Agglomeration Of Graphene Research Articles

One-pot method to reduce and functionalize graphene oxide via vulcanization accelerator for robust elastomer composites with high thermal conductivity

A high-efficiency and rapid one-step approach was developed to simultaneously reduce and functionalize graphene oxide (GO) with vulcanization accelerator 2-mercaptobenzothiazole (M) under mild conditions (2 h, 80 °C, neutral and non-toxic environmental condition). The reduced GO chemically grafted with ca. 25 wt% M (M-G) not only eliminated the harmful blooming of vulcanization accelerator but also reduced the irreversible graphene agglomerates and improved the compatibility between graphene and elastomer, aiding the uniform dispersion of M-G nanosheets in elastomer matrix and enhancing the graphene-elastomer interfacial interaction. As a result, elastomer composites with M-G nanosheets showed much better combination of high tensile strength, large extensibility and superior thermal conductivity than elastomer composites with hydrazine hydrate reduced GO containing equal filler and vulcanization accelerator contents. The approach of using rubber additives to reduce and functionalize GO may provide some new insights in the green production of organically modified graphene and in the designing of high performance rubber/graphene materials.

Effect of functional groups on the agglomeration of graphene in nanocomposites

A base wash procedure was used to partially remove the oxygen functional groups from the graphene oxide (GO) flakes to prepare the base-washed GO (BwGO). It is found that the base wash treatment does not alter the physical properties (size, thickness etc.) of the GO significantly but the chemical composition is changed. Nanocomposites were prepared by incorporating the BwGO flakes obtained in a poly(vinyl alcohol) (PVA) matrix. It was found the storage modulus of the nanocomposites is enhanced from 4.4 GPa to 6.5 GPa with 5 wt% of BwGO. This is in agreement with the micromechanical estimation obtained by using Raman spectroscopy that follows the interfacial stress transfer from the matrix to the BwGO fillers. The lower effective modulus of BwGO than GO as calculated using the classical ‘rule of mixtures’ is due to the loss of functional groups on GO that serve as a surfactant to prevent the flakes from re-agglomerating. An agglomeration factor ηa is therefore proposed and a concept of ‘effective volume fraction’ is introduced to quantify and evaluate the level of agglomeration of fillers in nanocomposites, which can be otherwise difficult to visualize optically. It is found that the removal of the functional groups causes the flakes to re-agglomerate, and reduces the ‘effective volume fraction’ by about 10–20%.

Aramid Nanofiber/Graphene/Carbon Nanotube Composite Electrodes for Structural Energy and Power

Multifunctional energy storage devices could prevent catastrophic failure in batteries or act as structural elements in vehicles, such electric cars and unmanned aerial vehicles, by simultaneously dissipating energy and bearing a load. Graphene is particularly interesting for multifunctional energy storage devices. Graphene paper has exhibited high stiffness (41.8 GPa) and graphene based supercapacitors have shown high capacity (205 F/g). However, mechano-electro-chemical coupling in multifunctional materials is largely unexplored. Herein we report on multifunctional composite electrodes consisting of graphene, aramid nanofibers (ANFs), and carbon nanotubes (CNTs) using vacuum-assisted self-assembly. CNTs were used to prevent graphene agglomeration and improve through plane conductivity. ANFs are nanoscale building blocks created from Kevlar thread, which is well known for its extremely high stiffness and strength. We hypothesize that the ANFs reinforce the composite and improve mechanical properties. The effects of CNTs and ANFs are explored by varying the amount of each component present in the composite. Electrochemical performance is evaluated using cyclic voltammetry and galvanostatic charge/discharge while mechanical performance is evaluated using tensile testing. Finally, plans for testing mechano-electro-chemical coupling are discussed.

