Graphene Flakes Research Articles

Synthesis of nitrogen-doped graphene oxide by nanosecond pulsed laser ablation of graphene in liquid for bioimaging applications

This work reports the synthesis of graphene oxide (GO) and nitrogen-doped graphene oxide (NGOs) by laser ablating graphene flakes in ethanol, utilizing liquid ammonia solution as the nitrogen source. Raman, FT-IR, and UV reveal the oxidation of graphene by laser ablation. Nitrogen doping was confirmed using FTIR and XPS analysis. XPS reveals the presence of pyrrolic, pyridinic, and graphitic nitrogen. The spherical shape and amorphous nature of NGOs are confirmed by HR-TEM analysis. FE-SEM examined the formation of different nanostructures of GO and NGO, and the average particle size was 40–50 nm. All samples show excitation-dependent PL emission with bluish-green emission, and nitrogen doping enhances the PL emission intensity. Time-resolved spectroscopy analysis shows the average lifetime improved by doping and increasing the nitrogen concentration. NGOs with remarkable quantum yields hold great promise for their application in bioimaging. We conducted cytotoxicity of the NGO samples against HeLa cancer cells using 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and selected the sample with lower cytotoxicity in cancer cells for bioimaging purposes. The NGOs with higher concentrations of nitrogen have less cytotoxicity and high photostability.

Graphene flakes for enhanced delivery of the enzyme to the lysosomes of patient-derived fibroblasts: Bio-persistence and kinetics of substrate degradation

Graphene flakes for enhanced delivery of the enzyme to the lysosomes of patient-derived fibroblasts: Bio-persistence and kinetics of substrate degradation

Fast Joule Heating for the Scalable and Green Production of Graphene with a High Surface Area.

The rapid development of electric vehicles, unmanned aerial vehicles, and wearable electronic devices has led to great interest in research related to the synthesis of graphene with a high specific surface area for energy applications. However, the problem of graphene synthesis scalability, as well as the lengthy duration and high energy intensity of the activation processes of carbon materials, are significant disadvantages. In this study, a novel reactor was developed for the green, simple, and scalable electrochemical synthesis of graphene oxide with a low oxygen content of 14.1%. The resulting material was activated using the fast joule heating method. The processing of mildly oxidized graphene with a high-energy short electrical pulse (32 ms) made it possible to obtain a graphene-based porous carbon material with a specific surface area of up to 1984.5 m2/g. The increase in the specific surface area was attributed to the rupture of the original graphene flakes into smaller particles due to the explosive release of gaseous products. In addition, joule heating was able to instantly reduce the oxidized graphene and decrease its electrical resistance from >10 MΩ/sq to 20 Ω/sq due to sp2 carbon structure regeneration, as confirmed by Raman spectroscopy. The low energy intensity, simplicity, and use of environment-friendly chemicals rendered the proposed method scalable. The resulting graphene material with a high surface area and conductivity can be used in various energy applications, such as Li-ion batteries and supercapacitors.

Machine Learning-Assisted Identification of Single-Layer Graphene via Color Variation Analysis.

Techniques such as using an optical microscope and Raman spectroscopy are common methods for detecting single-layer graphene. Instead of relying on these laborious and expensive methods, we suggest a novel approach inspired by skilled human researchers who can detect single-layer graphene by simply observing color differences between graphene flakes and the background substrate in optical microscope images. This approach implemented the human cognitive process by emulating it through our data extraction process and machine learning algorithm. We obtained approximately 300,000 pixel-level color difference data from 140 graphene flakes from 45 optical microscope images. We utilized the average and standard deviation of the color difference data for each flake for machine learning. As a result, we achieved F1-Scores of over 0.90 and 0.92 in identifying 60 and 50 flakes from green and pink substrate images, respectively. Our machine learning-assisted computing system offers a cost-effective and universal solution for detecting the number of graphene layers in diverse experimental environments, saving both time and resources. We anticipate that this approach can be extended to classify the properties of other 2D materials.

Energy Decomposition Scheme for Rectangular Graphene Flakes.

