Graphene Particles Research Articles

Improvement of the chemical, thermal, mechanical and morphological properties of polyethylene terephthalate–graphene particle composites

The graphene powder was used as a reinforcement in polyethylene terephthalate (PET) with various weight percentages 0.1, 0.5, 1 and 2 wt%. To prepare PET/graphene powder composites, melt-mixing process was followed. The crosslinking degree between PET and functionalized graphene increased, which was indicated by carbonyl indexes (Fourier transform infrared spectra) when interfaced with PET. The results of thermal properties showed that adding 2 wt% of graphene composites improved the thermal stability, transition glass temperature $$T_\mathrm{g}$$ , crystallinity temperature point and chemical properties of PET. The results of thermal gravimetric analysis showed that the highest addition of graphene (2 wt%) into the PET slightly improves both the residue yields and thermal stability. The tensile strength of PET was highly increased with the increased loading of graphene, and the elongation was reduced, compared with PET without filler. The results of X-ray diffraction curves showed that 2% incorporation of graphene into PET has good interfacial interaction and higher intensity. The scanning electron microscopy micrographs showed a high compatibility between the pure PET and graphene composite chains.

Graphene particles supported on silica as sorbent for residue analysis of tetracyclines in milk employing microextraction by packed sorbent.

This paper describes the use of graphene-based sorbents for determination of four tetracyclines in milk. The synthesized materials were combined with microextraction by packed sorbent (MEPS) to act as the sample preparation step. The extraction performance of these sorbents was compared to commercial phases, and graphene supported on silica provided the best results. The analytical method optimization was carried out by employing experimental design. Firstly, an evaluation of the experimental variables (elution solvent, use of EDTA, ionic force, and pH of the washing solution) was made by a 24-1 factorial experimental design. The variables sampling, washing and elution cycles of MEPS were further optimized under a full 23 experimental design. The validation parameters were determined under optimized conditions resulting in a linearity ranging from 15 to 110μg/L with R2 values above 0.98, and LOQs ranging from 0.05 to 0.9μg/L. The accuracy ranged from 87.9 to 118.4% and intra/inter-day precision reported by the RSDs were lower than 19%. The proposed and validated method was successfully applied to the analysis of 11 milk samples from different animals, revealing traces of tetracyclines in only two of them. This study focused on the evaluation of graphene-based sorbents combined with MEPS for tetracycline analysis provided equivalent or even better results than other proposed methods, suggesting being a sensitive, fast and reliable alternative method for the determination of tetracyclines in milk samples.

Tensile behavior of aluminum alloy (AA7050) metal matrix composite reinforced with graphene fabricated by stir and squeeze cast processes

Metal matrix composites based on aluminum alloy AA7050 reinforced with graphene nanoparticles are fabricated using stir casting and squeeze casting techniques. Mechanical characteristics studies were performed on both the stir cast and squeeze cast composite specimen. Taguchi's L27 orthogonal array was used for the design of experiments. Certain parameters like melting temperature (775, 800 and 825°C), stirring speed (300, 400 and 500rpm) and graphene content (0.3, 0.5 and 0.7wt%) with three levels were considered for the experiments. Based on the experimental results, analysis of variance (ANOVA) was conducted to determine the level of influence of the parameters on the tensile strength of the specimens. The microstructural result shows that graphene particles are uniformly distributed in the aluminum matrix only in the composites with 0.3wt % graphene irrespective of the process followed for the fabrication of composite samples. It is being found that the tensile properties of both stir cast and squeeze cast samples have been enhanced for 0.3wt% of graphene in the AA7050 composites. Increasing the graphene content beyond 0.3wt% results in cluster formation.

Dispersion and Rheological Properties of Aqueous Graphene Suspensions in Presence of Nanocrystalline Cellulose

The possibility and feasibility of nanocrystalline cellulose (NCC) for dispersing hydrophobic graphene in aqueous solutions were studied in the present work. The dispersion properties of graphene particles in aqueous media as a function of various amounts of NCC were investigated. The rheological behavior of NCC-dispersed graphene suspensions was studied, and a polynomial model was proposed and employed to simulate the obtained shear flow of graphene suspensions. The results of UV–Vis analysis and sedimentation test suggested that the increased NCC addition significantly led to the improved dispersion properties of graphene suspensions. Rheological behavior measurements demonstrated that graphene suspensions exhibited a reduction trend in the shear viscosity, shear stress, and viscoelasticity with the increased amount of NCC addition. Meanwhile, the shear viscosity and shear stress of graphene suspensions were found to show a dependency on the process temperature. The above results supported the conclusion that NCC is a promising candidate for improving the dispersion and flowability of graphene in aqueous media.

