Assembly Of Graphene Research Articles

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.

Size of graphene sheets determines the structural and mechanical properties of 3D graphene foams

Graphene is recognized as an emerging 2D nanomaterial for many applications. Assembly of graphene sheets into 3D structures is an attractive way to enable their macroscopic applications and to preserve the exceptional mechanical and physical properties of their constituents. In this study, we develop a coarse-grained (CG) model for 3D graphene foams (GFs) based on the CG model for a 2D graphene sheet by Ruiz et al (2015 Carbon 82 103–15). We find that the size of graphene sheets plays an important role in both the structural and mechanical properties of 3D GFs. When their size is smaller than 10 nm, the graphene sheets can easily stack together under the influence of van der Waals interactions (vdW). These stacks behave like building blocks and are tightly packed together within 3D GFs, leading to high density, small pore radii, and a large Young’s modulus. However, if the sheet sizes exceed 10 nm, they are staggered together with a significant amount of deformation (bending). Therefore, the density of 3D GFs has been dramatically reduced due to the loosely packed graphene sheets, accompanied by large pore radii and a small Young’s modulus. Under uniaxial compression, rubber-like stress–strain curves are observed for all 3D GFs. This material characteristic is dominated by the vdW interactions between different graphene layers and slightly affected by the out-of-plane deformation of the graphene sheets. We find a simple scaling law between the density ρ and Young’s modulus E for a model of 3D GFs. The simulation results reveal structure–property relations of 3D GFs, which can be applied to guide the design of 3D graphene assemblies with exceptional properties.

Unraveling crack stability and strain localization in staggered composites by fracture analysis on the shear-lag model

Bio-inspired composites can achieve excellent toughness while maintaining their strength through hierarchical microstructure designs combining strong and brittle reinforcements and soft yet ductile matrices. The interfaces between reinforcements and matrices transfer loads through shear deformation and deflect cracks along themselves to dissipate a considerable amount of energy. In this way, the catastrophic failure, which is common in monolithic reinforced materials due to the severe stress concentration near the defects, is deferred in hierarchical composites. Yet, recent computations and experiments suggest that strain localization arising from the unstable crack propagation along interfaces leads to the composites failure. In this study, fracture analysis is carried out on staggered composites with the brick-and-mortar structure. An analytical formula predicting the onset of strain localization emerges from the analysis and is validated by finite element analysis. Furthermore, showing good agreements with independent tensile tests on multi-layer graphene assemblies, our model demonstrates its applicability to explain the strain localization in composites consisting of interfaces that function through re-formable bonds. Characteristic length scales emerging from the analysis can be used to guide the composites design to optimize material toughness and ductility.

Aggregation prevention: reduction of graphene oxide in mixed medium of alkylphenol polyoxyethylene (7) ether and 2-methoxyethanol.

Graphene has attracted great interest due to its extensive applications in optoelectronic and electronic circuits and devices. However, reduction of graphene oxide (GO) to graphene is a process in which hydrophilic GO converts to hydrophobic graphene. Very little is known about the aggregation of graphene and the cause of performance degradation by general chemical reduction methods as the single reaction medium presents difficulty in satisfying the good dispersion of hydrophilic GO and hydrophobic graphene simultaneously. In this paper, we report a mixed medium of alkylphenol polyoxyethylene (7) ether (OP-7) and 2-methoxyethanol (EGM) for the preparation of graphene. The strong polar nature of EGM provides a good dispersion environment for GO, while the π–π interaction between the π-electrons in nonionic surfactant OP-7 aromatic ring structure and the π-electrons in graphene make the hydrophobic graphene well dispersed and prevent aggregation. Moreover, the reduction temperature is not high and the reduction time is short. The electrical conductivity of graphene without high-temperature treatment reached 14 000 S m−1. We have found the potential reduction mechanism of graphene and fundamentally solved the problem of aggregation. Our findings make it possible to process graphene materials using low-cost mixed medium processing techniques, providing a valuable reference for the large-scale preparation of graphene.

