Review of Potential Environmental and Health Risks of the Nanomaterial Graphene

Several future applications have been suggested for the nanomaterial graphene, and its production is increasing dramatically. This study is a review of risk-related information on graphene with the purpose of outlining potential environmental and health risks and guide future risk-related research. Available information is presented regarding emissions, environmental fate, and toxicity of graphene. The results from this study indicate that graphene could exert a considerable toxicity and that considerable emission of graphene from electronic devices and composites are possible in the future. It is also suggested that graphene is both persistent and hydrophobic. Although these results indicate that graphene may cause adverse environmental and health effects, the results foremost show that there are many risk-related knowledge gaps to be filled and that the emissions of graphene, the fate of graphene in the environment, and the toxicity of graphene should be further studied.     

Molecular dynamics simulations of the aggregation behaviour of overlapped graphene sheets in linear aliphatic hydrocarbons

Molecular dynamics simulations were used to investigate the aggregation of two partially overlapped graphene sheets in hexane, dodecane and eicosane. When partially overlapped graphene sheets are adjacent to one another, they will expel the adsorbed layers of the solvent molecules on the graphene surface, and the amount of overlap will increase. When the overlapped regions of the graphene sheets are separated by solvent molecules, they cannot expel the adsorption layers between them, and so the sheets remain separated. The driving force for aggregation is the van der Waals interaction between the two graphene sheets, while the van der Waals interaction between the graphene sheets and the solvent molecules inhibits graphene aggregation. The diffusion rate of the hydrocarbon molecules with shorter chain lengths is higher. Thus, they diffuse faster during graphene aggregation, which leads to a higher rate of graphene overlapping in the shorter hydrocarbons. This work provides useful insights into graphene aggregation in linear hydrocarbon solvents of varying lengths at the nanoscale.     

First principle study of cysteine molecule on intrinsic and Au-doped graphene surface as a chemosensor device

To search for a high sensitivity sensor for cysteine, we investigated the adsorption of cysteine on intrinsic and Au-doped graphene sheets using density functional theory calculations. Binding energy is primarily determined by the type of atom which is closer to the adsorbed sheet. Compared with intrinsic graphene, Au-doped graphene system has higher binding energy value and shorter connecting distance, in which strong Au-S, Au-N and Au-O chemical bond interaction play the key role for stability. Furthermore, the density of states results show orbital hybridization between cysteine and Au-doped graphene sheet, but slight hybridization between the cysteine molecule and intrinsic graphene sheet. Large charge transfers exist in Au-doped graphene-cysteine system. The results of DOS and charge transfer calculations suppose that the electronic properties of graphene can be tuned by the adsorption site of cysteine. Therefore, graphene and Au-doped graphene system both possess sensing ability, except that Au-doped graphene is a better sensor for cysteine than intrinsic graphene.     

Blood compatible graphene/heparin conjugate through noncovalent chemistry

Blood compatible graphene/heparin conjugate is simply formulated through noncovalent interaction between chemically reduced graphene and heparin. Charge repulsion of negatively charged heparin on graphene plates renders hydrophobic graphene to be solublized in aqueous media without any precipitation or aggregation even after 6 months. Unfractioned heparin (UFH) with higher molecular weight was effective for graphene solubilization while low molecular weight heparin (LMWH) was not. Noncovalently interacting heparin chains on graphene plates preserve their anticoagulant activity after conjugation with graphene. Graphene/UFH conjugate shows much enhanced anti factor Xa (FXa) activity of 29.6 IU/mL compared with pristine graphene oxide (GO; 1.03 IU/mL).     

Coarse-grained molecular simulation of self-assembly nanostructures of CTAB on nanoscale graphene

Coarse-grained molecular dynamics simulation has been performed to study the aggregated morphology of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), adsorbed on nanoscale graphene surfaces. The CTAB surfactants can self-assemble on graphene to form various supramolecular morphologies and structures. The effect of packing density, thickness of graphene sheet and width of graphene nanoribbon on the CTAB–graphene self-assembly has been investigated. The buoyant densities of various graphene–CTAB assemblies were calculated, which increase with surfactant coverage and number of graphene layers. This result demonstrates that density gradient can be used to isolate graphenes with various layers. This simulation provides larger-scale microscopic insight into the supramolecular self-assembly nanostructures for the CTAB surfactants aggregated on graphene, which could be valuable to guide fabrication of graphene-based hybrid nanocomposites.     

