Graphene-based Material Research Articles

Fabrication and Analysis of Chemically-Derived Graphene/Pyramidal Si Heterojunction Solar Cells

In the study, the chemically-derived reduced graphene oxide flakes on the pyramidal Si substrate to construct the heterojunction solar cells via simple spin-coating process have been presented. The total reflectance of chemically-derived graphene on pyramidal Si is ~12% at the wavelength of 550 nm which is remarkably reduced compared with that of reduced graphene oxide on planar Si. By modifying the density and distribution of reduced graphene oxide flakes on Si, the power conversion efficiency of 5.20% is achieved. Additionally, the simulated absorbance of different-thick graphene is implemented to optimize the performance of graphene/pyramidal Si devices. The fabrication technique for rGO-based devices has the merits of simplicity, large scale, high throughput and low cost, which is a new starting point in the direction of graphene-based material for the applications of next generation optoelectronics.

Study on the structure and electrocatalytic activity of graphene-based nanocomposite materials containing (SCN)n

Novel graphene-based nanocomposite material was prepared in order to fabricate superior metal-free catalyst for oxygen reduction. The nanocomposite was synthesized by a facile and cost-effective solid-solid reaction between GO and KSCN, where the thiocyatate fragments undergo polymerization. The structure of polythiocyanogen (SCN)n in this nanocomposite was compared to the structure of (SCN)n prepared by different methods. The structural characterization of synthesized polymers was performed using SEC, XRD, SEM, FTIR, TGA/DTG, XPS, and elemental analysis. It was determined that the structure of polymer is characterized by polyazomethine chains. The solid-solid reaction between GO and KSCN occurs on the edges of GO to form a characteristic curled morphology, which emerges due to the attachment of short oligomeric (SCN)n chains at the edges of GO. The curled structure is beneficial for the adsorption of small molecules and ions. The linear sweep voltammetry measurements revealed remarkable catalytic performance towards oxygen reduction reaction (ORR) of product the nanocomposite material. In acidic media efficiency of ORR on the nanocomposite material was ∼5 times higher compared to that of commercial catalyst. Investigation of the mechanism of ORR onto the nanocomposite indicated that the protonated nitrogen atoms in oligomer active sites can act as catalysts.

Electrochemical monitoring of biointeraction by graphene-based material modified pencil graphite electrode

Recently, the low-cost effective biosensing systems based on advanced nanomaterials have received a key attention for development of novel assays for rapid and sequence-specific nucleic acid detection. The electrochemical biosensor based on reduced graphene oxide (rGO) modified disposable pencil graphite electrodes (PGEs) were developed herein for electrochemical monitoring of DNA, and also for monitoring of biointeraction occurred between anticancer drug, Daunorubicin (DNR), and DNA. First, rGO was synthesized chemically and characterized by using UV–Vis, TGA, FT-IR, Raman Spectroscopy and SEM techniques. Then, the quantity of rGO assembling onto the surface of PGE by passive adsorption was optimized. The electrochemical behavior of rGO–PGEs was examined by cyclic voltammetry (CV). rGO-PGEs were then utilized for electrochemical monitoring of surface-confined interaction between DNR and DNA using differential pulse voltammetry (DPV) technique. Additionally, voltammetric results were complemented with electrochemical impedance spectroscopy (EIS) technique. Electrochemical monitoring of DNR and DNA was resulted with satisfying detection limits 0.55µM and 2.71µg/mL, respectively.

Electrochemical Supercapacitance Properties of Reduced Graphene Oxide/Mn2O3:Co3O4 Nanocomposite

Graphene-based composite material was prepared and its electrochemical supercapacitive properties were investigated. The composite material comprises of mixed manganese oxide (Mn2O3) and cobalt oxide (Co3O4) crystal distributed on the reduced graphene oxide (RGO) matrix. Structure and morphology of the composite was studied by X-ray diffractometry, high resolution transmission electron microscopy and scanning electron microscopy. The surface functional groups and chemical composition were confirmed by Fourier transform infrared spectroscopy, Raman scattering spectroscopy and X-ray photoelectron spectroscopy. Thermal stability was investigated by thermo gravimetric analysis. Electrochemical supercapacitive performance of the composite was investigated by cyclic voltammetry (CV) and chronopotentiometry. CV and chronopotentiometry results suggested that electrochemical performance of the composite material is better than RGO and mixed Mn2O3 and Co3O4. Specific capacitance of composite was obtained 210 F g−1 at scan rate of 5 mV s−1 and 184 F g−1 at current density of 2 A g−1, respectively. Moreover, the composite showed high cyclic stability with the retention of about 87% capacitance after 1000 charge/discharge cycles. These results suggest the importance and potential of graphene based composite in supercapacitor application.