Spontaneous rolling-up and assembly of graphene designed by using defects.

The inverse Stone-Wales defect is a typical defect in graphene, which causes local bumps and local deformation in graphene sheets. Our molecular dynamics simulations show that the spontaneous rolling up of graphene sheets can be induced by orderly distributed inverse Stone-Wales defect bumps, when defective graphene is cut into small strips. This spontaneous process is mainly dominated by the defect density and tailored graphene size. When the tailored length is longer than the upper threshold length, graphene sews up as a curly one-dimensional structure: heart-shaped nanotube. For medium length graphene (the length is in between the lower threshold value and upper threshold value), the results reveal that graphene finally curls into a completely or incompletely stitched nanotube similar to a cylindrical shell. This spontaneous process is produced by a high-frequency damped vibration accompanied by elastic and viscoelastic deformation in defective graphene. Thus, the properties of vibration are further investigated for graphene that has the tailored length shorter than the lower threshold length. This kind of graphene gradually forms a curved nanoribbon rather than a nanotube. It is also found that the bending rigidity of defective graphene is larger than that of pristine graphene.

An ionic liquid-magnetic graphene composite for magnet dispersive solid-phase extraction of triazine herbicides in surface water followed by high performance liquid chromatography.

A new ionic liquid-magnetic graphene (IL-MG) composite was used as the adsorbent in magnetic dispersive solid-phase extraction to rapidly extract and isolate triazine herbicides from surface water. IL-MG was synthesized by a simple and time-saving one-pot strategy where the synthesis of magnetic Fe3O4, the modification with an IL, and the reduction of graphene oxide to graphene were conducted at the same time. An IL was applied to enrich the interaction mechanism between IL-MG and analytes (π-π, hydrophobic interaction, and electrostatic interaction). Moreover, the IL and Fe3O4 nanoparticles acted as spacers, inserting between the layers of graphene to prevent the aggregation of graphene, which improved the adsorption ability because of the large specific surface area of IL-MG. The resultant IL-MG had hierarchical flake structures and showed a high adsorption capacity (8266.0-12 324.1 μg g-1) toward triazine herbicides. Under suitable conditions, the linearity for triazine herbicides was achieved in the range of 0.55-500 ng mL-1 with a detection limit of 0.09-0.15 ng mL-1 and a quantitation limit of 0.31-0.51 ng mL-1, and the enrichment factor was 83-fold, which indicated that the proposed method could be successfully applied for the determination of triazine herbicides in surface water.

Photoluminescence mechanism and applications of Zn-doped carbon dots.

Heteroatom-doped carbon dots (CDs) with excellent optical characteristics and negligible toxicity have emerged in many applications including bioimaging, biosensing, photocatalysis, and photothermal therapy. The metal-doping of CDs using various heteroatoms results in an enhancement of the photophysics but also imparts them with multifunctionality. However, unlike nonmetal doping, typical metal doping results in low fluorescence quantum yields (QYs), and an unclear photoluminescence mechanism. In this contribution, we detail results concerning zinc doped CDs (Zn-CDs) with QYs of up to 35%. The zinc ion charges serve as a surface passivating agent and prevent the aggregation of graphene π–π stacking, leading to an increase in the QY of the Zn-CDs. Structural and chemical investigations using spectroscopic and first principle simulations further revealed the effects of zinc doping on the CDs. The robust Zn-CDs were used for the ultra-trace detection of Hg2+ with a detection limit of 0.1 μM, and a quench mechanism was proposed. The unique optical properties of the Zn-CDs have promise for use in applications such as in vivo sensing and future phototherapy applications.

A novel three-dimensional pyridine-pillared graphene assembly for enhanced electron transfer and photocatalytic hydrogen evolution

Novel 1,2-di(pyridine-4-ly)ethyne pillared GO composites with high photocatalytic activity were achieved with rare earth ions as interfacial linkers.

