbon nanotube and its shell of graphene. Photocurrent density–voltage characteristics of the DSSCs, using commercial graphene nanopowder (GNP), MWCNT, and MWCNT@rGONR as the CE materials were obtained at 100 mW cm–2. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrocatalytic abilities of the films...

Improving the efficiency of a poly(3-hexylthiophene)-CuInS2 photovoltaic device by incorporating graphene nanopowder

In the present work, the effect of incorporation of graphene on the poly(3-hexylthiophene) (P3HT):CuInS 2 quantum dot (CIS QD)-based solar cell has been studied. For this purpose, the concentration of graphene is varied from 0 to 0.01% w/w in P3HT–CIS (1:0.5) film. It is found that graphene does not deteriorate the absorption of the composite film. It assists in dissociating the photogenerated excitons (both in P3HT and QDs) owing to its two-dimensional structure and high electron affinity as is evident by photoluminescence (PL) quenching. At 0.01% w/w concentration of graphene about ∼95% of PL is quenched. The electrical characteristics show that the incorporation of graphene enhances the efficiency of the device by establishing interconnected conducting pathways in the volume of polymer matrix. The maximum efficiency is observed to be 1.5% at 0.005% w/w content of graphene. However, at higher concentration, i.e., 0.01% w/w, the device starts deteriorating.

The nature of high surface energy sites in graphene and graphite

Variations in the adsorption enthalpies of acetone to few-layer graphene and graphite nanopowders were analyzed as a function of surface coverage. The adsorption enthalpies were measured by inverse gas chromatography at low monolayer coverage levels (0.1–20%). The adsorption enthalpies increased from −13kcal/mol at the lowest coverage to −7.5kcal/mol. We fitted the measured adsorption enthalpies as a function of coverage using a two-state model and estimated the number of high-energy sites on both materials. The graphite powder had seven times more high-energy sites than the few-layer graphene, which explains why the adsorption enthalpies for graphite increased more slowly with increasing coverage. We also performed a theoretical study based on density functional theory calculations using a functional that accounts for dispersive interactions to elucidate the nature of the high-energy adsorption sites. The calculated adsorption enthalpies ranged from −16 to −1kcal/mol while the adsorption enthalpy to a plain graphite surface was −9kcal/mol. The high-energy adsorption sites were localized on surface steps and edge-cavities. The adsorption enthalpies at very low coverage therefore corresponded to adsorption on steps and edge cavities, while those measured at coverage levels of ∼4% or more reflected adsorption to the flat surface.

The Effect of Carbon Additives on the Microstructure and Conductivity of Alkaline Battery Cathodes

This paper describes research to understand the relationships between materials, microstructure, and performance for primary alkaline battery cathodes composed primarily of electrolytic manganese dioxide (EMD). Specifically, the effect of various carbon additives on electronic transport within cathodes was investigated. Of the various carbon additives investigated, TIMCAL BNB90 was the best performer and graphene nanopowder was the next best. These additives had the lowest Scott density and highest BET surface area of the tested additives, and exhibited well-connected and elongated carbon pathways in SEM/FIB cross sections. Additionally, this work shows a decrease in electronic conductivity for the porous cathode in the presence of KOH electrolyte. The two top-performing cathodes, when wet with concentrated KOH had a conductivity that was about 30% below that of the dry conductivity.

Evaluation of Amperometric Dot Microsensors for the Analysis of Serotonin in Urine Samples

In this study, twenty-four amperometric dot microsensors based on carbon materials, (e.g., graphite (G) and graphene (GR) and carbon nanopowder (CN)), unmodified and modified with TiO2, and phthalocyanines: basic phtalocyanine (Pc), FeIIIphthalocyanine (FeIIIPc) and FeIIphthalocyanine (FeIIPc) are evaluated and tested for their ability for the analysis of serotonin (5-HT) in biological fluids (e.g. urine samples), using differential pulse voltammetry (DPV). Cyclic voltammetry (CV) was used to optimize the working conditions, e.g., pH, and electrolyte for the amperometric dot microsensors revealing (0.1 mol L−1) KCl and pH = 3.0 phosphate buffer as the optimum electrolyte and pH conditions for the assay of serotonin. The selected amperometric dot microsensors with preference to the G-FeIIIPc followed by the GR-FeIIIPc modified microsensors were used for the reliable analysis of serotonin in urine samples, with recoveries higher than 94.00%.

Properties of graphene nanopowder and multi-walled carbon nanotube-filled epoxy thin-film nanocomposites for electronic applications: The effect of sonication time and filler loading

Graphene nanopowder (GNP) and multi-walled carbon nanotube (MWCNT)-filled epoxy thin-film composites were fabricated using ultrasonication and the spin coating technique. The effect of sonication time (10, 20 and 30min) and GNP loading (0.05–1vol%) on the tensile and electrical properties of GNP/epoxy thin-film composites was investigated. The addition of GNP decreased the material’s tensile strength and modulus. However, among the tested samples, the GNP/epoxy composites produced using 20min of sonication time had a slightly higher tensile strength and modulus, with a lower electrical percolation threshold volume fraction. The effect of sonication time was supported by morphological analysis, which showed an improvement in GNP dispersion with increased sonication time. However, GNP deformation was observed after a long sonication time. The GNP/epoxy composites at different filler loadings showed higher electrical properties but slightly lower tensile properties compared with the MWCNT/epoxy composites fabricated using 20min of sonication time.

