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We study the time evolution of the populations in a two-dimensional (2D) graphene system by employing a few-cycle laser pulse with a linear polarization. Specifically, we present a comparative numerical analysis of the population dynamics of graphene in three different model configurations. Our results show that the Rabi-like oscillations and intraband population inversion can be observed in the population spectrum, which originated from the periodicity of a few-cycle laser pulse and the intraband Coulomb scattering. Also, coherent population oscillations are produced across the Dirac point when the Rabi frequency of the laser field which is used to couple the interband transition is much larger than that couples the intraband transition, and vice versa. These investigations may be helpful to enhance the performance of graphene-based ultrafast electronic and optoelectronic devices, including light-emitting devices, touch screens, photodetectors, and ultrafast lasers. [ABSTRACT FROM AUTHOR]

Abstract The multiple effect of pristine graphene (pG) toxicity on cardiovascular developmental defects was assessed using zebrafish as a model. Recently, the nanotoxicity is emerging as a critical issue, and it is more significant in embryogenesis. Especially, graphene and its derivatives have attracted a lot of interest in biomedical applications. However, very little is known about the toxic effects of pG which has been widely used carbon nanomaterial according to concentration and its effects on biological and cardiovascular development. In the present study, we examined the development of zebrafish embryos by exposing to pG (5, 10, 15, 20 and 25 μg/L) under different developmental toxicity end-points such as cardiotoxicity, cardiovascular defect, retardation of cardiac looping, apoptosis and globin expression analysis. For this, the developmental cardiotoxicity of pG at different concentrations and the specific cardiovascular defects thereof were elucidated for the first time. As a result, the exposure to pG was found to be a potential risk factor to cardiovascular system of zebrafish embryos. However, a further study on the variations of physical, molecular properties and mechanisms of nanotoxicity which vary depending on production method and surface functionalization is required. In addition, the potential risks of pG flakes to aquatic organisms and human health should be considered or checked before releasing them to the environment. Graphical abstract Image 1 Highlights • Significant effects of pG on cardiotoxicity, cardiovascular defect, retardation of cardiac looping and other end-points. • More green spots in the head, trunk and tail region show the presence of apoptotic cells and growth inhibition. • The inhibition of blood formation affects early cardiovascular development, microvasculature and heart maturation. • Zebrafish embryos exhibit a dose-dependent increase in developmental abnormalities with good sensitivity to pG. • PG nanomaterials have potential risks to aquatic organisms. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) have attracted significant interests due to their unique chemical and physical properties. In this study, we investigated the potential effects of hydroxyl-modified GQDs (OH-GQDs) on the human esophageal epithelial cell line HET-1A. Our data revealed significant cytotoxicity of OH-GQDs which decreased the viability of HET-1A in a dose and time-dependent manner. The moderate concentration (25 or 50 µg/ml) of OH-GQDs significantly blocked HET-1A cells in G0/G1 cell cycle phase. An increased percentage of γH2AX-positive and genomically unstable cells were also detected in cells treated with different doses of OH-GQDs (25, 50, and 100 µg/ml). Microarray data revealed that OH-GQDs treatment down-regulated genes related to DNA damage repair, cell cycle regulation and cytoskeleton signal pathways indicating a novel role of OH-GQDs. Consistent with the microarray data, OH-GQDs disrupted microtubule structure and inhibited microtubule regrowth around centrosomes in HET-1A cells. In conclusion, our findings provide important evidence for considering the application of OH-GQDs in biomedical fields. [ABSTRACT FROM AUTHOR]

Understanding of the interaction of graphene with natural polysaccharides (e.g., alginate) is crucial to elucidate its environmental fate. We investigated the impact of alginate on the agglomeration and stability of 14 C-labeled few-layer graphene (FLG) in varying concentrations of monovalent (NaCl) and divalent (CaCl 2 ) electrolytes. Enhanced agglomeration occurred at high CaCl 2 concentrations (≥5 mM) due to the alginate gel networks formation in the presence of Ca 2+ . FLG enmeshed within extended alginate gel networks was observed under transmission electron microscope and atomic force microscope. However, background Na + competition for binding sites with Ca 2+ at the alginate surfaces shielded the gelation of alginate. FLG was readily dispersed by alginate under environmentally relevant ionic strength conditions (i.e., <200 mM Na + and <5 mM Ca 2+ ). In comparison with the bare FLG, the slow sedimentation of the alginate-stabilized FLG (158 μg/L) caused continuous exposure of this nanomaterial to freshwater snails, which ingested 1.9 times more FLG through filter-feeding within 72 h. Moreover, surface modification of FLG by alginate significantly increased the whole-body and intestinal levels of FLG, but reduced the internalization of FLG to the intestinal epithelial cells. These findings indicate that alginate will act as a stabilizing agent controlling the transport of FLG in aqueous systems. This study also provides the first evidence that interaction of graphene with natural polysaccharides affected the uptake of FLG in the snails, which may alter the fate of FLG in aquatic environments. [ABSTRACT FROM AUTHOR]