Graphene enhances the cardiomyogenic differentiation of human embryonic stem cells

Graphene has drawn attention as a substrate for stem cell culture and has been reported to stimulate the differentiation of multipotent adult stem cells. Here, we report that graphene enhances the cardiomyogenic differentiation of human embryonic stem cells (hESCs) at least in part, due to nanoroughness of graphene. Large-area graphene on glass coverslips was prepared via the chemical vapor deposition method. The coating of the graphene with vitronectin (VN) was required to ensure high viability of the hESCs cultured on the graphene. hESCs were cultured on either VN-coated glass (glass group) or VN-coated graphene (graphene group) for 21 days. The cells were also cultured on glass coated with Matrigel (Matrigel group), which is a substrate used in conventional, directed cardiomyogenic differentiation systems. The culture of hESCs on graphene promoted the expression of genes involved in the stepwise differentiation into mesodermal and endodermal lineage cells and subsequently cardiomyogenic differentiation compared with the culture on glass or Matrigel. In addition, the culture on graphene enhanced the gene expression of cardiac-specific extracellular matrices. Culture on graphene may provide a new platform for the development of stem cell therapies for ischemic heart diseases by enhancing the cardiomyogenic differentiation of hESCs.     

石墨烯的环境行为及其对环境中污染物迁移归趋的影响

石墨烯是当前研究最热的碳纳米材料,具有独特的理化特性,在各领域具有广阔的应用前景.随着其生产和使用量的不断增大,石墨烯不可避免地会进入到环境中,从而给生态环境和人类健康带来风险.深入理解石墨烯在环境中的行为和归趋,探讨石墨烯对污染物环境行为的影响,对于科学客观评价石墨烯的环境风险具有十分重要的意义.本文对石墨烯的环境行为及其对污染物迁移归趋的影响进行了综述,主要介绍了石墨烯在水环境中的胶体特性和稳定性,以及在多孔介质中的迁移,重点探讨了石墨烯与重金属和有机物之间的相互作用,并从吸附机理、石墨烯与土壤组分之间的相互作用、石墨烯对污染物在环境中迁移及生物有效性的影响、石墨烯的定量方法等方面对该研究领域的前景和重点进行了展望,以期为该领域的深入研究提供借鉴并拓展新的思路.     

Multiscale Graphene‐Based Materials for Applications in Sodium Ion Batteries

Scrupulous design and smart hybridization of bespoke electrode materials are of great importance for the advancement of sodium ion batteries (SIBs). Graphene‐based nanocomposites are regarded as one of the most promising electrode materials for SIBs due to the outstanding physicochemical properties of graphene and positive synergetic effects between graphene and the introduced active phase. In this review, the recent progress in graphene‐based electrode materials for SIBs with an emphasis on the electrode design principle, different preparation methods, and mechanism, characterization, synergistic effects, and their detailed electrochemical performance is summarized. General design rules for fabrication of advanced SIB materials are also proposed. Additionally, the merits and drawbacks of different fabrication methods for graphene‐based materials are briefly discussed and summarized. Furthermore, multiscale forms of graphene are evaluated to optimize electrochemical performance of SIBs, ranging from 0D graphene quantum dots, 2D vertical graphene and reduced graphene oxide sheets, to 3D graphene aerogel and graphene foam networks. To conclude, the challenges and future perspectives on the development of graphene‐based materials for SIBs are also presented.     

Ultra-sensitive suspended graphene nanocomposite cancer sensors with strong suppression of electrical noise

The cancer sensor based on suspended layer-by-layer self-assembled graphene reported in the paper exhibits an ultra high sensitivity due to graphene material properties in nature. By simply immersing the substrate alternatively into charged graphene suspensions and polyions, graphene nanoplatelets are self-assembled in the channel as the sensing region, followed by SF(6) dry etching to suspend the structure. Conductance shift curves demonstrate that the suspended graphene sensors functionalized with specific anti-PSA antibodies as bioreceptor are capable of detecting prostate specific antigen down to 0.4 fg/ml (11 aM), at least one order of magnitude lower than unsuspended devices. The noise spectra analysis confirms the lower level of 1/f noise in suspended graphene devices. Carbon nanotube sensor under the same conditions of design, manufacture, and measurement are implemented to compare with graphene devices, showing the prominent advantages of graphene as a sensing material.     

Facile Synthesis of 3D MnO2–Graphene and Carbon Nanotube–Graphene Composite Networks for High‐Performance,Flexible, All‐Solid‐State Asymmetric Supercapacitors

The integration of graphene nanosheets on the macroscopic level using a self‐assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene‐based networks, manganese dioxide (MnO₂)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all‐solid‐state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low‐temperature, and low‐cost. The as‐prepared MnO₂–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all‐solid‐state asymmetric supercapacitor was synthesized with MnO₂–graphene foam as the positive electrode and CNT‐graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high‐voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.     

Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties

In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene.     

