Graphite Nanoflakes Research Articles

High-efficiency transformation of amorphous carbon into graphite nanoflakes for stable aluminum-ion battery cathodes.

Highly efficient strategies for the transformation of amorphous carbon into graphite with high graphitization and crystallinity features have been significantly pursued in recent years; however, critical issues, including high processing temperature, insufficient graphitization, introduction of catalyst impurities, complicated post-purification procedures, and generation of greenhouse gas, still remain in traditional approaches. For significantly addressing these challenges, herein, a highly efficient catalyst-free, eco-friendly and low-temperature electrochemical transformation strategy was proposed for the preparation of highly graphitized porous graphite nanoflakes. Using inert SnO2 as an anode in CaCl2-LiCl molten salts, the graphitization transformation of amorphous carbon materials could be realized at 700 °C, approaching the record in high-efficiency converting amorphous carbon to graphite; moreover, systematical analysis was performed to understand the electrochemical transformation of amorphous carbon into highly graphitized graphite nanoflakes. For extending their valuable applications, the as-prepared graphite nanoflakes were further utilized as cathodes in aluminum-ion batteries, which exhibited significantly promising energy storage performance; moreover, an initial discharge capacity of 63.6 mA h g-1 at a current density of 200 mA g-1 was achieved, which eventually became 55.5 mA h g-1 with a coulombic efficiency of 95.4% after 1000 cycles; thus, these cathodes exhibited stable long-term cycling performance. The combination of low-temperature electrochemical transformation and the subsequent high-performance applications of these nanoflakes in energy storage indicates that the proposed strategy is highly efficient for the transformation and utilization of abundant amorphous carbon resources for the realization of high value-added applications.

Comparative Study of Mechanically Milled MoS₂ and MoSe₂ in Graphite Matrix as Anode Materials for High-Performance Lithium-Ion Batteries.

Nanocomposites of MoS2/graphite and MoSe2/graphite were formed from two-dimensional materials (MoS2 and MoSe2) and graphite using a one-step ball-milling method (high energy mechanical milling, HEMM). As anode materials for lithium-ion batteries (LIBs), these nanocomposites showed higher specific capacity and greater stability during long cyclic operation compared to their pure counterparts (MoS2 and MoSe2). X-ray diffraction and transmission electron microscopy revealed that graphite nanoflakes were effectively exfoliated and covered MoS2 or MoSe2 layers to form homogeneous nanostructures via HEMM. As a result, the electrochemical performances of both MoS2/graphite and MoSe2/graphite were excellent; the specific capacities were as high as 684.8 (MoS2/graphite) and 787.3 mAh g-1 (MoSe2/graphite) after 100 cycles. Also, when compared with MoS2/graphite, the MoSe2/graphite nanocomposite showed higher specific capacity and better rate capability performance due to larger interlayer spacing, leading to fast and facile movement of Liions. Overall, we demonstrate that homogeneous nanocomposites between similar layered materials (MoS2, MoSe2 and graphite) can be easily synthesized via one-step HEMM, which can be used as excellent anode materials for LIBs.

Water Dispersible Few-Layer Graphene Stabilized by a Novel Pyrene Derivative at Micromolar Concentration.

The search for graphene or few-layer graphene production methods that are simple, allow mass production, and yield good quality material continues to provoke intense investigation. The present work contributes to this investigation through the study of the aqueous exfoliation of four types of graphene sources, which are namely graphite and graphite nanoflakes with different morphologies and geographical origins. The exfoliation was achieved in an aqueous solution of a soluble pyrene derivative that was synthesized to achieve maximum interaction with the graphene surface at low concentration (5 × 10−5 M). The yield of bilayer and few-layer graphene obtained was quantified by Raman spectroscopic analysis, and the adsorption of the pyrene derivative on the graphene surface was studied by thermogravimetric analysis and X-ray diffraction. The whole procedure was rationalized with the help of molecular modeling.

