Exfoliation Of Graphite Research Articles

Simultaneous exfoliation/fluorination for the preparation of fluorinated exfoliated graphite with high power densities in primary lithium batteries

Fluorinated carbons combining accordion-like morphology, high content of (C2F)n phase (43%), and residual non-fluorinated carbons were synthetized by two routes, i.e. fluorination of expanded graphite and simultaneous exfoliation/fluorination of expandable graphite. The latter allows the synthesis in a one-step process to be achieved. Accordion-like morphology allows the accommodation of LiF without detrimental accumulation onto the fluorocarbon sheet edges during the discharge in primary lithium battery. The faradic yield is then close to 100 % up to a discharge rate of 6C. Residual sp2 carbons (sub-fluorination) ensure the electron flux during the electrochemical process and enhance the power density (9828 W.Kg-1). High content of (C2F)n phase results in a flat galvanostatic discharge curve. The combination of those features results in a good compromise between energy and power densities, making fluorinated exfoliated graphite one of the best cathodes for primary lithium batteries.

Superior tribological properties of highly-loaded graphite/A356 surface composites fabricated using friction stir processing

In this work, friction stir processing (FSP) was used to prepare graphite (Gr) / A356 alloy composites with superior tribological properties. The Gr content and number of FSP passes (up to three passes) were used as processing variables. The microstructure, hardness and wear resistance of the composites were studied and compared with a neat sample. The microstructural studies demonstrated that super-fine Gr particles were uniformly distributed and in-situ sub-micron Al4C3 particles were formed after three FSP passes. Hardness measurements proved that all composites exhibited higher hardness than the neat sample. The composite prepared using two Gr loading rounds and three FSP passes achieved the highest hardness value of 331 kg.f/mm2, which is more than 4 times that of the neat sample. Additionally, the wear rate of this composite was approximately 57 % lower than that of the neat sample. The superior hardness and wear resistance of the fabricated composites are attributed to the in-situ exfoliation of graphite and the formation of super-fine Al4C3 particles during FSP.

Evaluating the Impact of Sonication Process on Graphene Oxide Structural Properties

Graphene oxide (GO) is one of the members of carbon-based nanomaterials and can be featured as graphene structure decorated with various oxygenated functional groups. Recently, various methods have been found for producing carbon-based nanomaterials with enhanced efficiency in several applications. The chemical process involves oxidizing graphite to GO using a powerful oxidizing chemical. Hummers method is one of the most known and versatile method for the production of GO nanomaterials because of its ease of application, parameter controllability and high yield. This process enables graphite oxidation and exfoliation into single- or multi-layered GO sheets. Exfoliation, the separation of graphene or graphitic layers, is a critical process in GO synthesis. Since exfoliation separates multilayered graphite oxide flakes or particles, it forms single layer GO by forcing oxidizing agents or solvent molecules between layers. The sonication process can exfoliate the oxidized layers, resulting in the formation of GO structure when the exfoliated layers consist of only one or a few layers of carbon atoms. Therefore, sonication procedure is among the key parameters of Hummers method that influences the characteristics of GO-based nanomaterials. In this study, the impact of sonication duration time and power parameters on morphological and structural characteristics of GO development was examined. For this purpose, characterization studies were performed by using Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and Raman spectroscopy analysis. The findings revealed that the increase in sonication power and time led to an increase in defects in the resulting GO structure.

Interfacial Decomposition Behaviour of Triethyl Phosphate‐Based Electrolytes for Lithium‐Ion Batteries

Triethyl phosphate (TEP) is a cheap, environmentally benign, and non‐flammable electrolyte solvent, whose implementation in lithium‐ion batteries is held back by its co‐intercalation into graphite anodes, resulting in exfoliation of the graphite structure. In this work, the electrode‐electrolyte interface behaviour of electrolytes containing up to 100% TEP was investigated and correlated to electrochemical performance. High capacity and stable cycling are maintained with up to 30% TEP in carbonate ester‐based electrolytes, but above this threshold the reversibility of Li+ intercalation into graphite drops sharply to almost zero. This represents a potential route to improved battery safety, while TEP can also improve safety indirectly by enabling the use of lithium bis(oxalato borate), a fluorine‐free salt with limited solubility in traditional electrolytes. To understand the poor performance at TEP concentrations of >30%, its solvation behaviour and interfacial reaction chemistry were studied. Nuclear magnetic resonance spectroscopy data confirms changes in the Li+ solvation shell above 30% TEP, while operando gas analysis indicates extensive gas evolution from TEP decomposition at the electrode above the threshold concentration, which is almost entirely absent below it. X‐ray photoelectron spectroscopy depth profiling of electrodes demonstrates poor passivation by the solid electrolyte interphase above 30% TEP and significant graphite exfoliation.