Preparation of flower-like CoFe2O4@graphene composites and their microwave absorbing properties

Novel flower-like CoFe2O4@graphene composites were prepared using a spray drying technique in combination with a solvothermal method, followed by calcination. Hundreds of uniform CoFe2O4 microspheres are encapsulated with gauzy graphene to form large flower-like composites. This unique structure effectively reduces agglomeration of graphene and enhances microwave absorption performances. The minimum reflection loss of as-obtained flower-like CoFe2O4@graphene composites reaches −42 dB at 12.9 GHz with a thickness of 2 mm, and the effective absorption frequency (RL < −10 dB) is 4.59 GHz from 11.2 to 15.79 GHz. Flower-like CoFe2O4@graphene composites show better microwave absorbing performance than pure CoFe2O4 microspheres. These CoFe2O4@graphene composites are promising as light weight, broad frequency bandwidth and strong absorption microwave absorbers.

Effect of reduced graphene oxide-carbon nanotubes hybrid nanofillers in mechanical properties of polymer nanocomposites

Graphene and carbon nanotubes (CNTs) have tremendous interest as reinforcing fillers due to their excellent physical properties. However, their reinforcing effect in polymer matrix is limited due to agglomeration of graphene and CNTs within the polymer matrix. Mechanical properties by the admixture of reduced graphene oxide (rGO) and CNTs in Poly (methyl methacrylate) (PMMA) prepared by solution mixing method has been investigated. The prepared samples are characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and Raman spectroscopy. The hybrid composite shows improvement in the mechanical properties compared to rGO/PMMA and MWCNTs/PMMA composites due to better interaction between rGO-MWCNTs and polymer matrix.

Intercalation Polymerization Approach for Preparing Graphene/Polymer Composites.

The rapid development of society has promoted increasing demand for various polymer materials. A large variety of efforts have been applied in order for graphene strengthened polymer composites to satisfy different requirements. Graphene/polymer composites synthesized by traditional strategies display some striking defects, like weak interfacial interaction and agglomeration of graphene, leading to poor improvement in performance. Furthermore, the creation of pre-prepared graphene while being necessary always involves troublesome processes. Among the various preparation strategies, an appealing approach relies on intercalation and polymerization in the interlayer of graphite and has attracted researchers’ attention due to its reliable, fast and simple synthesis. In this review, we introduce an intercalation polymerization strategy to graphene/polymer composites by the intercalation of molecules/ions into graphite interlayers, as well as subsequent polymerization. The key point for regulating intercalation polymerization is tuning the structure of graphite and intercalants for better interaction. Potential applications of the resulting graphene/polymer composites, including electrical conductivity, electromagnetic absorption, mechanical properties and thermal conductivity, are also reviewed. Furthermore, the shortcomings, challenges and prospects of intercalation polymerization are discussed, which will be helpful to researchers working in related fields.

The Effect of CNTs on Performance Improvement of rGO Supported Fe-Nx/C Electrocatalysts for the Oxygen Reduction Reaction

As a widely investigated category of non-precious metal electrocatalysts for the oxygen reduction reaction (ORR), metal-Nx-C materials are gaining increasing attention both in the rational synthesis of catalysts and in the study of structure-activity relationships. Carbon supports are important to the performance of these catalysts toward the ORR. Graphene has been used in many electrocatalysts due to its notable characteristics, such as large specific surface area, and high conductivity, but it is further limited by the tendency to agglomerate. Here, carbon nanotubes (CNTs) were employed to effectively suppress the agglomeration of graphene. The binary carbon complex was loaded with iron phthalocyanine (FePc), achieving better activity than commercialized Pt/C (30 wt%) with a positive shift of half-wave potential of 20 mV after heat-treatment at 750°C. SEM, TEM, XPS and XAS measurements revealed that the insertion of CNTs not only suppressed the stacking of graphene layers, but also enhanced the catalytic performance during the RRDE and Zn-air battery tests in alkaline electrolyte by exposing more ORR active sites in the Fe-Nx structure.