UV Photopatternability and Electrical Properties of GnF/SU-8 Composites Controlled by GnF Concentration

The GnF/SU-8 composites are new polymer matrix composites (PMCs) composed of graphite nanoflakes (GnFs) bound together by SU-8 photoresist. The PMCs therefore have excellent ultraviolet (UV) photopatternability and high electrical properties. In spite of the unique material properties of GnF/SU-8 composites, much still remains uncertain about their controllability in both UV photopatternability and electrical properties. Here, we investigate 7 kinds of GnF/SU-8 composites having different GnF concentrations of 5.0 to 25.0 wt.% to characterize the changes in the UV photopatternability (i.e., polymerized thickness and photopattern quality) and electrical conductivity of GnF/SU-8 composites caused by a variation in GnF concentration. The polymerized thickness of GnF/SU-8 composites is measured to be in the range of 4.06 to 23.99 μm, which is inversely proportional to GnF concentration and also directly proportional to UV dose (i.e., 345 to 3,450 mJ/cm2) because of the screening effect of GnF existed in the composites; the photopattern quality at the edge is in inverse proportion to GnF concentration. An increase in GnF concentration leads to a significant change in the electrical conductivity of GnF/SU-8 composites in a proportional way (up to 25.34 S/m). The GnF/SU-8 composites are expected to be widely used as UV photopatternable and electrically conductive PMCs for diverse engineering applications.

Synergistic effects of graphite nano-flakes and submicron SiC particles on the characteristics of spark plasma sintered ZrB2 nanocomposites

ZrB2 ceramic (Z), ZrB2–25 vol% SiC composite (ZS) and ZrB2–25 vol% SiC composite doped with 5 wt% graphite (ZSG) were fabricated by spark plasma sintering process. The sintered samples were compared to investigate the effects of submicron SiC particles and graphite nano-flakes on sinterability, microstructure and mechanical properties of ZrB2-based ceramic matrix composites. Spark plasma sintering at 1900 °C for 7 min under 40 MPa resulted in fully dense ZS and ZSG samples but a relative density of 96.1% was achieved for Z sample. The growth of ZrB2 grains was effectively decelerated by addition of submicron SiC particles and graphite nano-flakes. Hardness values of 13.1, 19.5 and 16.6 GPa were measured for Z, ZS and ZSG samples, respectively, which verify the hardening effect of SiC and softening effect of graphite in ZrB2-based composites. By the simultaneous addition of SiC and graphite into ZrB2 matrix, the indentation fracture toughness of ZSG sample reached 6.7 MPa m½, meaningfully higher than those of Z and ZS samples with toughness values of 3.2 and 4.3 MPa m½, respectively. Such an improvement in the fracture toughness of ZSG nanocomposite was attributed to the presence of graphite nano-flakes as well as the in-situ formed ZrC and B4C nano-particles. Flexural strength of Z, ZS and ZSG samples reached 445, 624 and 631 MPa, respectively. Although SiC had a remarkable strengthening effect in the ZrB2-based ceramic, the addition of graphite together with SiC had not a significant impact on the flexural strength of composite material.

Mechanoelectrical properties of a GnF/PDMS composite controlled by the aspect ratio and concentration of GnF

A functional polymer-matrix composite (PMC) with controllable material properties is emerging as a promising material for the smart sensors in structural health monitoring (SHM). A GnF/PDMS composite is developed as a new functional PMC by blending graphite nanoflakes (GnFs) with polydimethylsiloxane (PDMS) where GnF and PDMS are used as a reinforcing/conductive filler and an elastic host matrix, respectively. We characterize the mechanoelectrical property-controllable GnF/PDMS composite, mainly focusing on the following issues: (i) determination of the best solvent for the preparation of a GnF/PDMS composite solution, (ii) exploration of changes in the mechanoelectrical properties of the functional PMC induced by variations in the aspect ratio (AR) and concentration of GnF. Among 9 kinds of common solvents, benzene shows both high GnF dispersibility and excellent PDMS compatibility, therefore being chosen as the optimal solvent. Variations in GnF AR (223–1017) and GnF concentration (1.0–25.0 wt.%) lead to significant changes in the elastic modulus, fracture strain, electrical conductivity, and gauge factor of the functional PMC in the ranges of 0.39–13.8 MPa, 0.09 to 2.54, 6.97 × 10−6 to 221.0 S/m, and 6 to about 37,000, respectively. The empirical models for predicting the mechanoelectrical properties of the functional PMC are also intensively studied. Our GnF/PDMS composite is expected to be used as a functional PMC for the development of smart sensors that detect deformation and fracture in structures.

