Direct Exfoliation Of Graphite Research Articles

Hybrid based on graphene nanoplatelets and carbon nanotubes obtained in a single‐step approach and its reinforcement effect in an epoxy matrix

AbstractA hybrid based on graphene nanoplatelets and carbon nanotubes (G‐CNT) is obtained through direct exfoliation of graphite in a liquid medium, and tested as reinforcement material in epoxy resin. CNT act as exfoliation material in contact with graphite under ultrasound irradiation, and the thickness of graphite decreases to produce graphene nanoplatelets in an easy one‐step method. The morphology of the hybrid, is observed through transmission electron microscopy micrographs exhibiting delamination of graphite. XRD, UV–vis, and atomic force microscopy (AFM) results provide evidence of the exfoliation of graphite by interaction with CNT. Ultrasonic process does not generate additional oxygenated groups on carbon structures, as it is supported by XPS spectra; and the disorder in the carbon structures detected in Raman spectra is attributed to defects originated by some fragmentations. Epoxy nanocomposites incorporating 0.3 wt% of G‐CNT display the highest enhancement in storage modulus (~2706 MPa), glass transition region increases meaning higher thermal stability, and glass transition temperature increases until 119°C. Impact resistance also enhances with 0.3 wt% of G‐CNT, obtaining ~95% of increment. The hybrid obtained by exfoliating graphite with CNT in one‐step improves the performance of nanocomposites, and it offer an easy and viable alternative to obtain hybrid systems.

Sustainable Graphene Production: New Insights into Cannabis sativa Engineered Carbon Dots Based Exfoliating Agent for Facile Production of Graphene

The direct exfoliation of graphite (Gr) produces high-quality graphene (G) having enormous industrial applications. Exploring sustainable sources as an exfoliating agent offers advantages in terms ...

Direct exfoliation of graphite and its Raman spectroscopic study

Direct exfoliating is a safer method for graphene preparation. However, it is important to synthesize a graphene with minimum structural defects since they will influence the properties of the devices. This paper focuses on two types of graphite exfoliation techniques, electrochemical and sonication, for the preparation of graphene oxides. The quality of the graphene oxides was studied using Raman Spectroscopy while the morphology was investigated by field emission scanning electron microscopy (FESEM). The results suggest that the graphene oxides synthesized using the electrochemical technique has the minimum number of layers while graphene oxides obtained from the sonication technique has the minimum defects.

Green and High-Efficiency Production of Graphene by Tannic Acid-Assisted Exfoliation of Graphite in Water

A green and high-efficiency method was developed to prepare low-cost and high-quality graphene on a large scale through direct exfoliation of graphite in aqueous media using tannic acid (TA) as the stabilizer. The influence of preparation parameters on graphene concentration (CG) and graphite exfoliation efficiency (CG/CG,i), including TA concentration (CTA), initial graphite concentration (CG,i), pH, ionic strength, sonication time, and cycles, was systematically investigated. Under the optimum conditions, the highest CG that can be attained is 1.25 mg·mL–1 with CG/CG,i equal to 2.5%, and 92% of the as-formed graphene are few-layer graphene (below 5 layers) with the electrical conductivity as high as 488 S·cm–1. Due to TA on the graphene surface acting as the dual roles of dispersant and interfacial regulator, the high-quality graphene can be uniformly dispersed and tightly integrated into polymer matrices for high-performance and multifunctional polymer nanocomposites. In a word, this contribution provi...

One-pot exfoliation, functionalization, and size manipulation of graphene sheets: efficient system for biomedical applications.

In this work, we reported a facile method to produce stable aqueous graphene dispersion through direct exfoliation of graphite by modified hyperbranched polyglycerol. Size of graphene sheets was manipulated by simultaneous exfoliation and sonication of graphite, and functionalized graphene sheets with narrow size distribution were obtained. The polyglycerol-functionalized graphene sheets exhibited highly efficient cellular uptake and photothermal conversion, enabling it to serve as a photothermal agent for cancer therapy.

Direct exfoliation of graphite into graphene in aqueous solution using a novel surfactant obtained from used engine oil