Upscaling Brønsted acid intercalation and exfoliation of graphite into graphene by polyoxometalate clusters for sodium-ion battery application

Non-oxidative intercalation of graphite avoids damage to graphene lattices and is a suitable method to produce high-quality graphene. However, the yield of exfoliated graphene is low in this process due to the poor delamination efficiency of guest species. In this study, a Brønsted acid intercalation protocol is developed involving polyoxometalate (POM) clusters (H6P2W18O62) as guests and intercalation of graphite is realized at the sub-nanometer scale. Theoretical simulation based on DFT elucidates the stepwise intercalation mechanism of Brønsted acid molecules and clusters. Unlike common molecules/ionic guests, intercalation of POM clusters induces large expansion and extensive donor–acceptor interactions among graphite interlayers. This significantly weakens the van der Waals forces and promotes exfoliation efficiency of graphene layers. The exfoliated graphene possesses outstanding features of large lateral size, thin thickness, and high purity, and shows excellent performance as the anode for high power sodium-ion batteries. This work proffers a new pathway toward non-oxidative intercalation of graphite for large-scale production of graphene.

Spatially confined radical addition reaction in the sub-nanometer scaled interlayers of electrochemically expanded graphene sheets

Here we report a spatially confined radical addition reaction which occurs in the sub-nanometer scaled interlayers of the expanded graphene sheets during the electrochemical exfoliation processes of graphite. Due to its chemical stability, challenge remains to functionalize graphene simultaneously during the preparation processes. To this, we use tetrachloroaluminate (AlCl4−) as the co-intercalation anions together with sulfate (SO42−) for the electrochemical exfoliation of graphite. We revealed the extremely irreversible intercalation of AlCl4− ions in graphite layers and the generation of C–Cl bonds during electrolysis. Chlorine and oxygen were homogeneously distributed on the basal plane of the obtained graphene, and the controlled functionalization was achieved by tuning the concentration of AlCl4− anions in the electrolyte solution, indicating the spatially confined chlorine addition reaction occurring between the sub-nanometer interlayers of expanded graphite. Furthermore, the chlorine and oxygen hybrid-substituted graphene exhibited excellent electrocatalytic performance for oxygen reduction reaction. This work demonstrates an innovative radical addition reaction in the confined space at nanometer or subnanometer scale and, meanwhile, provides a direct functionalization of graphene during the electrochemical exfoliation of graphite.

Carbon-based thin films as a suitable alternative to metallized films for the preparation of radioactive sources

A new method for radionuclide labeling by the use of graphene thin films was previously presented. In this work, a comparison among low energy radioactive sources supported on carbonaceous thin films on polyvinyl chloride-polyvinyl acetate copolymer (VYNS), based on the use of aqueous solutions is investigated as a feasible alternative to the traditional metallized films avoiding the downside of the loss of many broken films. Graphene-based materials were prepared by both oxidation-exfoliation-reduction and direct graphite exfoliation routes. In addition, multiwalled carbon nanotubes (MWCNTs) thin films were also evaluated. The stability of both carbonaceous materials aqueous dispersions were studied by using ionic and non-ionic surfactants. Solid carbon-based materials were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) whereas the colloidal nature of the aqueous dispersions was verified by the measurement of Tyndall effect and the morphology of thin films was evaluated by Scanning Electron Microscopy (SEM). 55Fe solutions were used to prepare the radioactive sources on the thin films by quantitative drop deposition. The quality of spectra was measured in a pressurized proportional counter. Results showed a resolution higher than 0.9 keV for all the tested sources. However, MWCNT-based along with non-surfactant sources presented non-adequate escape peaks and low energy tails. On the contrary, all the graphene-based sources prepared using surfactants to stabilize aqueous solutions presented an energy resolution comparable to that of the metallized source while offering notable advantages in terms of cost efficiency and reliability of the as-prepared supports.

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material.