Enhanced local controllable laser patterning of polymers induced by graphene/polystyrene composites

To achieve an enhanced local controllable laser patterning for polymers, the composite powder of graphene/polystyrene was successfully designed and prepared. The design idea of this composite was inspired by the π-π stacking (interaction) between aromatic rings of polystyrene (PS) and basal planes of graphene. Compared with pure graphene, the results showed that only 0.0038wt% (38ppm) of the graphene/PS composite powder endowed polymers with an enhanced laser patterning performance. The results of SEM revealed that many spherical PS particles (340–370nm) were tightly adsorbed to the surface of graphene via π-π stacking, serving as the isolating substance to successfully prevent the graphene re-agglomeration. Both XPS and micro-Raman spectroscopy observed that, after irradiation of 1064nm near infrared (NIR) pulsed laser, the carbonization degree of polymer using the composite powder of graphene/PS was much higher than that of only using pure graphene. This far higher degree of carbonization was contributed from the dual role of the local carbonization of PS particles in the composite and the good dispersity of the composite powder, resulting in a much better contrast to the patterns. Importantly, after using this new composite powder, the defect in patterns caused by graphene agglomeration also no longer existed.

Alginate affects agglomeration state and uptake of 14C-labeled few-layer graphene by freshwater snails: Implications for the environmental fate of graphene in aquatic systems.

Understanding of the interaction of graphene with natural polysaccharides (e.g., alginate) is crucial to elucidate its environmental fate. We investigated the impact of alginate on the agglomeration and stability of 14C-labeled few-layer graphene (FLG) in varying concentrations of monovalent (NaCl) and divalent (CaCl2) electrolytes. Enhanced agglomeration occurred at high CaCl2 concentrations (≥5mM) due to the alginate gel networks formation in the presence of Ca2+. FLG enmeshed within extended alginate gel networks was observed under transmission electron microscope and atomic force microscope. However, background Na+ competition for binding sites with Ca2+ at the alginate surfaces shielded the gelation of alginate. FLG was readily dispersed by alginate under environmentally relevant ionic strength conditions (i.e., <200mM Na+ and <5mM Ca2+). In comparison with the bare FLG, the slow sedimentation of the alginate-stabilized FLG (158μg/L) caused continuous exposure of this nanomaterial to freshwater snails, which ingested 1.9 times more FLG through filter-feeding within 72h. Moreover, surface modification of FLG by alginate significantly increased the whole-body and intestinal levels of FLG, but reduced the internalization of FLG to the intestinal epithelial cells. These findings indicate that alginate will act as a stabilizing agent controlling the transport of FLG in aqueous systems. This study also provides the first evidence that interaction of graphene with natural polysaccharides affected the uptake of FLG in the snails, which may alter the fate of FLG in aquatic environments.

Significant improvement in static and dynamic mechanical properties of graphene oxide–carbon nanotube acrylonitrile butadiene styrene hybrid composites

Herein, hybridization of graphene nanosheets and carbon nanotubes (CNTs) has been made to solve the problem of restacking of graphene nanosheets and agglomeration of CNTs. The multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO) and graphene oxide–carbon nanotubes (GCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites have been prepared using micro-twin-screw extruder. The effect of these reinforcements on static and dynamic mechanical properties of composites is studied. The ultimate tensile strength and elastic modulus for 7 wt.% GCNT–ABS composites show enhancement of 26.1 and 71.3% over pure ABS matrix, respectively. Various parameters such as coefficient “C” factor (the ratio of storage modulus of the composite to polymer in glassy and rubbery regions), degree of entanglement, crosslink density and adhesion factor have been calculated to analyze the interaction between fillers and polymer matrix. The 3-D hybrid structure of GCNTs overcomes the associated problem of CNTs agglomeration and graphene restacking. GCNT hybrid composites show higher dispersion as well as effectiveness for increased filler amount as compared to RGO and MWCNTs based composites. GCNTs prove its superiority over MWCNTs and RGO by showing a synergistic effect in the glass transition temperature and storage modulus. Raman spectroscopy and scanning electron microscopy are used to confirm the interaction and distribution of the filler and matrix, respectively.