Large-scale production of high-quality graphene is very critical for practical applications of graphene materials and devices. Exfoliation of graphite in an aqueous solution of surfactants is one of the most promising approaches to produce graphene. In this study, a novel anionic surfactant [sulfonated used engine oil (SUEO)], which was prepared from used engine oil, was employed to exfoliate the graphite nanoplatelets into graphene sheets in an aqueous solution under sonication to form a stable dispersion. The efficiency of SUEO for exfoliating and dispersing graphene was investigated and compared with that of traditional surfactants, such as sodium dodecyl sulfate, sodium dodecyl benzene sulfate, cetyl trimethyl ammonium bromide, and polyvinylpyrrolidone. Result showed that the graphene dispersion with excellent stability had a higher concentration (0.477 mg/mL) than others at 0.5 g/L optimal SUEO dosage in 4 h sonication time. The superior performance of SUEO can be attributed to its special molecular structures, whose hydrophobic moieties contain cycloalkanes/aromatics with different molecular weights and/or side chain –R with different lengths. Structural diversities are very helpful to the “jigsaw-puzzle” process on the graphene surface, where the total interfacial energy of the mixture system was minimized. Microscopic (SEM, TEM, and AFM) and spectroscopic (XRD, XPS, and Raman) measurements revealed that the dispersion consisted of few-layer graphene sheets with lower levels of defects or oxidation. This study presents a new class of dispersing agents for graphene that assists in the exfoliation process in water with high concentration and the stabilization of the graphene sheets against reaggregation.

Multi-layer graphene reinforced aluminum – Manufacturing of high strength composite by friction stir alloying

The paper reports manufacturing of a multi-layer graphene embedded composite of aluminium alloys by direct exfoliation of graphite into graphene with the help of Friction Stir Alloying (FSA). The formation of this nano composite and optimization of the process parameters led to an approximately two-fold increase in the strength, without loss in ductility, due to the dispersion of the graphene in aluminium. The manufacturing process is scalable and cost effective as it uses graphite powder and aluminium sheets as the raw materials. The presence of graphene layers in the metal matrix was confirmed using Raman spectroscopy as well as TEM. The graphene sheet thickness was measured using AFM after extracting it from the composite. Molecular dynamic simulation results reveal the evolution of newer structures and defects that have resulted in the enhanced properties of the nano-composite. These findings open up newer possibilities toward efficient and scalable manufacturing of high strength high-ductility metal matrix based graphene nano-composites.

Black tea assisted exfoliation using a kitchen mixer allowing one-step production of graphene

A kitchen mixer is one of the possible tools for the exfoliation of graphene. While organic solvents such as NMP or DMF are suitable for the exfoliation of graphite, the majority are toxic and dangerously harmful when exposed to humans and the environment. Therefore, an alternative solvent must be proposed for green and sustainable production of graphene. In this initial work, we have developed a new synthesis method for graphene through the direct exfoliation of graphite in commercial black tea. We found that our maximum yield concentration of graphene is Y = 0.032 mg ml−l after 15 min of mixing. From the data of Raman, the level of defects in our produced graphene is suggested as being very minor (ID/IG = 0.17), despite possible graphene functionalization by oxygen groups in tea. Incorporation of our graphene into PMMA results in shifting the onset temperature from 300 °C to 326 °C, which impressively validates the potential of the produced graphene as a thermal reinforcement material for polymer composites.

Direct exfoliation of graphite in water with addition of ammonia solution

To bring graphene closer to its real-world applications, finding a green, low-cost, environment-friendly and less toxic solvent for production of high-quality graphene is highly demanded. However, water, the most widely used green solvent, is generally considered to be a poor solvent for hydrophobic graphene. In this study, we exfoliate graphene nanosheets directly in basic water without surfactants, polymers or organic solvents. The addition of a small amount of ammonia solution achieves the exfoliation of few-layer graphene nanosheets from pristine graphite. Diverse characterization methods are employed to investigate the morphology and quality of as-prepared graphene sheets. The release of gaseous ammonia plays the key role in exfoliation of graphene. The concentration of stable graphene dispersions can reach 0.058mg/mL.

Electrochemical Synthesis and Characterization of Flavin Mononucleotide‐Exfoliated Pristine Graphene/Polypyrrole Composites

AbstractThe electrochemical generation of graphene‐polypyrrole composite films is presented here by using pristine, oxide‐free graphene flakes obtained through the direct exfoliation of graphite in water with flavin mononucleotide (FMN) as a colloidal stabilizer (FMN−G‐PPy films): an environmentally friendly methodology. The best potential and current ranges for the electropolymerization of pyrrole in the presence of FMN−G, trying to avoid parallel over‐oxidation/degradation processes, were determined from voltammetric responses of the different solutions. Then, a parallel study of the electrogeneration of FMN−G‐PPy films on clean Pt electrodes by using cyclic voltammetry, potentiostatic or galvanostatic conditions, was performed. The subsequent electrochemical characterization of the resulting films and parallel energy‐dispersive X‐ray spectroscopy analysis of different oxidized states revealed the separate oxidation/reduction of graphene and polypyrrole inside the material. Graphene reactions (n‐doping) drive the exchange of cations, whereas polypyrrole reactions (p‐doping) drive the exchange of anions. The specific charge storage in FMN−G‐PPy, 207 mC mg−1, is higher than that stored in polypyrrole, 141 mC mg−1, indicating some synergy. An unexpected high content of anions was found in deeply reduced materials. The surface morphology of the oxidized and reduced materials generated by different methodologies was studied by using scanning electron microscopy.