Chemical vapour deposition of freestanding sub-60 nm graphene gyroids

The direct chemical vapour deposition of freestanding graphene gyroids with controlled sub-60 nm unit cell sizes is demonstrated. Three-dimensional (3D) nickel templates were fabricated through electrodeposition into a selectively voided triblock terpolymer. The high temperature instability of sub-micron unit cell structures was effectively addressed through the early introduction of the carbon precursor, which stabilizes the metallized gyroidal templates. The as-grown graphene gyroids are self-supporting and can be transferred onto a variety of substrates. Furthermore, they represent the smallest free standing periodic graphene 3D structures yet produced with a pore size of tens of nm, as analysed by electron microscopy and optical spectroscopy. We discuss generality of our methodology for the synthesis of other types of nanoscale, 3D graphene assemblies, and the transferability of this approach to other 2D materials.

PEO-Linked MoS2–Graphene Nanocomposites with 2D Polar–Nonpolar Amphoteric Surfaces as Sulfur Hosts for High-Performance Li–S Batteries

Layered MoS2–graphene nanocomposites with 2D polar–nonpolar amphoteric surfaces, which were used to confine sulfur for Li–S batteries, have been successfully fabricated through the assembly of polar MoS2 layers and nonopolar graphene with poly(ethylene oxide) cross-linking. Benefiting from the high conductivity of graphene and the strong chemical bonding between polar MoS2 and polysulfides, the MoS2–graphene composites not only ensure unimpeded electrical conducting to the insulating sulfur but also effectively entrap polysulfides therein. The ex situ study further reveals that the MoS2–graphene composites enable spatially regulated Li2S deposition by the preferential deposition of solid Li2S product onto the polar MoS2 layers, making a large amount of fast electron transport paths exposed on graphene for further sulfur reduction. Therefore, the obtained MoS2–sulfur–graphene nanocomposites present excellent rate performance and cycling stability with high reversible capacities of 895 mA h g–1 at 0.2 C aft...

Effect of graphene nanoplatelet edges on the iodide/triiodide redox reaction

Carbon electrodes have been extensively studied for the development of Pt-free dye-sensitized solar cells. In this study, the influence of graphene nanoplatelet edges on the activity of an electrolyte reaction was investigated. The reaction activities of graphene nanoplatelet aggregates (GNAs) and graphene nanoplatelets (GNs), which have different surface areas, were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The charge transfer resistances (RCT) of the GNAs and GNs were determined from EIS to be 12Ω and 1.4×103Ω, respectively. The coefficient components (AW) of the diffusion impedance, known as the Warburg impedance, of GNAs and GNs were 63ΩHz0.5 and 1.2×102ΩHz0.5, respectively. From these results, it was found that the edge plane area of the graphene aggregates affects both the reaction resistance and electrolyte diffusion in the carbon film.

Hierarchical hole-enhanced 3D graphene assembly for highly efficient capacitive deionization

A hole-rich graphene framework (HGF) has been successfully prepared through lyophilization combined with thermal treatment at 200 °C. As the advanced three-dimensional (3D) graphene mesh assembly, the monolithic HGF was directly compacted to form capacitive deionization (CDI) electrode without grinding and binder so that the intact 3D structure can be reserved. The presence of original 3D structure combined with hierarchical hole structure in HGF plays important role in improving the CDI performance. The desalination capacities of HGF can reach up to 8.0 mg g−1, 16.9 mg g−1, and 29.6 mg g−1 in NaCl aqueous of 80 mg L−1, 270 mg L−1, and 572 mg L−1 respectively, which significantly exceeds other carbon-based materials at 2.0 V.