The Nucleation Process in the Preparation of Graphene Films by Pulsed Laser Deposition

The nucleation process of graphene films prepared by pulsed laser deposition has been investigated in detail. It is found that graphene nucleates at the steps on the substrate surface firstly, from aggregation of nuclei into particles. High pulsed laser energy offers large incident energy for carbon particles deposited on the surface of the substrate, which is beneficial to the nucleation of graphene. A lot of steps are formed on the copper substrate due to the high temperature, so that the high incident energetic carbon species are able to form a stable nucleus at the steps. As the incident particles increases, the graphene nuclei are combined to grow together. Further, it is found that graphene tends to form few layer graphene particles instead of large graphene sheets.

Graphene interactions with human endothelium

The discovery of graphene boosted an interdisciplinary research based on its unique properties and possible applications in biomedicine. Multiple scientific reports concerning graphene interactions with adherent cells showed the potential use of graphene as a biomaterial in tissue engineering.In this study we examined the influence of pristine graphene, as a monolayer coating or flake suspension, on human endothelial cells (HUVEC) isolated from umbilical veins. Umbilical cords were obtained from healthy gravidas after the cesarean section procedures. Cytotoxicity, proliferation and cell morphology study were performed using various methods, including colorimetric and luminescent cell assays, optical and fluorescence microscopy.The cytotoxicity assay confirmed dose and time dependent cytotoxicity of tested graphene flakes (G1APS~5000nm and G2APS~450nm). Even the lowest concentration of graphene (10μg/ml) significantly inhibited cell proliferation. The difference between the two tested flake sizes was more distinct during cell mortality study, indicating the greater cytotoxic effect of the smaller graphene particles. Graphene suspended in the cell culture medium created aggregates. Cell imaging revealed efficient accumulation of nanoflakes inside the cells, especially those of the smaller size.The morphology of the cells seeded on graphene‐coated SiO2 substrates was recorded using fluorescence microscopy. Endothelial cells were immunostained for actin cytoskeleton to characterize its organization, stress fibers creation, cell adhesion and spreading. After a 72h incubation, both the cells incubated on graphene SiO2 substrates and on the reference material for cell plating, reached confluence. No difference in cell shape and morphology was detected. Graphene was shown to be a suitable surface for endothelial cell growth.Our preliminary investigation confirmed cytotoxic effect of pristine graphene flakes on adherent cells, however demonstrated that CVD grown graphene is not toxic for human endothelial cells. These data show promise for using graphene monolayers in tissue engineering or as a substrate material for implant devices.Support or Funding InformationWUM grant: 2M2‐W2‐16This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hexagonal platelet graphite and its application in Li-ion batteries

Highly crystalline graphite powder was prepared from the low temperature (800–1000 °C) graphitization of renewable materials using a magnesium catalyst. The magnesium catalyst was easily removed, resulting in a highly pure graphite product. The graphite has an interesting microstructure, consisting of mainly hexagonal platelets (up to 10 μm), and some graphene particles. This unique microstructure results in a high specific surface area. However, the graphite has a high density and a degree of graphitization higher than some conventional artificial graphites made at 2850 °C. When cycled in Li half-cells, the graphite displays good cycling stability and high reversible capacity (up to 370 mAh g−1). After carbon coating, the surface area of the graphite is greatly reduced, and its coulombic efficiency is greatly improved, resulting in performance that is comparable to commercial high surface area battery synthetic graphites. Graphite made by low temperature Mg catalyzation of renewable plant derived precursors represents a new direction for research in the development of primary synthetic graphites and the application of sustainable materials. We anticipate that Mg catalyzed graphites could have interesting applications in batteries, as catalyst supports or in other fields.

