Ball-milled Graphite Research Articles

Graphite nanosheets - polypropylene composites from in toluene delaminated graphite using atactic polypropylene as dispersant

Composites of polypropylene (PP) and graphite nanosheets (GN) are prepared by melt blending PP with a master batch of GN suspended in atactic polypropylene (Mw = 129.000 g/mol). aPP/GN master batches were obtained by wet ball-milling graphite in toluene using the aPP as dispersant. The procedure gives single flakes of GN with crystallite out-of-plane thickness as low as 17.7 nm. PP/aPP/GN composites were obtained with finely dispersed GN, predominantly as single nanosheets from master batches containing aPP dispersant and graphite. Crystallization of the iPP in the composites is facilitated by the presence of aPP and GN. PP spherulites are formed as the graphitic fillers act as strong nucleating agents: the dimensionality of the crystal growth (n = 2-3) and the crystallinity increases with increasing filler content in isothermal and non-isothermal crystallizations. The yield strength of the composites can be enhanced up to 20% by the presence of GN; the presence of aPP counteracts a decrease in elongation at break. Composites prepared from parent graphite or GN without aPP show larger aggregates of nanosheets in the composites.

Broadband Absorber for the Microwave Region Using Ball-Milled Graphite Gratings

A broadband absorber for the microwave region based on a dielectric structure with ball-milled graphite gratings has been proposed. In this absorber, electromagnetic waves in the frequency range of 5.4 to 18 GHz are absorbed efficiently with more than 90% absorptivity. The ball-milled graphite with high a imaginary part of its permittivity used in this work can exhibit dielectric loss to some extent, while there is almost no magnetic loss owing to its low permeability. By comparing the electric field of a single absorbing layer and our grating structure, we found that a λ/4 resonance mode with a narrowband property is excited in the single-layer structure, while the cavity-mode resonance and the edge diffraction effects are the main reasons for the broadband absorption of our designed grating structure. This result provides a guideline for microwave-absorbing materials to greatly extend their bandwidth using a simple structure.

Vein graphite-based counter electrodes for dye-sensitized solar cells

This paper describes the use of ball-milled vein graphite and ball-milled floated graphite counter electrode (CE) materials in dye-sensitized solar cells. The vein graphite used was ball milled, sieved and fraction of particle sizes in the 45–63 μm was used (BMG). Another fraction in the same size range was floated in water to get ball-milled floated graphite (BMFG). Both samples were extensively characterized by electrochemical techniques, Raman spectroscopy and by Total Carbon Analysis. The performance of dye-sensitized solar cells (DSCs) prepared using these CEs were optimized for their adhesion, sintering temperature and thickness. Best performances were obtained for the DSC with CE prepared using graphite:morphol mass ratio of 5:3, sintering temperature of 350 °C and the thickness of 250 μm. Most of the impurities in ball-milled graphite can be removed by the floating technique and the DSC fabricated with ball-milled floated graphite based CE gives 24% better performance than that constructed using just ball-milled graphite based CE. The best conversion efficiency observed is 6.47%. Though this is less than that obtained using Pt CE, it is still very useful in practical applications as per cost considerations.

Heavily aluminated graphene nanoplatelets as an efficient flame-retardant

Substantial amounts of aluminum (Al), which is one of the most abundant elements and period III post-transition metals, can be incorporated into graphene nanoplatelets (GnPs) by ball-milling graphite in the presence of solid Al beads. After thoroughly etching away any unreacted Al residues, the structure and properties of the resultant aluminated GnPs (AlGnPs) were characterized using various analytical techniques including transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The results indicate that AlGnPs contain a considerable amount of Al (30.9 wt%, by TEM energy dispersive X-ray spectrum) and display good dispersibility in various solvents, including water. Next, composite films from aqueous AlGnP/poly(vinyl alcohol) (1/4, wt/wt) solutions were cast and tested for flame retardation. The results indicate that AlGnPs could serve as an outstanding flame retardant that operates by both chemical (condensation) and physical (cooling and blocking) mechanisms. This suggests that AlGnPs may provide a promising option for a new, cost-effective, eco-friendly, yet efficient flame retardant.

Sucrose-mediated mechanical exfoliation of graphite: a green method for the large scale production of graphene and its application in catalytic reduction of 4-nitrophenol

A simple and green method for the large scale production of graphene by ball-milling of graphite with sucrose is exploited here.