Exfoliation of graphite and the discovery of the unique properties of graphene─graphite's single layer─have raised significant attention to layered compounds as potential precursors to 2D materials with applications in optoelectronics, spintronics, sensors, and solar cells. In this work, a new orthorhombic polymorph of yttrium bromide, oC16-YBr3 was synthesized from yttrium and CBr4 in a laser-heated diamond anvil cell at 45 GPa and 3000 K. The structure of oC16-YBr3 was solved and refined using in situ synchrotron single-crystal X-ray diffraction. At high pressure, it can be described as a 3D framework of YBr9 polyhedra, but upon decompression below 15 GPa, the structure motif changes to layered, with layers comprising edge-sharing YBr8 polyhedra weakly bonded by van der Waals interactions. The layered oC16-YBr3 material can be recovered to ambient conditions, and according to Perdew-Burke-Ernzerhof-density functional theory calculations, it exhibits semiconductor properties with a band gap that is highly sensitive to pressure. This polymorph possesses a low exfoliation energy of 0.30 J/m2. Our results expand the list of layered trivalent rare-earth metal halides and provide insights into how high pressure alters their structural motifs and physical properties.

Synthesis of 3D FeS embedded into N, S co–doped carbon nanotube/graphene framework for electrochemical application

Constantly striving to develop a facile and scalable way to construct advanced electrodes is essential for the advancement of batteries and electrocatalysis. In this work, an artful K2FeO4 oxidation cooperated with subsequent annealing process is proposed to produce 3D FeS embedded into N, S co–doped carbon nanotube/graphene (FeS/NSCNT/NSG) framework, which simultaneously achieves successful exfoliation of graphite, effective N, S co–doping and desirable integration of 3D framework by FeS and carbon matrix. The adopted procedure is simple, rapid and recyclable. Furthermore, the obtained FeS/NSCNT/NSG exhibits a unique 3D architecture, high doping level and favorable FeS dispersion status, thus displaying excellent performance towards lithium–ion batteries and oxygen evolution reaction. Undoubtedly, our research opens a new pathway for the development of advanced electrodes for energy storage and conversion devices.

High‐performance graphitic nanoplatelets & high‐density polyethylene nanocomposites

AbstractHeptene‐graphitic nanoplatelets (HtGNP) serve as a filler for high density polyethylene (HDPE), generated through a mechanochemical reaction involving graphite and 1‐heptene. Various analyses indicate the efficient exfoliation of graphite into HtGNP, characterized by exceptional traits. Consequently, HtGNP & HDPE_5 nanocomposites, produced via the solution process, exhibit significantly increased tensile strength and Young's modulus, boasting corresponding increases of 27.7% and 13.7% compared to pure HDPE. Thus, owing to their outstanding performance, HtGNP emerges as a promising option in the form of a novel reinforcing additive for various hydrocarbon polymers.

Aromatic Amino Acid-Dependent Surface Assembly of Amphiphilic Peptides for One-Step Graphite Exfoliation and Graphene Functionalization.

Amphiphilic peptides show great potential for exfoliating graphite and functionalizing graphene. However, the variety of amino acids complicates our understanding of the underlying mechanisms. In this study, we designed four peptides (C6W1, C6W2, C6W4, and C6W6) with different amounts of aromatic tryptophan amino acids and two additional peptides (C6F4 and C6Y4) by substituting tryptophan with aromatic phenylalanine or tyrosine. This allowed us to investigate the processes and mechanisms of graphite exfoliation and graphene functionalization. Using experimental and computational methods, we discovered that peptides containing tryptophan demonstrated higher exfoliation efficiency and increased tryptophan content further improved this efficiency, resulting in more peptide-functionalized graphene layers. Significantly, the primary driving force for the surface-assisted assembly of peptides on graphite is the π-π stacking interaction between the aromatic ring contributed by aromatic amino acids and the hexagonal rings of the graphite surface. This interaction leads to a layer-by-layer exfoliation mechanism. Our research offers valuable insights into peptide design strategies for one-step graphite exfoliation and graphene functionalization in aqueous environments.

Effect of composite processing technique on tribological properties of 3D printed PLA-graphene composites

The present study investigates the effect of processing method on the tribological behavior of 3D-printed Polylactic acid (PLA)/graphene composite samples. Two different methods, electrochemical (EG) and chemical exfoliation (HG) of graphite, are used to prepare graphene fillers. The PLA/graphene composites are processed using two different solvents, chloroform (CHCl3) and dimethylformamide (DMF). Various PLA/graphene composite combinations are prepared by varying filler type, solvent type, and filler loading. The 3D printable composite feedstock filaments are prepared using a single-screw Desktop extruder. Fused Filament Fabrication (FFF) is employed to print samples for tribological tests. The coefficient of friction (COF) and wear rate are evaluated using the ball-on-flat reciprocating sliding wear tests. It was observed that COF was reduced by 76 % with 0.5 wt% loading of filler. The wear mechanism has changed from predominant abrasive wear in neat PLA to adhesive wear for composites. Further, the interactive effect of process parameters is studied using ANOVA. The results indicate that filler type and filler loading significantly influence weight loss. The solvent type has a minimum effect.