A methodology for the structural analysis of graphene‐related materials using parameterized principal component analysis (PCA), ideal for large‐scale data treatment, is introduced. First, we review different aspects of Raman spectroscopy for structural and functional characterization of sp2‐bonded carbon materials, which are important for understanding the problem. The parameterized PCA is then introduced and applied to 2 different scenarios: to identify different sp2 carbon structures and to identify graphene samples with different numbers of layers. Automating these Raman spectroscopy analysis techniques is desired for large‐scale industrial applications. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials have received significant attention in the last decade due to their interesting properties. Its electrical and thermal conductivity and strength make graphene well suited for a variety of applications, particularly for use as a composite material in plastics. Furthermore, much work is taking place to utilize graphene as a biomaterial for uses such as drug delivery and tissue regeneration scaffolds. Owing to the rapid progress of graphene and its potential in many marketplaces, the potential toxicity of these materials has garnered attention. Graphene, while simple in its purest form, can have many different chemical and physical properties. In this paper, we describe our toxicity evaluation of pristine graphene and a functionalized graphene sample that has been oxidized for enhanced hydrophilicity, which was synthesized from the pristine sample. The samples were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, thermogravimetric analysis, zeta-potential, atomic force microscopy and electron microscopy. We discuss the disagreement between the size of imaged samples analyzed by atomic force microscopy and by transmission electron microscopy. Furthermore, the samples each exhibit quite different surface chemistry and structure, which directly affects their interaction with aqueous environments and is important to consider when evaluating the toxicity of materials both in vitro and in vivo. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphene, a crystalline allotrope or carbon, presents numerous useful properties; however, its toxicity is yet to be determined. One of the most dramatic and irreversible toxic abilities of carbon nanomaterials is the induction of DNA fragmentation produced by endogenous cellular endonucleases. This study demonstrated that pristine graphene exposed to cultured kidney tubular epithelial cells is capable of inducing DNA fragmentation measured by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, which is usually associated with cell death. TUNEL (cell death) and endonuclease activity measured using a near infrared fluorescence probe was significantly higher in cells containing graphene aggregates detected by Raman spectroscopy. The elevation of TUNEL coincided with the increased abundance of heme oxygenase 1 (HO-1), heat shock protein 90 (HSP90), active caspase-3 and endonucleases (deoxyribonuclease I [DNase I] and endonuclease G [EndoG]), as measured by quantitative immunocytochemistry. Specific inhibitors for HO-1, HSP90, caspase-3, DNase I and EndoG almost completely blocked the DNA fragmentation induced by graphene exposure. Therefore, graphene induces cell death through oxidative injury, caspase-mediated and caspase-independent pathways; and endonucleases DNase I and EndoG are important for graphene toxicity. Inhibition of these pathways may ameliorate cell injury produced by graphene. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Due to the distinctive physical, electrical, and chemical properties of graphene nanomaterials, numerous efforts pursuing graphene-based biomedical and industrial applications are underway. Oxidation of pristine graphene surfaces mitigates its otherwise hydrophobic characteristic thereby improving its biocompatibility and functionality. Yet, the potential widespread use of oxidized graphene derivatives raises concern about adverse impacts on human health. The p53 tumor suppressor protein maintains cellular and genetic stability after toxic exposures. Here, we show that p53 functional status correlates with oxygen functionalized graphene ( f-G) cytotoxicity and genotoxicity in vitro. The f-G exposed p53-competent cells, but not p53-deficient cells, initiated G0/G1 phase cell cycle arrest, suppressed reactive oxygen species, and entered apoptosis. There was p53-dependent f-G genotoxicity evident as increased structural chromosome damage, but not increased gene mutation or chromatin loss. In conclusion, the cytotoxic and genotoxic potential for f-G in exposed cells was dependent on the p53 functional status. These findings have broad implications for the safe and effective implementation of oxidized graphene derivatives into biomedical and industrial applications. Published 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Nanomaterial synthesis and handling in a non-sterile environment can result in the final product becoming contaminated with bacterial endotoxin or lipopolysaccharides (LPB). During toxicological testing, the effects caused by endotoxin-contaminated nanomaterials can be misinterpreted in the end-point analysis (such as cytotoxicity and immune responses) and could result in erroneous conclusions. The objective of this study was twofold: (i) to test different carbon-based nanomaterials (CBNs) [pristine graphene and multi-wall carbon nanotubes (MWCNTs)] for the presence of endotoxin and develop strategies for depyrogenation, and (ii) to compare the immune response exhibited by macrophages after exposure to native CBNs versus depyrogenated CBNs. The gel-clot limulus amebocyte lysate (LAL) and chromogenic-based LAL assays were used to detect endotoxins. Results revealed that the CBNs contained greater amounts of endotoxin than are approved by major regulatory agencies (0.5 EU ml−1). Three repeated cycles of autoclaving reduced the endotoxin in the test materials. Macrophages were incubated with pyrogenated and depyrogenated pristine graphene and MWCNTs to test differences in phagocytosis, cytotoxicity, and expression of genes involved in macrophage activation. The uptake of depyrogenated CBNs was significantly reduced as compared with pyrogenated CBNs. Exposure of macrophages to depyrogenated CBNs resulted in a distinct pattern of gene expression for TLR signaling, NOD-like receptor signaling, and downstream signal transduction molecules. Furthermore, macrophages exposed to both types of CBNs showed the downregulation of TLR5 and NLRC4 inflammasomes. The results of this study reaffirm that assessment of endotoxin and other bacterial contamination is critical when evaluating the cellular toxicity of nanomaterials. Published 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Published 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