Nitrogen-doped graphene by all-solid-state ball-milling graphite with urea as a high-power lithium ion battery anode

Abstract Nitrogen-doped graphene nanosheets (NGNS) are prepared by a novel mechanochemical method via all-solid-state ball-milling graphite with urea. The ball-milling process does not only successfully exfoliate the graphite into multi-layer ( 94%) by pyrindic-N and pyrrolic-N which facilitates the NGNS with enhanced electronic conductivity and Li-ion storage capability. For the first time, we demonstrate that the all-solid-state prepared NGNS exhibits, especially at high currents, enhanced cycling stability and rate capability as Lithium ion battery (LIB) anode active material when compared to pristine graphite and undoped graphene in half-cell configuration. The method presented in this article may provide a simple, clean, economical and scalable strategy for preparation of NGNS as a feasible and promising anode material for LIBs.

Metalloid tellurium-doped graphene nanoplatelets as ultimately stable electrocatalysts for cobalt reduction reaction in dye-sensitized solar cells

One feasible alternative to Pt catalyst in dye-sensitized solar cells (DSSCs) is metalloid tellurium (Te)-doped graphene nanoplatelets (TeGnPs). These were prepared by ball-milling graphite in the presence of Te crystals. Introduction of Te at the edges of TeGnPs was confirmed with various analytical techniques including time of flight secondary ion mass spectrometry (TOF-SIMS). The resultant TeGnPs are herein evaluated as counter electrode (CE) materials for the cobalt reduction reaction (CRR) in DSSCs. TeGnP-CE exhibits much lower charge transfer resistance (Rct=0.15Ωcm2) than that (Rct=1.77Ωcm2) of Pt-CE. More importantly, TeGnP-CE displays an extreme electrochemical stability for the Co(bpy)32+/3+ (bpy=2,2'-bipyridine) redox couple even after 1000 potential cycles. The SM315-based DSSC fabricated with TeGnP-CE shows a better power conversion efficiency (PCE=11.58%) than that with Pt-CE (11.03%), suggesting that TeGnP-CE could be one of the best alternatives to Pt-CE in DSSCs.

Edge-halogenated graphene nanoplatelets with F, Cl, or Br as electrocatalysts for all-vanadium redox flow batteries

The catalytic activity of V2+/V3+ and VO2+/VO2+ redox couples on the halogen-doped graphene nanoplatelets (F-, Cl-, and Br-GNPs) is studied by ball-milling graphite flakes with fluorine (F2), chlorine (Cl2), and bromine (Br2) molecules, respectively. Using the edge-selectively halogenated graphene materials with different edge exfoliation degrees, the vanadium redox reactions can be significantly facilitated by having abundant edge defects with large surface area in the order: Br-GNP>Cl-GNP>F-GNP. The influence of halogen functionalization on graphene nanoplatelets towards vanadium redox couples is further confirmed by stack-type vanadium redox flow batteries that demonstrates better cell performance than graphene nanoplatelets without dopant at the edges. Notably, the Br-GNP showed unique electrochemical performance of increased initial charge/discharge capacity and improved rate capability, respectively. It was found that halogen doping on graphene-based materials can promote vanadium redox reactions by creating effective active sites, and the electrocatalytic activity is dependent on edge exfoliation degree and well-preserved basal planes.

Characterization of reactive graphene oxide synthesized from ball – milled graphite: its enhanced reinforcing effects on cement nanocomposites

In this study, commercial graphite powder (GP) of particle size 100 micron was subjected to high energy ball-milling (HEBM) to produce ball-milled graphite powder (BMGP) of particle size 780 nm. Both GP and BMGP were converted to respective graphene oxides (GOs) (labeled as GO1 and GO2) using Hummer’s method, which were then characterized using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X- ray diffraction (XRD). GO1 and GO2 were then investigated for their effects on compressive strength of cement mortar matrix at different curing times of 7, 14, and 28 days. Effect of variation of concentration (ranging between 0.125 and 1.00 wt% of cement) of GO1 and GO2 on the strength of matrix was examined. Microstructures of GO1-cement mortar nanocomposite and GO2-cement mortar nanocomposite were studied after 28 days of curing using SEM. Obtained results show that addition of 1.00 wt% GO1 and GO2 showed best performance by increasing the strength to 63 and 78%, respectively, in comparison to the unreinforced control sample. Improved performance of GO2 was attributed to more number of reactive sites of GO nanosheets induced by ball-milling treatment of graphite precursor.