Reduced Graphene Synthesis via Eco-Friendly Electrochemical Exfoliation Method

A novel approach to mass producing graphene without inadvertent damage was needed to meet the increasing demand for the material. Graphite electrochemical exfoliation (EE) is an intriguing method for the large-scale, quick, and easy manufacture of graphene. Using leftover whey as an electrolyte, the EE of commercial graphite was examined in this work. It was shown that a straightforward and affordable exfoliation technique may produce graphene that, in the absence of functionalization or surfactant, forms a stable dispersion in the waste solvent. Because wastewater is acidic, it has been shown that storing it at +4 degrees aids EE. X-ray diffraction (XRD) was used to satisfactorily validate the manufactured graphene's existence. The results point to a low-cost method of producing graphene and graphene oxide.

Sonication-enhanced microfluidization for low-cost graphite exfoliation

Sonication-enhanced microfluidization for low-cost graphite exfoliation

Preparation of magnetic composite sorbent based on exfoliated graphite with metallic iron, cobalt and nickel using melamine as a reducing agent

Known preparation methods of the magnetic sorbents based on exfoliated graphite (EG) with metallic phase take several hours and requires the use of a large amount of reducing gas at a high temperature, which is not technologically advanced. The aim of the work is to obtain EG modified with iron, cobalt, and nickel using new simple method. This method includes the thermal treatment in nitrogen atmosphere of the mixture of expandable graphite, Mn+ nitrates (Mn+ = Fe3+, Co2+, Ni2+) and melamine. The thermal decomposition of melamine leads to formation of ammonia, which reduces the products of the Mn+ nitrates decomposition (α-Fe2O3, Co3O4/CoO, NiO) to metallic iron, cobalt and nickel. The use of different amount of melamine as reducing agent leads to the formation of mixtures with different compositions containing iron oxides Fe3O4, FeO, metallic iron α-Fe, Fe-C alloy γ-(Fe,C) and iron carbide Fe3C, which were confirmed by Mossbauer spectroscopy. Metallic Co and Ni on the EG surface is formed in nitrogen atmosphere by reduction with carbon even without melamine. Obtained EG/Fe has the highest saturation magnetization of 54.7 emu/g. EG/Co and EG/Ni have lower saturation magnetization of 40.1 and 12.0 emu/g, which is due to lower saturation magnetization of the individual metals.

Impact of solvent temperature on graphite shear exfoliation efficiency

Liquid phase exfoliation (LPE) of graphite is a promising pathway for graphene flakes (GF) due to its scalability and cost-effectiveness. However, the method has significant limits at the industrial scale, such as low yield of GF and long processing times. In this study, we investigate the effect of organic solvents such as N-methyl-2-pyrrolidone (NMP) and methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean) temperature on shear-induced exfoliation. The GF concentration was successfully obtained 0.62 mg/ml in NMP and 0.68 mg/ml in PolarClean within just 2 h at 263 K, without surfactants or any additional additives. These results revealed the improved exfoliation efficiency due to changes in solvent polarity, surface tension, and dispersion stability with increased viscosity. In addition, we investigate the optimization conditions required for liter-scale shear-induced exfoliation of graphite in PolarClean. As-prepared GF has significant potential as an effective nanofiller for enhancing the mechanical strength of commercial polymers. This study not only advances the understanding of the LPE mechanisms but also paves the way for the industrial application of this method in the green synthesis of graphene-based nanocomposites.