3D nitrogen-doped graphene foam with encapsulated germanium/nitrogen-doped graphene yolk-shell nanoarchitecture for high-performance flexible Li-ion battery

Flexible electrochemical energy storage devices have attracted extensive attention as promising power sources for the ever-growing field of flexible and wearable electronic products. However, the rational design of a novel electrode structure with a good flexibility, high capacity, fast charge–discharge rate and long cycling lifetimes remains a long-standing challenge for developing next-generation flexible energy-storage materials. Herein, we develop a facile and general approach to three-dimensional (3D) interconnected porous nitrogen-doped graphene foam with encapsulated Ge quantum dot/nitrogen-doped graphene yolk-shell nano architecture for high specific reversible capacity (1,220 mAh g−1), long cycling capability (over 96% reversible capacity retention from the second to 1,000 cycles) and ultra-high rate performance (over 800 mAh g−1 at 40 C). This work paves a way to develop the 3D interconnected graphene-based high-capacity electrode material systems, particularly those that suffer from huge volume expansion, for the future development of high-performance flexible energy storage systems.

Magnetically recoverable graphene-based nanocomposite material as an efficient catalyst for the synthesis of propargylamines via A3coupling reaction

The magnetically separable Au NPs–Fe3O4–rGO catalyst provides a robust and efficient route for the A3coupling reaction of secondary amines, terminal alkynes and aldehyde with tolerance of diverse functional groups for the synthesis of propargylamine in high yields.

Graphene-Based Systems for Enhanced Energy Storage

Extensive global research efforts have focused on the exploitation of graphene for enhanced energy storage. Novel graphene-based composite material electrodes have been developed, in many cases with reports of outstanding performance. However, the development of these composites involve extremely complex and costly procedures/methods whose scalability and eventual commercial exploitation is extremely hard [1]. Within the present activity the use of graphene nanotechnology is exploited to manufacture electrodes for supercapacitors. The goal however is to achieve electrodes with increased specific energy density (compared to the currently commercially available products) using proven and simple manufacturing procedures that can easily be scaled-up and offer competitive products. The roadmap was developed under the framework of European Space Agency highlighting the main advantages brought up from this technology. The activity is separated in three parallel routes; the development and test planning of small–scale production of graphene based materials via the tape casting technology, the establishment of a reliable and low cost industrial production process (scale-up) for these materials and the development and testing of an energy storage demonstrator that shall incorporate the novel electrodes and exhibit their favorable characteristics in energy storage applications for use in space.

A graphene-based porous carbon material as a stationary phase for gas chromatographic separations

The GPCM column exhibits high resolving capability for structural and positional isomers from nonpolar to polar nature.

Soluble graphene composite with aggregation-induced emission feature: non-covalent functionalization and application in explosive detection

Herein, a soluble graphene-based material exhibiting the aggregation-induced emission (AIE) feature was prepared for the first time via wet chemistry by the chemical reduction of graphene oxide (GO).

A comparative study on few-layer graphene production by exfoliation of different starting materials in a low boiling point solvent

Three different graphite-based powders (expandable graphite and two different nano-graphite powders) were investigated as starting materials for an effective liquid phase exfoliation process in isopropyl alcohol (IPA). The prepared dispersions were analyzed and compared in terms of their graphene concentration, stability, number of graphene layers and quality, as well as the electrical conductivity of the prepared graphene-based materials. Good quality graphene dispersions (ID/IG<0.3) with a relatively high concentration (∼1.1mg/ml) were prepared in IPA within 90min sonication time by utilizing a high specific surface area (∼175m2/g) nano-graphite powder derived from natural graphite. Transmission electron microscope analyses of this sample revealed mostly folded and scrolled few layer graphene (FLG) sheets (<5 layers) entangled each other. The electrical conductivity of the thin film prepared from this dispersion was ∼15 and 86S/m, before and after annealing, respectively. FLG prepared from expanded graphite, obtained by thermal treatment of expandable graphite, exhibited both much higher quality (ID/IG<0.09) and electrical conductivity (∼2104 and 19,200S/m before and after annealing, respectively) when dispersed in IPA for 90min. However, the graphene-based material concentration of the prepared dispersion was relatively low (∼0.06mg/ml).

Toxicity and transformation of graphene oxide and reduced graphene oxide in bacteria biofilm.