One-step preparation of graphene nanosheets via ball milling of graphite and the application in lithium-ion batteries

An improved method for mass production of good-quality graphene nanosheets (GNs) via ball milling pristine graphite with dry ice is presented. We also report the enhanced performance of these GNs as working electrode in lithium-ion batteries (LIBs). In this improved method, the decrease of necessary ball milling time from 48 to 24 h and the increase of Brunauer–Emmett–Teller surface area from 389.4 to 490 m2/g might be resulted from the proper mixing of stainless steel balls with different diameters and the optimization of agitation speed. The as-prepared GNs are investigated in detail using a number of techniques, such as scanning electron microscope, atomic force microscope, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray diffractometer, and Fourier transform infrared spectroscopic. To demonstrate the potential applications of these GNs, the performances of the LIBs with pure Fe3O4 electrode and Fe3O4/graphene (Fe3O4/G) composite electrode were carefully evaluated. Compared to Fe3O4-LIBs, Fe3O4/G-LIBs exhibited prominently enhanced performance and a reversible specific capacity of 900 mAh g−1 after 5 cycles at 100 and 490 mAh g−1 after 5 cycles at 800 mA g−1. The improved cyclic stability and enhanced rate capability were also obtained.

Nitrogen-doped graphene by ball-milling graphite with melamine for energy conversion and storage

N-doped graphene was prepared by ball milling of graphite with melamine. It was found that ball-milling reduced the size of graphite particles from 30 to 1 μm and facilitated the exfoliation of the resultant small particles into few-layer N-doped graphene nanosheets under ultrasonication. The as-prepared N-doped graphene nanoplatelets (NGnPs) exhibited a nitrogen content as high as 11.4 at.%, making them attractive as efficient electrode materials in supercapacitors for energy storage and as highly-active metal-free catalysts for oxygen reduction in fuel cells for energy conversion.

Preparation of polyvinylpyrrolidone-decorated hydrophilic graphene via in situ ball milling

Graphene sheets were processed by in situ ball-milling graphite flakes in an ethanol solution of polyvinylpyrrolidone (PVP). Results showed exfoliation of graphite into graphene, with surfaces decorated with PVP. This new PVP-functionalized graphene could be further dispersed in varieties of polar solvents, including ethanol, dimethylformamide, and water. Resulting homogeneous solution has more than 4 months of storage stability, with the highest concentration of graphene reaching 1.7300 mg/ml.

Ball-Milling of Graphite and Multi-Wall Carbon Nanotubes

The structural modification of graphite and multi-wall carbon nanotubes (MWCNTs) during ball-milling was examined. A comparison of structures after ball-milling was made between graphite and MWCNTs. The ball milling parameters were also examined: milling atmospheres, milling methods, milling mode and the addition of additive materials. In some experiments, hard materials such as alumina or silica were added to graphite and MWCNTs as additives to see whether graphite and MWCTs were shortened by ball-milling. The ball-milling of graphite and MWCNTs with liquid additives reduced the agglomeration of MWCNT and transformed graphite to graphenes. The ball-milling of MWCNTs under impact mode usually resulted in the formation of an amorphous phase, whereas that under friction mode induced the fattening of nanotubes. The results showed that a variety of carbon nanomaterials could be obtained by the proper controlling of ball milling. The structurally modified graphite and MWSNTs are expected to be utilized for energy storage application.

Molybdenum phosphide-graphite nanomaterials for efficient electrocatalytic hydrogen production

Clean hydrogen energy technology is an alternative to a fossil fuel-based energy economy. Efficient and economical catalysts are necessary for large-scale hydrogen generation. We report MoP and MoP-graphite nanosheets prepared by ball milling commercial compounds as efficient electrocatalytic materials for hydrogen generation via the hydrogen reduction mechanism. The hydrogen generated through electrochemical catalysis was evaluated using gas chromatography. The effects of ball milling time and proportions of MoP-graphite nanosheets on electrocatalytic activity were investigated. The new nanomaterials were characterized using powder XRD, SEM and BET surface area measurements. The results suggest superior electrocatalytic performance with a balance of ball-milled MoP and graphite. A Tafel slope of 63mV/dec was obtained for this new material.