Graphite/Metal Electrodes for Electrochemical Exfoliation: Few Layers Graphene with Low Defects

Graphene was obtained by electrochemical exfoliation of graphite and metal/graphite electrodes of different compositions and electrical conductivities. Metal/graphite electrodes were prepared using high purity copper and nickel precursor and commercial graphite. Processes of rapid expansion and direct exfoliation of graphite in a H2SO4 solution were observed using voltages from 2V to 15V and currents of 0.03 mA to 0.08 mA. The total time for each process was one hour and the maximal concentration of few layers graphene flakes was 0.002 mg/mL. X rays powder diffraction of the expanded electrodes showed the effect of the electrochemical process in the crystallinity and the increasing of interlayer distance. A characterization of a large amount of graphene flakes was performed by Raman spectroscopy and optical microscopy. Typical size of the flakes are between 1 μm and 10 μm and the Raman spectra indicate number of layers from single or bilayers to approximately ten layers. The greatest variations in thickness of flakes are observed when the intercalation process concludes before the expansion of the layers. A low degree of oxidation and of structural defects was characteristic of the experiments with lower acid concentration.

Direct exfoliation of graphite into graphene in aqueous solutions of amphiphilic peptides.

Different amphiphilic peptides were used to mediate the direct exfoliation of graphite into few-layered graphene flakes in aqueous solutions. Charge was found to be an important parameter in determining their graphite exfoliating efficiency. The anionic molecules were more favorable than the cationic ones leading to a higher efficiency. The gemini-type peptide IleIleIleCys-CysIleIleIle (I3C-CI3) exhibited the highest efficiency, which might be attributed to its specific physicochemical properties and interactions with graphene sheets. I3C-CI3 adsorbed onto the graphene surface as either monomers or self-assembled nanoaggregates. These adsorbed species increased both electrostatic and steric repulsions between the graphene/I3C-CI3 composites. More interestingly, the graphene/I3C-CI3 composites showed a reversible pH-dependent dispersion/aggregation. This behavior resulted from the pH-sensitive protonation of the peptide molecules and was rarely found in the graphene dispersions exfoliated by traditional surfactants. Moreover, the graphene/I3C-CI3 dispersion was used to fabricate free-standing macroscopic composite films that contained different nanostructures. The study expands the library of available agents for direct graphite exfoliation to produce graphene sheets. Employing peptide molecules as graphene exfoliating and stabilizing agents avoids the use of toxic reagents, which may allow fabrication of functional composite materials for biocompatible applications.

Functionalized graphene nanomaterials: new insight into direct exfoliation of graphite with supramolecular polymers.

A novel urea-cytosine end-capped polypropylene glycol (UrCy-PPG) can self-assemble into a long-range ordered lamellar microstructure on the surface of graphene, due to the strong specific interactions between UrCy-PPG and graphene. In addition, the graphene composite produced exhibits a high conductivity (∼1093 S m(-1)) with a dramatic thermo-responsive ON/OFF resistance-switching behavior (10 consecutive cycles).

Preparation of CO2-switchable graphene dispersions and their polystyrene nanocomposite latexes by direct exfoliation of graphite using hyperbranched polyethylene surfactants

Herein the preparation of CO2-switchable graphene dispersions by noncovalent exfoliation of graphite in water using a CO2-switchable star copolymer surfactant is described.

BioGraphene: Direct Exfoliation of Graphite in a Kitchen Blender for Enzymology Applications.

A high yielding method for the aqueous exfoliation of graphite crystals to produce high quality graphene nanosheets in a kitchen blender is described here. Bovine serum albumin (BSA), β-lactoglobulin, ovalbumin, lysozyme, and hemoglobin as well as calf serum were used for the exfoliation of graphene. Among these, BSA gave the maximum exfoliation efficiency, exceeding 4mgmL(-1)h(-1) of graphene. Quality of graphene produced was examined by Raman spectroscopy, which indicated 3-5 layer graphene of very high quality and very low levels of defects. Transmission electron microscopy indicated an average size of ~0.5μm flakes. The graphene/BSA dispersions were stable over pH 3.0-11, and at 5°C or 50°C, for more than 2 months. Current approach gave higher rates of BSA/graphene (BioGraphene) in better yields than other methods. Calf serum, when used in place of BSA, also gave high yields of good quality BioGraphene and these preparations may be of direct use for cell culture studies. A simple example of BioGraphene preparation is described that can be adapted in most laboratories, and graphene-adsorbed glucose oxidase is nearly as active as the free enzyme. Current approach may facilitate large-scale production of graphene in most laboratories around the world and it may open new opportunities for biological applications of graphene.

