石墨烯/玻璃块体复合材料的制备及性能

本文报道了还原氧化石墨烯/钠钙硅(rGO/SLS)玻璃块体复合材料的热压制备和力学性能。首先以3-氨基丙基三乙氧基硅烷为表面活性剂修饰玻璃粉微粒;然后在水溶液中带负电的氧化石墨烯(GO)纳米片通过静电自组装与被氨基修饰过带正电的玻璃颗粒相结合生成复合颗粒。通过高温真空热压烧结,GO被还原成rGO,从而原位生成rGO/SLS玻璃块状复合材料。结果表明,rGO均匀分布在玻璃基质中,并明显增强了复合材料的机械性能。rGO/SLS玻璃块体复合材料中rGO的含量为0.5%(质量分数)时,复合材料的弯曲强度比纯的SLS玻璃提高了约一倍。     

Conducting glass fibers of giant thermosensitivity by cladding drawing

Strong and conducting glass fibers are produced from reduced graphene oxide and soda-lime-silica (rGO/SLS) glass by a novel process of cladding drawing. GO nanosheets are bound to the SLS glass particles through an electrostatic assembly and are well distributed in the hot-pressed rGO/SLS bulk composites. These bulks are subsequently BN-cladded, from which rGO/SLS fibers are drawn. Results confirm the rGO sheets are well dispersed inside the fibers and become wrinkled due to the contraction of glass matrix while cooling. Mechanical properties of as-prepared fibers have been greatly improved, with tensile strength two times that of pure SLS fibers. As rGO concentration increases, a conducting network of rGO sheets forms along the fibers, which can survive intensive wear. Thanks to the wrinkled configuration of rGO sheets, the conductivity of the composite fibers is extremely sensitive to temperature, nearly 25 times that of flat rGO sheets, making the fibers potential built-in temperature sensors.     

Synthesis of manganese (IV) oxide at activated carbon on reduced graphene oxide sheets via laser irradiation technique for organic binder-free electrodes in flexible supercapacitors

We report a novel, green, scalable technique to synthesize binder-free, high-purity conductive composite comprising activated carbon (AC), manganese dioxide nanorods (MnO₂), and reduced graphene oxide sheets (rGO) for flexible supercapacitors with outstanding electrochemical performance. UV pulsed laser irradiation of GO-based composite dispersion (AC/GO or MnO₂@AC/GO) in ethanol aqueous medium was used to induce a photocatalytic reduction of GO and simultaneous anchor AC particles or AC loaded MnO₂ nanorods (MnO₂@AC) on the reduced GO sheets (rGO) at room temperature and atmospheric pressure. rGO sheets serve as a large surface area, conductive binder to enhance the ion adsorption, electrical conductivity, and mechanical flexibility of supercapacitor electrodes. This laser-induced photocatalytic reduction method was used to prepare two different rGO-based colloidal composites AC/rGO (CG) and MnO₂@AC/rGO (MCG). The prepared rGO-based colloidal composites were used to fabricate symmetric supercapacitors (CG//CG and MCG//MCG) and asymmetric supercapacitors (MCG//CG) in which MCG is the positive electrode and CG is the negative one. All prepared rGO-based supercapacitors demonstrated significant improvement in their electrochemical performance compared with rGO-free AC based supercapacitors. The enhancement in the electrochemical properties of rGO-based supercapacitors could be attributed to the intrinsic characteristics of rGO, such as high surface area, excellent electrical conductivity, and super mechanical flexibility. Our approach is a one-step, scalable, cost-effective synthesis technique to produce all binder-free AC/rGO based composites for flexible energy-storage devices.     

In Situ Processing of Graphene/Leucite Nanocomposite Through Graphene Oxide/Geopolymer

Graphene/leucite nanocomposites (rGO/leucite) were prepared through in situ reduction of graphene oxide/geopolymer (rGO/KGP) composites. The effects of rGO on the microstructure and mechanical properties with respect to the geopolymer matrix after the high‐temperature treatment were investigated systematically. The results show that GO is first partially reduced in the geopolymeric solution and then completely under the post high‐temperature treatment. The rGO sheets undergo no interfacial reactions with the matrix even after thermal treatment. The rGO/geopolymer composites fully transform to rGO/leucite composites after being treated at 1000°C for 30 min in an argon atmosphere. Significant improvements in mechanical properties were achieved through rGO reinforcement giving flexural strength, elastic modulus, and fracture toughness of 91.1 MPa, 60.5 GPa, and 2.04 MPa·m^1/2, increased by 120%, 8%, and 1.5%, respectively, compared with the leucite matrix alone.     

