Graphite Nanoflakes Research Articles

Biomimetic structure-driven high strength and toughness in continuous SiC skeleton-reinforced graphite composites

Graphite-matrix structural composites with excellent mechanical properties and long-term reliability are ungently required in aerospace and nuclear industries. However, the enhancement of graphite-matrix composites by mainstream surface coating techniques or second-phase particle reinforcement is rather limited. Inspired by the structural-functional feature of plant cells, silicon carbide (SiC, cytoderm) coated mesocarbon microbeads (MCMB, cytoplasm) powders were prepared by combustion synthesis (CS), which were then densified via spark plasma sintering (SPS) to obtain the biomimetic cellular-structured SiC-reinforced MCMB (M@SiC) composites. The in-situ formed SiC ‘cytoderm’ ensures good interfacial bonding and contributed to the densification of the composites. Additionally, the continuous SiC skeleton and cellular-structured configuration improved the mechanical properties of M@SiC composites. Owing to the complex crack deflection, branching and bridging effects at the MCMB/SiC interfaces and graphite nanoflakes inside MCMB, the biomimetic M@SiC composite with SiC content of 47 vol% exhibited strengthening and toughening, with flexural strength and fracture toughness of 245 MPa and 3.82 MPa m1/2, respectively. The developed biomimetic graphite-matrix composites with excellent mechanical properties are expected to be applied in reusable spacecrafts and high-temperature gas-cooled reactors.

Impact of graphite nanoflakes and gamma radiation on the mechanical, electrical, and thermal properties of EPDM/modified BaTiO3 composites

The effect of graphite nanoflakes (GNFs)/modified barium titanate (MBT) hybrid fillers on the mechanical, electrical, and thermal properties of ethylene-propylene-diene monomer (EPDM) was extensively investigated in the current study. Moreover, the effect of gamma irradiation on the different properties of the prepared nanocomposites was investigated. To accomplish this goal, EPDM/MBT composites with various GNFs contents (0, 2, 4, 6, and 8 phr) were fabricated using a conventional roll mill. Graphite was expanded by heating and subsequently modified using tween 80 surfactant, resulting in the formation of GNFs. The presence of various functional groups on the surface of the modified BaTiO3 particles was verified by Fourier transform infrared spectroscopy (FTIR). The scanning electron microscopy (SEM) analysis revealed a uniform dispersion of GNFs in EPDM/MBT composites, with a concentration up to 6 phr. The study revealed that the mechanical properties of the nanocomposites were reinforced by the inclusion of GNFs up to 6 phr. The irradiated EPDM/MBT/6 phr GNFs nanocomposite exhibited the maximum elastic modulus value of 4.8 MPa, which was approximately 32 % higher than that of the corresponding unirradiated nanocomposite. The thermal conductivity of the irradiated EPDM/MBT/8 phr GNFs nanocomposite increased from 0.213 W/m.K to 0.260 W/m.K (22 %), while the dielectric constant increased from 4.475 to 5.551 (24 % increase) at 103 Hz as compared to the pure EPDM/MBT composite. The enhanced electric and thermal performance of GNFs can be attributed to the mobility of their π-electrons.

Development and comparison of multi-walled carbon nanotubes and graphite nanoflakes dispersed solar salt: Structural formation and thermophysical properties

A molten salt energy storage has proven to be a promising candidate for medium and high-temperature thermal energy storage (TES) applications. Improving the thermophysical properties, such as specific heat capacity (Cp) and thermal conductivity (k) is crucial to deciding the charging/discharging characteristics of the energy storage system. In this study, 1 wt% of two variant carbon allotropes, such as multi-walled carbon nanotubes (MWCNTs) and graphite nanoflakes (GNFs), were dispersed in solar salt (i.e., MWCNTs nanosalt and GNFs nanosalt) using wet preparation method. Thermophysical properties of the prepared nanosalts were evaluated using different analytical techniques and compared with pristine solar salt. The specific heat capacity was measured from 50 °C to 350 °C, and the maximum specific heat capacity enhancement in 1 wt% of MWCNTs dispersed solar salt was 18 %. The enhancement in 1 wt% of GNFs dispersed solar salt was 12.5 % at 200 °C (in solid phase). Similarly, in the liquid phase (at 350 °C), MWCNTs dispersed solar salt improves Cp by 6.2 %, while GNFs dispersed solar salt exhibits negligible improvement in Cp. Further, a modified transient plane source (MTPS) technique was used to measure the thermal conductivity of both carbon nanosalts in the solid phase (30–100 °C). The maximum thermal conductivity enhancement observed for MWCNTs dispersed solar salt and GNFs dispersed solar salt was 5.8 % and 11.7 %. Finally, thermogravimetric analysis was conducted to evaluate the thermal stability of the MWCNTs nanosalt and GNFs nanosalt at a maximum temperature of 700 °C, and found that the MWCNTs nanosalt show better thermal stability than the GNFs nanosalt.