Graphene conductive additives for lithium ion batteries: Origin, progress and prospect

This paper gives a critical review on the scientific origin, current research progresses and application prospects of graphene conductive additives applied in lithium-ion batteries (LIBs) and emphasizes that the electron transport (enhancement of electron conductance by graphene) and ion diffusion (steric effect of graphene for ion diffusion) should be considered comprehensively for a real mass application. Due to the high electronic conductivity, two-dimensional planar geometrical structure and the ″most flexible and thinnest″ character, our group proposed that graphene is a very promising conducting additive for LIBs. Through ″plan-to-point″ contact model with active material particles, graphene can improve the electronic conductivity of the electrode laminate with much less addition fraction, and hence enhance the energy density of the LIBs. Therefore, graphene shows much better performance than other types of conductive additives, such as carbon black, conducting graphite and even carbon nanotube. Due to the size difference of active material particles, the optimized addition fraction of graphene is different. For example, 2 wt% of graphene works best for LiFePO4, while the most suitable addition amount of graphene in LiCoO2 is only 1 wt%. At the same time, graphene and conducting carbon black can work together to construct a much more efficient conductive network. This kind of binary conductive additive can build high speed pathway for electron both in long and short distance (that is, electrons can transport in the whole electrode and gain access to the whole surface of the active material particle simultaneously), and further improve the electrochemical performance of active materials. Hence, hybrid material containing graphene and carbon black is fabricated to use directly as a novel binary conductive additive. Other than the improvement of the electron conduction, the introduction of graphene brings a bottleneck for its application in LIBs, which has been reported by our group in 2012 based on a 10 Ah LIB using graphene as conductive additive, that is, the steric effect for lithium ion diffusion. Ion diffusion in the porous electrode will be retarded by planar graphene because it is very hard to penetrate through the hexagonal carbon ring for lithium ions. Many efforts have been made by our group to illustrate this effect. We found that it is the thickness and tortuosity of the electrode laminate that determines and the situation varies with different active material. When it comes to LiFePO4, the ion steric effect is not obvious when the electrode is thin (e.g. thinner than 26 μm). When the electrode sheet is thicker (>39 μm), the rate performance of LiFePO4 becomes worse when the graphene addition increases. However, when it comes to LiCoO2, which is large in particle size, the steric effect from graphene disappears. It can be attributed to the pore tortuosity of the electrode. Since the particle size of LiCoO2 is much larger, the electrode is not as tortuous as that of LiFePO4 electrode. Therefore, ions diffuse easily along the electrode thickness direction. Nevertheless, it should be noted that the steric effect in LiFePO4 electrode can be elimated by introducing pores on the surface of graphene or making ribbon-like graphene to provide more diffusion path for lithium ions in the porous electrode. From the practical points, the dispersion of graphene in the active materials is a vitally important but a tough job. In order to construct an efficient conducting network, graphene should be well dispersed and cover every particle of the active material in the electrode. Agglomeration of graphene will not construct a good conducting network, and even bring adverse effects for the ion diffusion. Normal mixing equipments alone cannot ensure good dispersion of graphene, and ultrasonication is an efficient pre-treatment step. New techniques with higher dispersion efficiency are expected to realize really uniform and monolayered dispersion of graphene in active materials, which is very important for mass application of graphene additives in LIBs.

In-Situ Fabrication of MOF-Derived Co-Co Layered Double Hydroxide Hollow Nanocages/Graphene Composite: A Novel Electrode Material with Superior Electrochemical Performance.

Rational design of a transition metal layered double hydroxide (LDH) and graphene composite is vitally important for designing high-performance supercapacitor electrodes. Although various methods are performed, the realization of high-performance is still impeded by the agglomeration of graphene and layered double hydroxide. Here, metal-organic framework derived cobalt-cobalt layered double hydroxide (Co-Co LDH) hollow nanocages, uniformly deposited on graphene nanosheets, are fabricated through facile in situ co-deposition and thermal ion-exchange reaction. Electrochemical investigation reveals that Co-Co LDH/15 mg graphene is rather outstanding, which delivers high specific capacitance of 1205 F g-1 , excellent rate capability (60.3 % capacitance retention is obtained after the current density increased 6.67 times), and cycling stability. The excellent performance of electrode is also confirmed by assembling an asymmetric supercapacitor, which delivers high energy density of 49.5 Wh kg-1 as well as the maximum power density of 7000 W kg-1 . The Co-Co LDH/graphene composite proves a promising concept for constructing hierarchical structure materials in the future.

