Assembly Of Graphene Research Articles

Modeling and Analysis of a Novel Ultrasensitive Differential Resonant Graphene Micro-Accelerometer with Wide Measurement Range.

A novel, ultrahigh-sensitivity wide-range resonant micro-accelerometer using two differential double-clamped monolayer graphene beams is designed and investigated by steady-state simulation via COMSOL Multiphysics software in this paper. Along with stiffness-enhanced optimized folded support beams, two symmetrical 3-GPa prestressed graphene nano-beams serve as resonant sensitive elements with a size of 10 μm × 1 μm (length × width) to increase the acceleration sensitivity while extending the measurement range. The simulation results show that the accelerometer with cascade-connected graphene and proof-mass assembly exhibits the ultrahigh sensitivity of 21,224 Hz/g and quality factor of 9773 in the range of 0–1000 g. This is remarkably superior to previously reported studies characterized by attaching proof mass to the graphene components directly. The proposed accelerometer shows great potential as an alternative to quartz and silicon-based resonant sensors in high-impact and highly sensitive inertial measurement applications.

Improved organic-inorganic/graphene hybrid composite as encapsulant for white LEDs: Role of graphene, titanium (IV) isopropoxide and diphenylsilanediol

We report a graphene embedded organic-inorganic hybrid (O-I hybrid) composites that can be utilized as robust encapsulants for white light emitting diodes (WLEDs). The effect of graphene and monomers on the thermal resistance, refractive index (RI), transparency, thermal conductivity, and thermal aging stability of the encapsulant were studied. This study has explicitly unveiled that the embedded graphene played a multifunctional role in producing a high-performance encapsulant. Compared with graphene free O-I hybrid encapsulant, RI, thermal conductivity and heat dissipation ability of the graphene embedded encapsulants were significantly improved. After continuous operation for 10 days, the color rendering index (Ra) of WLED with graphene embedded encapsulants changed from 89.5 to 89.2 (driving current 100 mA), while the correlated color temperature (CCT) altered from 4535 to 4546. Its luminous efficiency changed from 82.9 to 81.2 lm/W. The WLEDs with graphene embedded O-I hybrid encapsulant exhibited long-term stability. This work has paved the way for rational design and assembly of graphene embedded composites as robust materials for various requirements of WLED applications.

Three-Dimensional NiS-MoS2/Graphene Heterostructured Nanohybrids as High-Performance Hydrodesulfurization Catalysts

A simplistic and scalable method for constructing three-dimensional (3D) highly porous aerogels composed of in situ formed NiS nanoparticles anchored onto two-dimensional (2D) MoS2/graphene assembly was reported. This process involves simple hydrothermal treatment followed by moderate thermal annealing. The as-synthesized nanohybrids were deeply investigated using several characterization techniques. The favorable interfacial interactions promoted the graphene surface to control the aggregation of layered MoS2 and uniform decoration of in situ formed NiS nanoparticles was achieved in the resulting nanohybrids. The resulting nanostructured 3D NiS-MoS2/graphene assembly produced synergistic effects and displayed remarkably enhanced hydrodesulfurization (HDS) performance toward dibenzothiophene conversion. The content of NiS cocatalyst controls the hydrogen spillover in the resulting nanoheterojunction catalysts and exhibits an enhanced HDS performance. The presented synthetic approach can be applied into th...