Modification in the crystallinity, optical and dielectric behavior of PVA polymer with CaTiO3 and graphite nanoflakes

Modification in the crystallinity, optical and dielectric behavior of PVA polymer with CaTiO3 and graphite nanoflakes

Ecofriendly Synthesis of Waste-Tire-Derived Graphite Nanoflakes by a Low-Temperature Electrochemical Graphitization Process toward a Silicon-Based Anode with a High-Performance Lithium-Ion Battery.

Here, the successful transformation of graphitic carbon with a high degree of graphitization and a nanoflake structure from pyrolytic tire carbon black was demonstrated. First, amorphous carbon black with a porous structure was obtained after pyrolysis and simple preacid treatments. Subsequently, the carbon black was converted into a highly graphitic structure at a relatively low temperature (850 °C) through a facile electrochemical route using molten salt, which is ecofriendly and has high potential for large-scale graphitization compared to conventional incineration techniques. Moreover, we further improved the crystallinity and uniformity of the product simultaneously by directly mixing the metal oxide catalyst Fe2O3 with a carbon precursor. The mechanism of this metal-catalyzed electrochemical graphitization has been discussed in detail. To confirm their potential in practical applications, the as-prepared graphitized nanoflakes were used as conductive additives for silicon anodes in lithium-ion batteries, which showed a performance comparable to those utilizing commercial Super-P additives, exhibiting an initial Coulombic efficiency of approximately 79.7% and a high capacity retention of approximately 45.8% after 100 cycles with a reversible capacity of 1220 mAh g-1 at a current rate of 400 mA g-1. Hence, successfully recovered waste-tire-derived carbon black utilizing a low-temperature Fe2O3-catalyzed electrochemical process opens a pathway in low-temperature graphitization toward a sustainable value-added application in the field of energy storage.

Expanded graphite/Co@C composites with dual functions of corrosion resistance and microwave absorption

The development of microwave absorption materials with good environmental adaptability is a hot topic in the electromagnetic protection field. In this research, Expanded graphite (EG)/ZIF-67 nanocubes-derived (Co@C) composites were successfully fabricated by electrostatic assembly and subsequent heat treatment. The results show that the involvement of an appropriate content of Co@C not only overcomes the problem of single EG impedance mismatch but also introduces additional magnetic loss for the absorber. At the thicknesses of 1.6 mm and 1.5 mm, an effective absorption bandwidth (EAB) of 4.52 GHz and a minimum reflection loss (RLmin) of −48.4 dB were achieved for the Z2-700 sample with a low filling ratio (20 wt%). The enhancement of EMW-absorption performance is attributed to the optimization of impedance matching and the synergistic action between multiple loss mechanisms. Electrochemical corrosion test showed that graphite nanoflakes of EG enhanced the transfer resistance during corrosion, and the corrosion resistance of pure Co@C was enhanced with the protection of EG. This work provides a reasonable attempt to design and fabricate efficient microwave absorption materials suitable for harsh environments.

A Study on High-Rate Performance of Graphite Nanostructures Produced by Ball Milling as Anode for Lithium-Ion Batteries.

Graphite, with appealing features such as good stability, high electrical conductivity, and natural abundance, is still the main commercial anode material for lithium-ion batteries. The charge-discharge rate capability of graphite anodes is not significant for the development of mobile devices and electric vehicles. Therefore, the feasibility investigation of the rate capability enhancement of graphite by manipulating the structure is worthwhile and of interest. In this study, an effective ball-milling process has been set up by which graphite nanostructures with a high surface area are produced. An in-depth investigation into the effect of ball milling on graphite structure as well as electrochemical performance, particularly rate capability, is conducted. Here, we report that graphite nanoflakes with 350 m2 g-1 surface area deliver retained capacity of ~75 mAh g-1 at 10 C (1 C = 372 mA g-1). Finally, the Li+ surface-storage mechanism is recognised by associating the structural characteristics with electrochemical properties.