Impact of graphene based material (GNMs) on bacteria biofilm has not been well understood yet. In this study, we compared the impact of graphene oxide (GO) and reduced graphene oxide (rGO) on biofilm formation and development in Luria-Bertani (LB) medium using Escherichia coli and Staphylococcus aureus as models. GO significantly enhanced the cell growth, biofilm formation, and biofilm development even up to a concentration of 500mg/L. In contrast, rGO (≥50mg/L) strongly inhibited cell growth and biofilm formation. However, the inhibitory effects of rGO (50mg/L and 100mg/L) were attenuated in the mature phase (>24h) and eliminated at 48h. GO at 250mg/L decreased the reactive oxygen species (ROS) levels in biofilm and extracellular region at mature phase. ROS levels were significantly increased by rGO at early phase, while they returned to the same levels as control at mature phase. These results suggest that oxidative stress contributed to the inhibitory effect of rGO on bacterial biofilm. We further found that supplement of extracellular polymeric substances (EPS) in the growth medium attenuated the inhibitory effect of rGO on the growth of developed biofilm. XPS results showed that rGO were oxidized to GO which can enhance the bacterial growth. We deduced that the elimination of the toxicity of rGO at mature phase was contributed by EPS protection and the oxidation of rGO. This study provides new insights into the interaction of GNMs with bacteria biofilm.

Detection of Endotoxin Contamination of Graphene Based Materials Using the TNF-α Expression Test and Guidelines for Endotoxin-Free Graphene Oxide Production.

Nanomaterials may be contaminated with bacterial endotoxin during production and handling, which may confound toxicological testing of these materials, not least when assessing for immunotoxicity. In the present study, we evaluated the conventional Limulus amebocyte lysate (LAL) assay for endotoxin detection in graphene based material (GBM) samples, including graphene oxide (GO) and few-layered graphene (FLG). Our results showed that some GO samples interfered with various formats of the LAL assay. To overcome this problem, we developed a TNF-α expression test (TET) using primary human monocyte-derived macrophages incubated in the presence or absence of the endotoxin inhibitor, polymyxin B sulfate, and found that this assay, performed with non-cytotoxic doses of the GBM samples, enabled unequivocal detection of endotoxin with a sensitivity that is comparable to the LAL assay. FLG also triggered TNF-α production in the presence of the LPS inhibitor, pointing to an intrinsic pro-inflammatory effect. Finally, we present guidelines for the preparation of endotoxin-free GO, validated by using the TET.

Electrochemical and Capacitive Properties of Carbon Dots/Reduced Graphene Oxide Supercapacitors.

There is much recent interest in graphene-based composite electrode materials because of their excellent mechanical strengths, high electron mobilities, and large specific surface areas. These materials are good candidates for applications in supercapacitors. In this work, a new graphene-based electrode material for supercapacitors was fabricated by anchoring carbon dots (CDs) on reduced graphene oxide (rGO). The capacitive properties of electrodes in aqueous electrolytes were systematically studied by galvanostatic charge-discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy. The capacitance of rGO was improved when an appropriate amount of CDs were added to the material. The CD/rGO electrode exhibited a good reversibility, excellent rate capability, fast charge transfer, and high specific capacitance in 1 M H2SO4. Its capacitance was as high as 211.9 F/g at a current density of 0.5 A/g. This capacitance was 74.3% higher than that of a pristine rGO electrode (121.6 F/g), and the capacitance of the CD/rGO electrode retained 92.8% of its original value after 1000 cycles at a CDs-to-rGO ratio of 5:1.

Gas Sensing Analysis of Ag-Decorated Graphene for Sulfur Hexafluoride Decomposition Products Based on the Density Functional Theory

Detection of decomposition products of sulfur hexafluoride (SF6) is one of the best ways to diagnose early latent insulation faults in gas-insulated equipment, and the occurrence of sudden accidents can be avoided effectively by finding early latent faults. Recently, functionalized graphene, a kind of gas sensing material, has been reported to show good application prospects in the gas sensor field. Therefore, calculations were performed to analyze the gas sensing properties of intrinsic graphene (Int-graphene) and functionalized graphene-based material, Ag-decorated graphene (Ag-graphene), for decomposition products of SF6, including SO2F2, SOF2, and SO2, based on density functional theory (DFT). We thoroughly investigated a series of parameters presenting gas-sensing properties of adsorbing process about gas molecule (SO2F2, SOF2, SO2) and double gas molecules (2SO2F2, 2SOF2, 2SO2) on Ag-graphene, including adsorption energy, net charge transfer, electronic state density, and the highest and lowest unoccupied molecular orbital. The results showed that the Ag atom significantly enhances the electrochemical reactivity of graphene, reflected in the change of conductivity during the adsorption process. SO2F2 and SO2 gas molecules on Ag-graphene presented chemisorption, and the adsorption strength was SO2F2 > SO2, while SOF2 absorption on Ag-graphene was physical adsorption. Thus, we concluded that Ag-graphene showed good selectivity and high sensitivity to SO2F2. The results can provide a helpful guide in exploring Ag-graphene material in experiments for monitoring the insulation status of SF6-insulated equipment based on detecting decomposition products of SF6.