Power from water and graphene

Since the birth of graphene in 2004, it has attracted great research interests of scientists. As the first true two-dimensional (2D) material, graphene has many advantages, such as large specific surface area, high intrinsic carrier mobility, strong mechanical strength, and superior flexibility. Graphene shows broad application prospects. As an important functionalized material, graphene oxide (GO) is 2D macromolecule rich in oxygen-containing functional groups. It has good hydrophilicity and is widely used as a chemical functionalized material in many related fields and applied to energy conversion and storage devices. However, converting the ideal properties of graphene and its derivatives into macrostructures or devices remains a challenge for scientists. The strong interaction between graphene sheets leads to their easy stacking, which greatly reduces their specific surface area and severely limits their efficient use of interfaces. Therefore, the applications of graphene in electronic devices, catalysis, energy storage and other fields have been greatly limited. The key to improve the performance of graphene is how to effectively prevent the stacking of graphene sheets. The assembly and processing of graphene with specific micro-/nano-morphology is conducive to better play the expertise of graphene, thus effectively enhancing the performance of graphene based devices. In this regard, there are lots of efforts have been devoted to the design of structure and morphology for graphene based materials. In the field of water-induced graphene energy converters, the interaction between water molecule and graphene is affected more by the morphology and microstructure change of graphene. As a new type of nano-material, graphene assembly can further expand its application scope. Due to the popularity of portable, flexible and wearable electronic devices, graphene materials have attracted a great deal of research interest from researchers in the field of energy converters. Graphene fibers and films are good solutions for portable needs. Graphene foam with compressibility also has important application value. In the field of hydropower, the moisture induced power generation of graphene oxide, most importantly, the construction of oxygen-containing radical gradients and the entry of water molecules. In a wet environment, water molecules can cause positive and negative charge separation, so that the potential difference appears on both sides of the material, resulting in the conversion of chemical potential energy into electrical energy. Moisture responds to the driver, depending on the affinity between the water and the GO layer. Water evaporation depends on the interaction between water molecules and carbon nanolayers. In this review, we summarized the current work of the major research teams at home and abroad on the assembly and processing of graphene, and the related work of graphene-based carbon materials in water-induced energy conversion, including the assembly and processing of graphene microstructures. As well as moisture power generation, moisture response drivers and water evaporation power generation, this will have guiding significance for the research of other types of materials in hydroelectric power generation. In the future, we still need to work hard in constructing the concentration and gradient of material functional groups to try to find out the actual applied electrical energy. In addition, many current carbon-based materials generate relatively low currents, and current researches on current increase are still continuing so that they can be applied in real life. Moreover, the interaction between carbon materials and water produces electricity. The mechanism still needs to be further explored, which will lay the foundation for future research on the production of electricity from other materials.

A stable hybrid anode of graphene/silicon nanowires array for high performance lithium-ion battery

In this study, a graphene/SiNWs microcomposite was used as the anode for Li-ion battery. The graphene was obtained by electrochemical exfoliation, SiNWs had porous and aligned structures to construct adequate ion transport paths and avoid aggregation of graphene. The graphene/SiNWs anode can effectively enhance the electrical conductivity and overcome volume changes of silicon during cycling. These results suggest that graphene/SiNWs is a promising material for high performance Li-ion battery applications.

Large-Scale Assembly and Mask-Free Fabrication of Graphene Transistors via Optically Induced Electrodeposition

Graphene, known as an alternative for silicon, has significant potential in microelectronic applications. The assembly of graphene on well-defined metal electrodes is a critical step in the fabrication of microelectronic devices. Herein, we present a convenient, rapid, and large-scale assembly method for deposition of Ag electrodes, namely optically induced electrodeposition (OIED). This technique enables us to achieve custom-designed and mask-free fabrication of graphene transistors. The entire assembly process can be completed within a few tens of seconds. Our results show that graphene-based transistors fabricated with Ag electrodes function as a p-type semiconductor. Transfer curves of different samples reveal similar trends of slightly p-type characteristics, which shows that this method is reliable and repeatable.

An ionic liquid functionalized graphene adsorbent with multiple adsorption mechanisms for pipette-tip solid-phase extraction of auxins in soybean sprouts

A new ionic liquid functionalized graphene-pipette-tip solid-phase extraction method coupled with high-performance liquid chromatography was established for the simultaneous extraction and determination of three auxins in soybean sprouts. The graphene adsorbent, with multiple adsorption mechanisms, was first synthesized by functional modification of pentafluorobenzyl imidazolium bromide ionic liquid through thiol-ene click chemistry. The ionic liquid was applied to prevent the aggregation of graphene; it also imbued graphene with the ability for π-π interactions, ionic exchange, electrostatic interactions, as well as hydrogen bonding (which is stronger than the interaction between water and analytes), by augmenting the adsorption mechanisms between the adsorbent and analytes. Under optimized conditions, linearity was achieved in the ranges 0.03–5.00 µg/g for indole-3-acetic acid and 1-naphthaleneacetic acid and 0.09–5.00 µg/g for 2,4-dichlorophenoxyacetic acid, with a detection limit of 0.004–0.026 µg/g; this adsorbent has been successfully applied for the determination of auxins in soybean sprouts.