Preparation and microwave absorption properties of tellurium doped black phosphorus nanoflakes and graphite nanoflakes composites

In this study, the TBG composites (composites of tellurium doped black phosphorus nanoflakes (Te/BP NFs) with graphite nanoflakes (GNFs)) were successfully prepared which showed excellent electromagnetic wave absorption performance. The permittivity and dielectric loss tangent of TBG composites increased with the increase of GNFs content. When the ratio of Te/BP NFs to GNFs was 1:1 (TBG-1–1 composite), the reflection loss reached −10 dB under the thickness range of 1–3 mm and frequency range of 5.25–18 GHz, and the minimum reflection loss was −31.07 dB at the frequency of 4.14 GHz. Moreover, the relationship between minimum reflection loss frequency and thickness of TBG-1–1 composite conformed to the λ/4 impedance matching model. Therefore, the TBG composites have great potential in the application of high-frequency electromagnetic wave fields.

Graphite Nanoflake-Modified Mo2C with Ameliorated Interfacial Interaction as an Electrocatalyst for Hydrogen Evolution Reaction.

Molybdenum carbide (Mo2C) is anticipated to be a promising electrocatalyst for electrocatalytic hydrogen production due to its low cost, resourceful property, prominent stability, and Pt-like electrocatalytic activity. The rational design of Mo2C-based electrocatalysts is expected to improve hydrogen evolution reaction (HER) performance, especially by constructing ultrasmall Mo2C particles and appropriate interfaces. Herein, composites of molybdenum carbide (Mo2C) quantum dots anchored on graphite nanoflakes (Mo2C/G) were fabricated, which realized a stable overpotential of 136 mV at 10 mA cm-2 for the HER with a small Tafel slope of 76.81 mV dec-1 in alkaline media, and operated stably over 10 h and 2000 cycles. The superior HER performance can be attributed to the fact that graphite nanoflakes could act as a matrix to disperse Mo2C as quantum dots to expose more active sites and guarantee high electronic conductivity and, more importantly, provide ameliorated interfacial interaction between Mo2C and graphite nanoflakes with appropriate hydrogen binding energy and charge density distribution. To further explore which kind of interfacial interaction is more favorable to improve the HER performance, density functional theory calculations and corresponding contrast experiments were also performed, and it was interesting to prove that Mo2C quantum dots anchored to the basal planes of defective graphite nanoflakes exhibit better electrochemical performance than those anchored on the edges.

Electrophoretic Deposition of a Composite Electrode Material of a Supercapacitor Based on Few-Layer Graphite Nanoflakes and Ni(OH)2

Electrophoretic Deposition of a Composite Electrode Material of a Supercapacitor Based on Few-Layer Graphite Nanoflakes and Ni(OH)2

Biomass-derived graphene-like carbon nanoflakes for advanced supercapacitor and hydrogen evolution reaction

It is valuable that graphene-like carbon materials are prepared from the biomass resources due to their unique two-dimensional structure, heteroatom enriched, and high specific surface area. Herein, we use egg white and graphene oxides as precursor and employ post-hydrothermal carbonization approach, freeze-drying technique, carbonization, and activation methods by KOH to prepare the graphite carbon nanoflakes with Fe7C3 @graphite carbon nanoflakes hybrid materials. Morphology tests imply that the formation of graphite carbon nanoflakes are mainly depended by activation step, it implies that carbon flakes are exfoliated via introducing K+ into carbon layers and further destroying the van der Waals force (VDWF). As a result, this hybrid materials exhibit an attractive capacitance (528 mF·cm−2 @1 mA·cm−2) and durability (91 @10 mA·cm−2, 4000 cycles). For hydrogen evolution reaction (HER), the as-collected samples also deliver a low overpotential and remarkable stability. We believe that the as-obtained hybrid materials have a greatly application value in energy storage devices.