Effects of substitution for carbon black with graphene oxide or graphene on the morphology and performance of natural rubber/carbon black composites

In this study, nanosheets including graphene oxide (GO) and reduced graphene oxide (rGO), were incorporated into natural rubber (NR), to study the effects of substituting GO or rGO for carbon black (CB) on the structure and performance of NR/CB composites. The morphological observations revealed the dispersion of CB was improved by partially substituting nanosheets for CB. The improvements in static and dynamic mechanical properties were achieved at small substitution content of GO or rGO nanosheets. With substitution of rGO nanosheets, significant improvement in flex cracking resistance was achieved. NR/CB/rGO (NRG) composites has a much lower heat build‐up value compared with NR/CB/GO (NG) composites at a high load of nanosheets. However, both GO and rGO tended to aggregate at a high concentration, which led to the poor efficiency on enhancing the dynamic properties, or even deteriorate the performance of rubber composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41832.     

Simultaneous in situ reduction,self-alignment and covalent bonding in graphene oxide/epoxy composites

Graphene oxide (GO)/waterborne epoxy (EP) composites are prepared using an easy, all aqueous, in situ polymerization method. GO is reduced in situ using hydrazine to achieve highly stable reduced graphene oxide (rGO)/EP dispersions, leading to the formation of composites with a self-aligned layered structure and highly anisotropic properties between the direction of alignment and that perpendicular to it. The strong covalent bonding between the epoxy and rGO and the highly aligned, ultralarge rGO sheets give rise to a remarkable percolation threshold of 0.12 vol.%, as well as much improved mechanical, electrical and thermal properties of the composites in the alignment direction. They outperform those containing GO sheets that are bonded to the epoxy matrix through a weaker π–π stacking mechanism.     

Simultaneous reduction and surface functionalization of graphene oxide and the application for rubber composites

The simultaneous reduction and functionalization of graphene oxide (GO) was realized through a chemical grafting reaction with a functionalization agent N,N-bis(3-aminopropyl)methylamine (APMEL). The reduced and functionalized reduced GO (rGO-APMEL) sheets can be well dispersed in water without any added surfactant and the formed stable rGO aqueous dispersion can be kept for a long time, which can be used for the preparation of rubber–graphene (GE) composites by latex mixing. The electrostatic interaction between rGO–APMEL (positively charged) and natural rubber latex particles (negatively charged) leads to the formation of NR/rGO–APMEL composites with strong interaction. Compared with blank NR, the tensile strength and modulus for NR/rGO–APMEL increase with the rGO–APMEL loading. Especially, when the filler content is 5 phr, the tensile strength of NR/rGO–APMEL-5 increases by 32.7%, as a control the tensile strength of NR/GO-5 and NR/rGO-5 decrease by 20.1 and 15.6%, respectively. The entanglement-bound rubber tube model was used to analyze the reinforcing effect of GE on NR/rGO–APMEL nanocomposites at a molecular level. This study may provide us a novel approach to prepare well dispersed and exfoliated rGO–polymer nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47375.     

A facile one step electrostatically driven electrocodeposition of polyviologen–reduced graphene oxide nanocomposite films for enhanced electrochromic performance

Polyviologen (PV)–reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one-step reductive electropolymerization of cyanopyridinium based precursor monomer (CNP) in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of graphene oxide occurs within the same potential window, electrocodeposition method was preferred for obtaining nanostructured PV–rGO films. Cyclic voltammetry experiments of PV–rGO displayed two well resolved, reversible one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. Vibrational spectral analysis with surface characterization revealed structural changes after composite formation along with subsequent reduction of GO within the polymer matrix. The PV–rGO nanostructured film exhibits a high-contrast electrochromism with low driving voltage induced striking color changes from transparent (0 V) to purple (−0.6 V), high coloration efficiency, fast response times and better cycling stability compared to a pristine PV film. This improved performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV²⁺ and negatively charged rGO, improved electrical conductivity and enlarged surface area accessed through reinforced nanostructured graphene sheets for tethering PV molecules.     