Composite coatings with nickel matrix and graphene as dispersed phase

Abstract The paper presents the results of the studies of nickel-graphene composite coatings deposited by the electrochemical reduction method. A bath with low concentration of nickel ions, graphene as dispersed particles and organic compounds were used for deposition of the composite coatings nickel-graphene. The results of investigations of coatings deposited from the electrolyte containing 0.33, 0.5 and 1 g/dm3 graphene and two surface-active compounds were shown. The particles content in the coatings, the surface morphology, the cross-sectional structures of the coated samples, thickness and internal stresses were measured. Voltammetric method was used for examination of the corrosion resistance of samples of composite coatings in 0.5 M NaCl solution. The obtained results suggest that the content of incorporated graphene particles increases with an increasing amount of graphene in plating bath. The applications of organic addition agents was advantageous because it caused compressive stresses in the coatings. All of the nickel-graphene composite coatings had better corrosion resistance than the nickel coatings.

Thermal characterization of ABS-Graphene blended three dimensional printed functional prototypes for electro chemical energy storage

This study highlights the thermal characterization of ABS-Graphene blended three dimensional (3D) printed functional prototypes by fused deposition modeling (FDM) process. These functional prototypes have some applications as electro-chemical energy storage devices (EESD). Initially, the suitability of ABS-Graphene composite material for FDM applications has been examined by melt flow index (MFI) test. After establishing MFI, the feedstock filament for FDM has been prepared by an extrusion process. The fabricated filament has been used for printing 3D functional prototypes for printing of in-house EESD. The differential scanning calorimeter (DSC) analysis was conducted to understand the effect on glass transition temperature with the inclusion of Graphene (Gr) particles. It has been observed that the reinforced Gr particles act as a thermal reservoir (sink) and enhances its thermal/electrical conductivity. Also, FT-IR spectra realized the structural changes with the inclusion of Gr in ABS matrix. The results are supported by scanning electron microscopy (SEM) based micrographs for understanding the morphological changes.

A density functional theory study of the role of functionalized graphene particles as effective additives in power cable insulation.

The role of a series of functionalized graphene additives in power cable insulation in suppressing the growth of electrical treeing and preventing the degradation of the polymer matrix has been investigated by density functional theory calculations. Bader charge analysis indicates that pristine, doped or defect graphene could effectively capture hot electrons to block their attack on cross-linked polyethylene (XLPE) because of the π–π conjugated unsaturated structures. Further exploration of the electronic properties in the interfacial region between the additives and XLPE shows that N-doped single-vacancy graphene, graphene oxide and B-, N-, Si- or P-doped graphene oxide have relatively strong physical interaction with XLPE to restrict its mobility and rather weak chemical activity to prevent the cleavage of the C–H or C–C bond, suggesting that they are all potential candidates as effective additives. The understanding of the features of functionalized graphene additives in trapping electrons and interfacial interaction will assist in the screening of promising additives as voltage stabilizers in power cables.

Large scale cathodic exfoliation of graphite using deep eutectic solvent and water mixture

ABSTRACTA short-time and low-cost synthesis route was used to produce large lateral size (from 2 to 15 μm) from monolayers to few layers of graphene by a two-step process of electrochemical exfoliation with a deep eutectic solvent in a mixture with water that can be reused, and ultrasonic bath. The graphene was characterized by SEM, TEM, AFM, Raman and electrochemical activity. During the electrochemical exfoliation, high expanded graphene particles were obtained and these were dispersed in a mixture of water with 5%wt ethylene glycol by an ultrasonic bath in order to complete the exfoliation process. An enhancement of the electrical conductivity of these dispersions was obtained with the increase of graphene concentration, 0.38 mg/mL, which best result was achieved with 30 wt% water and a DC voltage of 10 V. It was possible to add a conductive layer to a glass substrate with the graphene obtained and Tyndall effect was observed.