Flexible Polyaniline/Reduced Graphene Oxide/Carbon Fibers Composites Applied As Electrodes for Supercapacitors

Introduction Reduced graphene oxide has received extraordinary attention due to its many special properties, such as good conductivity, mechanical resistance, high accessible surface area (2630 m2 g-1), and good flexibility. These properties makes it the best candidate for flexible electrode materials. Nevertheless, according the literature, the facile agglomeration of graphene, due to the strong Π-Π interactions between their individual sheets, decreases the performance of graphene based materials [1]. In this context, the carbon fibers have been shown to be an ideal support for reduced graphene oxide (rGO). The carbon fiber (CF) offers the advantage for using as electrodes because its 3D structure decreases the packaging of the graphene sheets. In addition, it is not necessary any substrates or binders to prepare the binary composite rGO/CF. Thus, the use of CF is a plausible strategy to maximize the energy density of supercapacitors due to its high surface area as well as its good thermal and chemical stabilities. On the other hand, Polyaniline (PAni) has been considered as a promising pseudocapacitive material due to its high theoretical specific capacitance, low cost, high conductivity, and easy synthesis. In this work were proposed a combination of both double layer capacitance (binary composite rGO/CF) and ternary composite of PAni/rGO/CF associating the PAni pseudocapacitance to enhance this electrode capacitive response. The rGO/CF and PAni/rGO/CF samples were evaluated electrochemically, aiming their performance as electrodes in supercapacitors. Experimental Part CF samples were produced from polyacrylonitrile (PAN) precursor at heat treatment temperature of 1000 ºC using temperature steps of 330 ºC/h under inert atmosphere of nitrogen, reaching the maximum during 30 min up to its cooling down to room temperature. CF were cut in size of 1 cm2 and previously weighed. The rGO electrodeposition on CF was performed under potentiostatic mode, at a fixed potential of -1.25 V vs. Ag/AgCl/KCl(sat) for 15 min in a 25 mL of the graphene oxide (3mg mL-1) + 0.1 mol L-1 LiClO4 aqueous solution. In sequence, the PAni was electrodeposited on rGO/CF binary composite under galvanostatic mode with current density of 5 mA cm2 for 10 min in 0.5 mol L-1 H2SO4 aqueous with 0.1 mol L-1 aniline. The obtained ternary composite PAni/rGO/CF was washed in acid solution and vacuum dried. The morphological and structural analysis were obtained by Scanning Electronic Microscopy with field emission gun (SEM-FEG) and Raman spectroscopy, respectively. The electrode electrochemical characterizations were studied by cyclic voltammetry (CV) and charge/discharge tests. These measurements were performed in 1.0 mol L-1 H2SO4solution using a conventional three electrode cell. Results and discussion The SEM-FEG images showed aggregates with irregular and flakes-like shape and high particle density on CF substrate, which is a characteristic of the rGO. After electrochemical deposition, an uniform PAni coating was observed on binary rGO/CF composite, as shown in Figure 1 (b). Their Raman spectrum showed the characteristic C-Ṅ+ stretching vibration bands of the radical cations observed between 1319 cm-1 and 1340 cm-1 related to PAni emeraldine salt. The ternary composite CV curves presented a quasi rectangular shape with apparent redox peaks characteristic of emeraldine salt, indicating that the charge storage occurs by two process, the electric double layer and pseudocapacitive reactions. The charge-discharge profile of the PAni/rGO/CF electrodes, carried out at a current density of 1 mA cm-1, showed linear charge/discharge profile which indicates that capacitance is mainly due to electric double layer formation. The curves of the PAni/rGO/CF ternary composite showed a long time of the charge/discharge, improving the capacitance value, probably attributed to the electrode high surface area associated with the PAni pseudocapacitive behavior. Conclusion The PAni/rGO/CF composite electrodes were synthesized by electrochemical polymerization. The ternary composite presented a better performance in terms of specific capacitance and electrochemical reversibility than those of the conventional PAni films. The results showed that this ternary composite has a great potential as new promising electrode for applications in supercapacitors. Acknowledgments This work was supported by FAPESP 2016/13393-9, CAPES 086/2013 e CNPq. References S. Wang et al. Journal of Power Sources 299 (2015) 347-355. Figure 1