We show-to our own surprise-that total electronic energies for a family of m × n rectangular graphene flakes can be very accurately represented by a simple function of the structural parameters m and n with errors not exceeding 1 kcal/mol. The energies of these flakes, usually referred to as multiple zigzag chains Z(m,n), are computed for m, n < 21 at their optimized geometries using the DFTB3 methodology. We have discovered that the structural parameters m and n (and their simple algebraic functions) provide a much better basis for the energy decomposition scheme than the various topological invariants usually used in this context. Most terms appearing in our energy decomposition scheme seem to have simple chemical interpretations. Our observation goes against the well-established knowledge stating that many-body energies are complicated functions of molecular parameters. Our observations might have far-reaching consequences for building accurate machine learning models.

Solution blending preparation of polyurethane/graphene composite: Improving the mechanical and anti-corrosive properties of the coating on aluminum surface

Graphene-based polyurethane composites (PU/G) are prepared by a simple solution blending method to disperse defect-free graphene flakes (prepared via liquid phase exfoliation process) into the polyurethane matrix. The PU/G composite with 1 wt% of graphene flakes performs the significant improvement (∼50 %) of the impact strength (124 kg.cm) and adhesion behavior (∼2.3 MPa) with respect to that of pristine PU. The PU/G coating with 2 wt% of graphene achieves the highest long-term anti-corrosion performance after 150 immersed days in 3 wt% NaCl solution (with the stable impedance modulus of ∼2.7 × 1010 Ω.cm2) or after 2500 h of salt spray exposure in 5 wt% NaCl solution (no corrosive traces detected on aluminum substrate).

The Influence of Graphene Oxide-Fe3O4 Differently Conjugated with 10-Hydroxycampthotecin and a Rotating Magnetic Field on Adenocarcinoma Cells.

Nanoparticles (e.g., graphene oxide, graphene oxide-Fe3O4 nanocomposite or hexagonal boron nitride) loaded with anti-cancer drugs and targeted at cancerous cells allowed researchers to determine the most effective in vitro conditions for anticancer treatment. For this reason, the main propose of the present study was to determine the effect of graphene oxide (GO) with iron oxide (Fe3O4) nanoparticles (GO-Fe3O4) covalently (c-GO-Fe3O4-HCPT) and non-covalently (nc-GO-Fe3O4-HCPT) conjugated with hydroxycamptothecin (HCPT) in the presence of a rotating magnetic field (RMF) on relative cell viability using the MCF-7 breast cancer cell line. The obtained GO-Fe3O4 nanocomposites demonstrated the uniform coverage of the graphene flakes with the nanospheres, with the thickness of the flakes estimated as ca. 1.2 nm. The XRD pattern of GO-Fe3O4 indicates that the crystal structure of the magnetite remained stable during the functionalization with HCPT that was confirmed with FTIR spectra. After 24 h, approx. 49% and 34% of the anti-cancer drug was released from nc-GO-Fe3O4-HCPT and c-GO-Fe3O4-HCPT, respectively. The stronger bonds in the c-GO-Fe3O4-HCPT resulted in a slower release of a smaller drug amount from the nanocomposite. The combined impact of the novel nanocomposites and a rotating magnetic field on MCF-7 cells was revealed and the efficiency of this novel approach has been confirmed. However, MCF-7 cells were more significantly affected by nc-GO-Fe3O4-HCPT. In the present study, it was found that the concentration of nc-GO-Fe3O4-HCPT and a RMF has the highest statistically significant influence on MCF-7 cell viability. The obtained novel nanocomposites and rotating magnetic field were found to affect the MCF-7 cells in a dose-dependent manner. The presented results may have potential clinical applications, but still, more in-depth analyses need to be performed.

Antibacterial highly sensitive eco-friendly wearable piezoresistive sensor for monitoring multiple physiological parameters