We report on a measurement technique that quantifies the adhesive force between multi-layers of graphene flakes and the cell wall of live Escherichia coli cells using atomic force microscopy (AFM) in-fluid Peak Force- Quantitative Nanomechanical Mapping mode. To measure the adhesive force, we made use of the negative charge of E. coli cells to allow them to stick to positively charged surfaces, such as glass or silicon, that were covered by poly-L-Lysine. With this approach, cells were held in place for AFM characterization. Both pristine graphene (PG) flakes and functionalized graphene (FG) flakes were put on the E. coli cells and measurements of lateral size, flake thickness, and adhesion were made. Using this approach, the measured values of the adhesive force between multi-layers of graphene flakes (total thickness of 50 nm) and E. coli was determined to be equal or greater than 431 ± 65pN for (PG) and 694 ± 98pN for the (FG). More interestingly, the adhesive force of a graphene flake (thickness 1.3 nm) with the cell is determined to be equal or greater than 38.2 ± 16.4pN for the (PG) and 34.8 ± 15.3pN for the (FG). These interaction values can play an important role in determining and understanding the possible toxicity of graphene flakes. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials (GBN) have many potential biomedical applications. However, information regarding their biological properties and interactions with cells and/or soluble factors within a complex tissue is limited. The objective of this study was to use the growing feather (GF) of chickens as a minimally invasive cutaneous test-site to assess and monitor leukocyte recruitment in response to intradermal GBN injection. Specifically, the dermis of 20 GFs per chicken was injected with 10 μl of phosphate-buffered saline (PBS)-vehicle or 10 μl of 300 μg ml−1 oxygen-functionalized (f) GBN (6 chickens/treatment). GFs were collected before- (0) and at 0.25, 1, 2, 3, 4, 5, and 7 days post-injection and used for leukocyte-population analysis of immunofluorescently stained pulp cell suspensions or histological examination. Based on flow-cytometric cell population analysis, lymphocytes and macrophages were the major leukocyte-populations infiltrating GFs in response to f-GBN presence. Compared with PBS-controls, levels of T cells (γδ-, αβ-, CD4- and CD8-T cells) were greatly elevated in f-GBN-injected GFs within 6 h and remained elevated throughout the 7-day examination period. f-GBN's effects on local tissue leukocyte recruitment were not reflected in the blood, except for a higher percentage of lymphocytes on 7 days. These observations together with a visual examination of f-GBN-injected GF tissue-sections suggest a delayed-type hypersensitivity-like, inflammatory cell-mediated response to the non-biodegradable f-GBN. The GF ' in vivo test-tube'system together with blood sampling provided unique insight into the time-course, qualitative, and quantitative aspects of immune system activities initiated by the presence of f-GBN in a complex tissue of a living animal. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials (GBNs) are quickly revolutionizing modern electronics, energy generation and storage, clothing and biomedical devices. Due to GBN's variety of physical and chemical parameters that define their toxicity and their aggregation in suspension, interpreting its toxicology without accurate information on graphene's distribution and behavior in live organisms is challenging. In this work, we present a laser-based optical detection methodology for noninvasive detection and pharmacokinetics analysis of GBNs directly in blood flow in mice using in vivo photoacoustic (PA) flow cytometry (PAFC). PAFC provides unique insight on how chemical modifications of GBNs affect their distribution in blood circulation and how quickly they are eliminated from the flow. Overall, PAFC provided unique data crucial for understanding GBN toxicity through real-time detection of GBNs using their intrinsic light absorption contrast. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphene has recently been attracting considerable interest because of its exceptional conductivity, mechanical strength, thermal stability, etc. Graphene-based devices exhibit high potential for applications in electronics, optoelectronics, and energy harvesting. In this paper, we review various growth strategies including metal-catalyzed transfer-free growth and direct-growth of graphene on flexible and rigid insulating substrates which are “major issues” for avoiding the complicated transfer processes that cause graphene defects, residues, tears and performance degradation in graphene-based functional devices. Recent advances in practical applications based on “direct-grown graphene” are discussed. Finally, several important directions, challenges and perspectives in the commercialization of ‘direct growth of graphene’ are also discussed and addressed. [ABSTRACT FROM AUTHOR]

A novel and efficient chemiluminescence (CL) probe was developed based on the sensitizing effect of graphene quantum dots (GQDs) on the morin–KMnO4 CL reaction for cypermethrin (CYPM). GQDs were prepared using an economic and green procedure, and characterized with the help of their distinctive emission and absorption patterns. Advanced morphological and structural investigations of the GQDs were conducted using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) analysis. The synthesized GQDs showed a remarkable promoting influence on the CL emission of the morin–KMnO4 reaction in the presence of cetyltrimethylammonium bromide (CTAB), offering a powerful and efficient new CL system. The mechanism of the sensitized CL system was described based on the electron transfer processes. In addition, CYPM, as a potent pollutant, could linearly suppress the emission of the KMnO4–morin–CTAB–GQD CL system. This turned the introduced CL system into a susceptible chemosensor for CYPM. Under the selected operating conditions, a linear relation of the CL response was attained over the CYPM concentration range of 0.3–22.0 mg L−1 with a limit of detection (LOD) of 0.08 mg L−1. The proposed method showed good features for the determination of CYPM and was satisfactorily employed for CYPM evaluation in real environmental water samples. [ABSTRACT FROM AUTHOR]

Transition metal vanadates have attracted much attention for high capacity anodes of lithium ion batteries (LIBs). However, they have obvious drawbacks (short cycle-lives and low rate performance) because of the intrinsically low electronic conductivity and serious volume variation during Li-ion desorption and insertion. In particular, pure Co3V2O8 micro-pencils (pCVO MPs) have a stable and regular crystal structure, large tap density and uniform grain size, but, unfortunately, they have not exhibited expected electrochemical performance. Herein, we report the successful preparation of reduced graphene oxide coated Co3V2O8 micro-pencils (rGO@CVO MPs) through a facile approach combining hydrothermal synthesis with thermal reduction. When tested as anodes for LIBs, rGO@CVO MPs exhibit superior electrochemical performance compared to that of pure Co3V2O8 micro-pencils (pCVO MPs). The anodes of rGO@CVO MPs show a high reversible capacity of 760 mA h g−1 over 200 cycles at 200 mA g−1, and 500 mA h g−1 can remain after 500 cycles at 1000 mA g−1, with an increase in 200 mA h g−1 in contrast to the pCVO MPs. It is consequently demonstrated that the composite material (rGO@CVO MPs) is a promising anode material for LIBs. [ABSTRACT FROM AUTHOR]