Enhanced toughness and strength of boron carbide ceramics with reduced graphene oxide fabricated by hot pressing

Boron carbide (B₄C) hybrids with different contents of graphene oxide (GO) were prepared by a heterogeneous co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as the cationic surfactant. The as-obtained mixtures were further hot-pressed at 1950 °C for 60 min under 30 MPa, by which B₄C–reduced GO (rGO) composites were fabricated. It was found that the addition of only 0.5 wt% rGO could alter the predominance of trans-granular fracture in monolithic B₄C ceramic material to mixed trans-granular and inter-granular modes in B₄C–rGO composites. The flexural strength and fracture toughness of the B₄C–2 wt% rGO were increased by 31% (from 350 to 455 MPa) and 83% (from 3.20 to 5.85 MPa·m^1/2), respectively, compared with those of pure B₄C. The improved mechanical properties are attributed to the mechanisms of pull-out and bridging of rGO and crack deflection, as evidenced by microstructural observations. The energy dissipation in the present B₄C–rGO composites was further verified using two micromechanical models.     

Electrical conductivity of silicon carbonitride‐reduced graphene oxide composites

Silicon carbonitride ceramics–reduced graphene oxide (SiCN–rGO) composites are synthesized using polyvinylsilazne (PVSZ) and GO as precursors and N‐dimethylformamide (DMF) as a solvent. We find that the electrical conductivity of SiCN–rGO composites exhibits nonmonotonic changes as a function of GO concentrations, in which the conductivity increases by six orders of magnitude from 7.41E‐09 (Ω/cm)^?1 to 4.35E‐03 (Ω/cm)^?1 after the integration of 0.2 wt% GO, followed by three orders of magnitude drop to 3.34E‐06 (Ω/cm)^?1 when 0.3 wt% GO is integrated. Based on the energy‐dispersive spectroscopy and Raman spectroscopy analysis, we conclude that the conductive behavior of SiCN–rGO composites is controlled by both the concentration and the distribution of “free‐carbon” in the composites.     

Accelerated differentiation of neural stem cells into neurons on ginseng-reduced graphene oxide sheets

Asian red ginseng was used for green reduction of chemically exfoliated graphene oxide (GO) into reduced graphene oxide (rGO). The reduction level and electrical conductivity of the ginseng-rGO sheets were comparable to those of hydrazine-rGO ones. Reduction by ginseng resulted in repairing the sp² graphitic structure of the rGO, while hydrazine-rGO showed more defects and/or smaller aromatic domains. The ginseng-rGO sheets presented a better stability against aggregation than the hydrazine-rGO ones in an aqueous suspension. Whilst the hydrophobic hydrazine-rGO films exhibited no toxicity against human neural stem cells (hNSCs), the hydrophilic GO and ginseng-rGO films (as more biocompatible films) showed proliferation of the stem cells after 3 days. On the other hand, the hydrazine-rGO and especially the ginseng-rGO films exhibited more differentiation of hNSCs into neurons (rather than glia) than the GO film, after 3 weeks. The accelerated differentiation on the rGO films was assigned to their higher capability for electron transfer. Meanwhile, the better differentiation on the ginseng-rGO film (as compared to the hydrazine-rGO film) was attributed to its higher biocompatibility, more hydrophilicity and the π−π attachment of ginsenoside molecules (as powerful antioxidants) on surface of the reduced sheets.     

Preparation and characterization of reduced graphene oxide-reinforced boron carbide ceramics by self-assembly polymerization and spark plasma sintering

A self-assembly polymerization process was used to prepare graphene oxide/boron carbide (GO/B₄C) composite powders, spark plasma sintering (SPS) was used to fabricate reduced graphene oxide/boron carbide (rGO/B₄C) composites at 1800 °C and 30 MPa with a soaking time of 5 min. The effects of rGO addition on mechanical properties of the composites, such as Vickers hardness, flexural strength and fracture toughness, were investigated. The results showed that GO/B₄C composite powders were successfully self-assembled and a network structure was formed at high GO contents. The flexural strength and fracture toughness of rGO/B₄C composites were 643.64 MPa and 5.56 MPa m^1/2, respectively, at 1 and 2.5 wt.% rGO content, corresponding to an increase of 99.11% and 71.6% when compared to B₄C ceramics. Uniformly dispersed rGO in rGO/B₄C composites played an important role in improving their strength and toughness. The toughening mechanisms of rGO/B₄C composites were explained by graphene pull-out, crack deflection and bridging.     