A statistical approach towards processing optimization of ZrB2–SiC–graphite nanocomposites. Part I: Relative density

The influence of sintering variables and nano-graphite addition on the densification behavior of ZrB2–SiC based ceramics has been investigated. The ZrB2 matrices, reinforced with 25 vol% submicron SiC particles and 0–10 wt% graphite nano-flakes, were fabricated by spark plasma sintering (SPS). The Taguchi design of experiment approach was employed to study the effects of SPS variables (temperature, dwell time, and pressure) and nano-graphite content. Statistical analysis of variance identified the SPS temperature and graphite content as the most influential parameters affecting the relative density of as-sintered ceramics, whereas the SPS pressure did not have an obvious impact on the densification process. The thermodynamical and microstructural analyses showed that the addition of graphite nano-flakes led to the removal of the thin oxide layers from the surfaces of the non-oxide starting materials. The elimination of such harmful oxides and the in-situ formation of nano-sized ZrC and B4C phases resulted in the enhancement of sinterability of ZrB2–SiC–graphite nanocomposites. A fully dense sample was achieved at optimal processing conditions; i.e. by sintering at 1900 °C for 7 min under 40 MPa and adding 5 wt% graphite nano-flakes.

Effect of the noncovalent functionalization of graphite nanoflakes on the performance of MnO2/C composites

In this paper, graphite nanosheets were modified by aminopyrene (Amin), 1-pyrenecarboxylic acid (PCA) and cetyltrimethyl ammonium bromide. Based on physical (field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy) and electrochemical tests (cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charging/discharging curves), their physical and chemical properties were investigated. The physical characterization and electrochemical performance analysis indicated that the different reducing agents, technical methods and small organic molecules significantly influenced the precipitation of MnO2. When the small organic molecule was PCA, the G/MnO2 composite material had the best electrochemical capacity and stability. PCA possesses four rings; therefore, PCA can interact with graphite layers and peel off the graphite to form MnO2/single-layer graphene. During the loading of MnO2, PCA did not influence the structure of MnO2 crystals. After modification by PCA, the MnO2/C composite possessed long-term cycling stability. The changes in the morphological and structural evolutions in nanocrystalline MnO2 for the MnO2/C composite differed from those observed for pure MnO2.

Effects of nano-graphite content on the characteristics of spark plasma sintered ZrB2–SiC composites

In this study, ZrB2–25vol% SiC composite containing 0, 2.5, 5, 7.5 and 10wt% graphite nano-flakes were prepared by spark plasma sintering (SPS) process at 1900°C for 7min under 40MPa. The fabricated composite samples were compared to examine the influences of nano-graphite content on the densification, microstructure and mechanical properties of ZrB2–SiC-based ultrahigh temperature ceramics. Fully dense composites were obtained by adding 0–5wt% nano-graphite, but higher amounts of additive led to a small drop in the sintered density. The growth of ZrB2 grains was moderately hindered by adding nano-graphite but independent of its content. The hardness linearly decreased from 19.5 for the graphite-free ceramic to 12.1GPa for the sample doped with 10wt% nano-graphite. Addition of graphite nano-flakes increased the fracture toughness of composites as a value of 8.2MPam½ was achieved by adding 7.5wt% nano-graphite, twice higher than that measured for the graphite-free sample (4.3MPam½). The in-situ formation of ZrC and B4C nano-particles as well as the presence of unreacted graphite nano-flakes led to a remarkable enhancement in fracture toughness through activating several toughening mechanisms such as crack deflection, crack bridging, crack branching and graphite pullout.