Melamine-modified graphene hydrogels (MA–GH) were successfully synthesized through a simple one-step method. The three-dimensional (3D) porous network of the graphene hydrogel composite was functionalized using melamine with multiple nitrogen-containing functional groups. Based on its unique network structure, large surface area and sufficient active sites, the synthesized 3D hydrogels displayed a high adsorption capacity (404.85 mg g−1), high removal rate of uranium(vi) (＞90% at ppm level, or ∼75% in simulated seawater) and large KUd value (8.52 × 104 mL g−1). The adsorption process was described well using pseudo-second-order kinetics and the Langmuir isotherm model. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic. Based on the above results, the MA–GH composites reveal promising potential as an adsorbent for capturing uranium(vi) in aqueous solution and simulated seawater. [ABSTRACT FROM AUTHOR]

The adsorption capacity of graphene for removing phenol from aqueous solutions was evaluated and compared to those obtained for three different commercial activated carbons. In this study, graphene, W-35 activated carbon, RB2H2 activated carbon, and Nuchar granular activated carbon were investigated. Various techniques such as X-ray diffraction, BET surface analysis, and scanning electron microscopy were used to characterize the adsorbents. The adsorption of phenol onto graphene was investigated under different experimental conditions including temperature, solution pH, adsorbent dosage, and initial concentration of phenol. For comparison, adsorption experiments of phenol onto the activated carbons were also conducted. The adsorption of phenol onto graphene and activated carbons could be described by the pseudo-second-order kinetic model and the Langmuir equilibrium isotherm. The maximum adsorption capacities predicted by the Langmuir isotherm for graphene, W-35, RB2H2, and Nuchar granular activated carbons were found to be 233, 200, 91, and 167 mg/g, respectively. The thermodynamic study demonstrated that the adsorption of phenol onto graphene and activated carbons is a spontaneous and exothermic process. Regeneration of graphene was found to be possible using sodium hydroxide or methanol as eluents over five adsorption-desorption cycles. [ABSTRACT FROM AUTHOR]

The application of NiAl-based alloy (NA) in the field of aerospace was limited by its poor tribological properties. For improving the tribological performance of NA, multilayer graphene (MLG) and TiSiC were added in NiAl matrix composites. Tribological behavior of NiAl matrix composites containing 1.5 wt.% MLG and 10 wt.% TiSiC (NMT) against SiN ball at 12 N-0.2 m/s from 25 to 750 °C was investigated. The results showed that NMT exhibited the excellent tribological behavior [lower friction coefficients (0.26-0.57) and less wear resistance (3.1-6.5 × 10 mm N m)] due to synergetic effect of MLG and TiSiC over a wide temperature range from 25 to 750 °C. At 25-350 °C, part of MLG enriched on worn surface could play a role in reducing friction and improving wear resistance. At 350-550 °C, although MLG gradually lost the lubricating properties, the partial decomposition of TiSiC could continually improve the tribological properties of NMT. At 550-750 °C, TiSiC on worn surface was oxidized to form lubricating film, while TiSiC in the subsurface played an important role in supporting the film, resulting in the excellent high-temperature tribological performance. The research had good guiding significance for the preparation of wide temperature range self-lubricating material and the study of synergetic effect of complex solid lubricants. [ABSTRACT FROM AUTHOR]

The use of carbon-based nanomaterials (CNMs) such as multiwalled carbon nanotubes (MWCNTs), graphene, and graphene oxide (GO) is increasing across many applications because of their unique and versatile properties. These CNMs may enter the aquatic environment through many pathways, creating the potential for organism exposure. The present study addresses the bioaccumulation and toxicity seen in Daphnia magna exposed to CNMs dispersed in sodium dodecyl benzene sulfonate (SDBS). In study I, D. magna were exposed to varying outer diameters of MWCNTs for 24 h in moderately hard or hard freshwater. Bioaccumulation of MWCNT was found in all treatments, with the highest concentrations (0.53 ± 0.27 μg/g) in D. magna exposed in hard freshwater ( p < 0.005). The median lethal concentration (LC50) was determined for D. magna exposed to CNMs in moderately hard and hard freshwater. In study II, D. magna were exposed to CNMs for 72 h in moderately hard freshwater to assess swimming velocity and generation of reactive oxygen species (ROS) detected by dichlorofluorescein fluorescence. An overall decrease was seen in D. magna swimming velocity after exposure to CNMs. The generation of ROS was significantly higher (1.54 ± 0.38 dichlorofluorescein mM/mg dry wt) in D. magna exposed to MWCNTs of smaller outer diameters than in controls after 72 h ( p < 0.05). These results suggest that further investigation of CNM toxicity and behavior in the aquatic environment is needed. Environ Toxicol Chem 2017;36:2199-2204. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Dielectric properties of composites near percolation threshold (fc) are often sensitive to thermal treatments, and the annealing temperature is usually associated with a polymer's rheological properties. In this study, the influences of the thermal treatment on dielectric properties are investigated for the polystyrene (PS) matrix composite reinforced by graphene nanoplatelets (GNP) fillers near fc. It can be found that the thermal treatment can not only increase the dielectric constant, but also decrease the dielectric loss for the PS/GNP composite. This interesting phenomenon possibly happens in the interfacial region of PS/GNP with the thickness about 4-6 nm according to the electron energy-loss spectroscopy (EELS) results. The free volumes around the interface can be easily altered by the movement of polymeric segments after annealing at the glass transition temperature. [ABSTRACT FROM AUTHOR]