Project Dragonfly: A feasibility study of interstellar travel using laser-powered light sail propulsion

Light sail-based propulsion systems are a candidate technology for interplanetary and interstellar missions due to their flexibility and the fact that no fuel has to be carried along. In 2014, the Initiative for Interstellar Studies (i4is) hosted the Project Dragonfly Design Competition, which aimed at assessing the feasibility of sending an interstellar probe propelled by a laser-powered light sail to another star system. We analyzed and designed a mission to the Alpha Centauri system, with the objective to carry out science operations at the destination. Based on a comprehensive evaluation of currently available technologies and possible locations, we selected a lunar architecture for the laser system. It combines the advantages of surface- and space-based systems, as it requires no station keeping and suffers no atmospheric losses. We chose a graphene-based sandwich material for the light sail because of its low density. Deceleration of the spacecraft sufficient for science operations at the target system is achieved using both magnetic and electric sails. Applying these assumptions in a simulation leads to the conclusion that 250kg of scientific payload can be sent to Alpha Centauri within the Project Dragonfly Design Competition's constraints of 100 year travel duration and 100GW laser beam power. This is only sufficient to fulfill parts of the identified scientific objectives, and therefore renders the usefulness of such a mission questionable. A better sail material or higher laser power would improve the acceleration behavior, an increase in the mission time would allow for larger spacecraft masses.

Activity origin and catalyst design principles for electrocatalytic hydrogen evolution on heteroatom-doped graphene

The hydrogen evolution reaction (HER) is a fundamental process in electrocatalysis and plays an important role in energy conversion through water splitting to produce hydrogen. Effective candidates for HER are often based on noble metals or transition metal dichalcogenides, while carbon-based metal-free electrocatalysts generally demonstrate poorer activity. Here we report evaluation of a series of heteroatom-doped graphene materials as efficient HER electrocatalysts by combining spectroscopic characterization, electrochemical measurements, and density functional theory calculations. Results of theoretical computations are shown to be in good agreement with experimental observations regarding the intrinsic electrocatalytic activity and the HER reaction mechanism. As a result, we establish a HER activity trend for graphene-based materials, and explore their reactivity origin to guide the design of more efficient electrocatalysts. We predict that by rationally modifying particular experimentally achievable physicochemical characteristics, a practically realizable graphene-based material will have the potential to exceed the performance of the metal-based benchmark for HER. Metal-free doped-graphene materials are emerging as electrocatalysts for energy conversions, but their activity remains low. Here, Jiao et al. explore the origins of catalytic activity for hydrogen evolution, suggesting pathways to metal-free catalysts with activity to rival metal-containing benchmarks.

Solution-processed P3HT-functional graphene for efficient heterojunction organic photoelectronics

Abstract

Ruthenium nanocrystal decorated vertical graphene nanosheets@Ni foam as highly efficient cathode catalysts for lithium-oxygen batteries