Recent progress in wearable biomedical devices has made real-time monitoring possible through non-invasive wearable strain sensors, which can transform physical or biological signals into electrical responses. This work has fabricated multifunctional wearable strain sensors by coating composites (SiE-µG) of electrochemically exfoliated micro-sized multi-layer graphene flakes (µG) and Silicone elastomer (SiE) onto stretchable textile-based orthopedic bandage having ZnO adhesive (SiE-µG@Bandage). The composite coated textile sensors exhibited a remarkable sensitivity of 18330, large stretchability of 35%, superior mechanical durability of 50000 cycles, minute detection limit of 0.04% strain, and fast response time of 400 and recovery time 900 ms. The SiE-µG@Bandage also showed antibacterial properties against Escherichia coli (E. coli) bacteria. Additionally, zinc oxide-based skin-friendly and non-toxic adhesive on the backside of the bandage allowed stable and conformal attachment with the skin. Owing to the above merits, the sensors have shown applicability in real-time monitoring of various physical activities, physiological signals, joint movements, yoga postures, and meditation. Furthermore, the relevance of the sensors in the man-machine interaction has been demonstrated via real-time monitoring of traffic signals by finger movements. Moreover, the exceptional performance and specific features of the SiE-µG@Bandage sensors have enabled their application as electronics skins in health care and preventive care.

Simultaneously enhancing sensitivity and operation range of flexible pressure sensor by constructing a magnetic-guided microstructure in laser-induced graphene composite

Flexible pressure sensors play an essential role in the development of flexible electronic systems, which have been widely used in recent times for human activity monitoring and personal healthcare. However, possessing both high sensitivity and a wide operation range for pressure sensor remains challenging, as these requirements are commonly incompatible with each other. Herein, a magnetic induced graphene composite-based pressure sensor (MIPS) is demonstrated by integrating laser induced graphene (LIG) with a patterned valley-peak microstructure and a graphene film doped with magnetic microspheres. Owing to the synergistic effect of the 3D valley-peak microstructures and intercalation-like microstructures within the LIG composite film, the MIPS demonstrates excellent sensing performance in both sensitivity and operation range. The conductive network formed by graphene flakes improves electromechanical response capability, while the incorporation of magnetic microspheres (MMs) promotes the proliferation of conductive pathways in a small applied pressure range, and the valley-peak structure further enhances compressive strength over a large operation range. Accordingly, the MIPS exhibit excellent sensing capability over a range of 0–830 kPa, with an exceptionally high sensitivity of 4426.12 kPa−1 and excellent mechanical stability and durability (2000 cycles at a pressure of 800 kPa). Additionally, we have developed a novel pressure mapping system utilizing the MIPS array, enabling real-time monitoring of pressure spatial distribution and intensity. Notably, the MIPS array exhibits remarkable potential in diverse applications, including the monitoring of human physiological signals and movement. This pressure sensor with a hierarchically composite microstructure presents a promising candidate for the rapid advancement of next-generation wearable bioelectronics.

Compact and accurate chemical mechanism for methane pyrolysis with PAH growth

A reliable and compact chemical mechanism of gas-phase methane pyrolysis leading to formation of large polycyclic aromatic hydrocarbon (PAH) molecules has been developed. This model is designed for studies of carbon nanostructure synthesis such as carbon black and graphene flakes, including soot growth kinetics. Methane pyrolysis with carbon nanostructure synthesis is a two-stage process where conversion of CH4 to C2H2 precedes the growth of PAH molecules from acetylene. We present a single chemical mechanism that accurately describes both stages. We have constructed a compact and accurate chemical mechanism capable of modeling both stages of methane pyrolysis based on the ABF [1] mechanism which was expanded with the most prominent reaction pathways from the mechanism by Tao [2] for small PAH molecules and HACA pathways for larger PAH molecules, up to 37 aromatic rings. The resulting mechanism was validated through comparison to multiple available sets of experimental data. Good agreement with the experimental data for both processes was obtained. Performance of the mechanism was tested for pyrolysis of methane-rich mixtures under long residence times leading to abundant formation of PAH molecules. It is shown that the inclusion of larger PAH species (up to A37) in the chemical mechanism is important for accurate prediction of the fraction of carbon converted to PAH molecules and, correspondingly, the residual fraction of acetylene in the mixture. The mechanism file is available upon request.