A Novel Cu–GNPs Nanocomposite with Improved Thermal and Mechanical Properties

Classical powder metallurgy followed by either hot isostatic pressing (HIPing) or repressing–annealing process was used to produce Cu–graphene nanoplatelets (GNPs) nanocomposites in this work. A wet mixing method was used to disperse the graphene within the matrix. The results show that a uniform dispersion of GNPs at low graphene contents could be achieved, whereas agglomeration of graphene was revealed at higher graphene contents. Density evaluations showed that the relative density of pure copper and copper composites increased by using the post-processing techniques. However, it should be noticed that the efficiency of HIPing was remarkably higher than repressing–annealing process, and through the HIPing, fully dense samples were achieved. The Vickers hardness results showed that the reconsolidation steps can improve the mechanical strength of the specimens up to 50% owing to the progressive porosity elimination after reconsolidation. The thermal conductivity results of pure copper and composites at high temperatures showed that the post-processing techniques could enhance the conductivity of materials significantly.

Hierarchical architecture of ultrashort carbon nanotubes/polyaniline nanocables coated on graphene sheets for advanced supercapacitors

Multilayer super-short carbon nanotubes (SSCNTs) could be prepared by tailoring raw multiwalled carbon nanotubes (MWCNTs) with mechanical-stirring and ultrasonic oxidation-cut method. The SSCNTs/polyaniline/reduced graphene oxide (SSCNTs/PANI/RGO) ternary hybrid composite was fabricated by reducing SSCNTs/PANI/GO precursor prepared by self-assembly from the complex dispersion of graphene oxide (GO) and the as-prepared SSCNTs/PANI nanocables, followed by redoping and reoxidation of the reduced PANI to restore the conducting structure of PANI in the ternary composite. The microscope images indicated that SSCNTs/PANI nanocables could uniformly distribute in the conductive network of graphene sheets and prevent the agglomeration of graphene. Such the hierarchical structure perfectly facilitates the contact between PANI for faradaic energy storage and electrolyte ions, and efficiently utilizes the double-layer capacitance of SSCNTs and graphene sheets at the electrode–electrolyte interfaces. The maximum specific capacitance of the SSCNTs/PANI/RGO composite achieved 845 F g−1, which was much higher than that of pure PANI and SSCNTs/PANI nanocables. Moreover, the ternary composite also showed the good cycling stability, retaining about 96% of its initial capacitance after 1000 cycles because of the synergistic effect and conductive network of SSCNTs/PANI nanocables and graphene sheets. Therefore, the combined effects between SSCNTs/PANI nanocables and graphene sheets taking advantage of both charging and faradaic processes could readily explain the excellent electrochemical performance for supercapacitors.

Progress on Preparation, Microstructure and Property of Graphene Reinforced Aluminum Matrix Composite

Graphene with unique two-dimensional structure and excellent mechanical properties, is one of the most ideal reinforcements. With the increasing progress of aluminum matrix composites, graphene reinforced aluminum matrix composites have attracted great interests. This paper mainly reviews the latest progress on preparation of graphene reinforced aluminum matrix composites, and especially discusses the effective dispersion technique of graphene. Meanwhile, the microstructure and interfacial structure of graphene reinforced aluminum matrix composites are also emphasized and discussed. The results showed that graphene can significantly improve the mechanical properties of composites and refine the matrix grain. By controlling preparation parameters, the graphene agglomeration can be effectively solved, and the adverse interface reaction between graphene and substrate can be avoided. Finally, the current challenges and solutions of graphene reinforced aluminum matrix composites were presented.

Au Nanochains Anchored on 3D Polyaniline/Reduced Graphene Oxide Nanocomposites as a High‐Performance Catalyst for Ethanol Electrooxidation

AbstractA nanocomposite containing Au, polyaniline (PANI) and reduced graphene oxide (RGO) has been synthesized by a two‐step method. The PANI can intermix with graphene to build a three‐dimensional (3D) structure, which is beneficial for uniform dispersion of Au networks with a mean diameter of 5.6 nm. In addition to its role as the support of Au, the presence of PANI is also favorable for avoiding the heavy agglomeration of graphene when the reduction occurs. Additionally, the introduction of graphene can not only boost the connections with PANI, but also accelerate the electron transfer between the electrolyte solution and catalysts. Electrochemical tests indicate that the Au/PANI/RGO hybrid exhibits high catalytic activity and stability for ethanol electrooxidation in alkaline conditions. The superior performance can be ascribed to the uniform dispersion of the Au nanocatalyst on the PANI/RGO support with a particular 3D structure, resulting in an increase of the electrochemically active surface area together with a synergic effect between the PANI, graphene and Au.