Catalyzing polysulfide conversion by g-C3N4 in a graphene network for long-life lithium-sulfur batteries

The practical application of lithium-sulfur batteries with a high energy density has been plagued by the poor cycling stability of the sulfur cathode, which is a result of the insulating nature of sulfur and the dissolution of polysulfides. Much work has been done to construct nanostructured or doped carbon as a porous or polar host for promising sulfur cathodes, although restricting the polysulfide shuttle effect by improving the redox reaction kinetics is more attractive. Herein, we present a well-designed strategy by introducing graphitic carbon nitride (g-C3N4) into a three-dimensional hierarchical porous graphene assembly to achieve a synergistic combination of confinement and catalyzation of polysulfides. The porous g-C3N4 nanosheets in situ formed inside the graphene network afford a highly accessible surface to catalyze the transformation of polysulfides, and the hierarchical porous graphene-assembled carbon can function as a conductive network and provide appropriate space for g-C3N4 catalysis in the sulfur cathode. Thus, this hybrid can effectively improve sulfur utilization and block the dissolution of polysulfides, achieving excellent cycling performance for sulfur cathodes in lithium-sulfur batteries.

Microstructure and properties of silver matrix composites reinforced with Ag-doped graphene

To reduce the aggregation of graphene, Ag particles were introduced in the graphene nanosheets by chemical reduction method, and the silver matrix composite reinforced with Ag-doped graphene nanosheets were fabricated by powder metallurgy. The synthesized Ag-doped graphene were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS), and the relative density, hardness along with electrical conductivity of the silver matrix composite reinforced with Ag-doped graphene were measured as well. The results show that silver ions and graphene oxide can be effectively reduced by ascorbic acid simultaneously, most of oxygen functional groups on the Ag-doped graphene sheets can be removed dramatically, and Ag-doped graphene inhibit the graphene aggregation effectively. Compared with pure Ag, the hardness of the 0.5 wt% Ag-doped graphene reinforced sliver matrix composite is increased by 35.1% and the electrical conductivity reaches up to 98.62% IACS (International Annealed Copper Standard). However, excessive addition of Ag-doped graphene is not beneficial for the improvement on the hardness and electrical conductivity of silver matrix composite.

Gaoquan Shi (1963‐2018): A Pioneer in the Chemistry of Graphene and Electrochemistry of Conjugated Polymers.

Gaoquan Shi (1963‐2018): A Pioneer in the Chemistry of Graphene and Electrochemistry of Conjugated Polymers.

Cost-effective three dimensional Ag/polymer dyes/graphene-carbon spheres hybrids for high performance nonenzymatic sensor and its application in living cell H2O2 detection

We describe a facile method to synthesize a new type of catalyst by electrodepositing Ag nanocrystals (AgNCs) on the different polymer dyes, Poly (methylene blue) (PMB) or Poly (4-(2-Pyridylazo)-Resorcinol) (PAR) modified graphene‑carbon spheres (GS) hybrids. The self-assembled GS take dual advantages of carbon spheres and graphene. Carbon spheres acts as nano-spacers prevent the aggregation of graphene and guarantee the fast electron transfer of GS. Secondly, polymerized dyes used here are beneficial for AgNCs growing as a linker. The effects of dyes on the growth habits, morphologies and catalytic properties for AgNCs were investigated. A novel electrochemical nonenzymatic sensor for hydrogen peroxide (H2O2) detection is fabricated based on the Ag/Polymer dyes/GS ternary composites modified glass carbon electrode (GCE) for the first time. It was found that the proposed electrodes, especially for Ag/PMB/GS/GCE, displayed a peculiar electrocatalytic activity towards H2O2 reduction synergistically as compared to Ag/PAR/GS/GCE or Ag/GS/GCE alone. Ag/PMB/GS/GCE showed a linear response over the H2O2 concentration range of 0.5 to 1112 μM. The detection limit and sensitivity is 0.15 μM and 400 μA mM−1 cm−2, respectively. These outstanding results enable the practical application of Ag/PMB/GS/GCE for the H2O2 tracking released from MCF-7 (human breast cancer cells) with satisfactory results.

Green Synthesis of Three-Dimensional MnO2/Graphene Hydrogel Composites as a High-Performance Electrode Material for Supercapacitors.