BIOSURFACTANT-MEDIATED SYNTHESIS OF GRAPHENE FLAKES FROM GRAPHITE FOR MICROBICIDAL ACTIVITY

A biologically prolific procedure involving microbes and biosurfactants as surface-active materials allows for the exfoliation of graphite into graphene flakes, harnessing microbial surface activity. In this study, the production of graphene flake has taken an unusual route with a biosurfactant as it is not the easiest method and is required in huge quantities. The biosurfactant was isolated from Pseudomonas aeruginosa. The microbe was isolated, cultured, and stored for surfactant production. The biosurfactant showed positive results for all the seven screening methods tested. The emulsification capacity was 62.7% indicating the highest stability of the biosurfactant to penetrate inside the kerosene. The production of biosurfactant in the mineral salt medium in a shaking condition provided a better result of the highest production which was then used for extraction purposes by autoclaving the culture. The exfoliation process took place once the production was over. The four main characterization techniques both spectroscopic and microscopic have revealed positive results for graphene flake production. The antimicrobial study was conducted to check the withstand capacity of the produced graphene flakes towards microbes and the results show the antimicrobial activity of the flakes. The sensitivity of graphene flakes against biotic discs was studied by antibiotic disc assay and the results show they are sensitive to the commonly administered antibiotics of today.

Photopatterning of conductive hydrogels which exhibit tissue-like properties.

Hydrogels are three-dimensional, highly tunable material systems that can match the properties of extracellular matrices. In addition to being widely used to grow and modulate cell behavior, hydrogels can be made conductive to further modulate electrically active cells, such as neurons, and even incorporated into multielectrode arrays to interface with tissues. To enable conductive hydrogels, graphene flakes can be mechanically suspended into a hydrogel precursor. The conductivity of the hydrogel can be increased by increasing the weight percentage of graphene flakes in the precursor while maintaining the mechanical properties of the formed gel similar to the properties of neural tissue. By using a photocrosslinkable hydrogel matrix, such as gelatin methacrylate, with a photoabsorber, the conductive precursor solutions can be crosslinked into predefined complex patterns. Finally, the formulations can be used to support the growth of sensory neurons, derived from human induced pluripotent stem cells, for more than 7 weeks while the neurons remain viable. These scaffolds can be patterned into components of multielectrode arrays, to enable ultrasoft electrodes with tissue-matched properties for further interactions, both in vitro and in vivo, with the nervous systems.

Mechanistic insight into the role of the aspect ratio of nanofillers in the gas barrier properties of polymer nanocomposite thin films

The introduction and processing parameters of 2D graphene flakes into a polymer matrix were altered in order to understand the impact of dispersed flake geometry on the physical properties of nanocomposites.

Differences in interaction of graphene/graphene oxide with bacterial and mammalian cell membranes.

Graphene, a single layer, hexagonally packed two-dimensional carbon sheet is an attractive candidate for diverse applications including antibacterial potential and drug delivery. One of the knowledge gaps in biomedical application of graphene is the interaction of these materials with the cells. To address this, we investigated the interaction between graphene materials (graphene and graphene oxide) and plasma membranes of cells (bacterial and mammalian cells). The interactions of four of the most abundant phospholipids in bacteria and mammalian plasma membranes with graphene materials were studied using density functional theory (DFT) at the atomic level. The calculations showed that the mammalian phospholipids have stronger bonding to each other compared to bacterial phospholipids. When the graphene/graphene oxide sheet is approaching the phospholipid pairs, the bacterial pairs exhibit less repulsive interactions, thereby a more stable system with the sheets was found. We also assembled bacterial and mammalian phospholipids into liposomes. We further observed that the bacterial liposomes and cells let the graphene flakes penetrate the membrane. The differential scanning calorimetry measurements of liposomes revealed that the bacterial liposomes have the lowest heat capacity; this strengthens the theoretical predictions of weaker interaction between the bacterial phospholipids compared to the mammalian phospholipids. We further demonstrated that graphene oxide could be internalized into the mammalian liposomes without disrupting the membrane integrity. The results suggest that the weak bonding among bacteria phospholipids and less repulsive force when graphene materials approach, result in graphene materials interacting differently with the bacteria compared to mammalian cells.

On the mechanical response of graphene-capped copper nanoparticles.