Preparation of thermo/pH-sensitive reduced graphene oxide interpenetrating hydrogel nanocomposites for co-delivery of paclitaxel and epirubicin

This study aimed to develop a thermo/pH-sensitive hydrogel for co-delivery of paclitaxel (PTX) and epirubicin (EPI) in tumor combination chemotherapy. First, pluronic F127/reduced graphene oxide (PF127/RGO) nanocomposites were prepared through the simultaneous reduction of graphene oxide and assembly of PF127 and RGO. Then, PTX was loaded onto PF127/RGO (PTX@PF127/RGO) by π–π stacking and hydrophobic interaction. Second, graphene double network hydrogels (GDL) were prepared using poly(N-isopropylacrylamide) and polyacrylic acid as crosslinked network and PTX@PF127/RGO as an additive. The structure and properties were investigated by infrared spectroscopy (IR), scanning electron microscopy (SEM), swelling rate tests (SR), and differential scanning calorimetry (DSC). Lastly, the hydrophilic drug EPI was encapsulated in the GDL matrix (EPI@PTX@GDL), which showed thermo/pH-dependent releasing behavior. Cell viability experiments demonstrated that the EPI@PTX@GDL showed a superior cytotoxicity against MCF-7 cells than single drug-loaded forms, whereas the blank GDL and RGO displayed no obvious cytotoxicity.

New Nanocomposite Materials with Improved Mechanical Strength and Tailored Coefficient of Thermal Expansion for Electro-Packaging Applications

In this research, copper nanocomposites reinforced by graphene nanoplatelets (GNPs) were fabricated using a wet mixing method followed by a classical powder metallurgy route. In order to find the best dispersion technique, ball milling and wet mixing were chosen. Qualitative evaluation of the structure of the graphene after mixing indicated that the wet mixing is an appropriate technique to disperse the GNPs. Thereafter, the influence of graphene content on microstructure, density, hardness, elastic modulus, and thermal expansion coefficient of composites was investigated. It was shown that by increasing the graphene content the aggregation of graphene is more obvious and, thus, these agglomerates affect the final properties adversely. In comparison with the unreinforced Cu, Cu–GNP composites were lighter, and their hardness and Young’s modulus were higher as a consequence of graphene addition. According to the microstructural observation of pure copper and its composites after sintering, it was concluded that grain refinement is the main mechanism of strengthening in this research. Apart from the mechanical characteristics, the coefficient of thermal expansion of composites decreased remarkably and the combination of this feature with appropriate mechanical properties can make them a promising candidate for use in electronic packaging applications.

A novel electroconductive graphene/fly ash-based geopolymer composite and its photocatalytic performance

Fly ash-based geopolymer (FAG) possesses extremely low electroconductivity (0.00086 S/m). A new study indicates that graphene could be used as an electron acceptor to improve electroconductivity of geopolymer. In this paper, an electroconductive graphene (GR)/fly ash-based geopolymer (GR/FAG) composite was synthesized by assembly of graphene into the matrix of alkali-activated fly ash-based geopolymer for first time. The results showed that the electroconductivity increased by 348.8 times when adding 1 wt% GR in FAG. The electrochemical impedance of 1.0GR/FAG was much smaller than that of the pure FAG. The N2 adsorption-desorption isotherms indicated that the graphene could effectively improve the microstructure and pore parameters of FAG. The SEM and EDS results displayed the flake graphene was covered by amorphous fly ash-based geopolymer gels. The XPS results demonstrated that the CC/CC binding energy was predominant surface state. The results of UV–Vis-DRS and PL spectra revealed that the absorption onsets of GR/FAG composites were red-shifted and the photoluminescence intensities progressively decreased with increasing graphene content. The photocatalytic degradation of indigo carmine dye was positive correlation with the electroconductivity of GR/FAG composite, and underwent a degradation mechanism of hydroxyl radical.

Carbon Nanotubes Loaded on Graphene Microfolds as Efficient Bifunctional Electrocatalysts for the Oxygen Reduction and Oxygen Evolution Reactions