The Li+ diffusion coefficients in Li+-adsorbed graphene systems were determined by combining first-principle calculations based on density functional theory with Kinetic Monte Carlo simulations. The calculated results indicate that the interactions between Li ions have a very important influence on lithium diffusion. Based on energy barriers directly obtained from first-principle calculations for single-Li+ and two-Li+ adsorbed systems, a new equation predicting energy barriers with more than two Li ions was deduced. Furthermore, it is found that the temperature dependence of Li+ diffusion coefficients fits well to the Arrhenius equation, rather than meeting the equation from electrochemical impedance spectroscopy applied to estimate experimental diffusion coefficients. Moreover, the calculated results also reveal that Li+ concentration dependence of diffusion coefficients roughly fits to the equation from electrochemical impedance spectroscopy in a low concentration region; however, it seriously deviates from the equation in a high concentration region. So, the equation from electrochemical impedance spectroscopy technique could not be simply used to estimate the Li+ diffusion coefficient for all Li+-adsorbed graphene systems with various Li+ concentrations. Our work suggests that interactions between Li ions, and among Li ion and host atoms will influence the Li+ diffusion, which determines that the Li+ intercalation dependence of Li+ diffusion coefficient should be changed and complex. [ABSTRACT FROM AUTHOR]

We present plasmonic devices, consisting of periodic arrays of graphene nanoribbons (GNRs) and a graphene sheet waveguide, to achieve controllable plasmon-induced transparency (PIT) by numerical simulation. We analyze the bright and dark elements of the GNRs and graphene-sheet waveguide structure. Results show that applying the gate voltage can electrically tune the PIT spectrum. Adjusting the coupling distance and widths of GNRs directly results in a shift of transmission dips. In addition, increased angle of incidence causes the transmission to split into multiple PIT peaks. We also demonstrate that PIT devices based on graphene plasmonics may have promising applications as plasmonic sensors in nanophotonics. [ABSTRACT FROM AUTHOR]

The capture and storage of CO2 have been suggested as an effective strategy to reduce the global emissions of greenhouse gases. Hence, in recent years, many studies have been carried out to develop highly efficient materials for capturing CO2. Until today, different types of porous materials, such as zeolites, porous carbons, N/B-doped porous carbons or metal-organic frameworks (MOFs), have been studied for CO2 capture. Herein, the CO2 capture performance of new hybrid materials, graphene-organic frameworks (GOFs) is described. The GOFs were synthesized under mild conditions through a solvothermal process using graphene oxide (GO) as a starting material and benzene 1,4-diboronic acid as an organic linker. Interestingly, the obtained GOF shows a high surface area (506 m2 g−1) which is around 11 times higher than that of GO (46 m2 g−1), indicating that the organic modification on the GO surface is an effective way of preparing a porous structure using GO. Our synthetic approach is quite simple, facile, and fast, compared with many other approaches reported previously. The synthesized GOF exhibits a very large CO2 capacity of 4.95 mmol g−1 at 298 K (1 bar), which is higher those of other porous materials or carbon-based materials, along with an excellent CO2/N2 selectivity of 48.8. [ABSTRACT FROM AUTHOR]

Due to their remarkable mechanical properties, graphene nanoplatelets (GNPs) are widely employed to reinforce matrix components such as cement materials. Recent findings have indicated that GNPs can be used as additives to improve the mechanical properties of cement. However, the enhancement mechanism is still indefinite. In order to investigate the reinforcement mechanism, this work studied the effect of GNPs on the hydration behaviour of Portland cement through an experimental investigation with isothermal calorimetry and thermogravimetric analysis. The results indicate that the addition of GNPs has little effect on the cement hydration process and the degree of hydration. As revealed by scanning electron microscopy and mini-slump tests, the GNPs were mechanically dispersed in the cement matrix. Special attention was paid to the physical functions between GNPs and cement and a possible mechanism is proposed to explain the formation pathway for GNP-cement composites. This research provides deeper understanding regarding the use of GNPs for reinforcing and toughening cement-based composites. [ABSTRACT FROM AUTHOR]

We present molecular dynamics simulations of monolayer graphene under uniaxial tensile loading. The Morse, bending angle, torsion and Lennard-Jones potential functions are adopted within the mdFOAM library in the OpenFOAM software, to describe the molecular interactions in graphene. A well-validated graphene model using these set of potentials is not yet available. In this work, we investigate the accuracy of the mechanical properties of graphene when derived using these simpler potentials, compared to the more commonly used complex potentials such as the Tersoff-Brenner and AIREBO potentials. The computational speed up of our approach, which scalesO(1.5N), whereNis the number of carbon atoms, enabled us to vary a larger number of system parameters, including graphene sheet orientation, size, temperature and concentration of nanopores. The resultant effect on the elastic modulus, fracture stress and fracture strain is investigated. Our simulations show that graphene is anisotropic, and its mechanical properties are dependant on the sheet size. An increase in system temperature results in a significant reduction in the fracture stress and strain. Simulations of nanoporous graphene were created by distributing vacancy defects, both randomly and uniformly, across the lattice. We find that the fracture stress decreases substantially with increasing defect density. The elastic modulus was found to be constant up to around 5% vacancy defects, and decreases for higher defect densities. [ABSTRACT FROM PUBLISHER]