Wrinkling and thermal conductivity of one graphene sheet under shear

Tersoff-potential - based molecular dynamics method is used to simulate wrinkling deformation of one graphene sheet under shear, and the obtained deformation is compared with analytical solutions of macro-membrane. Furthermore, thermal conductivity of the wrinkled graphene at different temperatures is calculated. It is found that (1) the wrinkling deformation of graphene sheet under shear is close to the analytical solutions of macro-membrane under shear, which implies that the solutions of macro-membrane are applicable to predict the wrinkling deformation of graphene sheets under shear; (2) the more serious the wrinkling of the graphene under shear is, the stronger the phonon scattering is and, therefore, the lower the thermal conductivity of the wrinkled graphene is; (3) within the temperature range of 400–700 K, the thermal conductivity of graphene sheet decreases with increase in temperature.     

Graphene-based pressure nano-sensors

We perform atomistic simulations to study the failure behavior of graphene-based pressure sensor, which is made of a graphene nanoflake suspended over a well in a silicon-carbide substrate and clamped on its surrounding edge by the covalent bonds between the graphene flake and the substrate. Two distinct types of mechanical failure are identified: the first one is characterized by complete detachment of the graphene nanoflake from the silicon-carbide substrate via breaking the covalent bonds between the carbon atoms of the graphene flake and the silicon atoms of the substrate; the second type is characterized by the rupture of the graphene nanoflake via breaking the carbon-carbon bonds within the graphene. The type of mechanical failure is determined by the clamped area between the graphene flake and the substrate. The failure pressure can be tuned by changing the clamped area and the well radius. A model is proposed to explain the transition between the two types of failure mode. The present work provides a quantitative framework for the design of graphene-based pressure sensors.     

Si-doped graphene: an ideal sensor for NO- or NO<Subscript>2</Subscript>-detection and metal-free catalyst for N<Subscript>2</Subscript>O-reduction

Exploring and evaluating the potential applications of two-dimensional graphene is an increasingly hot topic in graphene research. In this paper, by studying the adsorption of NO, N₂O, and NO₂ on pristine and silicon (Si)-doped graphene with density functional theory methods, we evaluated the possibility of using Si-doped graphene as a candidate to detect or reduce harmful nitrogen oxides. The results indicate that, while adsorption of the three molecules on pristine graphene is very weak, Si-doping enhances the interaction of these molecules with graphene sheet in various ways: (1) two NO molecules can be adsorbed on Si-doped graphene in a paired arrangement, while up to four NO₂ molecules attach to the doped graphene with an average adsorption energy of −0.329 eV; (2) the N₂O molecule can be reduced easily to the N₂ molecule, leaving an O-atom on the Si-doped graphene. Moreover, we find that adsorption of NO and NO₂ leads to large changes in the electronic properties of Si-doped graphene. On the basis of these results, Si-doped graphene can be expected to be a good sensor for NO and NO₂ detection, as well as a metal-free catalyst for N₂O reduction.     

Controlling Optical Absorption of Graphene in Near-infrared Region by Surface Plasmons

Nowadays, graphene has many applications in optical instruments, biosensors, gas sensors, photovoltaic cells, and so on. In this study, we aimed at investigating the optical properties of graphene under the influence of plasmons created in one-dimensional photonic crystal structure by making use of the absorption spectrum. We put the gold photonic crystal in adjacent to graphene and placed an antireflection layer on top of it. Then, we studied the behavior of graphene absorption peaks in a near-infrared region. By analyzing the graphene behavior in this region, we observed that graphene absorption was increased up to 40% and graphene absorption value in absorption peak, absorption peak wavelength, absorption spectra width, and also its absorption spectra in a wide wavelength range from 1000 to 2500 nm, could be controlled by making use of different factors such as the substance of antireflection layer and photonic crystal geometric dimensions. This structure can make many applications possible for graphene such as using it to build biosensors to identify uric acid and some of the lipids that have specific significances in detecting atherosclerotic lesions as well as diagnosing the states of disease.     

Graphene: Substrate preparation and introduction

This technical note describes the transfer of continuous, single-layer, pristine graphene to standard Quantifoil TEM grids. We compare the transmission properties of pristine graphene substrates to those of graphene oxide and thin amorphous carbon substrates. Positively stained DNA imaged across amorphous carbon is typically indiscernible and requires metal shadowing for sufficient contrast. However, in a practical illustration of the new substrates properties, positively stained DNA is imaged across pristine graphene in striking contrast without the need of metal shadowing. We go onto discuss technical considerations and the potential applications of pristine graphene substrates as well as their ongoing development.     