Efficient fabrication of high-quality graphene via alternating-current co-intercalation and microwave-assisted expansion

To facilitate the transformation of inexpensive and abundant graphite resources into two-dimensional graphene materials with promising applications, the development of efficient, cost-effective, and scalable technologies for large-scale production of high-quality graphene is crucial. Here, we propose an effective electrochemical dual-electrode co-intercalation exfoliation strategy. During the process, precise control of the electrochemical intercalation is achieved by adjusting the working bias and alternating current (AC) cycle, while ensuring the ion insertion rate through gradual voltage escalation. Repeated insertion of cations and anions under AC accelerates the graphite exfoliation. Following complete ion inserting, suitable microwave processing was employed to achieve rapid graphite expansion. Ultimately, ultra-sonication in NMP is employed to achieve final exfoliation between graphite layers. The resulting few-layer graphene (2–3 layers) exhibited minimal defects (ID/IG = 0.0405), low oxygen content (C/O = 44.62), high yield (95.3 %), and excellent conductivity (625 S/cm), enabling its potential commercialization and large-scale application. This outcome also serves as a significant reference for the commercial production of environmentally friendly and cost-effective graphene.

Facile Preparation of High-Performance Reduced Graphene Oxide (RGO)/Copper (Cu) Composites Based on Pyrolysis of Copper Formate.

Graphene has attracted much interest in many scientific fields because of its high specific surface area, Young's modulus, fracture strength, carrier mobility and thermal conductivity. In particular, the graphene oxide (GO) prepared by chemical exfoliation of graphite has achieved low-cost and large-scale production and is one of the most promising for Cu matrix composites. Here, we prepared a high strength, high electrical conductivity and high thermal conductivity reduced graphene oxide (RGO)/Cu composite by directly heating the GO/copper formate. The oxygen-containing functional groups and defects of RGO are significantly reduced compared with those of GO. The tensile yield strength and thermal conductivity of RGO/Cu composite with RGO volume fraction of 0.49 vol.% are as high as 553 MPa and 364 W/(m·K) at room temperature, respectively. The theoretical value of the tensile yield strength of the composite is calculated according to the strengthening mechanism, and the result shows that it agrees with the experimental value. After hot-rolling treatment, the ductility and conductivity of the composite materials have been greatly improved, and the ductility of the RGO/Cu composite with RGO volume fraction of 0.49 vol.% has been increased to four times the original. This work provides a highly efficient way to fabricate a high-performance RGO-reinforced Cu composite for commercial application.

Sustainable graphene production for solution-processed microsupercapacitors and multipurpose flexible electronics

The growing demand for portable and wearable electronics, Internet of Things microdevices, and wireless sensor networks has led to the development of miniaturized energy storage devices, such as microsupercapacitors (mSCs). With excellent electrical conductivity and high surface area in a layered structure, graphene materials are ideal for mSCs, but current manufacturing methods still hinder their widespread integration. Here, we propose a sustainable approach for the rapid and eco-friendly production of few-layer graphene flakes based on the exfoliation of graphite in water by a combination of high-shear mixing and a high-pressure airless spray. An all-carbon composite paste with high electrical conductivity and tunable viscosity was designed to fabricate planar, interdigitated mSCs on polyethylene terephthalate (PET). The flexible, metal-free mSCs achieved a Coulombic efficiency close to 100%, with areal and volumetric capacitances of 6.16 mF cm−2 and 2.46 F cm−3, respectively. The maximum energy density exceeds 200 μWh cm−3 with 91.5% capacitance retention after 10000 galvanostatic chargedischarge cycles. The mSCs retain the same performance when subjected to a wide bending range and can be easily modularized to adjust the voltage and capacitance outputs. Finally, high-performance coatings for electromagnetic interference shielding and wearable strain sensors are also fabricated to demonstrate the multipurpose applicability of the graphene-based paste.

Spatially Confined Radical Addition Reaction for Electrochemical Synthesis of Carboxylated Graphene and its Applications in Water Desalination and Splitting.

Due to the chemical stability of graphene, synthesis of carboxylated graphene still remains challenging during the electrochemical exfoliation of graphite. In this work, a spatially confined radical addition reaction which occurs in the sub-nanometer scaled interlayers of the expanded graphene sheets for the electrochemical synthesis of highly stable carboxylated graphene is reported. Here, formate anions act as both intercalation ions and co-reactant acid for the confinement of electro-generated carboxylic radical (●COOH) in the sub-nanometer scaled interlayers, which facilitates the radical addition reaction on graphene sheets. The controllable carboxylation of graphene is realized by tuning the concentration of formate anions in the electrolyte solution. The high crystallinity of the obtained product indicates the occurrence of spatially confined ●COOH addition reaction between the sub-nanometer interlayers of expanded graphite. In addition, the carboxylated graphene have been used for water desalination and hydrogen/oxygen reduction reaction. Therefore, this work provides a new method for the in situ preparation of functionalized graphene through the electrolysis and its applications in water desalination and hydrogen/oxygen reduction reactions.