In this work, the authors discuss a systematic method of characterizing the damage process in graphene. The mathematical formulation is limited to the elastic range. In the elastic constitutive equation for graphene, both the second-order and third-order elastic stiffnesses are considered. The formulation is performed within the framework of Continuum Damage Mechanics. Thus, both the hypotheses of elastic strain equivalence and elastic energy equivalence are utilized. In addition to the classical damage variable that is defined in terms of the cross-sectional area, a new damage variable is introduced and defined in terms of the surface area. This particular damage variable is suited for general nanomaterials, especially graphene. Both the scalar and tensorial formulations are presented. The special case of plane stress in graphene is illustrated as an example using the derived general equations and some interesting results are obtained. [ABSTRACT FROM AUTHOR]

Graphene and its derivatives are the new carbon nanomaterials with the prospect for great applications in electronics, energy storage, biosensors and medicine. However, little is known about the toxicity of graphene or its derivatives in the case of occasional or repeated ocular exposure. We performedin vitroandin vivostudies to evaluate the toxicity of graphene oxide (GO) exposure to the eye. Primary human corneal epithelium cells (hCorECs) and human conjunctiva epithelium cells (hConECs) were exposed to GO (12.5–100 μg/mL). Acute GO exposure (2 h) did not induce cytotoxicity to hCorECs. However, short-term GO exposure (24 h) exerted significant cytotoxicity to hCorECs and hConECs with increased intracellular reactive oxygen species (ROS). Glutathione (GSH) reduced the GO-induced cytotoxicity. We further performed acute eye irritation tests in albino rabbits according to the Organization for Economic Cooperation and Development (OECD) guidelines, and the rabbits did not exhibit corneal opacity, conjunctival redness, abnormality of the iris, or chemosis at any time point after the instillation of 100 μg/mL of GO. However, 5-day repeated GO exposure (50 and 100 μg/mL) caused reversible mild corneal opacity, conjunctival redness and corneal epithelium damage to Sprague-Dawley rats, which was also alleviated by GSH. Therefore, our study suggests that GO-induced time- and dose-dependent cytotoxicity to hCorECs and hConECs via oxidative stress. Occasional GO exposure did not cause acute eye irritation; short-term repeated GO exposure generally resulted in reversible damage to the eye via oxidative stress, which may be alleviated by the antioxidant GSH. [ABSTRACT FROM AUTHOR]

In the present work, the toxicity of three forms of graphene: pristine graphene (pG), graphene oxide (GO), and reduced graphene oxide (rGO) was investigated using a chicken embryo model. Fertilized chicken eggs were divided into the control group and groups administered with pG, GO, and rGO, in concentrations of 50, 500, and 5000 μg/ml. The experimental solutions were injected in ovo into the eggs, and at day 18 of incubation, the embryo survival, body and organ weights, the ultrastructure of liver samples, and the concentration of 8-hydroxy-2′-deoxyguanosine (8-OHdG) in the livers were measured. Survival of embryos decreased significantly after treatment with all types of graphene, but not in a dose-dependent manner. The body weights were only slightly affected by the highest doses of graphene, while the organ weights were not different among treatment groups. In all experimental groups, atypical hepatocyte ultrastructure and mitochondrial damage were observed. The concentration of the marker of DNA damage 8-OHdG in the liver significantly decreased after pG and rGO treatments. Further in vivo studies with different animal models are necessary to clarify the level of toxicity of different types of graphene and to estimate the concentrations appropriate to evaluate their biomedical applications and environmental hazard. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional engineered nanomaterial, is now being used in many applications, such as electronics, biological engineering, filtration, lightweight and strong nanocomposite materials, and energy storage. However, there is a lack of information on the potential health effects of graphene in humans based on inhalation, the primary engineered nanomaterial exposure pathway in workplaces. Thus, an inhalation toxicology study of graphene was conducted using a nose-only inhalation system for 28 days (6 h/day and 5 days/week) with male Sprague-Dawley rats that were then allowed to recover for 1-, 28-, and 90-day post-exposure period. Animals were separated into 4 groups (control, low, moderate, and high) with 15 male rats (5 rats per time point) in each group. The measured mass concentrations for the low, moderate, and high exposure groups were 0.12, 0.47, and 1.88 mg/m³, respectively, very close to target concentrations of 0.125, 0.5, and 2 mg/m³. Airborne graphene exposure was monitored using several real-time instrumentation over 10nm to 20 μ for size distribution and number concentration. The total and respirable elemental carbon concentrations were also measured using filter sampling. Graphene in the air and biological media was traced using transmission electron microscopy. In addition to mortality and clinical observations, the body weights and food consumption were recorded weekly. At the end of the study, the rats were subjected to a full necropsy, blood samples were collected for blood biochemical tests, and the organ weights were measured. No dose-dependent effects were recorded for the body weights, organ weights, bronchoalveolar lavage fluid inflammatory markers, and blood biochemical parameters at 1-day post-exposure and 28-day post-exposure. The inhaled graphenes were mostly ingested by macrophages. No distinct lung pathology was observed at the 1-, 28- and 90-day post-exposure. The inhaled graphene was translocated to lung lymph nodes. The results of this 28-day graphene inhalation study suggest low toxicity and a NOAEL of no less than 1.88 mg/m³. [ABSTRACT FROM AUTHOR]