The electrochemical performance of lithium-oxygen (Li-O2) batteries can be markedly improved through designing the architecture of cathode electrodes with sufficient spaces to facilitate the diffusion of oxygen and accommodate the discharge products, and optimizing the cathode catalyst to promote the oxygen reduction reaction and oxygen evolution reaction (OER). Herein, we report the synthesis of ruthenium (Ru) nanocrystal-decorated vertically aligned graphene nanosheets (VGNS) grown on nickel (Ni) foam. As an effective binder-free cathode catalyst for Li-O2 batteries, the Ru-decorated VGNS@Ni foam can significantly reduce the charge overpotential via the effects on the OER and achieve high specific capacity, leading to an enhanced electrochemical performance. The Ru-decorated VGNS@Ni foam electrode has demonstrated low charge overpotential of ~0.45 V and high reversible capacity of 23 864 mAh g−1 at the current density of 200 mA g−1, which can be maintained for 50 cycles under full charge and discharge testing condition in the voltage range of 2.0–4.2 V. Furthermore, Ru nanocrystal decorated VGNS@Ni foam can be cycled for more than 200 cycles with a low overpotential of 0.23 V under the capacity curtained to be 1000 mAh g−1 at a current density of 200 mA g−1. Ru-decorated VGNS@Ni foam electrodes have also achieved excellent high rate and long cyclability performance. This superior electrochemical performance should be ascribed to the unique three-dimensional porous nanoarchitecture of the VGNS@Ni foam electrodes, which provide sufficient pores for the diffusion of oxygen and storage of the discharge product (Li2O2), and the effective catalytic effect of Ru nanocrystals on the OER, respectively. Ex situ field emission scanning electron microscopy, X-ray diffraction, Raman and Fourier transform infrared measurements revealed that Ru-decorated VGNS@Ni foam can effectively decompose the discharge product Li2O2, facilitate the OER and lead to a high round-trip efficiency. Therefore, Ru-decorated VGNS@Ni foam is a promising cathode catalyst for rechargeable Li-O2 batteries with low charge overpotential, long cycle life and high specific capacity. A three-dimensional graphene-based material has an architecture that enhances lightweight lithium-oxygen batteries in multiple ways. A team led by Guoxiu Wang from the University of Technology Sydney in Australia searchs for a cathode that would alleviate some problems associated with lithium-oxygen batteries, such as their poor cycling stability and the high voltages needed to recharge them. The researchers designed a more porous type of cathode that contained vertical graphene nanosheets to prevent oxygen pathways becoming clogged by discharge products. Attaching the open-network, highly conductive carbon nanomaterials to nickel foam yielded a material containing many channels and voids for lithium by-products. Adding catalytic ruthenium nanoparticles to the graphene network resulted in a cathode that dropped recharging overpotentials significantly — from 1.5 to 0.23–V — while remaining stable for over 200 cycles. We report the synthesis of ruthenium nanocrystal-decorated vertically aligned graphene nanosheets grown on nickel foam. As an effective binder-free cathode for Li-O2 batteries, it can significantly reduce the charge overpotential via their effects on the oxygen evolution reaction and achieve high specific capacity, leading to an enhanced electrochemical performance.

Non-aqueous synthesis of ultrasmall NiO nanoparticle-intercalated graphene composite as active electrode material for supercapacitors

With the vast exploration of the applications of graphene, researchers are assessing different methods for fabricating graphene-based electrode material with high capacitance but low material and energy costs. In this study, reduced graphene oxide/nickel oxide (RGO/NiO) nanocomposites were prepared using a non-aqueous solvent-based method followed by calcination. Nickel acetate tetrahydrate and tert-butanol were used as the precursor and solvent, respectively. Ultrasmall nickel oxide nanoparticles, ca. 8.0nm in size, were deposited on the surface of the graphene sheets simultaneously with the partial reduction of graphene oxide. The resulting RGO/NiO electrode exhibited a high capacitance of 689Fg⿿1 at a current density of 0.8Ag⿿1. After 1500 cycles, the specific retention and the coulombic efficiency yielded to 86.34% and 96.39%, respectively, which supports the viability of this composite as an alternative activated material with high electrochemical performance.

Thickness of functionalized graphene oxide sheets plays critical role in tissue accumulation and urinary excretion: A pilot PET/CT study

We have recently reported that administration of thin graphene oxide (GO) sheets in the systemic circulation of rodents leads to rapid urinary excretion for the majority of injected dose and accumulation by the reticuloendothelial system organs for the remaining dose. In this study, graphene oxide was functionalized with a chelating moiety (DOTA, (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid)) and labeled with [64Cu] for positron emission computed tomography (PET/CT) imaging. The thin functionalized graphene oxide material (f-GO-thin) consisted of a few layers (∼5nm) in thickness. Aging of the f-GO-thin material led to re-stacking of the flakes that resulted in materials of increased thickness (f-GO-thick) without altering their lateral dimension. These two types of f-GOs were comparatively studied pharmacologically to reveal the previously unexplored in vivo role of graphene oxide sheet thickness. Our results showed that a significantly larger fraction of the thicker GO sheets (47.5% of injected dose) remained within the body of living animals 24h after intravenous administration, residing mainly in the spleen and liver. The thinner GO sheets were predominantly (76.9% of injected dose) excreted through the glomerular filter into the urine. This pilot study provides an initial correlation between graphene-based material structure and pharmacological profile that is imperative towards understanding of how 2D structures behave in vivo to give information on potential biomedical applications.