Hydrogen on graphene investigated by inelastic neutron scattering

Inelastic neutron scattering experiments and ab-initio calculations have been used to investigate the vibrational modes, in a wide energy region between 0 and 200 meV, of hydrogenated graphene produced by chemical method. The results show the presence of atomic hydrogen chemisorbed at the graphene surface. At 10 K, the measured high energy density of states is remarkably similar to that of hydrogenated ball-milled graphite, in which hydrogen is most likely bonded to C atoms at the edges. In fact, in both hydrogenated graphene and hydrogenated ball-milled graphite, the high frequency modes (100-200 meV) show strong similarities with the C-H bending modes of the coronene molecule, in which hydrogen is bonded at the edges. This hypothesis has been supported by ab-initio calculations.

Powder properties of hydrogenated ball-milled graphite

Ball milling is an effective way of producing defective and nanostructured graphite. In this work, the hydrogen storage properties of graphite, ball-milled in a tungsten carbide milling pot under 3bar hydrogen for various times (0–40h), were investigated by TGA-Mass Spectrometry, XRD, SEM and laser diffraction particle size analysis. For the conditions used in this study, 10h is the optimum milling time resulting in desorption of 5.5wt% hydrogen upon heating under argon to 990°C. After milling for 40h, the graphite became significantly more disordered, and the amount of desorbed hydrogen decreased. After milling up to 10h, the BET surface area increased while particle size decreased; however, there is no apparent correlation between these parameters, and the hydrogen storage properties of the hydrogenated ball-milled graphite.

Oxygen reduction reaction in a droplet on graphite: direct evidence that the edge is more active than the basal plane.

Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.

A novel method for fabrication of Fe catalyst used for the synthesis of carbon nanotubes

Carbon nanotubes (CNTs) have been grown by decomposition of propane over a nanocamposite catalyst by chemical vapour deposition (CVD). The catalyst was prepared from an aluminum/iron oxide/graphite mixture milled in a high-energy ball-milling equipment. Scanning and transmission electron microscopies, Raman spectroscopy and X-ray diffraction measurements have been carried out in order to investigate the catalyst and synthesized CNTs. The results show that iron nanoparticles are produced in an alumina and ball-milled graphite matrix. This produced nanocomposite is used as a catalyst to synthesize CNTs via CVD successfully. The yield of CNTs formation was greatly influenced by the milling time and deposition temperature.

Investigation of the effects of graphite flake alignment on thermal emissivity by applying a magnetic field during coating of an aluminum sheet

In this study we investigated the effects of graphite flake alignment on thermal emissivity by applying a magnetic field during coating of aluminum sheets with graphite. The coating paste was prepared by ball milling graphite flakes with an organic binder. The graphite flake content was 9.1, 13.0, 16.7, 20.0, or 23.1 wt.%. After coating of aluminum sheets with the paste by dipping, a magnetic field was applied vertically to the coated aluminum sheet by use of neodymium magnets. It was observed that the graphite flakes were aligned at an angle to the surface by application of the magnetic field. In contrast, in the absence of the magnetic field the graphite flakes were aligned horizontally on the aluminum sheets. The surface roughness of specimens prepared by use of a magnetic field (MF; R a = 10.172–14.654 μm) was more than twofold that of specimens for which no magnetic field was applied (NMF; R a = 4.564 μm). The thermal emissivity of MF9 (9.1 wt.% graphite; e = 0.80) was higher than that of NMF9 (9.1 wt.% graphite; e = 0.77). The thermal emissivity of MF20 (20.0 wt.% graphite) was 0.91, the highest in this study. It was shown that flakes aligned at an angle to the surface contribute to enhanced thermal emissivity. Well aligned graphite flakes are therefore expected to enable high thermal dissipation from electronic components.

Graphene Nanoplatelets Doped with N at its Edges as Metal‐Free Cathodes for Organic Dye‐Sensitized Solar Cells

Challenging precious Pt-based electrocatalysts for dye-sensitized solar cells (DSSCs), graphene nanoplatelets that are N-doped at the edges (NGnPs) are prepared via simply ball-milling graphite in the presence of nitrogen gas. DSSCs based on specific nanoplatelets designated "NGnP5" display superior photovoltaic performance (power conversion efficiency, 10.27%) compared to that of conventional Pt-based devices (9.96%). More importantly, the NGnP counter electrode exhibits outstanding electrochemical stability and electrocatalytic activity with a cobalt-complex redox couple.