Graphene/polydimethylsiloxane nanocomposite strain sensor

The objective of this research is to fabricate graphene nanopowder composites based on polydimethylsiloxane (PDMS) and to characterize the gauge factor of the graphene/PDMS composites for the use of strain sensors. The fabrication of graphene/PDMS composites can be accomplished by simple sonication and micro molding processes. We found that the measured gauge factors strongly depend on the concentration of graphene flakes in the composites. Obtained gauge factor of the graphene/PDMS composite strain sensor reached about 233 at a graphene concentration of 8.33 vol.%, which was measured within a strain range of 2%.

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid

The graphene nanopowder for electro-catalytic oxidation of dopamine and uric acid in the presence of ascorbic acid has been investigated by cyclic voltammetry, linear polarization and chronoamperometry. The graphene nanopowder modified electrode was prepared using the drop coating method, which displayed excellent electrocatalytic activity towards the oxidation of dopamine and uric acid compared with the bare glassy carbon electrode in phosphate buffer solution at pH = 7.0. Linear responses for dopamine and uric acid were obtained in the ranges of 3.3 μmol/L to 249.1 μmol/L and 6.7 μmol/L to 386.3 μmol/L with detection limits of 1.5 μmol/L and 2.7 μmol/L (S/N = 3), respectively. The response time was less than 2 s in case of dopamine and 3 s in case of uric acid, respectively. The results demonstrated that the graphene nanopowder had potential for detecting dopamine and uric acid.

Structure of Graphite Nanosheets Formed by Plasma Discharge in Liquid Ethanol

Graphite nanosheets (GNSs) were synthesized by low-current plasma discharge in ultrasonically cavitated liquid ethanol. Effective elimination of the byproducts was confirmed by different techniques. The results indicated that there were two types of ordering along the crystallographic caxis in the GNSs, which were ABAB- and turbostratic stacking of successive graphene layers. Most of the GNSs were estimated to be between 8.8 and 30 nm thick, and their lateral sizes ranged from several hundred nanometers up to 11 μm with an average size of 4–5 μm. A simple mechanism for GNS formation by exfoliation of graphene layers covering the Fe–Pt alloy nanoparticles is proposed. The measured conductivity of GNSs was comparable to that of the reference graphene nanopowder and reference single graphene sheets.

Fabrication of ionic polymer actuator with graphene nanocomposite electrodes and its characterization

In the present study, a novel ionic polymer actuator employing a graphene nanocomposite (GN) as its electrodes was fabricated. By a conventional solvent mixing of a graphene nanopowder and polystyrene, a GN solution was prepared. The solution was then utilized in a dip coating process of an ionic polymer membrane, forming a thin liquid GN layer on the surfaces of the ionic polymer membrane. After removing the solvent from the coated film, the solidified conducting GN layer could be obtained, which was used as the electrodes in the ionic polymer actuator. An electrical property of the GN layer formed by the present method was characterized, confirming the possibility of the present GN in the actuator applications. Simple and reverse bending motions of the fabricated actuator were also investigated, verifying the usefulness of both the GN layer and the present simple fabrication method.

A novel core–shell multi-walled carbon nanotube@graphene oxide nanoribbon heterostructure as a potential supercapacitor material

A novel core–shell heterostructure with multi-walled carbon nanotubes as the core and graphene oxide nanoribbons as the shell (MWCNT@GONR), fabricated by the facile unzipping of MWCNTs with the help of microwave energy, was used as a supercapacitor (SC) electrode material. Graphene nanopowder (GNP) and multi-walled carbon nanotubes (MWCNTs) have also been applied as SC materials for comparison. A smooth surface and a tube-like structure are found for the GNP and MWCNTs, respectively, while for the MWCNT@GONR material, graphene oxide sheet structures are observed on both sides of central nanotube cores that retain their tube-like structure. The specific capacitance is much better for the SC electrode with the MWCNT@GONR (252.4 F g−1) compared to the SC electrodes with commercial MWCNTs (39.7 F g−1) and GNP (19.8 F g−1), as determined using cyclic voltammetry (CV) at a scan rate of 50 mV s−1, which is due to the defective edges of the nanostructures in the former. The SC electrode with the MWCNT@GONR also exhibits good stability and capacitance retention even after 1000 cycles of galvanostatic charge–discharge testing, indicating its potential as a SC material. CV, galvanostatic charge–discharge (GC/D) and electrochemical impedance spectroscopy (EIS) were applied to analyze the SC performance.

Carbon–graphene nanocomposite cathodes for improved Co(ii/iii) mediated dye-sensitized solar cells

Cobalt-based electrolytes have significantly advanced the tunability and performance of dye-sensitized solar cells. The typically used platinum cathodes are expensive and non-optimal for cobalt complexes, motivating the search for replacements. Graphene nanopowders are a viable alternative but they are mechanically unstable as catalysts due to their poor substrate adhesion. Here we report a new type of carbon–graphene nanocomposite that maintains the catalytic performance of graphene with enhanced adhesion via a conductive carbon matrix. These nanocomposites were synthesized by carbonizing mixtures of graphene nanoplatelets with a carbon-source, poly(acrylonitrile). The resulting materials had tunable performance with a low charge transfer resistance of ∼1 Ω cm2 using as little as 20% graphene. Dye-sensitized solar cells fabricated with these carbon–graphene nanocomposites had enhanced fill factors and enhanced power conversion efficiencies as compared to platinum cathodes. Accelerated mechanical aging led to the complete detachment of graphene-only electrodes whereas carbon–graphene nanocomposites were stable.