Enhanced microwave absorption properties of graphite nanoflakes by coating hexagonal boron nitride nanocrystals

We report herein the synthesis of a novel hexagonal boron nitride nanocrystal/graphite nanoflake (h-BNNC/GNF) composite through a wet-chemistry coating of graphite nanoflakes and subsequent in-situ thermal treatment process. The characterization results of X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectrum, and X-ray photoelectron spectroscopy demonstrate that h-BNNCs with diameter of tens of nanometers are highly crystallized and anchored on the surfaces of graphite nanoflakes without obvious aggregation. The minimum reflection loss (RL) value of the h-BNNC/GNF based absorbers could reach −32.38dB (>99.99% attenuation) with the absorber thickness of 2.0mm. This result is superior to the other graphite based and some dielectric loss microwave absorption materials recently reported. Moreover, the frequency range where the RL is less than −10dB is 3.49–17.28GHz with the corresponding thickness of 5.0–1.5mm. This reveals a better electromagnetic microwave absorption performance of h-BNNC/GNFs from the X-band to the Ku-band. The remarkable enhancement of the electromagnetic microwave absorption properties of h-BNNC/GNFs can be assigned to the increase of multiple scattering, interface polarization as well as the improvement of the electromagnetic impedance matching of graphite nanoflakes after being coated with h-BNNCs.

Melamine resin/graphite nanoflakes hybrids and its vacuum-assisted prepared epoxy composites with anisotropic thermal conductivity and improved flame retardancy

Melamine resin/graphite nanoflakes hybrids (MGNH) were synthesized by in situ polymerization. The SEM and TEM demonstrate that melamine resin was self-deposited on the surface of the flakes. MGNH is uniform sheeted hybrids which exhibits excellent dispersiveness. MGNH/epoxy composite (MGNH/EP) is prepared via vacuum-assisted method. The special prepared method endows MGNH/EP with interesting anisotropic thermal conductivity. The coefficient of thermal conductivity of the composite in normal direction is 0.4024 W m−1 K−1, while that of MGNH/EP in horizontal direction is 1.5596 W m−1 K−1. The optical microscope image of the composite suggests that the nanoflake is arranged as a parallel conduction medium, it is demonstrated that direct flake-flake conduction can form heat-transfer passages, which contributes to the higher thermal conductivity of the composite in horizontal direction. Also, MGNH/EP shows excellent flame retardant properties, evidenced by the dramatically reduced peak heat release rate and 51% of total heat release values compared with neat EP obtained from a microcombustion calorimeter. The reduced fire hazard can mainly attributed to the synergistic effects of melamine resin and graphite nanoflakes.

In situ intercalation polymerization approach to polyamide-6/graphite nanoflakes for enhanced thermal conductivity

Abstract Traditional polymer composites generally present limited thermal conductivity (TC) even highly loaded with highly thermally conductive fillers due to the lack of large interfacial thermal resistance between the fillers and the surrounding polymers. In this work, polyamide-6/graphite nanoflakes (PA6/GnF) composites with high TC can be obtained through a one-step in situ intercalation polymerization. The caprolactam onium ion (CL ⊕ ) catalysted by 6-aminocaproic acid can effectively intercalate into the interlayer of expanded graphite (EG) and lead to the separation of EG into GnF after in situ polymerization. Thereafter the homogeneous dispersions of GnF with ordered arrangement and strong interfacial interactions between PA6 and GnF can be formed within the PA6/GnF composites, which can favor the formation of the consecutive thermal conductive pathways or networks at a relatively low EG loading. The obtained composites, at only EG loading of 12 wt%, exhibit a high TC (2.49 W/mK), corresponding to an enhancement of 678% compared to that of neat PA6. This strategy offers new insights into the fabrication of graphene based composites, and provides a straightforward and highly industrializable process for fabrication of high-performance GnF-based thermally conductive composites.

Electrochemically Driven Transformation of Amorphous Carbons to Crystalline Graphite Nanoflakes: A Facile and Mild Graphitization Method

AbstractAlthough, in the carbon family, graphite is the most thermodynamically stable allotrope, conversion of other carbon allotropes, even amorphous carbons, into graphite is extremely hard. We report a simple electrochemical route for the graphitization of amorphous carbons through cathodic polarization in molten CaCl2 at temperatures of about 1100 K, which generates porous graphite comprising petaloid nanoflakes. This nanostructured graphite allows fast and reversible intercalation/deintercalation of anions, promising a superior cathode material for batteries. In a Pyr14TFSI ionic liquid, it exhibits a specific discharge capacity of 65 and 116 mAh g−1 at a rate of 1800 mA g−1 when charged to 5.0 and 5.25 V vs. Li/Li+, respectively. The capacity remains fairly stable during cycling and decreases by only about 8 % when the charge/discharge rate is increased to 10000 mA g−1 during cycling between 2.25 and 5.0 V.