Self‐Assembly of Organic Building Blocks with Directly Exfoliated Graphene to Fabricate Di‐ and Tricomponent Hybrids

AbstractIn this work, we developed a strategy to fabricate self‐assembled aggregates encapsulating graphene from direct exfoliation of graphite. Naphthalene‐anhydride‐appended glutamic acid (NG) and pyrene‐appended glutamic acid (PG) were utilized to exfoliate graphite to generate few‐layer graphene in basic aqueous media. Acidification‐triggered self‐assembly of PG could encapsulate graphene sheets to give graphene@microsheet hybrids. Melamine (Mm) was introduced to induce the morphological transformation of PG from microsheets to twisted fibers with columnar packing. In the presence of graphene, this transformation allowed the fabrication of twisted‐fiber‐encapsulated graphene (graphene@twist fiber). Tricomponent hybrids were also built up via in situ preparation of gold nanoparticles (AuNPs) on the negatively charged surface of few‐layer graphene during the self‐assembly process. This study presents an approach to construct directly exfoliated graphene‐based hybrids through self‐assembly.

Synthesis of pyrene‐capped polystyrene by free radical polymerization and its application in direct exfoliation of graphite into graphene nanosheets

ABSTRACTIt is of great practical significance to acquire pyrene‐capped polymer, which has proven an excellent dispersant of nanocarbons, in an accessible way. Taking synthesis of pyrene‐capped polystyrene (PyPS) as the example, free radical polymerization was demonstrated to be an attractive option to satisfactorily fulfill such mission. For this, a new azo‐based pyrenyl compound was designed, synthesized, and used as initiator. The molecular structure of PyPS was studied as a function of polymerization temperature and content of chain transfer agent of 1‐dodecanethiol. Following the successful synthesis, a PyPS polymer structured as 1.04 pyrene groups per chain was chosen as dispersant for preparation of graphene. The results showed that 0.2 mg/mL of PyPS in chloroform permits 67.4 μg/mL of graphene nanosheets to be prepared by liquid‐phase exfoliation of graphite. In contrast, only 8.5 μg/mL of graphene nanosheets could be obtained in pure chloroform. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2175–2185

Synthesis of few layer graphene by direct exfoliation of graphite and a Raman spectroscopic study

The exfoliation of graphene from pristine graphite in a liquid phase was achieved successfully via sonication followed by centrifugation method. Ultraviolet–visible (UV–vis) spectra of the obtained graphene dispersions at different exfoliation time indicated that the concentration of graphene dispersion increased markedly with increasing exfoliation time. The sheet-like morphology of the exfoliated graphene was revealed by Scanning Electron Microscopy (SEM) image. Further, the morphological change in different exfoliation time was investigated by Atomic Force Microscopy (AFM). A complete structural and defect characterization was probed using micro-Raman spectroscopic technique. The shape and position of the 2D band of Raman spectra revealed the formation of bilayer to few layer graphene. Also, Raman mapping confirmed the presence of uniformly distributed bilayer graphene sheets on the substrate.

High-concentration aqueous dispersions of graphene produced by exfoliation of graphite using cellulose nanocrystals

Stable high-concentration aqueous dispersions (>1mgml−1) of single and few-layer graphene flakes were produced by direct exfoliation of graphite using cellulose nanocrystals (CNC). Biodegradable and widely available from renewable sources, CNC have proven to be very efficient graphene stabilizers even at low concentrations (0.2mgml−1), thus enabling remarkably high graphene/CNC ratios (up to 3.8).

A direct route towards preparing pH-sensitive graphene nanosheets with anti-cancer activity

Graphene nanosheets were prepared by the direct exfoliation of graphite in an aqueous lysozyme solution using ultrasonication. Atomic force microscopy studies indicated that the nanosheets possessed small lateral dimensions of less than three layers. Raman spectroscopy suggested that defects were introduced by the sonication process. These defects were primarily edge defects, not basal-plane defects. Cytotoxicity studies revealed that the lysozyme-supported nanosheets possessed anticancer activity at certain micromolar concentrations. Three other proteins and gold nanoparticles prepared with those proteins were examined as aids in graphene exfoliation. The overall protein or nanoparticle charge played an important role in the graphite exfoliation to graphene. All of the graphene dispersions were sensitive to pH. Changing the pH reversibly converted the graphene from a highly dispersed state to an aggregated state and vice versa. Although no lateral dimension differences were observed in the nanosheets prepared using the nanoparticles, their cell viability percentages varied depending on the particular protein used.