Investigation on the Impact of Differently Treated PM2.5 on Cell Viability of Human Bronchial Epithelial Cells (Beas-2b) and the Construction of Bio-Hazard Index

After PM2.5 is inhaled by the human body, various pathogens such as influenza viruses, can cause many respiratory diseases, causing local clogging of the lungs and causing damage. At present, the research on the effect of PM2.5 on human bronchial epithelial cells (BEAS-2B) and the toxicity of the respiratory system only focuses on the single source PM2.5. The effects of different native PM2.5 on human bronchial epithelial cells (BEAS-2B) and the toxicity of the respiratory system have not been reported. In this paper, the effects of artificial PM2.5 graphene particles, sterilized atmospheric PM2.5 particles and unsterilized atmospheric PM2.5 particles on the viability of immortalized human bronchial epithelial cells (BEAS-2B) are investigated. The Bio-hazard Index describing the effects of PM2.5 on human respiratory health is constructed based on the change of BEAS-2B cell viability under different PM2.5 concentrations in the cell culture. The index can evaluate the pysiological impact of PM2.5 on the human body, and is more intuitive than the current AQI, which only discribes the physical concentration of PM2.5 in the air. The index thus provides a more accurate hazard prevention warning for susceptible population.

Heat Treating Studies of Graphene Reinforced Aluminium Metal Matrix Composite

Metal matrix composites (MMC’s) consist of a metallic matrix combined with dispersed graphene particulate phases as reinforcement. In this research work strength behaviour and tensile characteristics of 2900 alloy matrix composites produced by a powder metallurgy process are investigated as a function of microstructure-strength properties. Two different Samples of Al alloy composites are prepared using 0.25, 0.5 and 0.75 wt% of graphene. Rockwell hardness and tensile properties of these samples are investigated using Instron testing machine. The results indicated that tensile properties of the composites significantly improved in the UTS, on incorporation of hard, graphene particles. The analysis of strength behaviour has revealed that the strength improves significantly with increase in microwave sintering method and the graphene percentage.

Exposure to airborne particles associated with the handling of graphene nanoplatelets

Background:It is recognized that engineering control measures are needed to reduce occupational exposure to engineered nanomaterials (NMs): of these, fume hoods are among the most widespread collective protection equipment used while handling NMs in occupational settings. It is known that in some circumstances, handling NMs in fume hoods can result in a significant release of NMs.Objective:To assess the effectiveness of fume hoods in reducing exposure while handling graphene nanoplatelets and to define the conditions that result in a lower dispersion of particles and thus less operator exposure.Methods:An experimental protocol was established to monitor the variations of airborne particle concentrations while handling graphene in fume hoods (transferring and pouring). The measurement locations were at the laboratory, inside the hood and at operator’s breathing zone. Handling tasks were performed under different operating conditions: the variable factors included hood face velocity and sash height.Results:Results of this study indicate that the handling of graphene nanoplatelets may pose a potential risk of contamination of the work environment and hence exposure of the involved operators, if adequate control measures are not taken. In fact, when inadequate or not sufficiently cautionary operational conditions were utilized, non-negligible increases in airborne graphene particle concentrations during the nanomaterial manipulation phases were observed.Conclusions:Some operating conditions (e.g., face velocity, sash height) can be adjusted to avoid relevant personal exposure conditions and contamination of the work environment by NMs, thus ensuring safer conditions.

Mechanical properties evaluation of hot extruded AA 2024 –Graphene Nanocomposites

Metal-matrix nano composites particularly the Graphene particle reinforced aluminum alloy based composites, have received considerable attention due to their attractive physical and other properties such as high strength, compressible property, tensile strength, and tribological characteristics. The current research work is aimed to synthesis composites with Graphene as reinforcement and aluminium alloy AA 2024 as matrix material. The consolidation is carried out through powder metallurgy (PM) and hot extrusion approach. The dispersion of Graphene is achieved through ultrasonic dispersion followed by ball milling. Hardness and SEM analysis was carried out on developed composites. Further, tensile strength measurement was performed on developed composites according to ASTM standards in Instron Universal Testing Machine. Improvement in the strength and possible reasons for crack initiations and fracture surface were extensively analysed to study the effect of reinforcement addition and its combinations in the aluminium alloy matrix.