A TiO2@reduced graphene oxide (TiO2@rGO) composite is synthesized successfully by a simple spray-drying method. The structural and morphological characterizations reveal that the TiO2@rGO composite has a sphere-like morphology with diameters of 5-15 µm, and each microsphere is actually a random aggregation of primary TiO2 nanoparticles, which are tightly covered by soft graphene sheets. The TiO2@rGO electrode exhibits enhanced electrochemical performance of high charge capacity (170 mA h g−1 at 0.1 C), long cycling life (87% of capacity retention after 300 cycles at 0.2 C), and high rate capability (55 mA h g−1 at 10 C). Compared with bare TiO2 microspheres, the improved electrochemical performance of the TiO2@rGO composite benefits from the introduction of graphene as a highly conductive, flexible, and large-surface-area scaffold to provide good electronic contact between active materials, suppress the aggregation of intermediate products, and alleviate the volume change during sodiation and desodiation. The encouraging experimental results suggest that the TiO2@rGO composite has great potential as a high-capacity and high-stability anode for the sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Graphene and graphene oxide receive much attention these years, because they add attractive properties to a wide range of applications and products. Several studies have shown toxicological effects of other carbon-based nanomaterials such as carbon black nanoparticles and carbon nanotubes in vitro and in vivo. Here, we report in-depth physicochemical characterization of three commercial graphene materials, one graphene oxide (GO) and two reduced graphene oxides (rGO) and assess cytotoxicity and genotoxicity in the murine lung epithelial cell line FE1. The studied GO and rGO mainly consisted of 2-3 graphene layers with lateral sizes of 1-2 µm. GO had almost equimolar content of C, O, and H while the two rGO materials had lower contents of oxygen with C/O and C/H ratios of 8 and 12.8, respectively. All materials had low levels of endotoxin and low levels of inorganic impurities, which were mainly sulphur, manganese, and silicon. GO generated more ROS than the two rGO materials, but none of the graphene materials influenced cytotoxicity in terms of cell viability and cell proliferation after 24 hr. Furthermore, no genotoxicity was observed using the alkaline comet assay following 3 or 24 hr of exposure. We demonstrate that chemically pure, few-layered GO and rGO with comparable lateral size (> 1 µm) do not induce significant cytotoxicity or genotoxicity in FE1 cells at relatively high doses (5-200 µg/ml). Environ. Mol. Mutagen. 57:469-482, 2016. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Background: Graphene, a monolayer of carbon, is an engineered nanomaterial (ENM) with physical and chemical properties that may offer application advantages over other carbonaceous ENMs, such as carbon nanotubes (CNT). The goal of this study was to comparatively assess pulmonary and systemic toxicity of graphite nanoplates, a member of the graphene-based nanomaterial family, with respect to nanoplate size. Methods: Three sizes of graphite nanoplates [20 μm lateral (Gr20), 5 μm lateral (Gr5), and <2 μm lateral (Gr1)] ranging from 8-25 nm in thickness were characterized for difference in surface area, structure,, zeta potential, and agglomeration in dispersion medium, the vehicle for in vivo studies. Mice were exposed by pharyngeal aspiration to these 3 sizes of graphite nanoplates at doses of 4 or 40 μg/mouse, or to carbon black (CB) as a carbonaceous control material. At 4 h, 1 day, 7 days, 1 month, and 2 months post-exposure, bronchoalveolar lavage was performed to collect fluid and cells for analysis of lung injury and inflammation. Particle clearance, histopathology and gene expression in lung tissue were evaluated. In addition, protein levels and gene expression were measured in blood, heart, aorta and liver to assess systemic responses. Results: All Gr samples were found to be similarly composed of two graphite structures and agglomerated to varying degrees in DM in proportion to the lateral dimension. Surface area for Gr1 was approximately 7-fold greater than Gr5 and Gr20, but was less reactive reactive per m2. At the low dose, none of the Gr materials induced toxicity. At the high dose, Gr20 and Gr5 exposure increased indices of lung inflammation and injury in lavage fluid and tissue gene expression to a greater degree and duration than Gr1 and CB. Gr5 and Gr20 showed no or minimal lung epithelial hypertrophy and hyperplasia, and no development of fibrosis by 2 months post-exposure. In addition, the aorta and liver inflammatory and acute phase genes were transiently elevated in Gr5 and Gr20, relative to Gr1. Conclusions: Pulmonary and systemic toxicity of graphite nanoplates may be dependent on lateral size and/or surface reactivity, with the graphite nanoplates > 5 μm laterally inducing greater toxicity which peaked at the early time points post-exposure relative to the 1-2 μm graphite nanoplate. [ABSTRACT FROM AUTHOR]

Our previous studies revealed that graphene had anticancer properties in experiments in vitro with glioblastoma multiforme (GBM) cells and in tumors cultured in vivo. We hypothesized that the addition of arginine or proline to graphene solutions might counteract graphene agglomeration and increase the activity of graphene. Experiments were performed in vitro with GBM U87 cells and in vivo with GBM tumors cultured on chicken embryo chorioallantoic membranes. The measurements included cell morphology, mortality, viability, tumor morphology, histology, and gene expression. The cells and tumors were treated with reduced graphene oxide (rGO) and rGO functionalized with arginine (rGO + Arg) or proline (rGO + Pro). The results confirmed the anticancer effect of graphene on GBM cells and tumor tissue. After functionalization with amino acids, nanoparticles were distributed more specifically, and the flakes of graphene were less agglomerated. The molecule of rGO + Arg did not increase the expression of TP53 in comparison to rGO, but did not increase the expression of MDM2 or the MDM2/TP53 ratio in the tumor, suggesting that arginine may block MDM2 expression. The expression of NQO1, known to be a strong protector of p53 protein in tumor tissue, was greatly increased. The results indicate that the complex of rGO + Arg has potential in GBM therapy. [ABSTRACT FROM AUTHOR]