Graphene hydrogels (GHs) and their composites have attracted wide attention because of the special structure of graphene assembly and exceptional electrochemical performance as electrodes for energy storage devices. Here, we report a GH with three-dimensional architecture prepared by a hydrothermal method via a self-assembled process in glucose and ammonia system as well as subsequent freeze-drying. The δ-MnO2/GH composite was then obtained by immersing GH in KMnO4 solution with a certain concentration under heat treatment. The asymmetric supercapacitor MnO2/GH//GH consisting of pseudocapacitive nanosheet-like δ-MnO2/GH as the cathode and electric double-layer capacitive GH as the anode provides high energy density of 34.7 W h/kg at a power density of 1.0 kW/kg. Importantly, it is found that the pseudocapacitive behavior of MnO2 has great effects on the rate performance of the supercapacitor, which is identified by kinetic analysis.

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.

(Invited) Graphene Oxide Liquid Crystals and Relevant Functional Nanostructures

Graphene Oxide Liquid Crystal (GOLC) is a newly emerging graphene based material, which exhibits nematic type colloidal discotic liquid crystallinity with orientational ordering of graphene oxide flakes in good solvents, including water. Since our first discovery of GOLC in aqueous dispersion at 2009, this interesting mesophase has been utilized over world-wide for many different application fields, such as liquid crystalline graphene fiber spinning, highly ordered graphene membrane/film production, prototype liquid crystal display and so on. Interestingly, GOLC also allow us a valuable opportunity for the highly ordered molecular scale assembly of functional nanoscale structures. This presentation will introduce our current status of GOLC research particularly focusing on the nanoscale assembly of functional nanostructures. Besides, relevant research works associated to the nanoscale assembly and chemical modification of various nanoscale graphene based materials will be presented.

Compressive deformation mechanism of honeycomb-like graphene aerogels

Graphene aerogels (GAs) are a kind of advanced graphene assemblies, which are quite elastic and can easily restore their original form after compression. The macroscale compression behavior of the GAs is the result of microstructural evolution of the graphene sheets. In this paper, the microstructural compression response of honeycomb-like GAs is investigated via coarse-grained molecular dynamics (CGMD) method. Based on the coarse-grained (CG) model of a single-layer graphene, honeycomb-like structures can be built and arranged layer-by-layer to form the complete GA model. CGMD simulations presented in this work are carried out with a TersoffCG potential, which was developed specifically for single-layer graphene. The effects of layer number, size of the graphene sheets and the interlaminar overlap pattern on the compressive behavior of the GAs are studied. Moreover, the stress distribution in graphene networks of the GAs during the compression process is analyzed. Different microscale strain concentrations and stress localizations are discovered in the GAs with different network patterns. Furthermore, a negative Poisson's ratio of the models within a certain range of compressive strain is found, which is related to both the microstructural arrangement and the deformation of graphene sheet.

Nanoparticle activated and directed assembly of graphene into a nanoscroll

Graphene nanoscrolls (GNS) have emerged as an important class of materials with applications in the field of lubrication, energy storage devices, and catalysis. However, the formation of GNS even with existing advanced experimental techniques could be very challenging. Here, we investigate the ability of diamond, nickel (Ni), platinum (Pt), and gold (Au) nanoparticles (NPs) in activating, guiding, and stabilizing the GNS by performing reactive molecular dynamics (RMD) simulations. NPs of certain diameters, when placed on a free-standing graphene sheet, can activate either wrapping or scrolling of the graphene. This activation is due to non-bonded interactions between graphene and NPs. However, for a complete wrap and scroll formation and its stabilization both graphene-graphene and NPNP interactions were also critical. Surface atoms of Ni and Pt NPs undergo reconstruction during the wrapping or scrolling of graphene, suggesting that the NP-graphene interactions are more favorable as compared to NPNP and graphene-graphene interactions. We have identified new energy criteria which must be satisfied to facilitate a complete GNS formation for the graphene-NP systems investigated in the present study. Overall, our study can provide a new method to design metal-graphene hybrid materials that can be used for a variety of applications.