Adsorption of organic dyes from aqueous solutions using surfactant exfoliated graphene

In this study, graphene exfoliated in the presence of surfactants was investigated as an adsorbent for the removal of organic dyes from aqueous solution. The resultant graphene particles were shown using zeta potential measurements to possess effective surface charges dominated by the charge of the adsorbed exfoliating surfactant. In this way, the overall charge on the particles, and hence the ability to adsorb dyes, was significantly enhanced compared to previously explored surfactant free systems. Furthermore, the graphene particles could be produced to have either positive or negative charge allowing the selective removal of anionic or cationic species from water respectively. The adsorption of the dyes from solution was demonstrated to be driven by electrostatic interactions with the adsorbed surfactant. The maximum removal of dye was achieved when cationic methylene blue was exposed to graphene exfoliated using the anionic surfactant, sodium dodecyl sulfate (SDS). Adsorption of methylene blue on SDS exfoliated graphene was strongly influenced by contact time and temperature, while variations in pH were shown to have a minor effect on adsorption. Indeed, the rate of adsorption was faster than previous studies due to the inherent 2D nature of the highly exfoliated graphene particles. The adsorption data was modelled using the Freundlich and Langmuir adsorption isotherms, whilst the pseudo-second order model and the intraparticle diffusion models were used to model the kinetics of the adsorption process. SDS exfoliated graphene particles exhibited a maximum adsorption capacity of 782.3 mg/g at 25 °C, greater than that of many other graphene-based materials. Thus, surfactant exfoliated graphene particles not only demonstrated excellent adsorption characteristics, but also the ability to maximize the amount of dye adsorbed based on solution conditions or the exfoliating surfactant.

Nanocrystalline nickel-graphene nanoplatelets composite: Superior mechanical properties and mechanics of properties enhancement at the atomistic level

A relatively easy-to-fabricate nanolayered metal composite with superior mechanical properties is introduced. The matrix is a nanocrystalline nickel in which the grain size is engineered to optimize the strength, and monolayer particles of graphene are embedded into the matrix as reinforcing interlayers. Atomistic-scale deformation mechanisms, and mechanics of hindering the dislocations propagation by graphene nanoplatelets with different configurations in the nanocrystalline metallic matrix, are investigated by molecular dynamics simulations. Molecular dynamics findings are utilized to engineer the nanostructure of a metal matrix composite. Nanocrystalline nickel-graphene nanolayered systems with optimum mechanical properties are identified and fabricated with a cost-efficient method. The nanostructure of the fabricated composites is examined via electron microscopy, and their mechanical performance is inspected via nanoindentation tests. The experimental results show that a nickel-graphene nanolayered system with 14% areal coverage of graphene particles at the interlayers has improved the hardness of the nanocrystalline nickel by almost 40%.

Crumpled Graphene Balls Stabilized Dendrite-free Lithium Metal Anodes

Summary With its high theoretical capacity and low electrochemical potential, Li metal itself would be the ideal anode for Li-ion batteries. However, practical use of the Li anode has been hindered by its tendency for dendritic growth, which leads to unstable solid electrolyte interphase, volume fluctuation during cycling, and even shorting of the battery. This problem can be solved by employing a conducting, lightweight, and lithiophilic scaffold that can stabilize high loading of Li during cycling and avoid its dendritic filament growth. Here we report that crumpled paper ball-like graphene particles can readily assemble to yield a scaffold with scalable Li loading up to 10 mA hr cm −2 within tolerable volume fluctuation. High Coulombic efficiency of 97.5% over 750 cycles (1,500 hr) was achieved. Plating/stripping Li up to 12 mA hr cm −2 on crumpled graphene scaffold does not experience dendrite growth.

Analytic approach to magneto-strain tuning of electronic transport through a graphene nanobubble: perspectives for a strain sensor

We consider the scattering of Dirac particles in graphene due to the superposition of an external magnetic field and mechanical strain. As a model for a graphene nanobubble, we find exact analytical solutions for single-particle states inside and outside a circular region submitted to the fields. Finally, we obtain analytical expressions for the scattering cross-section, as well as for the Landauer current through the circular region. Our results provide a fully-analytical treatment for electronic transport through a graphene nanobubble, showing that a combination of a physical magnetic field and strain leads to valley polarization and filtering of the electronic current. Moreover, our analytical model provides an explicit metrology principle to measure strain by performing conductance experiments under a controlled magnetic field imposed over the sample.

Optimisation of hybridisation effect in graphene reinforced polymer nanocomposites

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm−1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.