Preparation and mechanical properties of Si3N4 nanocomposites reinforced by Si3N4@rGO particles

A new type of reduced graphene oxide-encapsulated silicon nitride (Si₃N₄@rGO) particle was synthesized via an electrostatic interaction between amino-functionalized Si₃N₄ particles and graphene oxide (GO). Subsequently, the Si₃N₄@rGO particles were incorporated into a Si₃N₄ matrix as a reinforcing phase to prepare nanocomposites, and their influence on the microstructure and mechanical properties of the Si₃N₄ ceramics was investigated in detail. The microstructure analysis showed that the rGO sheets were uniformly distributed throughout the matrix and firmly bonded to the Si₃N₄ grains to form a three-dimensional carbon network structure. This unique structure effectively increased the contact area and load transfer efficiency between the rGO sheets and the matrix, which in turn had a significant impact on the mechanical properties of the nanocomposites. The results showed that the nanocomposites with 2.25 wt.% rGO sheets exhibited mechanical properties that were superior to monolithic Si₃N₄; the flexural strength increased by 83.5% and reached a maximum value of 1116.4 MPa, and the fracture toughness increased by 67.7% to 10.35 MPa·m^1/2.     

One-step electrosynthesis of MnO2/rGO nanocomposite and its enhanced electrochemical performance

We present a facile one-step electrochemical approach to generate MnO₂/rGO nanocomposite from a mixture of Mn₃O₄ and graphene oxide (GO). The electrochemical conversion of Mn₃O₄ into MnO₂ through potential cycling is expedited in the presence of GO while the GO is reduced into reduced graphene oxide (rGO). The MnO₂ nanoparticles are evenly distributed on the rGO nanosheets and act as the spacer to prevent rGO nanosheets from restacking. This unique structure provides high electroactive surface area (1173?m² g^?1) that improves ions diffusion within the MnO₂/rGO structure. As a result, the MnO₂/rGO nanocomposite exhibits high specific capacitance of 473?F?g^?1 at 0.25?A?g^?1, which is remarkably higher (3 times) than the Mn₃O₄/GO prior conversion. In addition, the electrosynthesized nanocomposite shows higher conductivity and excellent potential cycling stability of 95% at 2000 cycles.     

Graphene and graphene oxide and their uses in barrier polymers

Currently, there is great interest in graphene‐based devices and applications because graphene has unique electronic and material properties, which can lead to enhanced material performance. Graphene may be used in a wide variety of potential applications from next‐generation transistors to lightweight and high‐strength polymeric composite materials. Graphene, which has atomic thickness and two‐dimensional sizes in the tens of micrometer range or larger, has also been considered a promising nanomaterial in gas‐ or liquid‐barrier applications because perfect graphene sheets do not allow diffusion of small gases or liquids through its plane. Recent molecular simulations and experiments have demonstrated that graphene and its derivatives can be used for barrier applications. In general, graphene and its derivatives can be applied via two major routes for barrier polymer applications. One is the transfer or coating of few‐layered, ultrathin graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), on polymeric substrates. The other is the incorporation of fully exfoliated GO or rGO nanosheets into the polymeric matrix. In this article, we review the state‐of‐the‐art research on the use of graphene, GO, and rGO for barrier applications, including few‐layered graphene or its derivatives in coated polymeric films and polymer nanocomposites consisting of chemically exfoliated GO and rGO nanosheets, and their gas‐barrier properties. As compared to other nanomaterials being used for barrier applications, the advantages and current limitations are discussed to highlight challenging issues for future research and the potential applications of graphene/polymer, GO/polymer, and rGO/polymer composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39628.     

Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes

This paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F g^?1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F g^?1), electrochemically reduced GO (EC-rGO) (27.6 F g^?1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F g^?1)-based electrodes.     