In this study, we investigated the mechanical behavior of pristine copper (Cu) nanoparticles (NPs) and Cu@graphene (Cu@G) hybrid NPs using molecular dynamics simulations. The longitudinal engineering strain was calculated as a measure of compression until reaching 25% of the initial size of the NPs. The stress-strain curves revealed the elastic-to-plastic transition in the Cu NPs at a longitudinal strain of 3.57% with a yield strength of 6.15 GPa. On the other hand, the Cu@G NPs exhibited a maximum average load point at a longitudinal strain of 6.81% with a yield strength of 8.26 GPa. The hybrid Cu@G NPs showed increased strength and resistance to plastic deformation compared to the pure Cu NPs, while the calculation of the elastic modulus indicated a higher load resistance provided by the graphene coverage for the Cu@G NPs. Furthermore, the analysis of atomic configurations, dislocations, and stress distribution demonstrated that the graphene flakes play a crucial role in preventing dislocation events and faceting in the Cu@G NPs by acting as a shock absorber, distributing the applied force on themselves, and producing a more homogeneous stress distribution on the Cu NPs; additionally, they prevent the movement of Cu atoms, reducing the occurrence of dislocations and surface faceting, thanks to their supportive effect. Overall, our findings highlight the potential of hybrid nanomaterials, such as Cu@G, for enhancing the mechanical properties of metallic NPs, which could have significant implications for the development of advanced nanomaterials with improved performance in a variety of applications.

Experimental observation and characterization of amorphous carbon generated in graphene on gold nanoparticles.

The interaction of graphene with gold nanoparticles is investigated using transmission electron microscopy. We observe gold-nanoparticle-mediated etching of graphene flakes, often leading to hole formation. Further, using a combination of high-angle annular dark field imaging and electron energy loss spectroscopy, we highlight that the catalytic effects of gold nanoparticles on graphene lead to the formation of amorphous carbon layers. From the extracted diffractograms, we observe regions with diffraction halos as well as some regions with a weak tetrahedral motif. Using independently performed Raman measurements, we confirm the presence of tetrahedral amorphous carbon as well as mixed graphitic-amorphous regions. For the amorphous carbon regions with mixed sp2-sp3 states, the Raman G peak is red-shifted to 1564 cm-1 and an I D/I G ratio of 0.63 indicates less than 20% sp3 content. For the tetrahedral amorphous carbon regions, we observe that the Raman G peak is at 1580 cm-1, close to that of monolayer graphene. However, there is no Raman D peak, i.e., I D/I G = 0, which indicates close to 100% sp3 content. The translation of the Raman G peak location and the I D/I G ratios is on par with the amorphization trajectory analysis of Ferrari and Robertson (Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 14095) and validates the conversion route of graphite to amorphous carbon to tetrahedral amorphous carbon. The presented method provides a promising pathway for creating defect-induced amorphous carbon at room temperature, which has a broader impact on the electronics and semiconductor industries.

Ready-to-use graphene-related material-added multi-grade oils: characterization and performance in car engine working conditions.

The need for energy efficiency is leading to the growing use of additives to enhance the performance of oil in automotive engines. Great interest is focused on nano-additives even if to date there is still no practical use in commercial liquid lubricants. Herein, the potential of industrially scalable and low-cost graphene-related materials (GRMs) as additives to enhance the performance of oil in automotive engines is explored. The use of polyalkylmethacrylate dispersants, the most common key additives to formulate "green technology" lubricant oils liquid-processed GRM, is explored, investigating the role of the lateral size and the chemical analysis in the stability of the lubricant GRM dispersions. Showing the maximum duration of stability and a production method that avoids the use of strong oxidants, rheological tests were then focused on multilayered graphene flakes with sub-micrometre lateral size mixed in two commercial oil grades (5W-30 and 5W-40) under conditions similar to those of engine operation. The addition of such a filler increases the viscosity without affecting the Newtonian fluid behavior, while four-ball tests show a reduction in wear, indicating improved lubrication performance. Finally, preliminary bench-test on a commercial car engine showed increased power output corresponding to enhanced engine efficiency. The results clearly indicate the effective improvement in lubricating commercial oils due to GRM additives.