AbstractAdvanced bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are promising to improve the efficiency of fuel cells and metal–air batteries. Among the state‐of‐the‐art efficient oxygen electrocatalysts, heteroatom‐doped carbon materials are favorable candidates. However, the enriched doping requires a highly exposed carbon skeleton. Here, we report a scalable route to prepare carbon nanotubes (CNTs) loaded on graphene microfolds (CGFs) by a low‐temperature spray‐drying procedure. Molecular‐level assembly of graphene and CNTs, mesoporous structures, and large specific surface areas permit the carbon skeleton of CGFs to be highly exposed. After doping with abundant nitrogen and phosphorous (5.58 at % for N, 0.1 at % for P), CGFs exhibit excellent bifunctional electrocatalytic activity for both the ORR and OER, with superb durability and methanol tolerance. The measured variance of the ORR and OER metrics (ΔE=Ej=10−E1/2) was low at 0.9 V versus reversible hydrogen electrode (vs. RHE), being within only 20 mV of Pt‐ and Ru‐based electrodes, and superior to transition‐metal‐based catalysts and other carbon catalysts. Such efficient overall electrocatalytic activity allows CGFs to be used for high‐performance oxygen electrodes in renewable energy devices.

Recent Advances in Sensing Applications of Graphene Assemblies and Their Composites

AbstractDevelopment of next‐generation sensor devices is gaining tremendous attention in both academia and industry because of their broad applications in manufacturing processes, food and environment control, medicine, disease diagnostics, security and defense, aerospace, and so forth. Current challenges include the development of low‐cost, ultrahigh, and user‐friendly sensors, which have high selectivity, fast response and recovery times, and small dimensions. The critical demands of these new sensors are typically associated with advanced nanoscale sensing materials. Among them, graphene and its derivatives have demonstrated the ideal properties to overcome these challenges and have merged as one of the most popular sensing platforms for diverse applications. A broad range of graphene assemblies with different architectures, morphologies, and scales (from nano‐, micro‐, to macrosize) have been explored in recent years for designing new high‐performing sensing devices. Herein, this study presents and discusses recent advances in synthesis strategies of assembled graphene‐based superstructures of 1D, 2D, and 3D macroscopic shapes in the forms of fibers, thin films, and foams/aerogels. The fabricated state‐of‐the‐art applications of these materials in gas and vapor, biomedical, piezoresistive strain and pressure, heavy metal ion, and temperature sensors are also systematically reviewed and discussed, and their sensing performance is compared.

Nanostructured Three-Dimensional (3D) Assembly of 2D MoS2 and Graphene Directly Build From Acidic Graphite Oxide.

A 3D highly interconnected macroporous network of reduced GO having finely dispersed few-layered 2D MoS2 nanosheets was constructed through direct use of acidic graphite oxide (GO) for the first time. This facile and technologically scalable process can afford efficient hydrodesulfurization electrocatalysts as potential anode materials at lower cost, and can circumvent the poor thermal stability and recyclability of the material. The strategy provided here can be the basis to design and develop practical processes to address the ultimate goal of large-scale manufacturing of hybrids composed of 2D materials for various energy and catalysis applications.

Hemoglobin immobilized in g-C3N4 nanoparticle decorated 3D graphene-LDH network: Direct electrochemistry and electrocatalysis to trichloroacetic acid

A 3D hybrid of graphitic C3N4 nanoparticle decorated in the assembly of graphene and Co2Al layered double hydroxide nanosheets (GR-LDH-C3N4) was prepared by simple hydrothermal treatment and subsequent calcination-recovery process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy clearly demonstrated that the g-C3N4 nanoparticle was successful incorporated into the porous GR-LDH nano-scaffold. Then the conductive composite and chitosan (CTS) were used to immobilize hemoglobin (Hb) on a carbon ionic liquid electrode (CILE) for fabrication of a trichloroacetic acid (TCA) biosensor. The spectroscopic results revealed that the immobilized Hb retained the native catalytic activity and conformation. Electrochemical results indicated that the GR-LDH-C3N4 film possessed the large electroactive surface area and fast heterogeneous electron transfer rate. Due to synergistic effects of three components, CTS/GR-LDH-C3N4-Hb/CILE gave rise to the excellent direct electrochemistry and electrocatalytic activity toward TCA. This bioelectrode exhibited a wide linear detection range from 0.2 to 36.0mM with a low detection limit of 0.05mM (3σ). The Michaelis–Menten constant of the developed bioelectrode was obtained as 3.30mM. Thus, the 3D porous GR-LDH-C3N4 architecture is a promising material for construction of the third-generation biosensors.