Electrochemically Driven Transformation of Amorphous Carbons to Crystalline Graphite Nanoflakes: A Facile and Mild Graphitization Method.

Although, in the carbon family, graphite is the most thermodynamically stable allotrope, conversion of other carbon allotropes, even amorphous carbons, into graphite is extremely hard. We report a simple electrochemical route for the graphitization of amorphous carbons through cathodic polarization in molten CaCl2 at temperatures of about 1100 K, which generates porous graphite comprising petaloid nanoflakes. This nanostructured graphite allows fast and reversible intercalation/deintercalation of anions, promising a superior cathode material for batteries. In a Pyr14 TFSI ionic liquid, it exhibits a specific discharge capacity of 65 and 116 mAh g-1 at a rate of 1800 mA g-1 when charged to 5.0 and 5.25 V vs. Li/Li+ , respectively. The capacity remains fairly stable during cycling and decreases by only about 8 % when the charge/discharge rate is increased to 10000 mA g-1 during cycling between 2.25 and 5.0 V.

Encapsulation of Graphite Nanoflakes for Improving Thermal Conductivity of Mesogenic Epoxy Composites

Graphite nanoflake (GN) is the most prominent filler for thermally conductive polymeric composites. However, the aggregation problem of GN has an adverse effect on the improvement of thermal conductivity of the composites. In this study, GR is decorated with melamine-formaldehyde (MF) by in situ polymerization, which successfully solves the well-known aggregation problem of GN. GN@MF is used as nanofillers for improving the thermal conductivity of the biphenyl mesogenic epoxy resin (MEP). Photomicrograph observations of MEP/GN@MF composites exhibit that GN@MF flakes are evenly dispersed in the polymer matrix, which demonstrate that GN@MF has excellent dispersion in the MEP matrix. The homogeneous dispersion of GN@MF in MEP favors the formation of the consecutive thermal conductive paths or networks. As a result, the MEP/GN@MF composite has a higher thermal conductivity than MEP/GN with the same content of loading.

Preparation of magnetic and conductive graphite nanoflakes/SrFe12O19/polythiophene nanofiber-nanocomposites and its radar absorbing application

This study, we synthesized graphite-nanoflakes (GNFs) by acid treatment and thermal shock and then using the ultrasonic irradiation technique to exfoliate flake-carbon. The SrFe12O19 nanoparticles (NPs) were coated by co-precipitate method on GNFs after by alkaline treatment. Finally nanocomposite (GNF/SrFe12O19/PTh) was prepared by in-situ oxidative polymerization method in presence of thiophene (Th) as monomer. The magnetic and electrical conducting properties of the resulting nanocomposites were measured by using vibrating sample magnetometer and standard four-point-probe method, respectively. The synthesized nanocomposites were characterized by X-ray diffraction (XRD) and fourier transform infrared spectra (FTIR). In addition, morphological analyses were investigated by scanning electron microscopy (SEM). A minimum reflection loss (RL) of GNFs/SrFe12O19/PTh with 50 % wt GNFs/SrFe12O19 as core were observed −28 and −39 dB at 9.7 and 12 GHz for a 1.5 mm thickness. The results indicated that we can perform good microwave shielding in X-band (8–12 GHz) by these nanocomposites.

Electrochemical sensing performance of nanodiamond-derived carbon nano-onions: Comparison with multiwalled carbon nanotubes, graphite nanoflakes, and glassy carbon