New carbon allotropes can be designed by combining sp, sp2 and sp3 three hybridization states. And the hybridization states or coordination numbers of carbon atoms can be changed by applying high pressure on carbon materials. In this study, a common high pressure phase (named as TBBC) transformed from AB-stacking graphyne or THD-graphene is predicted. Its kinetic stability is examined using finite displacement method. We find that the sp2 and sp3 hybridized carbon atoms behave different vibration features at high frequency region. Both graphene-like and diamond-like vibration peaks occurs. Phase transition energy barriers from both graphyne and THD-graphene to TBBC are estimated. Electronic structure calculations show that the TBBC is an indirect semiconductor with a bandgap of 0.66 eV. The ideal tensile strength of TBBC is high in [0001] and [ 1 1 ¯ 00 ] directions, but is weak along [ 1 2 ¯ 10 ] direction. [ABSTRACT FROM AUTHOR]

The element carbon possesses various stable and metastable allotropes; some of them have been applied in diverse fields. The experimental evidences of both carbon chain and graphdiyne have been reported. Here, we reveal the mystery of an enchanting carbon allotrope with sp-, sp2-, and sp3-hybridized carbon atoms using a newly developed ab initio particle-swarm optimization algorithm for crystal structure prediction. This crystalline allotrope, namely m-C12, can be viewed as braided mesh architecture interwoven with multigraphene and carbon chains. The m-C12 meets the criteria for dynamic and mechanical stabilities and is energetically more stable than carbyne and graphdiyne. Analysis of the B/G and Poisson’s ratio indicates that this allotrope is ductile. Notably, m-C12 is a superconducting carbon with Tc of 1.13 K, which is rare in the family of carbon allotropes. [ABSTRACT FROM AUTHOR]

The micro-scale patterns in graphene on Si/SiO2 substrate were fabricated using ultrashort 515 nm laser pulses. For both picosecond and femtosecond laser pulses two competitive processes, based on photo-thermal (ablation) and photochemical (oxidation/etching) effects, were observed. The laser-induced etching of graphene starts just below the threshold energy of graphene ablation: 1.7 nJ per 280 fs pulse and 2.7 µJ per 30 ps pulse. Whilst etching is not sensitive to thermal properties of graphene and provides uniform patterns, the ablation, in contrast, is highly affected by defects in the graphene structure like wrinkles and bilayer islands. The mechanisms of ultrafast laser interaction with graphene are discussed. [ABSTRACT FROM AUTHOR]

This paper elucidates the effect of silicon carbide nanoparticles (SiCNP) and graphene nanoplatelets (GNPs), on their own and together, on the densification behavior and fracture toughness of alumina (Al2O3) ceramic matrix. This was investigated by using the high-frequency induction heat sintering (HFIHS) process. While the addition of each nanostructure caused varying degrees of grain refinement and enhancement of mechanical properties, the incorporation of as little as 0.5 wt.% GNPs along with 5.0 wt.% SiCNP promoted uniform dispersion of the latter due to the lateral surface area of the graphene nanosheets with their two-dimensional morphology. There was an associated reduction in grain size from 1500 to 300 nm upon the addition of both types of nanoscale reinforcements. Extensive electron microscopy of the as-produced nanocomposites indicated the presence of SiCNP within, as well as at, the grain boundary areas whereas the 2D GNPs anchored between neighboring grains. Fractography of the samples revealed a transition from a mixed intergranular/transgranular mode for SiCNP or GNP-reinforced nanocomposites to transgranular fracture mode for the hybrid nanocomposites with improvements in fracture toughness and microhardness by 160 and 27%, respectively, largely due to the synergic role of the nanostructured reinforcements and their distinctly different toughening mechanisms. A new toughening model is proposed for the hybrid nanocomposites by taking into consideration crack deflection and pull-out effects due to SiCNP and the atomic level slip-stick driven GNPs inter-layer slithering. It was found that the addition of GNPs facilitates SiCNP dispersion that subsequently develops dense, fine-grained microstructures after a short-cycle, pressure-assisted consolidation process. [ABSTRACT FROM AUTHOR]

Atomic hydrogen exists ubiquitously in graphene materials made by chemical methods. Yet determining the effect of hydrogen on the electrochemical performance of graphene remains a significant challenge. Here we report the experimental observations of high rate capacity in hydrogen-treated 3-dimensional (3D) graphene nanofoam electrodes for lithium ion batteries. Structural and electronic characterization suggests that defect sites and hydrogen play synergistic roles in disrupting sp2 graphene to facilitate fast lithium transport and reversible surface binding, as evidenced by the fast charge-transfer kinetics and increased capacitive contribution in hydrogen-treated 3D graphene. In concert with experiments, multiscale calculations reveal that defect complexes in graphene are prerequisite for low-temperature hydrogenation, and that the hydrogenation of defective or functionalized sites at strained domain boundaries plays a beneficial role in improving rate capacity by opening gaps to facilitate easier Li penetration. Additional reversible capacity is provided by enhanced lithium binding near hydrogen-terminated edge sites. These findings provide qualitative insights in helping the design of graphene-based materials for high-power electrodes. [ABSTRACT FROM AUTHOR]