Enhancing the electrical properties of graphite nanoflake through gamma-ray irradiation

Understanding changes in material properties through external stimuli is critical to validating the expected performance of materials as well as engineering material properties in a controlled manner. Here, we investigate a change in the c-axis electrical properties of graphite nanoflakes (GnFs) induced by gamma-ray irradiation, using conductive probe atomic force microscopy (CP-AFM). The fundamentals behind the change in their electrical properties are elucidated by analyzing the interlayer spacing, graphitization, and morphology. An increase in gamma-ray irradiation dose for GnFs leads to an exponential increase in the electrical conductance and a gradual decrease in the interlayer spacing, while accompanying indistinguishable changes in their morphology. Our experimental results suggest that the c-axis electrical conductance enhancement of GnFs with gamma-ray irradiation might be attributed to a reduction in interlayer spacing, though the created defects may also play a role. This study demonstrates that gamma-ray irradiation can be a promising route to tailor the electrical properties of GnFs.

Humidity-Independent, Highly Sensitive and Selective NO2 Sensor Based on In2O3 Nanoflowers Decorated With Graphite Nanoflakes

Metal oxide semiconductor (MOS) gas sensor is an effective tool for NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detection. However, their performance is seriously influenced by humidity due to water vapor poisoning, and it remains a challenge to develop an anti-humidity NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> MOS sensor. In this work, a humidity-independent, highly sensitive and selective NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor based on In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoflowers decorated with graphite nanoflakes was fabricated, which exhibited excellent anti-humidity and stability (response fluctuation within 7%) in a wide relative humidity (RH) range of 20% - 90%. The fabricated sensor had a high response of 10 to ppb level NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (RH 80%). Besides, the sensor exhibited good selectivity, low operating temperature (75 °C) and rapid response speed (50 s to 5 ppm NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The reason for the excellent anti-humidity function was investigated. Large amounts of polar groups were formed on the graphite nanoflakes after hydrothermal treatment, which enhanced the interaction between the graphite and In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and made the surface of the composites have a strong water absorption function. Moreover, the intrinsic hydrophobic property of the graphite can effectively block the interference of water vapor to the moisture-sensitive In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . Our work provides a new idea for enhancing the anti-humidity performance of the MOS sensors and can broaden their applications in a variety of complex environments.

Mesoscopic scale rearrangements of graphite nanoflake open edges under mild annealing treatments

The paper presents an effect of mild annealing treatments on structural ordering and open edge morphology of graphite nanoflakes (GNF). Thin graphite flakes were obtained from the bulk highly oriented pyrolytic graphite by a prolonged grinding in a pure argon atmosphere and were annealed at T = 670 K for 24 h either in vacuum or in the air. Modification of GNF open edges was studied with high-resolution transmission electron microscopy (HRTEM) and 2D-Fourier analysis of the open edge area HRTEM-images. The morphology of the GNF edges evolve differently under annealing, revealing itself in the azimuthal width of the two-dimensional fast-Fourier transform (2D-FFT) maxima. After annealing in the air, the width decreased, while the vacuum treatment lead to its growth. We relate the former to the open edge flattening via removal of the edge defects by transformation to the gaseous carbon oxides, the latter – to the opposite process of defect accumulation in vacuum with the transformation of the near-edge structure to the less ordered one. The correlation is found between the intensity of the (101) powder X-ray diffraction maximum and the azimuthal width of the FFT-peaks indicating the direct relation of these quantities.

Effect of modified graphite nanoflakes on curing, mechanical and dielectric properties of nitrile rubber nanocomposites

Effect of modified graphite nanoflakes on curing, mechanical and dielectric properties of nitrile rubber nanocomposites

Synthesis of nanostructured carbon derived from the solid-state reaction between iron and boron carbide

In this work, new carbide-derived carbons (CDCs) generated by the solid-state reaction between Fe and B4C were produced as nanostructured powders. Thermodynamic calculations were used to define the composition range and the process window for the reaction. Initially, samples with Fe + 5 wt%B4C were produced by traditional powder metallurgy techniques to analyse the reaction between the materials. As CDC nanoflakes were found, the amount of B4C was increased in order to improve the graphite productivity and an acid treatment was used to extract the nanoflakes. The results showed that it is possible to use this method to obtain powders of nanostructured turbostratic graphite in high quantity (yield of ∼87%). This is the first method ever presented that allows obtaining 2D turbostratic graphite nanoflakes derived from the reaction between Fe and B4C as powders with potential applications in tribology and other fields yet to be explored.

(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing.

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterial-fraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔEp = 28mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and β-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1µM, L.R. 0.5-150µM; NADH: LOD = 0.6µM, L.R. 2.5-200µM) at low overpotential (+ 0.15V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.