Symmetry transformations and novel solutions for the graphene thermophoretic motion equation with variable heat transmission using Lie group analysis

The single-layer graphene flake is an amazing tool in recent industry, it has many uses in biosensors, photonics and water filtration because of its outstanding electronic, thermal, and mechanical properties. In this letter, we have studied the graphene variable heat transmission thermophoretic motion (vcGT) equation using the symmetry group method. As a result, a Lie group of four vector fields is yielded. By using a linear combination of those vector fields the vcGT equation becomes a nonlinear ordinary differential equation, and by using the F-expansion technique then different types of solitary waves like periodic Jacobi elliptic waves, soliton, kink soliton and trigonometric waves were found which cover other solutions in the literature such as solitons and have additional new solutions like the periodic Jaocbi waves. Finally, we have discussed the effect of the variable heat transmission on the wave propagation for three different wave structures: Jacobi periodic wave, bright soliton and the trigonometric sec wave. It was found that in the real physical situation corresponding to the variable heat transmission the waves take a parabolic shape.

A Scalable Furnace Technique to Grow Silicon Nanoparticles for High-Performance Li-Ion Battery Anodes

Lithium-ion battery (LIB) technology is one of the key technologies to lower the emission from fossil fuel while maintaining stable supply of energy to the society. One way to increase the capacity of LIBs is to add silicon to the graphite anode, since silicon can store much more lithium ions than graphite. Silicon does however expand and contract during lithiation and delithiation, leading to cracks which deteriorates the performance of the LIB anode. Mechanical cracking can be avoided by using sufficiently small silicon nanoparticles. Several high-performance schemes utilizing silicon nano materials such as nanoparticles, nanotubes, nanorods etc. have been demonstrated but industrial-scale implementation of these solutions still poses a challenge. The Siemens process is one of the most commonly used methods to create silicon nanoparticles and uses chemical vapor deposition (CVD) processes involving silane or silane derivatives as precursors. Due to the flammable and toxic nature of silane, the CVD process requires special handling care and expensive instrumentation. In this work, a novel scalable furnace technique to create silicon nanoparticles attached to graphene flakes LIB anode applications is presented. With this technique, we can avoid the silane precursor. In addition, the instrumentation requirements of the furnace technique are quite simple and inexpensive and the technology is compatible with already established industrial-scale electrode manufacturing techniques.In the work presented here we demonstrate how silicon nanoparticles are grown from micro sized silicon powder onto graphene flakes using simple thermal treatment. Thermal gravitometry, mass spectrometry and differential scanning calorimetry was used to show how silicon powder and a binder can be converted to silicon nanoparticles by simple pyrolysis. The silicon nanoparticles are grown on top of graphene flakes to create a LIB anode. The anode, when tested in a half cell assembly shows a capacity that is considerably higher than standard graphene/graphite electrodes.

A theoretical modelling of strengthening mechanism in graphene-metal nanolayered composites

Graphene-metal nanolayered composites (GMNCs) are a new generation of nano-structural composites characterized by a very high density of graphene reinforced interfaces (GRI) between metal nanolayers. Compared to traditional graphene flake reinforced composites, GMNCs have much higher strength, toughness and ductility due to the excellent ability of GRI on constraining dislocation motion and crack propagation. Despite numerous experimental and numerical studies on the mechanical behavior of GMNCs, the underlying strengthening mechanism is still not fully understood due to the absence of appropriate theoretical model. This paper proposes a continuum mechanics based theoretical model to explain the strengthening mechanism in GMNCs. In this model, the metal matrix and the GRI are simulated as homogenous elastic medium of infinite extend and inextensible thin membrane of zero thickness, respectively. Using the theoretical model, two boundary value problems namely (i) A circular prismatic dislocation loop approaching to the GRI and (ii) A mixed mode I/II penny-shaped crack near the GRI are formulated to reveal the two key strengthening mechanism: dislocation blocking and crack shielding, respectively. The two problems are solved analytically by the Generalized Kelvin's Solution (GKS) based method for 3D elasticity and Fredholm integral integration technique. Exact closed form solution for the Peach-Koehler (P-K) force on the dislocation loop is obtained. An efficient numerical scheme is developed to solve the Fredholm integral integration for the crack problem with very high accuracy. It is shown that our theoretical model can well capture and explain the strengthening mechanism observed in experiments. Moreover, the dominant role of Poisson's ratio on the strengthening efficiency is also revealed by our model. This finding implies the exciting possibility that the strength of GMNCs can be tailored by controlling the Poisson's ratio of the metal matrix. The present theoretical modeling can provide valuable insights into the mechanics-based design of GMNCs.