Preparation of highly conductive reduced graphite oxide/poly(styrene-co-butyl acrylate) composites via miniemulsion polymerization

Polymer/reduced graphite oxide (rGO) composite nanoparticles with a high electrical conductivity were synthesized using the miniemulsion polymerization technique. The rGO was modified with a reactive surfactant, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), to facilitate monomer intercalation into the rGO nanogalleries. The AMPS-modified rGO was emulsified in the presence of styrene (St) and butyl acrylate (BA) monomers, and the stable miniemulsion was polymerized to form poly(St-co-BA)/rGO composite latex nanoparticles. The transition in the composite nanoparticles from an electrical insulator to an electrical conductor occurred at an rGO content of 10 wt% (relative to the monolayer content), yielding an electrical conductivity of 0.49 S/cm. The electrical conductivity of the composite nanoparticles reached 2.22 S/cm at 20 wt% rGO, yielding a much better conductivity than other polymer composites prepared using a GO filler. Importantly, the miniemulsion polymerization method for fabricating poly(St-co-BA)/rGO composite nanoparticles is easy, green, low-cost, and scalable, providing a universal route to the rational design and engineering of highly conductive polymer composites.     

Enhancing Toughness in Boron Carbide with Reduced Graphene Oxide

Ceramics typically have very high hardness, but suffer from poor toughness. Here, we use graphene to enhance the toughness of bulk boron carbide ceramics. The reduced graphene oxide (rGO) platelets are homogenously dispersed with boron carbide particles after sintering at 1350°C, under high pressure of 4.5 GPa with a multi‐anvil apparatus. Fracture toughness of the composites is increased ~131% (from ~3.79 to ~8.76 MPa·m^1/2) at 1.5 vol% rGO platelets as a result of a toughing effect of graphene along with a little sacrificing of the hardness and elastic modulus, compared with those of pure boron carbide. The remarkably enhanced fracture toughness in the boron carbide ceramics is associated with graphene sheets crack bridging and graphene interface sliding effect. This study holds much significance for the understanding and development of high‐performance graphene reinforcing ceramics.     

Microfluidic synthesis of ultrasmall Co nanoparticles over reduced graphene oxide and their catalytic properties

We prepared a one-stage microfluidic-based method for continuous synthesis of cobalt (Co) nanoparticles over reduced graphene oxide (rGO) to produce Co/rGO composites. These were generated by the coreduction of Co²⁺ ions and GO with NaBH₄ which was confined within discrete aqueous plugs segmented by octane as continuous phase. Owing to the excellent transfer properties from recirculation in these plugs, ultrasmall Co nanoparticles were distributed homogeneously on the GO sheets without using any surfactants. As compared to batch methods, the average size of Co nanoparticles and the relative standard deviation decreased from 4.0 ± 1.42 nm and 35.9% to 2.0 ± 0.45 nm and 22.6%, respectively. The as-prepared Co/rGO composites exhibited superior activity towards the catalytic reduction of p-nitrophenol to p-aminophenol with NaBH₄ compared with Co nanoparticles and rGO; this enhanced activity could be attributed to the synergistic effect between Co nanoparticles and rGO.     

Synthesis of conducting graphene/Si3N4 composites by spark plasma sintering

Graphene/silicon nitride (Si₃N₄) composites with high fraction of few layered graphene are synthesized by an in situ reduction of graphene oxide (GO) during spark plasma sintering (SPS) of the GO/Si₃N₄ composites. The adequate intermixing of the GO layers and the ceramic powders is achieved in alcohol under sonication followed by blade mixing. The reduction of GO occurs together with the composite densification in SPS, thus avoiding the implementation of additional reduction steps. The materials are studied by X-ray photoelectron and micro-Raman spectroscopy, revealing a high level of recovery of graphene-like domains. The SPS graphene/Si₃N₄ composites exhibit relatively large electrical conductivity values caused by the presence of reduced graphene oxide (∼1 S cm⁻¹ for ∼4 vol.%, and ∼7 S cm⁻¹ for 7 vol.% of reduced-GO). This single-step process also prevents the formation of highly curved graphene sheets during the thermal treatment as the sheets are homogeneously embedded in the ceramic matrix. The uniform distribution of the reduced GO sheets in the composites also produces a noticeable grain refinement of the silicon nitride matrix.