Carbon nano-onions (CNOs) are emerging carbon nanomaterials with unique microstructure and electronic properties. CNOs are 0-D carbon analogs of 1-D carbon nanotubes (CNTs) and 2-D graphenes. CNOs are composed of sp2-bonded, concentric nanographene shells surrounding a hollow core. Microstructure, electrochemical properties, and biosensing performances of nanodiamond-derived CNOs (N–CNOs) were studied in comparison with other popular carbon electrodes: multiwalled carbon nanotubes (MWCNTs), graphite nanoflakes (GNFs), and glassy carbon (GC). First, morphology and microstructure of N–CNOs were characterized by scanning and transmission electron microscopies (SEM, TEM), X-ray diffraction (XRD), and Raman spectroscopy. Chemical composition and chemical functional groups were probed by X-ray photoelectron spectroscopy (XPS). Raman spectra of N–CNOs showed a large value of ID/IG, indicating that N–CNOs include defects, i.e., exposed edge planes. Second, electrocatalytic activity of N–CNOs toward oxygen reduction reaction was tested in comparison with MWCNTs, GNFs, and GC. Last, biosensing performances of N–CNOs were studied. Cyclic voltammetric and differential pulse voltammetric measurements were carried out for the detection of redox-active biomolecules such as dopamine, epinephrine, and norepinephrine. The results showed remarkable electrochemical activities of N–CNOs with high sensitivity, high selectivity, and stable electrode responses for the detection of biologically important molecules.

Highly Flexible and Planar Supercapacitors Using Graphite Flakes/Polypyrrole in Polymer Lapping Film.

Flexible supercapacitor electrodes have been fabricated by simple fabrication technique using graphite nanoflakes on polymer lapping films as flexible substrate. An additional thin layer of conducting polymer polypyrrole over the electrode improved the surface conductivity and exhibited excellent electrochemical performances. Such capacitor films showed better energy density and power density with a maximum capacitance value of 37 mF cm(-2) in a half cell configuration using 1 M H2SO4 electrolyte, 23 mF cm(-2) in full cell, and 6 mF cm(-2) as planar cell configuration using poly(vinyl alcohol) (PVA)/phosphoric acid (H3PO4) solid state electrolyte. Moreover, the graphite nanoflakes/polypyrrole over polymer lapping film demonstrated good flexibility and cyclic stability.

Influence of graphite nano-flakes on densification and mechanical properties of hot-pressed ZrB2–SiC composite

Hot pressed monolithic ZrB2 ceramic (Z), ZrB2–20vol% SiC composite (ZS20) and ZrB2–20vol% SiC–10vol% nano-graphite composite (ZS20Gn10) were investigated to determine the influence of graphite nano-flakes on the sintering process, microstructure, and mechanical properties (Vickers hardness and fracture toughness) of ZrB2–SiC composites. Hot pressing at 1850°C for 60min under 20MPa resulted in a fully dense ZS20Gn10 composite (relative density: 99.6%). The results disclosed that the grain growth of ZrB2 matrix was efficiently hindered by SiC particles as well as graphite nano-flakes. The fracture toughness of ZS20Gn10 composite (7.1MPam1/2) was essentially improved by incorporating the reinforcements into the ZrB2 matrix, which was greater than that of Z ceramic (1.8MPam1/2) and ZS20 composite (3.8MPam1/2). The fractographical observations revealed that some graphite nano-flakes were kept in the ZS20Gn10 microstructure, besides SiC grains, which led to toughening of the composite through graphite nano-flakes pull out. Other toughening mechanisms such as crack deflection and branching as well as crack bridging, due to the thermal residual stresses in the interfaces, were also observed in the polished surface.

Voltammetric Determination of 4-Nitrophenol at Graphite Nanoflakes Modified Glassy Carbon Electrode

Voltammetric determination of 4-nitrophenol (4-NP) has been carried out on graphite nanoflakes (GNFs) modified glassy carbon electrode (GCE) (GNFs/GCE). The GNFs were easily prepared by paired electrolysis of graphite rods in a blank solution of NaOH. In comparison with GCE, the GNFs/GCE showed higher electrocatalytic activity (positive shift of peak potential and onset potential) toward the 4-NP reduction. Under the optimized conditions, the oxidation peak currents varied linearly with a concentration range for 4-NP of 1−6000 μM (over three consecutive calibration curves) with a detection limit of 0.7 μM (3 σ/slope) and quantification limit of 2.3 μM (10 σ/slope). The proposed method exhibited several advantages including easy fabrication, low cost, good sensitivity, high stability, good reproducibility, high selectivity and very broad linear range, and was successfully applied to detect 4-NP in water samples with satisfied results.