Dual Electrostatic Assembly of Graphene Encapsulated Nanosheet‐Assembled ZnO‐Mn‐C Hollow Microspheres as a Lithium Ion Battery Anode

AbstractGraphene encapsulated nanosheet‐assembled ZnO‐Mn‐C hierarchical hollow microspheres are produced through a simple yet effective dual electrostatic assembly strategy, followed by a heating treatment in inert atmosphere. The modification of graphene sheets, metal Mn, and in situ carbon leads to form 3D interconnected conductive framework as electron highways. The hollow structure and the open configuration of hierarchical microspheres guarantee good structural stability and rapid ionic transport. More importantly, according to the density functional theory calculations, the oxygen vacancies in the hierarchical microspheres would cause an imbalanced charge distribution and thus the formation of local in‐plane electric fields around oxygen vacancy sites, which is beneficial for the ionic/electronic transport during cycling. Due to this multiscale coordinated design, the as‐fabricated graphene encapsulated nanosheet‐assembled ZnO‐Mn‐C hierarchical hollow microspheres demonstrate good lithium storage properties in terms of high reversible capacity (1094 mA h g−1 at 100 mA g−1), outstanding high‐rate long‐term cycling stability (843 mA h g−1 after 1000 cycles at 2000 mA g−1), and remarkable rate capability (422 mA h g−1 after total 1600 cycles at 5000 mA g−1).

Reduction of graphene oxide by UHV annealing

A series of chemically treated graphene oxide (GO) samples, destined for the preparation of several composite materials, was studied by X‐ray photoelectron spectroscopy (XPS). From their comparison, the 3‐mercaptopropyl trimethoxysilane was identified as the most effective reducing agent among the used procedures. The influence of ultrahigh vacuum annealing up to 600°C on the chemical composition and carbon electronic configuration in reduced GO samples was further investigated by XPS and Auger electron spectroscopy. All the samples before and after thermal treatments were analyzed in situ by XPS and Auger electron spectroscopy, paying a particular attention to the shape of C KVV spectra described by the values of D parameter. The changes of chemical composition and carbon configuration reflected in the D parameter revealed the full reduction of GO to graphene after annealing in ultrahigh vacuum at 600°C. The successful reduction of GO to graphene was also confirmed by Raman spectroscopy. Obtained bulk samples of graphene aggregates remained stable in air, testifying the irreversibility of this reduction.

Controlled Spacing of Few-Layer Graphene Sheets Using Molecular Spacers: Capacitance That Scales with Sheet Number

Preventing graphene sheet aggregation while retaining full accessibility to the total graphene surface area is key to optimizing the performance of graphene supercapacitors. Spacer species can be added to graphene assemblies to prevent aggregation, but typical methodologies do not allow accurate assessment of the extent of sheet separation nor whether spacing groups block some of the surface area. In this work we have grafted sub-10 nm films of aryl spacer groups to chemical vapor deposition-grown few layer graphene (FLG) sheets using aryldiazonium salts. Using a layer-by-layer strategy that relies on individually handling each FLG sheet, 3-sheet stacks were prepared and electrochemically interrogated. By comparing the differential and integral capacitances of modified and unmodified single FLG sheets and 3-sheet stacks, we show that in the 3-sheet stacks of modified FLG, the grafted spacer groups fully separate the FLG sheets and allow complete double layer formation at all FLG-solution interfaces. The s...

Layer-by-layer self-assembly of reduced graphene oxide on bamboo timber surface with improved decay resistance

Because bamboo is easily attacked by many fungi, and conventional preservatives have many disadvantages including environmental pollution and human health damage, bamboo products should be protected with environmentally friendly methods. Herein, a novel and efficient process for fabrication of antifungal bamboo timber by coating with graphene materials is presented. The crystal phase, morphology, microstructure and other physicochemical properties of the as-prepared samples were characterized by XRD, Raman, SEM, EDX, XPS and FTIR. XRD studies and Raman spectrum confirmed that graphene oxide was reduced to graphene aggregates in the one-step hydrothermal reduction process. SEM images proved that reduced graphene oxide (RGO) nanoplates were deposited on bamboo timber surface by layer-by-layer self-assembly. EDX proved the carbon element composition of RGO coating on the bamboo surface. XPS and FTIR indicated strong interaction of hydrogen bond between bamboo substrate and RGO coating. The anti-fungal activity of bamboo timber with RGO coating was improved significantly when bamboo was infected by Gloeophyllum trabeum and Panerochaete chrysosporium.