N-butylamine-modified graphite nanoflakes blended in ferroelectric P(VDF-TrFE) copolymers for piezoelectric nanogenerators with high power generation efficiency

In this study, the effects of n-butylamine-modified graphite nanoflakes (BMGNFs) on the crystalline phase transition, ferroelectric behaviors, and piezoelectric energy harvesting properties of poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) copolymers are investigated. To confirm the blending of BMGNFs in P(VDF-TrFE), X-ray spectroscopy and Fourier-transform infrared spectroscopy (FTIR) are performed. Additionally, X-ray diffraction, FTIR, field-emission scanning electron microscopy, and atomic force microscopy are performed to analyze the crystallization of the polar β-phase of BMGNF-blended P(VDF-TrFE) copolymers. For P(VDF-TrFE) copolymers blended with pure graphite nanoflakes (GNFs), the crystallization of the polar β-phase is enhanced, but a high dielectric loss induced by the leakage current is clearly observed. The dielectric loss can be effectively reduced through the modification of GNFs by n-butylamine, which improves the remnant polarization and coercive electric field of metal-ferroelectric-semiconductor devices. Furthermore, the piezoelectric nanogenerators comprising BMGNF-blended P(VDF-TrFE) copolymers present a high open-circuit output voltage of 4.9 V and a high short-circuit output current of 4.5 μA for more than 500 times of cycling tests, exhibiting a high generating power density of 33.73 mW/m2 under a load resistance of 3 MΩ. Hence, the P(VDF-TrFE) copolymers blended with n-butylamine-modified GNFs show superior ferroelectric and piezoelectric behaviors, rendering them promising candidates for applications in future organic sensors and self-powered consumer electronics.

The preparation of mass producible, highly-cycling stable Si/C anode materials with nano-sized silicon crystals embedded in highly amorphous silicon matrix

sThe commercial applications of silicon nanomaterials as anode in lithium-ion batteries must solve two important problems, namely low expansion and long-term cycle stability. The former is related to nano-silicon structure, while the latter depends on silicon/carbon composite structure and preparation process. In order to suppress volume expansion appeared during lithiation, this paper selects a kind of silicon nanoparticles (SiNPs) with a high degree of amorphization (81.9%), and designs a stable silicon/carbon composite material structure. Inside this structure, graphite nanoflakes (GNFs) with high specific surface are used as the skeleton, which can provide enough surface area for SiNPs to adhere and avoid the local accumulation of SiNPs. Outside this structure is uniformly coated with a layer of amorphous carbon. Raman and x-ray diffraction results show that after the high-temperature carbonization, the nano-silicon in the composite material still maintains a high degree of amorphization (67.1%) and the average crystallite size of Si has only increased from 3.7 to 9.5 nm. The initial Coulombic efficiency and reversible specific capacity of the composite material are 86.7% and 1374.8 mAh g−1, respectively. After mixing with commercial graphite, the initial Coulombic efficiency and reversible specific capacity are 93.7% and 426.4 mAh g−1, respectively. LiNi0.8Co0.1Mn0.1O2 (NCM811) is used as the cathode to produce a soft-pack battery. After 900 cycles at room temperature, the capacity remains 86.2%. The silicon/carbon anode material reported in this paper is of great potential for commercialization.

Electrochemical detection of 5-hydroxytryptamine using sustainable SnO2-Graphite nanocomposite modified electrode

The precise function of serotonin and dopamine hugely influence the drug specification and treatment. Serotonin receptors or 5-hydroxytryptamine (5-HT) actively participate in neuro transmission and influence various biological and neurological functions. Considering its importance benefiting the detection and development, herein, SnO2, a thermally stable and conductive material was prepared by multi-step synthesis protocol and used for the sensing of 5-HT. Besides, graphite being an effective electron promoter and active catalyst was synthesised using a sustainable approach and composited with SnO2. The electrochemical detection of 5-HT was done with SnO2-G nanocomposite, and modified silicone-SnO2-G nanocomposite electrode. The addition of graphite nanoflakes substantially improves the response behaviour of So-Sn-G electrode with the calculated electroactive surface area of 0.291 cm2. Further, the cyclic voltammetry plots at various scan rate shows the reduced over-potential (0.6628 V) and improved response of current signals (4.314 μA) owing to synergistic electrocatalytic activity of the So-Sn-G electrode. The differential pulse voltammetry reveals the linearity and improved detection limit with correlation coefficient of 0.9944, owing to excellent detection of 5-HT for prolonged duration.