One-step approach to reduce and modify graphene oxide via vulcanization accelerator and its application for elastomer reinforcement

An efficient and rapid one-step approach to prepare organically modified graphene from graphene oxide (GO) by using nontoxic rubber vulcanization accelerator N-cyclohexyl-2-benzothiazolesulfenamide (CZ) as reducing and modifying agent was presented. CZ was highly effective in reducing graphene oxide in a short time (1h) under a mild condition (70°C). Meanwhile, the reduced graphene decorated with 20wt% CZ molecules exhibited a good solubility in organic solvents, which significantly reduced the irreversible graphene agglomerates and improve the compatibility between graphene and elastomer. Consequently, elastomer composites with CZ reduced and modified GO possessed a combination of high tensile strength and large extensibility, showing 82% and 21% increases respectively, in comparison with elastomer composites with hydrazine hydrate reduced GO containing equivalent filler and CZ content. One-step reaction, short reaction time, mild reaction conditions and high-efficiency make the approach of using rubber additives a promising strategy for the eco-friendly production of graphene and may uncover an extensive family of building blocks for constructing high performance elastomer/graphene composites.

Graphene nanosheet-induced toughening of yttria-stabilized zirconia

Graphene nanosheet (GNS)-reinforced yttria-stabilized tetragonal zirconia polycrystals (TZP) were synthesized using spark plasma sintering (SPS), and the influences of the added GNSs on microstructure evolution and the microscopic mechanical properties of the sintered composites were investigated. Raman spectroscopy and microstructure observation corroborated that these added GNSs, which can survive the harsh SPS processing condition, homogeneously distribute in the matrix of all composites to hinder significantly the grain growth. In comparison with the monolithic TZP, the indentation fracture toughness of a GNS/TZP composite reaches maximum value and increases by up to ~36% (from ~4.1 to ~5.6 MPa m0.5) even at 0.5% weight fraction, GNS pullout, crack bridging, crack deflection, and crack branching are responsible for the increased fracture toughness. The computed energy dissipation by GNS pullout decreases with increasing the number of graphene layers due to weak bonding between them, and therefore, graphene agglomeration would impair toughening effect. Moreover, scratch studies suggest that GNS/TZP composites exhibit improved scratch resistance due to the fact that GNSs are promising reinforcing and lubricating nanofillers in ceramic composites.

3D flexible O/N Co-doped graphene foams for supercapacitor electrodes with high volumetric and areal capacitances

3D flexible O/N co-doped graphene foams (GF) have been designed and fabricated successfully via combining the compression/hot curing strategy with chemical reduction and hydrothermal treatment, in which melamine foams were used not only as the source of N/O functional groups for the introduction of pseudocapacitance but also as the sacrificial template to inhibit the agglomeration of graphene. Also, the mechanism for method of the compressing/hot curing has been investigated systematically. And the resultant GF demonstrates excellent mechanical strength and flexibility. When the compacting GF is used as free-standing electrodes for supercapacitor, it exhibits more excellent ability of charge storage than that of pristine graphene foams. And 10 MPa-GF electrodes delivers high areal capacitance of 375 mu F cm(-2) at a current density of 1 A g(-1), excellent rate capabilities and superior cycling stability of above 100%. According to the analysis of capacitance contribution for 10 MPa-GF electrode, the pseudocapacitance originated from N/O functional groups is up to-65% of the contribution of total capacitance. Moreover, the symmetric supercapacitor comprised of 10 MPa-GF electrodes presents a maximum energy density of 16 Wh kg(-1) (8 Wh L-1) and a maximum power density of 17 kW kg(-1) (8.6 kW L-1). Published by Elsevier B.V.