Single-layer CVD-grown graphene decorated with metal nanoparticles as a promising biosensing platform

A new approach to the development of a single-layer graphene sensor decorated with metal nanoparticles is presented. Chemical vapor deposition is used to grow single layer graphene on copper. Decoration of the single-layer graphene is achieved by electroless deposition of Au nanoparticles using the copper substrate as a source of electrons. Transfer of the decorated single-layer graphene on glassy carbon electrodes offers a sensitive platform for biosensor development. As a proof of concept, 10 units of glucose oxidase were deposited on the surface in a Nafion matrix to stabilize the enzyme as well as to prevent interference from ascorbic acid and uric acid. Amperometric linear response calibration in the μmoll(-1) is obtained. The presented methodology enables highly sensitive platforms for biosensor development, providing a scalable roll-to-roll production with a much more reproducible scheme when compared to the graphene biosensors reported previously based on drop-cast of multi-layer graphene suspensions.     

Creation of 3D Textured Graphene/Si Schottky Junction Photocathode for Enhanced Photo‐Electrochemical Efficiency and Stability

This work presents a novel photo‐electrochemical architecture based on the 3D pyramid‐like graphene/p‐Si Schottky junctions. Overcoming the conventional transfer technique by which only planar graphene/Si Schottky junctions are currently available, this work demonstrates the 3D pyramid‐like graphene/p‐Si Schottky junction photocathode, which greatly enhances light harvesting efficiency and exhibits promising photo‐electrochemical performance for hydrogen generation. The formation of 3D pyramid‐like graphene/p‐Si Schottky junctions exhibits enhanced electrochemical activity and promotes charge separation efficiency compared with the bare pyramid Si surface without graphene. The inherent chemical inertness of graphene significantly improves the operational stability of 3D graphene/p‐Si Schottky junction photo‐electrochemical cells. The 3D pyramid‐like graphene/p‐Si Schottky junction photocathode delivers an onset potential of 0.41 V and a saturated photocurrent density of ?32.5 mA cm^?2 at 0 V (vs RHE) with excellent stability comparable to values reported for textured or nanostructured p‐Si photocathodes coated with ultrathin oxide layers by the conventional atomic layer deposition technique. These results suggest that the formation of graphene/Si Schottky junctions with a 3D architecture is a promising approach to improve the performance and durability of Si‐based photo‐electrochemical systems for water splitting or solar‐to‐fuel conversion.     

Electronic,transport, magnetic,and optical properties of graphene nanoribbons and their optical sensing applications: A comprehensive review

Low dimensional materials have attracted great research interest from both theoretical and experimental point of views. These materials exhibit novel physical and chemical properties due to the confinement effect in low dimensions. The experimental observations of graphene open a new platform to study the physical properties of materials restricted to two dimensions. This featured article provides a review on the novel properties of quasi one-dimensional (1D) material known as graphene nanoribbon. Graphene nanoribbons can be obtained by unzipping carbon nanotubes (CNT) or cutting the graphene sheet. Alternatively, it is also called the finite termination of graphene edges. It gives rise to different edge geometries, namely zigzag and armchair, among others. There are various physical and chemical techniques to realize these materials. Depending on the edge type termination, these are called the zigzag and armchair graphene nanoribbons (ZGNR and AGNR). These edges play an important role in controlling the properties of graphene nanoribbons. The present review article provides an overview of the electronic, transport, optical, and magnetic properties of graphene nanoribbons. However, there are different ways to tune these properties for device applications. Here, some of them, such as external perturbations and chemical modifications, are highlighted. Few applications of graphene nanoribbon have also been briefly discussed.     

Modeling the physisorption of bisphenol A on graphene and graphene oxide

The physisorption of bisphenol A (BPA) on pristine and oxidized graphene was studied theoretically via calculations performed at the PBE-D3 level (including dispersion force corrections). Three stable conformations of BPA on graphene were found. A lying-down configuration was energetically favored because the presence of π–π stacking and dispersion forces increased interactions. In addition, the adsorption of BPA on the edges of graphene oxide was enhanced when adsorption occurred on carboxyl and carbonyl groups, whereas the adsorption strength decreased when adsorption occurred on hydroxyl groups. The highest physisorption strength was obtained on the surface of graphene oxide due to the presence of π–π stacking and dispersion forces (which provided the greatest contribution to the adsorption energy) as well as hydrogen bonds (which provided a smaller contribution), indicating that oxidized graphene is a better candidate than pristine graphene for BPA removal. On the other hand, an increase in electrophilicity was observed after the physisorption of BPA in all systems (with respect to graphene and BPA in their isolated forms), with the adsorbent acting as the electron acceptor. Finally, molecular dynamics simulations performed using the PM6 Hamiltonian showed that the adsorption of BPA on graphene is stable.